Empathy List Archives

BS

Bob Stewart

Sat, Oct 1, 2016 6:32 PM

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? Bob

MD

Magnus Danielson

Sat, Oct 1, 2016 7:52 PM

Bob,

Just try it. Compare it and see how the initial noise slope behaves and
compare it to other measurements.

Similar phase-measurement setups have been used in historic context.

What ends up being the best method for you is a combination of what
tools you have available and dare to bring into use.

I haven't tried this approach thought.

One if the key elements to make it work well would be if you can trigger
the measurements so you know what time-base you have. If your
observations is at 1.2 s or 1.8 s rather than something more common you
need to know, and best way is to steer it from a good source.

Cheers,
Magnus

On 10/01/2016 08:32 PM, Bob Stewart wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Bob, Just try it. Compare it and see how the initial noise slope behaves and compare it to other measurements. Similar phase-measurement setups have been used in historic context. What ends up being the best method for you is a combination of what tools you have available and dare to bring into use. I haven't tried this approach thought. One if the key elements to make it work well would be if you can trigger the measurements so you know what time-base you have. If your observations is at 1.2 s or 1.8 s rather than something more common you need to know, and best way is to steer it from a good source. Cheers, Magnus On 10/01/2016 08:32 PM, Bob Stewart wrote: > I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? > Bob > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

BC

Bob Camp

Sat, Oct 1, 2016 8:14 PM

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi What is the beat note coming out of the DMTD? Put another way: DMTD involves three oscillators. Two are on roughly the same frequency and the third is offset from the other two. The difference frequency is typically something like 10 Hz. It does not *have* to be 10 Hz, but that is one way to do it. So, moving on using 10 Hz (which may be wrong): If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change at 10 MHz. The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a signal processing chain that will tolerate the carrier being “in band”. Between the two … not such a great way to do it. It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic range can be *much* less. Bob > On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: > > I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? > Bob > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

BS

Bob Stewart

Sat, Oct 1, 2016 8:30 PM

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

  From: Bob Camp <kb8tq@n1k.org>

To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi Bob, I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. Bob From: Bob Camp <kb8tq@n1k.org> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Saturday, October 1, 2016 3:14 PM Subject: Re: [time-nuts] Measuring phase with an HP 3456A? Hi What is the beat note coming out of the DMTD? Put another way: DMTD involves three oscillators. Two are on roughly the same frequency and the third is offset from the other two. The difference frequency is typically something like 10 Hz. It does not *have* to be 10 Hz, but that is one way to do it. So, moving on using 10 Hz (which may be wrong): If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change at 10 MHz. The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a signal processing chain that will tolerate the carrier being “in band”. Between the two … not such a great way to do it. It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic range can be *much* less. Bob > On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: > > I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? > Bob > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

BC

Bob Camp

Sat, Oct 1, 2016 11:24 PM

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

  From: Bob Camp <kb8tq@n1k.org>

To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

HI DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > Bob > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > offset from the other two. The difference frequency is typically something like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: >> >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

BS

Bob Stewart

Sat, Oct 1, 2016 11:44 PM

Hi Bob,Can you tell me what you mean by "just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise."? What inputs do you assume I have? I don't think I can attach two 10MHz inputs to a soundcard and expect anything useful.

Bob

  From: Bob Camp <kb8tq@n1k.org>

To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 6:24 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

From: Bob Camp kb8tq@n1k.org
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi Bob,Can you tell me what you mean by "just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise."? What inputs do you assume I have? I don't think I can attach two 10MHz inputs to a soundcard and expect anything useful. Bob From: Bob Camp <kb8tq@n1k.org> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Saturday, October 1, 2016 6:24 PM Subject: Re: [time-nuts] Measuring phase with an HP 3456A? HI DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > Bob > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > offset from the other two. The difference frequency is typically something like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: >> >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

BA

Bob Albert

Sat, Oct 1, 2016 11:46 PM

I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms.

Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have.

Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it.
Bob

On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote:

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

From: Bob Camp kb8tq@n1k.org
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms. Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have. Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it. Bob On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote: HI DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > Bob > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > offset from the other two. The difference frequency is typically something like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: >> >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

BC

Bob Camp

Sat, Oct 1, 2016 11:58 PM

Hi

If you have two inputs into the mixer, one comes from one OCXO and the other comes from another OCXO.

If you set the EFC voltage on one or the other OCXO so the output of the mixer is zero, the inputs are 90 degrees apart. At that point the mixer has a maximum phase sensitivity and the carrier is surpassed.

Bob

On Oct 1, 2016, at 7:44 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
Can you tell me what you mean by "just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise."? What inputs do you assume I have? I don't think I can attach two 10MHz inputs to a soundcard and expect anything useful.

Bob

From: Bob Camp kb8tq@n1k.org
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 6:24 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

  From: Bob Camp <kb8tq@n1k.org>

To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi If you have two inputs into the mixer, one comes from one OCXO and the other comes from another OCXO. If you set the EFC voltage on one or the other OCXO so the output of the mixer is zero, the inputs are 90 degrees apart. At that point the mixer has a maximum phase sensitivity and the carrier is surpassed. Bob > On Oct 1, 2016, at 7:44 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > Can you tell me what you mean by "just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise."? What inputs do you assume I have? I don't think I can attach two 10MHz inputs to a soundcard and expect anything useful. > > Bob > > > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 6:24 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > HI > > > DMTD = Dual Mixer Time Difference > > Single Mixer = what is commonly used for most things. > > If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. > > Bob > > > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > > > Hi Bob, > > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > > > Bob > > > > From: Bob Camp <kb8tq@n1k.org> > > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > > Sent: Saturday, October 1, 2016 3:14 PM > > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > > > Hi > > > > What is the beat note coming out of the DMTD? > > > > Put another way: > > > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > > offset from the other two. The difference frequency is typically something like 10 Hz. > > It does not *have* to be 10 Hz, but that is one way to do it. > > > > So, moving on using 10 Hz (which may be wrong): > > > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > > at 10 MHz. > > > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > > such a great way to do it. > > > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > > range can be *much* less. > > > > Bob > > > > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: > >> > >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? > >> Bob > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com > >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > >

BS

Bob Stewart

Sun, Oct 2, 2016 12:13 AM

Hi Bob Albert,

I'm having trouble following it, as well, and I started it. So, let's back up. Completely eliminate the use of the term "DMTD". I didn't post that. I'm only interested in measuring phase with the 3456A, which is a voltmeter.

So, I have two disciplined OCXOs, a DBM, an LPF, and a 3456A. The question is this: "Can I use the 3456A to measure the phase angle (not phase noise) more precisely than the 5370A" under very specific circumstances; i.e. the frequencies are known to be very, very close between the two inputs? One of the obvious limitations on getting a directly convertible phase output is that the mixer only allows me to directly measure 180 degrees of phase difference, and without some external referent, I won't know which 180 degree spread that is. So, I suspect that I will need part of the answer from the 5370A (or even a 5335 or 5334). And even then there's the problem of getting the two measuring devices (the DBM and the TIC) to agree on where phase zero is. But I think I can easily get over the phase zero problem with software, and this will need software in any case.

Bob
-----------------------------------------------------------------
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Bob Albert <bob91343@yahoo.com>

To: Discussion of precise time and frequency measurement time-nuts@febo.com; Bob Stewart bob@evoria.net
Sent: Saturday, October 1, 2016 6:46 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms.

Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have.

Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it.
Bob

On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote:

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

From: Bob Camp kb8tq@n1k.org
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi Bob Albert, I'm having trouble following it, as well, and I started it. So, let's back up. Completely eliminate the use of the term "DMTD". I didn't post that. I'm only interested in measuring phase with the 3456A, which is a voltmeter. So, I have two disciplined OCXOs, a DBM, an LPF, and a 3456A. The question is this: "Can I use the 3456A to measure the phase angle (not phase noise) more precisely than the 5370A" under very specific circumstances; i.e. the frequencies are known to be very, very close between the two inputs? One of the obvious limitations on getting a directly convertible phase output is that the mixer only allows me to directly measure 180 degrees of phase difference, and without some external referent, I won't know which 180 degree spread that is. So, I suspect that I will need part of the answer from the 5370A (or even a 5335 or 5334). And even then there's the problem of getting the two measuring devices (the DBM and the TIC) to agree on where phase zero is. But I think I can easily get over the phase zero problem with software, and this will need software in any case. Bob ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Bob Albert <bob91343@yahoo.com> To: Discussion of precise time and frequency measurement <time-nuts@febo.com>; Bob Stewart <bob@evoria.net> Sent: Saturday, October 1, 2016 6:46 PM Subject: Re: [time-nuts] Measuring phase with an HP 3456A? I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms. Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have. Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it. Bob On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote: HI DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > Bob > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > offset from the other two. The difference frequency is typically something like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: >> >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

BA

Bob Albert

Sun, Oct 2, 2016 12:53 AM

You are firing those acronyms at me too quickly. I don't know what most of them signify.
If you have two oscillators, I assume that somehow you lock them to the same frequency; otherwise the phase difference will be changing. Which one is the reference, and why?
If you want to measure phase angle I would think a Lissajous pattern would be one way. Another would be to synchronize a sweep from one channel and use delaying sweep to compare the other. Another would be to build a calibrated phase shifter.

Using a voltmeter requires a discriminator. Plus, the voltage for 180 degrees or zero degrees must be calibrated to find the ratio and thus the sine or cosine of the phase difference.
And while I never asked why we want to do this, I am reserving that question for later.
Bob

On Saturday, October 1, 2016 5:17 PM, Bob Stewart <bob@evoria.net> wrote:

Hi Bob Albert,

I'm having trouble following it, as well, and I started it. So, let's back up. Completely eliminate the use of the term "DMTD". I didn't post that. I'm only interested in measuring phase with the 3456A, which is a voltmeter.

So, I have two disciplined OCXOs, a DBM, an LPF, and a 3456A. The question is this: "Can I use the 3456A to measure the phase angle (not phase noise) more precisely than the 5370A" under very specific circumstances; i.e. the frequencies are known to be very, very close between the two inputs? One of the obvious limitations on getting a directly convertible phase output is that the mixer only allows me to directly measure 180 degrees of phase difference, and without some external referent, I won't know which 180 degree spread that is. So, I suspect that I will need part of the answer from the 5370A (or even a 5335 or 5334). And even then there's the problem of getting the two measuring devices (the DBM and the TIC) to agree on where phase zero is. But I think I can easily get over the phase zero problem with software, and this will need software in any case.

Bob
-----------------------------------------------------------------
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Bob Albert <bob91343@yahoo.com>

To: Discussion of precise time and frequency measurement time-nuts@febo.com; Bob Stewart bob@evoria.net
Sent: Saturday, October 1, 2016 6:46 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms.

Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have.

Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it.
Bob

On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote:

HI

DMTD = Dual Mixer Time Difference

Single Mixer = what is commonly used for most things.

If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise.

Bob

On Oct 1, 2016, at 4:30 PM, Bob Stewart bob@evoria.net wrote:

Hi Bob,
I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns.

Bob

From: Bob Camp kb8tq@n1k.org
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, October 1, 2016 3:14 PM
Subject: Re: [time-nuts] Measuring phase with an HP 3456A?

Hi

What is the beat note coming out of the DMTD?

Put another way:

DMTD involves three oscillators. Two are on roughly the same frequency and the third is
offset from the other two. The difference frequency is typically something like 10 Hz.
It does not have to be 10 Hz, but that is one way to do it.

So, moving on using 10 Hz (which may be wrong):

If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle
at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm
of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change
at 10 MHz.

The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around
at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a
signal processing chain that will tolerate the carrier being “in band”. Between the two … not
such a great way to do it.

It’s much easier to simply hook up a single mixer (half of what you have already) and look at
the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic
range can be much less.

Bob

On Oct 1, 2016, at 2:32 PM, Bob Stewart bob@evoria.net wrote:

I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover?
Bob

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

You are firing those acronyms at me too quickly. I don't know what most of them signify. If you have two oscillators, I assume that somehow you lock them to the same frequency; otherwise the phase difference will be changing. Which one is the reference, and why? If you want to measure phase angle I would think a Lissajous pattern would be one way. Another would be to synchronize a sweep from one channel and use delaying sweep to compare the other. Another would be to build a calibrated phase shifter. Using a voltmeter requires a discriminator. Plus, the voltage for 180 degrees or zero degrees must be calibrated to find the ratio and thus the sine or cosine of the phase difference. And while I never asked why we want to do this, I am reserving that question for later. Bob On Saturday, October 1, 2016 5:17 PM, Bob Stewart <bob@evoria.net> wrote: Hi Bob Albert, I'm having trouble following it, as well, and I started it. So, let's back up. Completely eliminate the use of the term "DMTD". I didn't post that. I'm only interested in measuring phase with the 3456A, which is a voltmeter. So, I have two disciplined OCXOs, a DBM, an LPF, and a 3456A. The question is this: "Can I use the 3456A to measure the phase angle (not phase noise) more precisely than the 5370A" under very specific circumstances; i.e. the frequencies are known to be very, very close between the two inputs? One of the obvious limitations on getting a directly convertible phase output is that the mixer only allows me to directly measure 180 degrees of phase difference, and without some external referent, I won't know which 180 degree spread that is. So, I suspect that I will need part of the answer from the 5370A (or even a 5335 or 5334). And even then there's the problem of getting the two measuring devices (the DBM and the TIC) to agree on where phase zero is. But I think I can easily get over the phase zero problem with software, and this will need software in any case. Bob ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Bob Albert <bob91343@yahoo.com> To: Discussion of precise time and frequency measurement <time-nuts@febo.com>; Bob Stewart <bob@evoria.net> Sent: Saturday, October 1, 2016 6:46 PM Subject: Re: [time-nuts] Measuring phase with an HP 3456A? I am having trouble following this thread. I assume we are trying to measure phase noise, but of course the result includes the noise of the local oscillator(s). Isn't the 3456A a voltmeter? I have one of those. In AC mode it has a bandwidth of more than 100 kHz and measures true rms. Someone please take the time and trouble to explain what is being done here. At this point I am imagining a mixer and a local oscillator and some unknown source. Quadrature? How do you accomplish that? Doesn't that require a 90 degree phase shift? With an analog phase shifter, or some more modern scheme? A diagram would be helpful. I am interested in this partly because I also want to measure phase noise (I can do it with a communications receiver or a deviation meter, both of which I have), and partly because I feel as though I am being left behind technologically speaking and want to keep up better than I have. Ever since data streams seem to take less bandwidth than that of the signals whose information they contain, I have been thoroughly confused. My classic textbooks don't have stuff like this. When someone talks about quadrature, it looks to me as though they are waving hands in the air, saying some incantations, and then come up with miracles. I know it works but I surely would love to understand it. Bob On Saturday, October 1, 2016 4:24 PM, Bob Camp <kb8tq@n1k.org> wrote: HI DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of progressed from looking at the output of the LPF on the scope to "I wonder what I would see on the 3456A?" sort of thing. I'm running a holdover/recovery test on the code and hardware changes to get a reliable 1PPS from my GPSDO, so there is some very slow movement over the range of 0 to 100ns. > > Bob > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and the third is > offset from the other two. The difference frequency is typically something like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You also need to have a > signal processing chain that will tolerate the carrier being “in band”. Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <bob@evoria.net> wrote: >> >> I've been spending a small amount of my time looking into making a sort of hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my scope for verification - an obvious step. Then I hooked it up to my 3456A just for grins. (The two DBM inputs are 10MHz outputs from two different GPSDOs). So, as I watch this, I think the obvious question: can this measure phase angle better than the 5370A? I guess I need to send it through a full 100ns of phase change to get a calibration value. So, who's been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

time-nuts@lists.febo.com

Measuring phase with an HP 3456A?