Normal operating specs of a Morion MV89?
You are certainly no where near -40 dBm into 50 ohms as the blog Bryan
posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you also
measured the output voltage with a 10x probe you could work backwards to
see how close you are to 50 Ohms output.
Roughly speaking it sounds like it will be in spec for amplitude, but to
definitive you will have to load it with 50 Ohms as others have suggested.
Anything can work plug your bnc cable into a 50 Ohm input instrument (even
if its ancient) and measure the output voltage on the OCXO with a 10X
probe. Or a near enough to 50 Ohm resistor as Tim suggested.
On Wed, Sep 28, 2016 at 4:58 PM, Tim Lister listertim@gmail.com wrote:
On Wed, Sep 28, 2016 at 11:46 AM, Tom Miller tmiller11147@verizon.net
wrote:
Just put a 47 or 56 ohm resistor from the output pin to ground and look
at
it with a X10 scope probe.
Do you get a sine wave? Over 1 volt pp?
Hi Tom, Scott, I used about two feet of a (Pomona) coax to
minigrabbers test lead and connected it direct to the scope and set
the attenuation to 1x in the channel menus. I attached the
minigrabbers to the RF and GND pins on the Morion since I didn't fancy
holding a probe near the ~50 degree C Morion case.. I got a nice clean
sine wave and the in-scope measurement routines reported 2.3 V
peak-to-peak. I had 1V/div set so I could fit the OCXO and GPSDO
outputs on the scope screen for comparison. (I haven't been able to
get a screen capture yet as I need to find a small enough capacity USB
key that will be supported by the scope)
Tim
Otherwise, you can open up the can and replace the output chip capacitor.
Regards
----- Original Message ----- From: "Scott Stobbe" <
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Wednesday, September 28, 2016 2:38 PM
Subject: Re: [time-nuts] Normal operating specs of a Morion MV89?
If you used a 10x probe (10 Meg || 10-15 pF) you may have a pretty weak
output, but if you could drive a meter of coax or a 1x probe to 800
mVrms
at 10 MHz your probably not too far off spec.
100 pF at 10 MHz is 160 Ohms.
On Wed, Sep 28, 2016 at 12:39 PM, Tim Lister listertim@gmail.com
wrote:
On Wed, Sep 28, 2016 at 4:14 AM, Bob Camp kb8tq@n1k.org wrote:
Hi
You have one of the many MV89A’s with an output problem. To be >
absolutely
sure of the output, you need to have the scope set to 50 ohm input.
If
it was set
to Hi-Z, the output is likely even lower…..
It seems that the scope is 1 MOhm input impedance and is not
changeable. I will have to see if we have any 50 Ohm in-line
terminators around that I can also borrow. Does anyone think that
there is any value in trying to pursue a return and replacement with
the ebay seller (being China, it's likely to be a long round-trip time
for both messages and parcels) or just live with it and move on
(potentially replacing the capacitor later if I get some way of
getting the casing open safely). From what Bob and others have said,
it seems that most of the MV89's have this problem so it seems
unlikely I would get a better one without a lot of trials.
Tim
wrote:
On Tue, Sep 20, 2016 at 12:56 PM, Bryan _ bpl521@outlook.com
wrote:
May also want to check the output amplitude. If memory serves me
correct it is very common for a capacitor inside this model number to
fail.
It can be fixed but requires a torch or a pretty heavy duty soldering
iron
to get the can open.
I managed to borrow a Tek TDS 2024B 200 MHz scope from work and
hooked
it up to the output of my MV89A. I get a peak-to-peak measurement of
2.3 V which if I have converted it right is ~11 dBm ? Alternatively
if
I turn on the FFT mode on the scope I get a peak value of -2.17 db
if
I am driving the cursor mode correctly. With the 10 MHz from the
radioshackus GPSDO used for triggering, it takes ~18 seconds for the
MV89 waveform to drift 1 cycle (this is without anything connected
on
the Uin or Uref pins).
Tim
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On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe scott.j.stobbe@gmail.com wrote:
You are certainly no where near -40 dBm into 50 ohms as the blog Bryan
posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you also
measured the output voltage with a 10x probe you could work backwards to
see how close you are to 50 Ohms output.
Roughly speaking it sounds like it will be in spec for amplitude, but to
definitive you will have to load it with 50 Ohms as others have suggested.
Anything can work plug your bnc cable into a 50 Ohm input instrument (even
if its ancient) and measure the output voltage on the OCXO with a 10X
probe. Or a near enough to 50 Ohm resistor as Tim suggested.
I obtained a (Pomona I think) 50 Ohm terminator/6db attenuator and
repeated the measurements with the MV89A, connecting the RF and GND
pins through a BNC cable and the terminator directly into the Channel
1 of the scope . I now get an amplitude on the scope FFT of -6.99 dB
measured with the cursors. According to the scope manual this is
referenced to 1 V rms so this would give a Vrms equivalent to -0.99 dB
i.e. 0.89 Volts. Assuming I've done the rest of the maths conversions
right, this would give a peak-to-peak value of 1.26 V and a power of
~11 dBm. (Assuming everything worked alright, I put the scope captures
up on our Owncloud at
https://cloud.lcogt.net/index.php/s/pHBV6EORT33ucjA - Channel 1 is the
MV89A, Channel 2 is the GPSDO output)
So I think this means my unit is behaving OK ?
Cheers,
Tim
If you used a 6db pad in conjunction with a 50 ohm termination you are spot
on. If you used a 6dB pad as a 50 ohm load, the effective load will be a
bit higher than 50 and the attenuation less than 6 dB. Either way sounds
like the output stage of your OCXO is in spec for 7 dBm into 50 ohms.
On Friday, 30 September 2016, Tim Lister listertim@gmail.com wrote:
On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.stobbe@gmail.com
javascript:;> wrote:
You are certainly no where near -40 dBm into 50 ohms as the blog Bryan
posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you
also
measured the output voltage with a 10x probe you could work backwards to
see how close you are to 50 Ohms output.
Roughly speaking it sounds like it will be in spec for amplitude, but to
definitive you will have to load it with 50 Ohms as others have
suggested.
Anything can work plug your bnc cable into a 50 Ohm input instrument
(even
if its ancient) and measure the output voltage on the OCXO with a 10X
probe. Or a near enough to 50 Ohm resistor as Tim suggested.
I obtained a (Pomona I think) 50 Ohm terminator/6db attenuator and
repeated the measurements with the MV89A, connecting the RF and GND
pins through a BNC cable and the terminator directly into the Channel
1 of the scope . I now get an amplitude on the scope FFT of -6.99 dB
measured with the cursors. According to the scope manual this is
referenced to 1 V rms so this would give a Vrms equivalent to -0.99 dB
i.e. 0.89 Volts. Assuming I've done the rest of the maths conversions
right, this would give a peak-to-peak value of 1.26 V and a power of
~11 dBm. (Assuming everything worked alright, I put the scope captures
up on our Owncloud at
https://cloud.lcogt.net/index.php/s/pHBV6EORT33ucjA - Channel 1 is the
MV89A, Channel 2 is the GPSDO output)
So I think this means my unit is behaving OK ?
Cheers,
Tim
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HI
On Oct 1, 2016, at 4:08 PM, Scott Stobbe scott.j.stobbe@gmail.com wrote:
If you used a 6db pad in conjunction with a 50 ohm termination you are spot
on. If you used a 6dB pad as a 50 ohm load, the effective load will be a
bit higher than 50 and the attenuation less than 6 dB. Either way sounds
like the output stage of your OCXO is in spec for 7 dBm into 50 ohms.
The scope is reading -11 dbm after a 6 db pad? Not sure where 7 dbm comes from.
On Friday, 30 September 2016, Tim Lister listertim@gmail.com wrote:
On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.stobbe@gmail.com
javascript:;> wrote:
You are certainly no where near -40 dBm into 50 ohms as the blog Bryan
posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you
also
measured the output voltage with a 10x probe you could work backwards to
see how close you are to 50 Ohms output.
Roughly speaking it sounds like it will be in spec for amplitude, but to
definitive you will have to load it with 50 Ohms as others have
suggested.
Anything can work plug your bnc cable into a 50 Ohm input instrument
(even
if its ancient) and measure the output voltage on the OCXO with a 10X
probe. Or a near enough to 50 Ohm resistor as Tim suggested.
I obtained a (Pomona I think) 50 Ohm terminator/6db attenuator
The 6 db pad
and
repeated the measurements with the MV89A, connecting the RF and GND
pins through a BNC cable and the terminator directly into the Channel
1 of the scope . I now get an amplitude on the scope FFT of -6.99 dB
measured with the cursors. According to the scope manual this is
referenced to 1 V rms so this would give a Vrms equivalent to -0.99 dB
i.e. 0.89 Volts. Assuming I've done the rest of the maths conversions
right, this would give a peak-to-peak value of 1.26 V and a power of
~11 dBm.
The -11 dbm.
That sounds a lot more like -5 dbm than +7 dbm. This is a pretty typical output
on a broken MV89.
Bob
(Assuming everything worked alright, I put the scope captures
up on our Owncloud at
https://cloud.lcogt.net/index.php/s/pHBV6EORT33ucjA - Channel 1 is the
MV89A, Channel 2 is the GPSDO output)
So I think this means my unit is behaving OK ?
Cheers,
Tim
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I think you have mistaken the tilde symbol as a negative sign. Tim's 11 dBm
is into the pad.
7 dBm +- 2 dB into 50 ohms is the spec for the mv89 no?
On Saturday, 1 October 2016, Bob Camp kb8tq@n1k.org wrote:
HI
On Oct 1, 2016, at 4:08 PM, Scott Stobbe <scott.j.stobbe@gmail.com
javascript:;> wrote:
If you used a 6db pad in conjunction with a 50 ohm termination you are
spot
on. If you used a 6dB pad as a 50 ohm load, the effective load will be a
bit higher than 50 and the attenuation less than 6 dB. Either way sounds
like the output stage of your OCXO is in spec for 7 dBm into 50 ohms.
The scope is reading -11 dbm after a 6 db pad? Not sure where 7 dbm comes
from.
On Friday, 30 September 2016, Tim Lister <listertim@gmail.com
javascript:;> wrote:
On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.stobbe@gmail.com
javascript:;> wrote:
You are certainly no where near -40 dBm into 50 ohms as the blog Bryan
posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you
also
measured the output voltage with a 10x probe you could work backwards
to
see how close you are to 50 Ohms output.
Roughly speaking it sounds like it will be in spec for amplitude, but
to
definitive you will have to load it with 50 Ohms as others have
suggested.
Anything can work plug your bnc cable into a 50 Ohm input instrument
(even
if its ancient) and measure the output voltage on the OCXO with a 10X
probe. Or a near enough to 50 Ohm resistor as Tim suggested.
I obtained a (Pomona I think) 50 Ohm terminator/6db attenuator
The 6 db pad
and
repeated the measurements with the MV89A, connecting the RF and GND
pins through a BNC cable and the terminator directly into the Channel
1 of the scope . I now get an amplitude on the scope FFT of -6.99 dB
measured with the cursors. According to the scope manual this is
referenced to 1 V rms so this would give a Vrms equivalent to -0.99 dB
i.e. 0.89 Volts. Assuming I've done the rest of the maths conversions
right, this would give a peak-to-peak value of 1.26 V and a power of
~11 dBm.
The -11 dbm.
That sounds a lot more like -5 dbm than +7 dbm. This is a pretty typical
output
on a broken MV89.
Bob
(Assuming everything worked alright, I put the scope captures
up on our Owncloud at
https://cloud.lcogt.net/index.php/s/pHBV6EORT33ucjA - Channel 1 is the
MV89A, Channel 2 is the GPSDO output)
So I think this means my unit is behaving OK ?
Cheers,
Tim
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