A better and easier way is to phase lock a crystal oscillator.
I would use a 50 MHz VCXO and divide the output by 2 to get a
25 MHz square wave.

Rick N6RK

On 1/18/2017 10:28 AM, Loren Moline WA7SKT wrote:

Are you talking about locking the 50MHz VCXO to my 10 MH. Standard? I want the 25MHz to be from my 10MHz OCXO which is my station standard which will locked to GPS eventually.

Loren WA7SKT

On Wed, Jan 18, 2017 at 4:01 PM -0800, "Richard (Rick) Karlquist" <richard@karlquist.commailto:richard@karlquist.com> wrote:

A better and easier way is to phase lock a crystal oscillator.
I would use a 50 MHz VCXO and divide the output by 2 to get a
25 MHz square wave.

Rick N6RK

On 1/18/2017 10:28 AM, Loren Moline WA7SKT wrote:

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Hi

What are you going to use the 25 MHz for? Will it drive any sort of radio? If so, cleaning up the phase
noise of the GPSDO is a very good idea. With a PLL, you can subtract noise. With a multiplier you
can only add noise. The narrow bandwidth PLL combined with a low nose VCXO is your friend in this case.

I would take the process one step further. I’d lock up a 100 MHz VCXO to the 10 MHz. Then you can get
100, 50, 25, and 20 MHz outputs. The 100 MHz is the key if you want to head up into the microwave
region.

Bob

This document covers various methods but I agree with Rick about phase
locking a separate crystal oscillator; harmonic frequency
multiplication is more useful at higher frequencies where other
methods are unavailable:

http://www.qsl.net/va3iul/Frequency_Multipliers/Frequency_Multipliers.pdf

An alternative very simple design I might try is a variation of the
active frequency multiplier where the 5th harmonic is filtered
directly from the output of the digital divide by two stage.

On Wed, 18 Jan 2017 18:28:32 +0000, you wrote:

Thanks Bob

Loren Moline  WA7SKT

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From: time-nuts time-nuts-bounces@febo.com on behalf of Bob Camp kb8tq@n1k.org
Sent: Wednesday, January 18, 2017 6:08 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 10MHz to 25MHz

Hi

What are you going to use the 25 MHz for? Will it drive any sort of radio? If so, cleaning up the phase
noise of the GPSDO is a very good idea. With a PLL, you can subtract noise. With a multiplier you
can only add noise. The narrow bandwidth PLL combined with a low nose VCXO is your friend in this case.

I would take the process one step further. I'd lock up a 100 MHz VCXO to the 10 MHz. Then you can get
100, 50, 25, and 20 MHz outputs. The 100 MHz is the key if you want to head up into the microwave
region.

Bob

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That is exactly what I have just done, using an HMC1031 to lock a good 100MHz OCXO to my GPSDO, using a very narrow filter bandwidth with decent 22uF ceramic caps in the loop filter. I’ve also made a second version using an XOR gate and an MC12080 prescaler and flipflops and fast comparators, but the HMC1031 version is way simpler and has a wider lock-in range. Hard to measure the performance as the noise appears lower than my E4406A can resolve, but with one 100MHz OCXO locked to the GPSDO and the other to my 10MHz Rb standard, and monitoring the relative phases using an AD8302, I see none of the (slight) glitchiness of the GPSDO reflected in the 100MHz locked output.

Neil

On Wed, Jan 18, 2017 at 5:40 PM, Loren Moline WA7SKT lmoline@hotmail.com
wrote:

The 25MHz WOULD be locked to your 10MHz GPSDO if you first locked a 100MHz
or 50MHz to the 10MHz then divided down.  Dividers work really well, they
can improve the phase noise, Multipliers always add phase noise.    Because
of this I have always wondered why we build our "standard" with such a low
frequency.  Why not a 100MHz GPSDO?  Why 10MHz

--

Chris Albertson
Redondo Beach, California

On 1/18/2017 6:34 PM, David wrote:

That's a useful trick to reduce the filtering burden.  Having said
that, if you need good spectral purity, the filtering is still
going to be very non-trivial.  The original poster is obviously
not an expert in filters and will not be successful trying that
approach, except for very low performance design.  Even if
you are a filter expert, components are hard to get.

Rick N6RK

Chris wrote:

Quartz crystals work better at lower frequencies, predominantly because
they have higher Q.  10MHz was chosen because it is low enough for
excellent performance but high enough to be directly useful (since an
accident of biology gave us ten fingers, we've created a base-10 world
and powers of 10 are favored in almost everything).

In prior times, 5MHz crystals held this position, and before that, 1MHz.
There is a good argument even today that the best 2.5MHz or 5MHz
crystals are better than the best 10MHz crystals, but not by enough to
make 2.5MHz or 5MHz standards popular any longer.

One lonely data point, which proves nothing:  My best crystal oscillator
is a Symmetricom clone of the double-oven HP 10811s (it came out of an
HP GPSDO, so apparently HP at one time used them interchangeably with
the 10811).  That OCXO uses a 5MHz crystal and a frequency doubler to
produce its 10MHz output.

Best Regards,

Charles