[time-nuts] 10 MHz Oscillator comparison part II
sandeenpa at yahoo.com
Tue Jan 11 23:39:09 UTC 2011
Wrote: However the exercise is probably pointless as the frequency difference between the 2 signals as seen at the output of the cascaded divide and mix chains are reduced by this scheme.
Umm. I guess I didn’t express my thoughts effectively enough.
The idea is to subtract 9 MHz in each DBM then take the 1 MHz error signal and use it to phase lock the next PLL at 10 MHz. Thus the error is multiplied by 10 in each section. So after four sections the error is multiplied by a factor of 10,000.
What I forgot to mention in my original post is the use of a decade counter (1/2 of a 74HC390) from the output of each PLL to one input of its phase detector so it would lock on the 1 MHz signal from the previous stage. Maybe this is what caused confusion, If so, I apologize. If I’ve still missed something please correct me.
This math is the same as multiplying 10 MHz to 10 GHz. What this method avoids is using very tricky-to-use frequencies. And I suspect much cheaper.
Wrote:< You can see the Tracor frequency error meter, used the same mixer method you describe but using 9 and 10 MHz frequency to mix together and a decade frequency multiplier. The limit of the system is the phase noise of the system and sources. The Tracor use an optional Xtal filter to limit the noise. The filter can be inserted for high multiplication rate or for noisy oscillators.
< See tracor schematic ttp://www.ko4bb.com/Manuals/09)_Misc_Test_Equipment/Tracor_527E.pdf
Thanks. I knew my method wasn’t original, I was trying just update it and make it both simpler and cheaper with newer chips
Wrote: <You need to multiply the input signals to a nominal 100 MHz then subtract 90 MHz using a mixer and repeat the process.
This may be true but I don’t understand why. I think my math process is the same as yours. I may need more “Edjurcation”.
Wrote: The normal term for a gizmo that multiplies and then mixes down is an error multiplier.
Also thanks to Urlich who sent me a PDF copy of the Quartzlock (UK) Limited ON IMPROVED METHOD OF RESOLVING THE FREQUENCY DIFFERENCE BETWEEN TWO VERY ACCURATE AND STABLE FREQUENCY SIGNALS.
Wrote:< Using the CD4046 (or HC4046) as the phase locked oscillator would probably be counterproductive as its phase noise is very high (its in effect an RC oscillator with an effective Q of around1/4)
A. I don’t know. Maybe there is a better IC choice for the PLL. I guess building one would prove its feasibility.
An additional thought came to me that might make the whole process easier.
ASS-U_ME we have a “gold standard” 10 MHz signal from a GPS, Rb, or cesium beam. We input it into our frequency counter’s external reference input.
We take the to-be-measured 10 MHz source and put it into the external input of a synthesized signal generator. Set the signal generator frequency output to 100 Mhz or 200 Mhz or whatever are your highest limits are of the generator/counter setup and count the difference using and extended start and stop signal for the counter.
If one has a HP 3336A/B (referenced to our “standard”) it can give up to a 1 micro-Hz clock signal. Or one can chain together a bunch of 74HC390 decade counters.
Wrote:< DMTD is the obvious way to do this, but let's go the old fashion way instead.
A. I don’t know what you mean by DMDT but am willing to try to learn.
Wrote:< Going down, how low do you want to go? 100 KHz will give you 100X.
A. I thought when dividing down one was also dividing the error.
Wrote:<Whatever way you do it, you are still stuck with the same old problem. The input needs to be on a very specific frequency. With some designs it can be a sub multiple of that frequency. With other designs it can be a multiple.
A. Not Necessarily. If one puts a DBM in each channel which is referenced to a common oscillator. Granted one may need to add a post mixer filter. But this is a diversion from the original issue.
Wrote:< Either way, 7.352 MHz is going to give you trouble. That's pretty much why the error multiplier boxes all went into storage in the 1970's...
A. I have no idea what 7.352 MHz is or why it will cause trouble. Could you please elaborate?
I blessed to have HP 5370’s, rubidium standards, a HP 3336B and GPS receivers and don’t really need to fabricate any equipment. My reason for posting is to come up with a relatively simple test equipment set-up that could be used by those who have a more modest budget or live where the test equipment we in North America can afford is unobtainiumly expensive.
Thanks to all who have commented as shared the actual results of their 10811 oscillators.
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