[time-nuts] Re: Phase noise of HP8663A 640 MHz reference? {External}

[Jim Muehlberg]

Sorry for not including the plot.  I guess the list won't accept inline 
images.

I did not include data from the PN9000 synthesizer referenced plots, 
because of course, you're not interested in the synthesizer noise, which 
dominated.

Jim

On 8/22/2022 2:45 PM, Jim Muehlberg via time-nuts wrote:
> Here are some PN plots from the PN9000.(mixer version, not the xcor 
> version)
>
> The upper plots are the 8663's v. the PN9000 synthesizer.  The lower 
> plot is the two 8663's, one is the VCO and the other is the DUT.  PN 
> data of the lower plot is attached.  I've got 2 more 8663s I can 
> measure, once my hernia belt is back from the cleaners.
>
> Jim
>
> On 2022-08-21 5:52 PM, ed breya via time-nuts wrote:
>> Tobias wrote
>>
>> "Hi Ed, could you share some info about your own 640 MHz source?
>> I would be very interested.
>> I do have an 8663A, but I have no idea about how good it actually is and
>> currently, I don't have a possibility to test it because I still lack an
>> 11729C carrier noise test set (but I would like to make something 
>> similar myself some day)."
>>
>>
>> The plan was to do the doubling and amplifying similar to the 
>> 8662A/8663A (which I think are about the same in this respect), 
>> except that I don't have anything like the mentioned 40 MHz and 160 
>> MHz crystal filters. Starting from the higher OCXO frequency should 
>> help some, depending on its noise performance.
>>
>> The filters I do have can't fix anything close-in, but should work 
>> very well on spurious content from almost any multiplier scheme. The 
>> first one especially is a single unit 160 MHz BPF made from two 
>> tubular coaxial ones cascaded. I didn't make it - it came this way as 
>> a commercial product. It has enormous stop-band suppression maybe 200 
>> dB (theoretical) by +/- 10 MHz away from fc, but large insertion loss 
>> about 10 dB. The plan was to double the 80 MHz OCXO into this filter, 
>> which should eradicate all spurious from below. The 320 and 640 MHz 
>> BPFs are more conventional.
>>
>> The 80 MHz OCXO was apparently quite common around 20-30 years ago. 
>> Despite this, I couldn't find any specs twelve years ago, and can't 
>> find any today, even though there seems to be plenty of them still 
>> around and for sale. The ones I have are Vectron 229-9237, and 
>> 229-5657-1, apparently the same except for mechanical construction.
>>
>> I have a bunch of similar units, mostly oddball frequencies in the 
>> 100 MHz range, and I did have to take some apart (soldered shut cans) 
>> over the years to modify for particular projects. I found they all 
>> used half-frequency crystals and built in doublers. The 80 MHz is no 
>> exception - a quick look on the SA shows it's a 40 MHz OCXO that's 
>> doubled up internally, so it's really only starting with a four times 
>> frequency versus multiplying a 10 MHz reference.
>>
>> Another thing I noticed is that the 640 MHz SAW BPF in the 11729C may 
>> not be for closer in spurious content, but mostly wide cleanup, and 
>> optimized to form a good oscillator when used for that mode. The 
>> manual says that the purpose of the filter is to reduce 120 MHz, 520 
>> MHz, and 760 MHz spurs. These and others naturally come from the 
>> rather complicated 8662A/8663A reference generator/multiplier system, 
>> and the 640 MHz output does not appear to have very much isolation 
>> from all this activity.
>>
>> So, if you make your own 640 MHz "clean and simple" by direct 
>> multiplication, with no side deals for other frequencies, the result 
>> will not include the extra stuff that would be coming from the 
>> generator. If you also start with a good HF OCXO with known specs, 
>> and do careful multiplication, filtering, and PLLing, I think it can 
>> beat the noise performance of the 8662A/8663A's 640 MHz source. How 
>> much? I dunno, but suspect that the hump from around 10 Hz to 10 kHz 
>> may be due in part to all the reference making and synthesizing 
>> action going on in there, that's somehow included in the 640 MHz 
>> output. That is, presuming the 10 MHz internal reference has no such 
>> hump. If it does, then it could be simply the result of the 
>> multiplication factor, and unavoidable.
>>
>> Ed
>>
>>
>>
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-- 

Jim Muehlberg
Senior Engineer

National Radio Astronomy Observatory
ngVLA Local Oscillator Lead

1180 Boxwood Estates Rd B-111
Charlottesville, VA 22903-4602
P 434.296.0270
F 434.296.0324
www.cv.nrao.edu/~jmuehlbe


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