[time-nuts] How far can I push a crystal?

[Robert LaJeunesse]

Ed,

Please forgive me for commenting, but I can't seem to follow your math. I 
suspect there may be additional details you have not related, no big deal there. 
It doesn't help that I'm not familiar with the 8566B, and the manual I grabbed 
from Didier's site doesn't give me numbers that match up with yours, so I'll 
just present my understanding based on your supplied numbers. 

To look at what you were doing more concisely I did a quick spreadsheet, and 
came up with this:
 10  MHz 
div by 100  
 0.1  MHz 
mult by 107  
 10.7  MHz 
div by 180  
 0.0594444  MHz 
mult by 169.224299  
 10.0594444  MHz 
mult by 120  
 1207.13333  MHz 
mult by 3  
 3621.40000  MHz 

So I'm not sure how you get from 59.4444KHz to 10.0594444MHz by a PLL unless you 
have a really good fractional scheme to do the 169.224299 multiplication. (The 
fractional part .224299 ~= 64082 / 258699 so it is a bit ugly to do.) Or are you 
mixing the 59.4444KHz with 10MHz and using the sum only? I'd think that would be 
difficult given that the difference frequency is not that far from the desired 
output.

Being the "nut" that I am I looked at some other ways to get from here to there, 
ending up with a simpler multiply-divide scheme like this:
 10 MHz 
div by 300  
 0.033333333 MHz 
mult by 953  
 31.76666667 MHz 
mult by 38  
 1207.133333 MHz 
mult by 3  
 3621.400000 MHz 
Unfortunately the intermediate 31.76666MHz is not commonly available in a 
crystal or VCXO, and too far to pull a 32MHz part, so a custom crystal would be 
needed. 

respectfully,

Bob LaJeunesse

p.s. Should you find it useful I've attached the spreadsheet I used.


----- Original Message ----
> From: Ed Breya <eb at telight.com>
> To: time-nuts at febo.com
> Sent: Fri, January 18, 2013 1:34:19 AM
> Subject: Re: [time-nuts] How far can I push a crystal?
> 
...
> 
> For  the curious: The 10.0594444... MHz is made by a PLL using the 59.4444... 
>kHz  reference, which is 10.7 MHz divided by 180. The 10.7 MHz is a from another 
>VCXO  (which can use a standard crystal, ceramic resonator, or ceramic IF filter 
>-  easy) that's phase locked to a 10 or 1 MHz reference, using two fixed 
>dividers.  The 10.0594444... MHz is used as the reference for a phase locked 
>microwave  brick oscillator, using n=120, to make 1207.1333... MHz, which is 
>exactly  one-third of 3621.4 MHz, the low-band upconversion IF of the HP8566B 
>spectrum  analyzer. The 1207.1333... MHz is harmonically mixed (m=3) with the 
>first LO of  the SA to produce the tracking signal centered in the passband of 
>the SA. All of  this is built into the modified carcass of an HP8443A tracking 
>generator,  originally built for older SA models. Using the new stuff, plus 
>parts of the  8443A, the net result is a 50 kHz to 250 MHz tracking generator, 
>with power up  to +10 dBm, leveled within about 1 dB, and with 130 dB step 
>attenuator range -  very nice for low RF and baseband work.
> 
...
> Ed
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