[time-nuts] How far can I push a crystal?
Robert LaJeunesse
rlajeunesse at sbcglobal.net
Fri Jan 18 15:05:25 UTC 2013
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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