[time-nuts] low noise multiplication to 100 MHz
dk4xp at arcor.de
Sat Jan 23 11:44:40 UTC 2016
Am 22.01.2016 um 22:40 schrieb jimlux:
> the oscillator is a HCMOS output, so figure swinging about 3.5V
> Output.. I'm feeding differential clock inputs on ADCs. I'll bet a
> +/- 300mV swing would work.
>> 4)Title said "Low Noise" needs better definition as to what kind of
>> noise and how far down. Are we to be concerned about harmonic and spur
>> content as compared to real random white noise?
> This is time-nuts.. it has to be perfect..
> But realistically, my source is probably going to be about -90dBc/Hz
> at 1 Hz, -125 at 10Hz, -145 at 100 Hz. I'm going up by a factor of
> 10, so I'd expect 20 dB worse plus a little..(nothing is perfect, eh?)
> Call it maybe -100 to -95 at 10 Hz, -125 to -120 at 100 Hz and so forth.
> harmonics are interesting: it's the sample clock into an ADC. So
> harmonics of the 100 aren't a big deal. harmonics of the 10 or 20
> are. If you have significant 90 or 110 contaminating the 100, then
> you get weird spurs.. (I had this problem on a software radio where
> the 50 MHz sample clock was contaminated with some 66 MHz from the CPU)
> Spurs cause the same issues.
> ON the other hand... spurs that are pretty low don't make much
> difference if you're digitizing a signal that is close to the noise
> floor: the spur multiplied by the desired signal is usually lower and
> down in the noise. Strong CW in band signals, though, are a real pain.
I think that top left board would not be far away:
in : 10 MHz LVDS or CMOS
out: 100 MHz CMOS 3V3
just a few hours wall clock time from layout to working as a
ham radio weekender, so please excuse my diy home board
Ok, the use of a 4046 descendant may not be the last word
from a timenut perspective, but I'll redo it with an osc of
my own anyway. Divider 100/10 is a LVC163 (161?) + lvc04.
< http://www.crystek.com/crystal/spec-sheets/vcxo/CVHD-950.pdf >
Digi-Key has 153 of them on a tape and 441 of a similar one , even
cheaper that seems to point to the same data sheet.
You can get the few dB missing close-in by transfer from your reference.
In the picture:
The bottom row of boards is a doubler 100->200 MHz using 2*BF862, slight
and diode doubler 200 -> 400 MHz, SAW filter to get rid of
100/200/300/500/600 +/-10 etc,
post amp to get a usable level again.
Still missing 400-> 800, 800->1600 to feed _my_ ADC clock input.
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