On 5/30/16 4:06 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
I was thinking about designing a 2 m (144-146 MHz) ->HF (28-30 MHz)
transverter, using a 116 MHz local oscillator feeding a level 30 mixer.
116 + 28 = 144
116 + 30 = 146
I'm wondering what's the best way to generate 116 MHz with very low phase
noise. Phase noise at < 20 kHz offset is particularly important, but 200
kHz would be fairly important. Outside that, it does not matter too much.
The ability to lock to 10 MHz would be "nice", but certainly not essential,
as absolute frequency stability would not be of prime importance. Getting
the phase noise as low as possible would be more important. I expect better
performance can be achieved if one forgets about locking the signal source
to something else, but I may be wrong.
An HP 8663A sig gen has <-147 dBc/Hz at 10 kHz offset, but I'd hope its
possible to produce something better than is possible in a commercial sig
gen that covers up to 2.5 GHz.
Multiply up from a clean source.
A $200 Wenzel streamline OCXO is -130 at 10 Hz, -155 at 100 Hz and -165
from 1 kHz out.
20logN is 21 dB, so you should be able to get -140 or better at 116MHz,
if you're careful.
A Wenzel ULN is about 10 dB quieter..
The 10 MHz ULN is about -175 dBc/Hz from 1kHz on out.
You can get a ULN for VHF (it won't be cheap) but they quote -175 dBc/Hz
at 10kHz out for 100 MHz oscillators.
The 8663 -145 at 10 kHz spec is for the rear panel 640 MHz output, I
believe.
On the front panel, from 0.01 to 119.9, with the H40 option, the spec is
-132 dBc, (-142 from 120-160 MHz)
Of course, you'd have to find a working 8663A (and keep it working).
The E8663B isn't as quiet (and is also obsolete).
The E8663D at 100 MHz is -150 dBc/Hz at 10 kHz out.
Dave
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