[time-nuts] HP-3586B SSB L.O. Mods...
paulswedb at gmail.com
Wed Mar 23 01:05:58 UTC 2011
Welll I sort of went past this and have a reasonable answer.
All system locked to a rb ref.
A HP8660 as source gen and set to 3 MC.
The 3586 if is 15.625KC.
Set a HP 3335 to the IF frequency and on a scope the signals lined right up
and are stable. Bob I think you or someone else mentioned this fact and I
Then I went to the audio out on the 3586. That signal should be 1.850KC.
Set the 3335 to 1.85 KC and watched the drift rate for USB and LSB.
The answer is for 1 cycle drift rate is;
2.68 seconds for lsb or 2.0X10-4 (This will bring responses)
9.97 seconds for usb or 5.4X10-5
Have to say that drift is way below what my ears can hear these days.
So though I could change the DDS for FMT use and drive the decimal point at
least 3 more digits to the left. I really have to say good enough and a
success from just two weeks ago.
On Tue, Mar 22, 2011 at 8:45 PM, Bob Camp <lists at rtty.us> wrote:
> My assumption is that to do any of this, some sort of calibrated clock on
> the sound card would be needed. Either a mod to the card, or some luck with
> the built in clock source. It's going to be needed weather you use an FFT or
> some other DSP process. For a "fully locked" system, mod the sound card for
> an external clock and whip up a phase locked loop to drive it.
> The mix down source would likely be purely digital. Inserted after you had
> the sample stream. My first choice would be to use a 2 KHz "stupid clock" (0
> 1 0 -1) with an 8 KHz sample rate. Pretty simple math.
> On Mar 22, 2011, at 6:23 PM, Alberto di Bene wrote:
> > On 3/22/2011 5:24 PM, Bob Camp wrote:
> >> The other approach would be to simply take the samples, do a mix down,
> >> get the phase from an ATAN calculation on the I/Q results. That would
> >> you pure phase and thus frequency.
> > How do you intend to generate the numeric LO stream to use for the mix
> down ? It must have a sampling rate
> > with a precision comparable to what you intend to measure...
> > 73 Alberto I2PHD
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