[time-nuts] HP-3586B SSB L.O. Mods...

paul swed paulswedb at gmail.com
Tue Mar 22 21:12:03 EDT 2011


Thanks Bob

On Tue, Mar 22, 2011 at 9:09 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> If you have a stereo sound card, you could digitize both the synthesizer
> output and the BFO. Mix them both down digitally. Do the angle conversion
> and compare the phase records. The sound card clock should pretty much drop
> out that way.
>
> Bob
>
> On Mar 22, 2011, at 9:05 PM, paul swed wrote:
>
> > 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
> > verified it.
> >
> > 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.
> >
> > Regards
> > Paul
> > WB8TSL
> >
> > On Tue, Mar 22, 2011 at 8:45 PM, Bob Camp <lists at rtty.us> wrote:
> >
> >> Hi
> >>
> >> 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.
> >>
> >> Bob
> >>
> >>
> >> 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,
> >> and
> >>>> get the phase from an ATAN calculation on the I/Q results. That would
> >> give
> >>>> 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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