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

[Bob Camp]

Hi

That's what I used to do for the FMT stuff. I just used a simple divider to get a 1 KHz tone.

Bob

On Mar 22, 2011, at 9:12 PM, paul swed wrote:

> 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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