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

Bob Camp lists at rtty.us
Wed Mar 23 07:38:45 EDT 2011


Hi

Deep dips in WWVB can be from several sources. One is the sunrise / sunset thing that seems to happen on a fairly regular basis. Once you take that out, I suspect that great big storms like the one between you and Colorado just might have some influence. Any antenna, even VLF is going to be sensitive to local disruption. The issue could be quite local. Never rule out alien invasion unless you have already checked the appropriate  topic related web sites....

Bob


On Mar 22, 2011, at 9:54 PM, paul swed wrote:

> I did indeed get spectrum lab to work. Its a new install on the bench laptop
> and I just reset everything to factory on spec lab. Then changed the FFT
> sample length to higher values like 500K and filter to rectangle. I'm easily
> reading the errors that I could see on the scope.
> Ref signal is wwvb at 60KC. Perfect is 1.85000000 KC
> I read 1.849922 and 1.850370.
> Pretty much the errors are lining up with the expected DDS errors. This gets
> addicting.
> Do like when the stuff works and the theory fits.
> Though will say WWVB is going through some deep dips tonight. Wonder whats
> cooking in the ether?
> Regards
> Paul
> WB8TSL
> 
> On Tue, Mar 22, 2011 at 9:29 PM, Bob Camp <lists at rtty.us> wrote:
> 
>> 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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>>>>>> 
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