[time-nuts] Cutler NAA on 24.0kHz....

paul swed paulswedb at gmail.com
Fri Aug 15 16:56:01 EDT 2014


Yes I can see on page 2 of the pdf thats the trick. Its a non costas loop
trick.
"The action of the MSK card doubles the phase shift".....
So it is the classic double the frequency stateless carrier recovery. that
may drop phase due to noise.
Regards
Paul
WB8TSL


On Fri, Aug 15, 2014 at 4:52 PM, paul swed <paulswedb at gmail.com> wrote:

> www.glkinst.com/test-equipment/manuals/Tracor*900A*.pdf
>
>
> On Fri, Aug 15, 2014 at 4:49 PM, paul swed <paulswedb at gmail.com> wrote:
>
>> David
>> Yes I have seen various comments and documents describing MSK that way.
>> But have to say the tracor 900 does not use that method to establish a
>> reference.
>> Its a few opamps perhaps one side acting as a phase delay summing with
>> the original and hitting a BPF. all of that running at 100Hz center
>> frequency.
>> Through this magic the 900 could use NAA as a phase tracking reference.
>> Its as if its a classic phase doubler. The documentation almost speaks to
>> that.
>> Its seriously simple.
>> Regards
>> Paul.
>> WB8TSL
>>
>>
>>
>> On Fri, Aug 15, 2014 at 4:31 PM, David I. Emery <die at dieconsulting.com>
>> wrote:
>>
>>> On Fri, Aug 15, 2014 at 03:09:23PM -0400, paul swed wrote:
>>>
>>> > I had discounted it because of the lack of info and totally unclear
>>> how to
>>> > get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
>>> > effects of the fsk on the carrier. Hmmm glad I am typing this.
>>> > It may be that the mark or the space is indeed exactly the true
>>> carrier and
>>> > that op amp circuit is notching out the shifted carrier. I will bet
>>> thats
>>> > the trick!
>>>
>>>
>>>         MSK is a kind of continuous phase differentially coded PSK in
>>> which the carrier phase smoothly shifts either EXACTLY plus 90 degrees
>>> or EXACTLY minus 90 degrees in EXACTLY one symbol time - in the MSK
>>> variety of PSK the transmitted carrier phase never stays the same as the
>>> it was the last symbol time.   When transmitting steady mark there are a
>>> series of these shifts plus 90 degrees (hi frequency mark) one after the
>>> other, and when transmitting steady space there is a series of minus 90
>>> degree shifts.
>>>
>>>         Obviously a steady negative phase shift is what is produced by
>>> a signal below a center "carrier" frequency and a steady positive
>>> phase shift by one above that frequency.   Thus the isomorphism with
>>> filtered FSK.
>>>
>>>         Effectively a QPSK (multi-arm Costas type) tracking loop should
>>> be able to track a MSK signal just as if it was a filtered QPSK signal
>>> with only 90 degree and minus 90 phase shifts each symbol time and
>>> generate
>>> a phase continuous recovered carrier.
>>>
>>>
>>>
>>>
>>>
>>> --
>>>   Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston,
>>> Mass 02493
>>> "An empty zombie mind with a forlorn barely readable weatherbeaten
>>> 'For Rent' sign still vainly flapping outside on the weed encrusted pole
>>> - in
>>> celebration of what could have been, but wasn't and is not to be now
>>> either."
>>>
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>>
>>
>



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