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

paul swed paulswedb at gmail.com
Fri Aug 15 16:52:16 EDT 2014


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.
> 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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