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

paul swed paulswedb at gmail.com
Fri Aug 15 16:49:16 EDT 2014


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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