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

paul swed paulswedb at gmail.com
Mon Aug 18 11:58:54 EDT 2014


I may build up the d-msk-r tracor circuit.

I seriously speculate it works as follows.
Tracor down converts NAA's signal to a 100 Hz IF.
The NAA signal is plus and minus 50 Hz msk or FSK
Making the mark 50 Hz and space 150 Hz. (Really don't know whats mark or
space nor does it matter)

The tracor d-msk-r acts as a doubler so 50 Hz becomes 100 Hz only for the
mark condition. The space goes to 300 Hz and the last stage bandpass filter
only passes the doubled mark signal at 100 Hz the signal that the Tracor
can lock to.
I believe the 300 Hz simply leaves gaps in the signal.
Purest of a guess.
When I looked at NAA in spectrum lab it did not appear as a traditional FSK
signal. Instead it was a clearly random signal without clearly defined mark
and space carriers. Kind of pointing to a OPSK like signal.

If the theory is true the d-msk-r only works on an IF of 100 Hz. The reason
tracor selected this IF over the others that could have been used.
Regards
Paul
WB8TSL








On Mon, Aug 18, 2014 at 11:17 AM, Paul Davis <
ziggy9+time-nuts at pumpkinbrook.com> wrote:

> Nat Semi App Note 72 page 18, par. 6.4 shows the configuration for
> bandpass active filter.  This matches the last LM3900 stage, so you would
> seem to be correct.  The shift in filter frequency for 200bps is because
> the higher modulation rate results in a greater frequency shift. It's like
> 50hz instead of the 25hz of the 100bps rate.
>
> Paul
>
> On Aug 17, 2014, at 4:35 PM, Robert LaJeunesse <lajeunesse at mail.com>
> wrote:
>
> It's simple, but not obvious. The LM3900 is a Norton amplifier, and while
> it has differential inputs they are current driven. (Most older op amps are
> voltage driven.) The LM3900 is powered from 10V, so I think of that as just
> above the maximimum output voltage. Both the upper amplifier and the second
> lower amplifier have 1M feedback resistors, and + inputs fed 10V by 1M bias
> resistors. That would bias the output at near the supply rail, turning
> these stages into something like half-wave rectifiers. Since the first
> lower stage has a 2M bias resistor it idles at about half supply, and
> behaves as a simple inverter. If my analysis is correct (and I worked at
> National when the LM3900 came out, a friend did apps for this odd new part)
> then the combining of the two outputs produces a negative going full wave
> rectification of the signal. The fourth LM3900 stage looks like an
> inverting bandpass filter, but I'd have to dig out some reference books to
> determine its behavior in more detail. As f
>  or the 100-200 switch I'm confused, why would the bandpass frequency be
> lowered for the higher modulation rate?
>
> Bob LaJeunesse
>
>
> Sent: Saturday, August 16, 2014 at 2:56 PM
> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
> To: "paul swed" <paulswedb at gmail.com>
> Cc: time-nuts at febo.com
> Subject: Re: [time-nuts] Cutler NAA on 24.0kHz....
> On 16 Aug 2014 at 13:35, paul swed wrote:
>
> >
> > Kenneth on the opamps that is correct.
> > But I put little U's to indicate phase. They actually represent the top
> half of
> > the input cycle.
>
> Yes, I saw those, but unless I am mistaken, you didn't add a "U" after the
> second opamp, which would have returned the phase to the input's.
>
> > In the top path it inverts once.
>
> I see twice: once through the first op amp and again through the second
> one.
> The second one then outputs to the IF.
>
> Anyway, to me, it is a very interesting and simple circuit.
>
> I LIKE "simple". I am a great believer in the KISS principle.
>
> Ken W7EKB
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