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Re: LF: MSK with a Class D transmitter...?

from [Andy Talbot] [Permanent Link][Original]
To: [email protected]
Subject: Re: LF: MSK with a Class D transmitter...?
From: Andy Talbot <[email protected]>
Date: Wed, 20 Apr 2011 21:50:59 +0100
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I assume you are genrating the MSK from soundcard output, in which case two options come to mind:
 
1)  Double the frequency.  Full wave rectify the audio sinusoid, pass the AC part of the result into a comparator and into the divider.  Alternatively, as the signal bandwidth is probably quite low, square up the audio to start with, feed into one inpiut of an XOR gate.  Delay the waveform by 90 deg and feed this into the othe side of the XOR.    Output of XOR to divider as before
 
2)   Remove the  divide by two, and replace with an inverter / buffer pair to generate the out of phase drive signals.   The  input now needs to be close to a 1:1 squarwave at output frequency.   Pass the soundcard audio into a comparator and make sure it gives a 50% duty cycles.
 
 
Andy
 
ps.
or 3)    Convince the software author the S/W needs modifying to give a 2.F output
 
 
On 20 April 2011 21:32, Scott Tilley <[email protected]> wrote:
Hi All

I wonder if someone can explain to me how to feed an MSK signal into a typical Class D transmitter?

I mean by typical that the TX has a 4013 type /2 system feeding two FET drivers to drive FETs in a push-pull configuration.

If I understand correctly due to the fact MSK does not have amplitude component to its signal that a non-linear transmitter can be used.

So, how do you do this with a Class-D TX as often used in LF/VLF?

Thanks,
Scott
VE7TIL




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