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RE: [FlexNet] pac sat help needed



Chris:

The key to a simple conversion is how the transmit signal is generated.

If unit is a crystal unit, fairly simple to add a varactor and direct FM the
transmitter..  And better if radio design is direct FM to begin with vs a
phase modulation approach...

However, if frequency synthesized, there are two basic design approaches,
one of which converts and one that doesn't..

1) If they generate the transmit signal directly with a PLL (Phase Locked
Loop) synthesizer circuit, and inject audio into the loop to modulate the
transmitter, it will not convert to 9k6 FSK.   The reason is that the PLL
circuit will strip off the low frequency modulation components form the data
signal..  ( I shouldn't say impossible, but darn difficult, as it can be
done by modulating both the PLL and the frequency standard )

2) However, if there is a separate transmit crystal oscillator, that is FM'd
and then upconverted to channel frequency with a signal from a separate
frequency synthesizer, it will run 9k6..

As to receiver side, be it a true discriminator or an IC Quadrature
demodulator, it is simply a matter of picking off the audio directly at the
demodulator, NOT off the speaker...

Examples of the up-convert scheme include the Motorola UHF MICOR radios and
at least one UHF band ALINCO design...

Examples of good crystal radios that direct FM are the Motorola MOCOM-70 and
MITREK series... (low band 30-50, high band 150-174, UHF 450-470 MHz)

Hope this helps....

73   John   WB2CIK

 > ----------
 > From: 	Christopher Maness[SMTP:kq6up@hotmail.com]
 > Sent: 	Tuesday, September 28, 1999 1:15 PM
 > To: 	amsat-bb@amsat.org; ke6rut@juno.com; k6lg@juno.com; flexnet@qth.net;
 > sailer@ife.ee.ethz.ch
 > Subject: 	[FlexNet] pac sat help needed
 > 
 > I need advice on building a pacsat station.  I have an older 10m FM rig
 > (TPL 
 > TR-29) for an IF receiver and converter for 70cm to 10m.  I want to modify
 > 
 > this radio for 9600b FSK because my HT (Kenwood TH-79a) is constructed
 > with 
 > surface mount components and modifying the HT looks very difficult if not 
 > impossible.  I have looked at all the Internet sites to find the
 > schematics 
 > for the 10m radio, and I was not able to find any.  Along with modifying 
 > this old radio I think it needs repair or an alignment.  This would not be
 > 
 > too difficult if I had the schematics.  What are some other options?  I
 > was 
 > also considering purchasing a cheap narrow band FM receiver (such as a 
 > weather radio) and feeding it the IF from another radio.  Most radios use 
 > 10.7MHz and 455KHz for their IF frequencies.  This would cut the cost and 
 > make modification simple.  Are there cheap 440 rigs that are relatively 
 > simple to modify for FSK?  I recall someone mentioning modifying an Alinco
 > 
 > 440 radio on the bb.  At this point I don't have the cash to buy a brand
 > new 
 > FT-847 (although I'd love to), but I would appreciate the help from
 > someone 
 > who has experience working on these kinds of projects.  Thank you in
 > advance 
 > and 73's de KQ6UP.
 > 
 > ______________________________________________________
 > Get Your Private, Free Email at http://www.hotmail.com
 > 
 > ---
 > Submissions flexnet@qth.net
 > 

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