Very good, understood most of that. I have the unit hooked up, and got the reciever to work just fine, the transmitter is working, so now I have a unit with a 440 transmit and a 2 meter receiver. Now here is where I got lost, how do I tie them so that when a signal is heard on two meters, it keys the 440 transmitter and sends the audio out to the transmitter. You mention that I need to take a voltage to the to the receiver oscillator, can you point me in the right direction, from where should I take the voltage, and where should it goto on the receiver board.Then what should I do with the mic audio to get it to the receiver?Thanks. Mathew
Mathew, perhaps a simpler approach would be to change the transmitter
exciter and final off the rear of the unit rather than change out the
receiver. Everything unplugs with a connector in the high current lead
going to the final amp. The squelch pot can be mounted on the system
board if there is not one there already. Find a 10 K or so pot that
will fit the holes and remove a jumper that is probably already in two
of the holes and you are set for the squelch. You should not need an
audio pot, and in fact could probably remove the audio output
transformer, or at least unplug the connector that connects the
transformer to the system board. A jumper from the regulated +10 volts
to the receiver oscillator is all that is required to make the radio
duplex. A separate receive antenna input must be provided. If you want
to use the internal CTCSS board, the signal at the RUS pin on the system
board can be used for COS, as it is already processed to require both
COS and CTCSS and makes a nice way to eliminate a long squelch tail
while the CTCSS decoder is shutting down. A jumper on the system board
must be cut to prevent the decoder from going into the encode mode while
the transmitter is keyed.
You will have to process the audio from the output that feeds the
audio/squelch pot to provide flat audio to the mic input. A series 15K
resistor with a .22 cap to ground will de-emphasize the discriminator
audio from the audio/squelch pot connection to the mic input. Put a 1
mFd cap in series with audio to the mic input to block the 10V mic bias
that is fed out of the transmitter exciter. A simple transistor switch
can be used from the RUS signal to the PTT to control the transmitter.
Enough current would need to be supplied to operate the T/R switch
unless you move a wire in the connector from one terminal to another
where the T/R relay is powered from the system board to keep the T/R
relay powered all the time. If the T/R relay is powered all the time, a
simple low current switching transistor with a 10K resistor from RUS to
the base and emitter grounded with the collector to the transmit control
will suffice.
Take a look in the repeater builder dot com list of LBIs for the GE
radios and search for your radio to find a schematic for the system
board. I have not looked for it, but might be there. All the
interconnections for repeater use are available on the system board.
This is the large board underneath the radio where the receiver and
exciter plug in. I remove the interface connector to the radio and
mount a small plate in its place with the power connecton brought
through the plate. You will have to supply +12 to a couple of terminals
on the system board as well as supplying the amplifier power. Ground
goes to the chassis and the negative lead to the amp.
I hope some of this helps. I have converted several of the Exec radios
to duplex use. No control of the radio is supplied using the above mod,
but the CTCSS signal gives a degree of protection. Note that no CTCSS
signal is transmitted, as the PL decoder is not full duplex, and must be
locked in the receive mode to use RUS as the COS. COS is available on
an adjacent pin on the interface connector to the front panel connector
which is removed if no CTCSS operation is desired.
73 - Jim W5ZIT
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