From: (John Boteler) (Phil Graham) writes:
>I am looking at putting up a full duplex link between my two repeaters.
>I have no experiance with Micors...

It's a shame, what you've been missing all this time :)

Since you don't mention whether you have
a mobile or a base, I shall assume a mobile since
it is the more likely choice.

>1) How to make the Micor FULL duplex?

o Split the receive and transmit antenna ports.
        The transmitter must operate through the chassis-mounted
        antenna network, so we usually drill a hole in the
        rear apron of the radio and mount a BNC connected
        to the receiver antenna port.

o Lift one side of the diode headed to Audio/Squelch board
        pin 7 to allow audio to pass during transmit.

o Connect Audio/Squelch board pin 1 to A/S board pin 4
        to supply 9.6V during transmit.

>2) How big is the Micor?  (I have to consider the rack space :-(

They are about 17 inches long by about 12 inches wide.
Don't you already have one?

>3) How to tune the Micor from 450-470 to 420-430?  (I guess some coils need

o Replace the front end coils with 420-450 split versions
        for Motracs (yes, Motorola had their eyes on our band
        way back then) but verify the location of the wire
        taps on the input and output coils or trim the 406-420
        government split coils.
        There is more to this than I can go into here, right now.

o Add about 1/4 turn to each of the three injection
        coils tucked into the end of the front end cavity
        to allow the injection filter to tune to your
        new multiplier output. Note that this will not
        be necessary if you use high-side injection to
        obtain a transmit-low/receive-high split for
        your MICOR. You can tack-solder a short bit
        of good solid wire to the end of the coils.

>4) Does it use Crystal elements or something else (raw Crystal?)?

Motorola call them "channel elements"; they are
TCXOs. Although crystal manufacturers seem to
be dropping like flies, I know for a fact
that International Crystal in 405-land knows
how to cut them. ICM part number 167908.

>5) Is there anything else I should know?

Yes, but I forgot it while I was typing #3 above.

Also, the MICOR generates its transmit frequency
by mixing the receiver injection signal with
an offset oscillator. If you end up with two
full-duplex radios, one of them must transmit
low and receive high. To accomplish this,
that radio must use a channel crystal cut
for high-side injection.

Example: to setup for 444.000 transmit and 449.000
receive, the radio would use a 16.7MC offset
oscillator, as usual. BUT, you would order
a channel crystal which is *higher* than the desired
receive frequency. The appropriate transmit
frequency is selected by tuning the exciter
filters to the required mixing product, namely

Channel oscillator: 449.000 + 11.7 = 460.700MC channel xtal

Transmit frequency: 460.700 - (11.7 + transmit offset) =
                    460.700 - 16.7 = 444.000MC

Note that you can order a different offset oscillator
to achieve a different transmit/receive split;
it need not be stuck at 5MC, particularly if
you want to make it tougher for someone
to screw with your links.

-- (John Boteler)
WARNING: You are subject to pre-emption!

Added by Dave Novotony -

To get the connections for the "outside world,"  I used the following:

COR - Audio/Squelch board, pin 8 gives +12 for squelched and ground for carrier.

RX Audio - A/S board pin 2 goes to the top of the volume and squelch pots.  This
is not de-emphasized here, so I used a 11k resistor in series and a 0.068mf cap
to ground.  Sounds great!  Good levels for the Link Com Audio board.

         pin 8-------------/\/\/\/\-----+-----
                              11K      --- .068

PTT - Used the pin on the front panel connector.  Low = PTT.  Be sure to put a
diode across the reed relay!

TX Audio - Used 1 uf capacitor as a DC block and then went directly into the
mic input on the front panel connector.  The audio shaping seems fine without
any mods.

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