From: firstname.lastname@example.org (John Boteler) email@example.com (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 >adjusting) 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 444.000MC. 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. -- firstname.lastname@example.org (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.