Concept:
 After working with Micor base/repeater station, and mobiles converted for duplex repeater service, It became clear that the mobile audio & squelch board worked better in duplex service than the one intended for the base/repeater station. Why? The mobile audio & squelch is internally wired differently. The biggest difference is with the circuitry associated with IC-202.  The original configuration of the Station Audio & Squelch board always seems to let some squelch noise through when the station is squelched.  The use of this modification will eliminate that.  This modification will configure the board to mute the audio just like a Mobile board would.

The second part of the modification involves rewiring the COS signal to come from the RUI pin (10) of the famous Micor Squelch chip (IC 202).  It is beyond me why Motorola didn't use this logic signal in the Station originally, as it's obviously the best place to get quality COS logic.

If you are having trouble locating a Station A&S board, or the one you have don't work properly, consider rewiring a Mobile A&S board for use in your station. Go here for information on using a Mobile A&S board in the Station.

Benefits:
1. Rewiring the shunt switches will allow more effective muting of the audio path.
2. Modify board to use "And Squelch". And Squelch is helpful in eliminating the squelch burst when using the Motorola PL decoder board.

Description:
 Presented here are step-by-step instructions on how to convert a TRN 6006 A (most common station audio & squelch board) for better duplex use in a base/repeater station.
Do Not Attempt  to convert the board without a Motorola manual explaining the TRN 6006 board.

Foil traces must be cut in order to redirect the signals on the board, so be careful.

Note: The 18 pins along the one end of the board are referred to as P903 pins.
The 6 pins  (9 pins on some models)  along the side that connect to the PL decoder are referred to as P201 pins.

Conversion:
1. Cut circuit trace leading from IC 202 pin 6 somewhere between the IC and the edge of the board. (NOTE: This trace is on the component side of the board, and there is no need to remove the IC.)
2. Connect a 100 k to 120 k ohm resistor from IC 202 pin 6 to ground at a convenient location.
3. Connect a jumper from IC 202 pin 10 to the trace that was cut leading out to P903 pin 8.
4. Connect a jumper wire from IC 202 pin 6 to the intersection of C 211 and C 213.
5. For "and squelch" cut jumper JU 204.  Nothing will be connected to IC 202 pin 8.
See explanation of "And Squelch."
6. Cut IC 202 pin 13 foil trace after trace connects to C235, a .22 uF cap. IC 202 pin 13 will only be connected through C235 to ground.
7.  If you don't want to have to run the Station Control Module in "PL Disable" mode to listen to Carrier only signals, cut the trace leading from IC 202 pin 14.  This disables the PL Enable lead on the squelch chip allowing either PL or Carrier signals to be heard on the local speaker regardless of the position of the PL Disable switch on the Station Control Module.

COS will now be recovered from P903 pin 8 (RUI,  now connected to IC 202 pin 10), logic is inverted. 0 volts unsquelched. 6-9 volts squelched. IC 202 pin 10 will have a 2.2 uF cap from this pin to ground. 

If you need positive logic, ground when squelched and a open when unsquelched,  a simple transistor inverter can be added. Instead of doing step 3 above, simply connect a 10K resistor from IC 202 pin 10 to the base of a NPN transistor (2N3904, 2N2222, M9642, etc). Connect the emitter of this transistor to ground and the collector to P903 pin 8. This can all be done neatly, 'dead bug' style, on the solder side of the circuit board.

Positive logic as described above can be used if you are using some of the OEM Micor cards as these require positive logic to operate properly. This will allow you commercial guys to continue using your squelch gate modules and community tone cards with the added benefit of fully muting the local speaker audio.

NEVER connect anything to Channel Activity Indicator, IC 202 pin 13, this will upset the operation of IC 202. There should be a .22 uF cap. from IC 202 pin 13 to board ground. This cap (C 235) should already exist.

Remember to cut JU201 if using PL board, and want to filter the PL tone out of the audio path to the speaker.  Optionally, cut JU202 when using the PL board to correct for audio response.  This can be done to taste.

If you need a way to feed good audio to a repeater controller and don't want to upset the way the Micor feeds audio to the speaker, check out the Micor Muteboard. The use of the Micor Muteboard allows the original Micor audio circuitry to be used to feed a local speaker with no repeat audio level interaction.

This modification was prepared by Kevin K. Custer  W3KKC, Jan 10 1998
Page updated July 28, 2001 to include Step 7.
Page updated September 1, 2005 to explain the COS modification.
Page updated November 30, 2005 to explain the OEM COS modification.

Comments welcome, email kuggie@kuggie.com           Back to Home