For the SRG "westlink" repeater, a custom control head was uses consisting of a box mounted on a 1 3/4" 19" rack panel. The controls right in front; power, local speaker, volume, squelch, PTT control, and a limiter meter, are handy for maintenance. There is a local speaker, COR-AF board, scanner board, and meter board mounted inside the box, with a lid for access to the adjustments. All interconnections are made either on a terminal strip or on the boards. There are several leds to indicate the status of the repeater. The cor/AF board takes in the un- squelched (flat) detected audio, is squelched, and equalized, if needed, then amplified to a usable level to drive the Tx channel element directly.

The following is a summary of the repeater hookup and functions:

Radio term Functions: strip: Remarks: Other remarks: -------------------------------------------------------------------------

Mic Hi 1 Local Mic audio emphasized

Mic Lo 2 Local Mic gnd same as Ref B-, ground

Spkr Hi 3

SW B+ 4 For Rx & Tx excitor

Spkr Lo 5 not a ground

Gnd 6 B- ref B-, ground

F1 Sel 7 F1 line

Limiter 8 M-1 was the old "F3 line"

F2 Sel 9 F2 line

Tx AF (flat) 10 repeat audio was the old "F-4 line"

Rx AF (flat) 11 "Det. audio" repeat audio source

Disc "M4" 12 M-4 was the old "PTT HI"

PTT LO 13 PTT Active low

Squelch wiper 14 to noise amp

Volume wiper 15 to audio amp

HUB 16 Hang Up Box; see text:HUB

A- (GND) 17 Strapped to ref -B inside P1

cor 18 see text:"COR" for point to use

Radio power 19 "GRN lead

20 Spare terminal was the old "ORG" lead

-------------------------------------------------------------------- THE RADIO

--------- The radio is mounted horizontally, on a 3 1/4" 19" rack steel panel. Steel is used because of the great horizontal torque on the panel. (You could mount the radio vertically, however you wouldn't have access to top and bottom without removing the radio. Also, the 2135 core is removed so you couldn't lock the radio on the bottom plate.

Other notes: ------------ Assuming you have a Mitrek manual, you might re-label the radio's functions on the appropriate schematics showing these modifications.

The boards in the control head each have their own precision voltage regulator, to keep out any power supply ripples. The meter board regulator is a 10v for running the as-stable circuit for the M-4 function.

The radio is ready for duplex-repeater operation. The UHF connector is the transmitter port and the BNC is the receiver port. I'd suggest to send in the channel elements to I.C.M. for re-crystal and compensation for the appropriate frequencies you wish to be on.

Both COR/AF and scanner boards are driven by the receiver "COR" point. It's optional which board you want the PTT out from to key the trans- mitter. This repeater uses the scan board PTT.

As you can see, you could have independent squelch threshold points for the scanner, AF and PTT actions. You will get a feel for the best way to set them.

Parts List: Time needed: first time: 1 week (40 hours)

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1 Mitrek radio T34JJA-3100A (30 watt), with control cable
1 box Bud #
1 lid Bud #
1 19" panel 1 3/4" Bud# with letter transfer kit and sealer
1 terminal strip, 20 lug #6 screws
21 feed thru cap, .001-.003 uf with nut and washer
1 BNC female connector, bulkhead with nut on one end
1 board RS-276-xxx
2 led, green
1 led, yellow
2 led, red
1 speaker 2" with glue for it and above leds
2 pot, 25K 1/8" shaft
15 resistor 1K 1/4 w
20 resistor, 10K 1/4w
20 resistor, 100K 1/4w
1 resistor, 220 1/4w
1 resistor, 1M 1/4w
5 transistor 2N3905
1 regulator, 7808, 09 or 10 *
4 cap elect 100uf/25v
2 cap elect, 10uf/25v
4 cap elect, 1-2.2uf/25v
5 trim pot, multi-turn 10K
2 trim pot, multi-turn 5M
2 IC socket, 8 DIP
2 ic socket, 14 DIP
1 ic socket, 16 DIP
6" wire, blk, red, blu, vio, wht, tan, pnk, org, , etc, etc,
4 self tapping screw, #6 (for lid)
10 4-40 screw 1/4" with 10 nuts
10 4-40 screw 1/2" with 10 nuts
2 6-32 screw with 2 nuts
1 cable clamp, 3/8" for inside the box
Heat shink or small tie wraps for bundling wire inside box
1 inline fuse and holder for "GRN" lead
1 tie down lug 3-5 lug

Tools: Drill and bits: 1/4", 1/8"
Second radio or service monitor for final alignment

PTT Hi enable (Tx exciter):

Run a jumper from the plate-through (B+) located at front of board, just below P4, to the plate-through just above R1005.

COR: J-1, Pin 18

Install a jumper from pin 18 to the plate through for the appropriate "COS" point you choose to use, either "L". "E", or "H". "L" & "E" have larger holes and are marked. For the "H" method connect the far end of the jumper to the plate-through just below C1, near the board edge. Install a jumper on the interconnect board, JU3-B. Limiter, M-1: J-1, pin 8; Install a jumper at the plate-through of the old F3 line, to J1001-1 Disc, M-4: J-1, Pin 12

Install a jumper from the plate-through next to Q1006 (J1001-4) to the plate through near and going to P10 pin 25 (old PTT Hi). Cut the run after the plate-through, which was going towards the PTT Hi circuit. (PTT Hi will get it's B+ from another jumper, in 3 steps later.)

CONTROL CABLE

------------- The control cable is plugged into the radio as usual, however, is cut shorter (about 6') and terminated with spade lugs for the rear terminal strip of the control head. The terminal numbers correspond to J-1 pins in the Mitrek manual. The station 12v power supply connects to pins 17, 19 (PA, since the PA B+ stays hot all the time), and to pin 4 (Equiva- lent to the green and orange leads), which is switched inside the control head. These runs should have inline fuses. (30 and 7.5 amp respectively). Transmitter Q703 mod was perform on 2-18-95.

This paragraph is for the "westlink" repeater only. The scanner switches both the receiver and transmitter channel elements F1, F2 at about a 15 Hz rate, fast enough to catch directional traffic. When the receiver hears the appropriate signal, it stops scanning and steers the transmitter on the appropriate frequency. It will repeat either direction, depending on who starts talking first. When the user unkeys the scanner resumes it's F1, F2 routine immediately. The two advantages with doing it this way is you need only one duplexer, feed line and antenna for the station. If your site charges by the number of stations this can be a savings. The duplexer is tuned in between the two pairs, so it's important to use adjacent repeater pairs to prevent duplexer loss. One disadvantage is there's usually a slight lag for any scanner to activate. This is added for each link-hop. Users may want to key up, then pause 1/2 second before talking. If using point L set COR/AF board, U1, pin 9 at un-squelch, and scan board U2, pin 9 at scan-stop/PTT action, at desired level of quieting. The "E" point is used in this Repeater.

This may be copied in complete form only for non-profit purposes, such as for the knowledge for the Amateur Radio Service, with AK2O credited as designer. Other arrangements please contact the author.

Copywrite: AK2O 7/6/2003