Fire It Up !

Revision 03/12/14


Well, just a minute.

1. Check all your wiring, look for solder bridges, make sure that the level shifter circuit is built correctly and connected correctly.

2. Disconnect the PA from the power supply. We don't need it for a while.

3. Disconnect the exciter radio from B+, we'll debug the receiver first.

4. Double double double check the wiring of the level shifter (you should have tested the circuit when you built it). When it is hooked up to 9.6V, you should get 6V or more out of it when you take the input low (ground) and essentially zero volts when the input is high ( 5V )

Test this before you try to use it with the receiver radio. If your level shifter circuit is bad or if the transistor is shorted, you can pop the squelch chip in the receiver radio and it will ruin your day.

Do not connect the level shifter board to either 9.6V or to the PL detect pin on the audio squelch board yet.

5. Connect the radio front panel that you saved to the receiver radio. You should have the receiver radio connected to 9.6V and the discriminator connections made, with the radio power turned off.

You should have a MICOR station test set, or you should have a speaker hooked up to the speaker output of the station.

Hold your breath and energize the station.

If you hear a loud humming coming from the station speaker or test set speaker, you do not have the audio/squelch board correctly inserted. Fix it before continuing. This condition will rapidly heat up the audio output transistors in the station.

Check the receiver radio and make sure that you have correct operation:

a. power up tone when you turn it on.
b. correct squelch control operation
c. correct volume control operation
d. PL position of the squelch control mutes the radio

If so, unplug the station.

6. Connect the level shifter board to 9.6V. Do not connect the output of the Level shifter board to the PL detect pin on the audio board.

Energize the station.

Again verify that the receive radio works correctly. At this point, the squelch control in the station should work as well. You may have to operate the PL defeat switch on the station control module. Note: the operation of the two squelch controls is independent of each other.

If the receiver radio squelch is locked open, you have a problem with the level shifter circuit. Fix it before you proceed.

If the radio squelch still works correctly, with the receiver radio squelch closed or in PL position (radio is silent) momentarily touch the output lead from the level shifter circuit to the PL detect pin of the audio/squelch board. Nothing should happen. If the station squelch opens, there is a problem with the level shifter circuit, fix it before you continue.

If nothing happens, unplug the station and solder the output of the level shifter to the PL detect pin of the audio board.

Plug the station in. Again, verify that the radio work correctly, and that the station squelch works correctly. If so, you can disconnect  the radio front panel - unplug it and save it in your bag of tricks. You'll need it again when we debug the exciter.


Signal Flow Step 1 - Tracing Repeater Keying from receiver to exciter

txrx-interconnect.jpg (184895 bytes)

CSQ/PL detect into audio/squelch board
Meter the input to the level shifter circuit from the receiver radio. When the radio (not station) squelch is opened, it should go low. With squelch closed, it should be 5V.

Meter the output of the level shifter circuit at the audio/squelch board to ground. When you open the squelch of the radio (not the station squelch) it should go high.

CSQ/PL detect from audio/squelch board to backplane
If everything is normal, meter from Pin 10 of the receiver interconnect board on the backplane to ground. When you open the squelch of the radio (not the station squelch) pin 10 should go high.

CSQ/PL detect from receiver 10 (backplane) to squelch gate (don't use a trunking station squelch has a missing transistor and won't work)
Squelch gate jumpers:
OUT - 1, 2, 5, 6, 11
IN - 3, 4, 7, 8, 9, 10, 12, 13 (set for delay value), 14 (PL), 15 (PL) Even if you use carrier squelch, put in the PL jumpers.
Meter Pin 14 of the squelch gate. Again when you open the radio squelch, Pin 14 should go high.

Meter Pin 18. It should go low and stay low for the interval set by jumper 13 (a flying lead that can be set for 0, 1, 2, 4, or 8 seconds. (for now, set it to 2 seconds)

RPTR PTT from squelch gate to station control module
Station Control Module Jumpers:
1-10 IN, 11-12 OUT (you may have to experiment with JU9)
If everything is normal, meter Pin 15 of the station control module. It again should go low. Meter Pin 10. It should go high.

RPTR PTT from station control module to F1/PL module.
F1/PL module jumpers:
J2 must be IN
Meter Pin 23. It should go high. Meter Pin 3. It should go low. Pin 3 is the final link in the Repeater PTT chain.

Meter the PTT lead of the exciter radio. It should go low. You may have to turn the exciter radio on to see this work correctly, since it provides the pull-up for this signal. If the exciter radio keys.....voila!




Step 2 - Tracing Repeater Audio from the Receiver to the exciter

If you have a speaker hooked up to the station or have a test set, open the station squelch. You should hear noise from the station speaker. Verify correct operation of the squelch control and volume control.

Use a small amplified speaker such as the one Radio Shack sells -- it's perfect. Don't use a signal is too high impedance and you will hear leakage which will confuse you.

Discriminator audio through audio board to backplane
Use Station Manual for reference

Check for presence of squelch noise at pin 15 of the receiver interconnect board (where your shielded lead from the receiver radio plugs in).

If OK, clip onto JU201 on the audio squelch board and hear squelch noise. If OK, touch pin 11 of the audio squelch board (Pre-amp out). Feed on-frequency RF with test tone into the receiver with the correct PL. You should hear it at pin 11. Leave the RF on, but shut down the PL. The audio at pin 11 should mute.  With the RF on and the PL off, operate the PL defeat switch on the station control module. You should hear audio at Pin 11.

At this point note that you will be able to hear off-air audio from the station speaker even in the presence of incorrect PL. Shut off the station speaker, or turn the station volume all the way down.

Use Control and Applications Manual for reference. Refer to the cross-connect chart for the backplane board.
Attach your amplifier to Pin 14 of the receiver interconnect board at the backplane. You should hear audio if the receiver un-mutes.

With audio present at receiver backplane 14, check for audio at Squelch gate 17 and line driver 13. If you do not have audio at these two locations, but you do have it at backplane 14, check for cut traces on the backplane.

Check for audio at Squelch gate Pin 11, F1/PL Pin 22, and transmitter backplane 24. Also check F1/PL pin 18 and Station Control Pin 16.

If OK, Check for audio at Pin 12 of the old exciter connector (the input to the new pot for exciter level.)

If all of this is OK, we should be ready to set audio levels.


Step 3 - Setting Repeat Audio Levels

If it is not already (you could'nt resist) turn on the exciter radio. Verify that it keys when correct RF and PL is fed to the receiver.

Adjust the discriminator comp pot on the audio squelch board for 3/4 or better.

Adjust the repeater level control on the squelch gate module for center.

Adjust the new exciter level pot for center.

Adjust the output control on the line driver module for center, as well as the input level control.

Apply RF to the receiver with 1000 Hz tone at 4.5 kHz deviation and correct PL at 750 Hz deviation. If you are using carrier squelch, use 5 kHz deviation

If you have the ability, monitor the transmit deviation. Juggle the settings of the disc comp pot, the repeater level control, and the new exciter level control so that all of the pots are in approximately the same clock position to get 5.25 kHz total deviation out of the exciter. This is 4.5 kHz of 1000 Hz tone + 750 Hz of PL. If you are using carrier squelch, set it for 4.5 kHz deviation.

To have proper audio gain structure through the station, none of these three pots should be grossly one way or the other. If any of them are lower than the others, it will probably be the new exciter level pot.

It may be that the disc comp pot will have to be wide open....depends on variables of the individual station.

Shut down the signal generator. Try repeating through the exciter with a radio. You should get good sounding audio (no distortion). Play with them to get the best sounding (cleanest) repeat audio.

Setting up the PA

Shut down the station and hook up B+ to the PA. Terminate the PA in a wattmeter and dummy load that will take 125 watts continuously and is rated for VHF with a low SWR. This must be a proper load, if it is not it will drive the power control board crazy.

Use a small screwdriver to turn the power output control on the power control board fully counterclockwise (all the way down). DO NOT ADJUST THE CURRENT LIMIT CONTROL. Identify them and know the difference.

Using either the station PTT slide switch on the station control module or the PTT switch on the side of the exciter radio, key the transmitter and slowly turn the power control up and verify that the PA is putting out power.

NOTE - At power levels below 3/4 of its ratings or so, the PA will probably make all kinds of weird noises over the air, kind of a screeching. It is unstable and parasitic when it is making this noise. Do not connect it to an antenna unless it is running at full power. If you want to know, look at it with a spectrum analyzer when it is will understand.

If the PA is making watts, set the wattmeter so that you can accurately read 100-120 watts. With the station keyed, turn up the power control until you make 110 watts (VHF) or 75 watts (UHF). (assuming a 110 watt or 75 watt PA). The screeching noise should stop at about 75 to 80 watts. You should be able to get about 120-125 watts out of the PA, but don't run it this hard. You should be able to get 110 watts without turning the power control all the way up.

You should be able to get 110-120 watts out of a healthy 75 watt UHF PA, but DO NOT run it this hard.

AGAIN - If you have a 110 watt VHF PA, you have to run it at 110 watts. It is unstable at lower power levels. If you want a 30 or 60 watt repeater, get a 30 or 60 watt PA !!

If you have a 75 Watt UHF PA, you have to run it at 75 watts.

If you have a 110 watt VHF intermittent duty PA, you may want to add a blower to it, especially if you have a long hang time and everybody waits for the hang time to drop.

The continuous duty PA's will run for days without heating up significantly.



Setting up tone remote control levels

line1-line2.jpg (167034 bytes)

Tone remote control (TRC) is the absolute best way to directly control a repeater over an audio line, or to interface it with voting comparators.

TRC works like this. When PTT is initiated, the TRC remote generates a short burst of 2175 Hz (guard tone-GT) at 0 dB immediately followed by a short burst of 1950 Hz (function tone for F1 - FT) at 0 dB, followed by continuous 2175 Hz at -30 dB (low level guard tone - LLGT) as long as the transmitter is to remain keyed. Removing the 2175 Hz LLGT will cause the transmitter to dekey nearly immediately (after transmission of reverse burst).

A notch filter in the f1/PL module of the station removes the 2175 Hz LLGT so it is not transmitted.

This tone sequence sounds like "DEEDLE-deeeeeee" It will key a transmitter in just a few hundred milliseconds.

The following assumes that you have a 4-wire line driver module and that you have correctly configured it by referring to the control and applications manual:

1. While putting 4.5-5 kHz deviation of 1000 Hz tone into the receiver, terminate the Line 2 terminals on the backplane with a 680 ohm resistor. Using a true RMS AC meter which will read DBM, set the output level for 0 dB.

2. Using a tone remote desk set or a voting comparator, key the desk set or comparator and observe the LLGT (the deeeeee) is at -30 while the device is terminated with a 680 ohm resistor. Feed a 1000 Hz tone into the device so that the 1000 Hz level out of it is 0 dB.  Adjust the output level of the device if neccessary. The point is that LLGT should be 30 dB below the 1000 Hz line level (motorola refers to it as reference level) which should be 0 dB. (0.707V into a 600 ohm termination.

3. Remove the termination resistor and connect the device to Line 1 of the station. The station should key when the tone sequence is sent. Verify that the 1000 Hz level is still 0 dB. If not, adjust the line out level of the device. Use the input level control of the line driver module to set 1000 Hz audio deviation for the station to the same value as the repeated audio.

After removing the termination resistors and hooking everything up, re-check the levels with the real-world terminations of the devices. Set your levels to an accuracy of plus or minus .1 that's one-tenth of a DB.

A two-wire line driver module is a little different, refer to the control and applications manual.

Tone signalling levels are very important, are critical to correct operation, and must be accurately set. These levels out of whack are the sole reason that people have trouble with tone remote control and with voting equipment. Levels that are set without proper termination will be wrong wrong wrong when hooked up.


Finish it.

At this point if everything is working, you can mount the receiver and exciter radios and put the station into service. Be sure to use the outer shields for both the receiver and transmitter compartments.

Final notes: We cannot provide support for people who are not capable of doing this mod and troubleshooting their stations. If you are not a serious and capable electronics person, you should not do this mod. If you do not have the manuals, you should not do this mod. If you refuse to use the manuals, you should not do this mod.

We assume that if somebody wants to do this mod, they "get it" from the beginning and just want to know how we did it. We cannot walk you through it any more than what this article provides.

We make no warranty as to suitability for purpose, or that the repeater will do what you want. After all, we cannot stand over you and watch. We will guarantee that there is probably an error in the copy somewhere, corrections will be cheerfully made. The only warranty we provide is a Kansas guarantee: If it breaks, you get to keep both pieces.

If you have a station that you want modified, we'll do it for you -- for a fee. If you want, we'll line up all the parts including the receiver and exciter radios. We WILL warrant that it will work correctly when it leaves here, and if you don't jack with the controls it will work when it gets to you, provided that the shipper has not trashed it.

I hope that you enjoy your upgraded station, and that it gives you years of battleship tough service.

When you get these machines figured out, you will come to appreciate how incredibly well they work and what great repeaters they are.

Best Wishes.

Greg Carttar