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Home Arrow II Portable Solid Element Yagis Open Stub J-Poles Fox Hunt Loops Instructions Parts

Repeater Controller Instructions

What it does

The repeater controller allows 2 radios, usually mobile units or HTs , to be connected via their speaker mike jacks to make a full-fledged repeater. The controller has many options allowing it to be configured for almost any need. One of the key advantages of this controller is that no internal connections are made to the radios; so a repeater can be put together without worries of violating FCC rules by making internal modifications to the radios.
There are two modes of operation, normal and cross-band. In normal mode, whatever is received on Radio 1 is retransmitted on Radio 2. Radio 1 is the system's receiver and is set to the repeater input frequency while Radio 2 is the transmitter and, of course, is set to the repeater output frequency. With most repeaters the transmitter only transmits. With the µ-controller, Radio 2's receiver (speaker jack) can be connected to the controller and a feature enabled that prevents the system from transmitting over anyone else on the frequency. A real plus for repeaters on shared non-protected pairs or GMRS.
When the µ-controller is set to cross-band mode, whatever is received on Radio 1 is retransmitted on Radio 2 (just like before) but now, whatever is received on Radio 2 is retransmitted on Radio 1. Of course, there are many dual band radios that have this feature built in, but few actually meet the FCC's requirements. The µ-controller can be easily configured for a full compliance cross-band repeater.
The controller has many additional options and features, all of which are user selectable and can be configured with any radio having a DTMF keypad. No special software or equipment is required for programming. All settings and ID are stored in EEPROM so once set they never go away, even when power is lost for an extended period of time.

How It Works

The µ-controller detects received signals using VOX and not carrier detect levels from inside the receiver, although there is the option for carrier detect input on radio 1 input. The audio output of the radio is greatly amplified and fed to the CPU, which monitors for activity that indicates a received signal. The system then acts accordingly by turning on the appropriate transmitter or holding the transmission until the frequency is clear (in the case of the carrier detect feature being enabled).
Rather than just detecting voice activity, the gain of the VOX circuit is set high enough to detect noise in the receiver's audio. There are 3 sources for this noise. One is the amplifier of the receiver, which all amplifiers (especially power amps) have some degree of. Another source is the transmitting radio and can come from background noise picked up by the mike, phase noise from the modulator circuit, etc. And finally, the quality (strength) of the received signal also affects noise level. Even with "full quieting" there is some degree of noise coming from the demodulator and amplifier that the repeater controller can detect and function as if it were connected to the receiver's carrier detect.


The controller has the ability to turn off the transmitter if it is on too long, which is a requirement of the FCC. There are user selectable times for the timeout of 1, 2, 3, 4 minutes or disabled (which is not really recommended but can be done). The controller keeps track of the time a transmitter is on. If it has been on for the selected period of time it sends a Morse TO, then the ID (if enabled), and turns off the transmitter. The system stays in the "Timeout State" until the input drops. The timeout resets when the input clears and the system returns to normal operation.

Timeout Reset

There are two options for measuring the timeout. In the normal (from the factory) mode, the timer runs on the status of the transmitter and not actually the input. As long as the radio is transmitting the timer is counting toward the timeout. If courtesy beep and squelch tail options are set, the timer is not reset until the transmitter drops, not when the courtesy beep sounds. Of course, a timeout isn't cleared until the input drops.
In the other timer mode, the timer is reset when there has been no input activity for .5seconds, which is the courtesy beep time. If the courtesy beep is enabled then the beep indicates a reset of the timeout timer. When in this mode the transmitter can stay on indefinitely as long as the input is reset before the timeout occurs. This mode is not recommended (or legal) for systems that are not using some sort of squelch control such as CTCSS or DCS.
It should be noted that the system can receive DTMF commands on both radios during a timeout- allowing for a reset (see enable/disable).

Squelch Tail

When the squelch tail is enabled, 1 or 2 seconds (depending on selection) of silence is transmitted after the input has dropped. A responding radio can come in before the repeater drops its transmitter thus eliminating the annoying white noise of squelch closing on everyone's receivers, making use of the repeater a little more pleasant. The squelch tail also lets others know they are actually hearing a repeater and not the talkers directly. A couple of things should be noted: the first is that this feature does not apply to cross-band mode; the second is that the transmitter must be allowed to drop within the timeout period to reset the timer if the timer reset on drop of transmit mode is selected.

Courtesy Beep

The controller can be set to generate a courtesy beep, which is a short tone generated .5 seconds after the input has dropped. The courtesy beep has two purposes: one is to let others know the person has actually stopped talking and they can now talk and the other (actually main one) is to let the person who was talking into the repeater know they actually made it. If they don't hear the beep when they stop transmitting, then they know they didn't hold the machine. When the timeout timer is set to the "reset on input dropped" mode, the courtesy beep also indicates the resetting of the timeout timer. It should be noted that the courtesy beep does not have to be enabled for the timeout reset on input drop to function. It just gives an audible indication of the reset. The courtesy beep feature applies to both modes of operation. In cross-band mode both radios transmit the beep to let users on both sides know the other is done and if they are making it into the repeater or not. It should be noted that the courtesy beep must be turned off when cross-banding to a repeater. Failure to do so will cause the repeaters to continually acknowledge each other.


The controller can be set to remove all DTMF tones passing through it. The Primary reason for doing this is to keep everyone from hearing any DTMF control codes and some users may want to prevent others from paging through their repeater. When this feature is enabled the controller turns off any transmitter that may be transmitting (Radio2 in normal mode, either in cross-band) when a DTMF digit is detected. The transmitter is held off for 1 second after the digit is gone to allow better muting of more digits. After no DTMF digits have been received for 1 second, the repeater returns to normal operation. It should be noted that even though the system isn't transmitting during the mute time, the timeout timer continues to run as if it were (something to be aware of).

Carrier Detect Hold

When the Carrier Detect Hold is enabled, the controller monitors for activity on Radio 2's receiver. If there is activity, the controller assumes the frequency is busy and will not turn on the transmitter. Once the signal is gone, the transmitter will be turned on as normal. This prevents the repeater from transmitting over others who may be sharing the frequency.
This feature only applies to the normal repeater mode. After all, if a signal is being received on Radio 2 it is being retransmitted on Radio 1 in cross-band mode. When CTCSS tones are used there are some things to consider. The radio 2 receiver can be set two ways: one is to use CTCSS decode, and in this case the repeater will only hear and not transmit over others using the same CTCSS. The other option (and best), is to set Radio 2 to no tone decode (squelch level only). It will then hear anyone on frequency and not transmit over them.

Remote Enable - Disable

The repeater can be enabled and disabled remotely with DTMF tones. The enable and disable codes (keys) are separate and can be programmed to any code sequence desired and can include any of the 16 DTMF digits. A key can be up to 15 digits long. Being separate, the enable code can be set to a long sequence so only the approved control person can turn the system on and the disable can be set to a short easy sequence to allow anyone to shut it down if the repeater is causing problems. The repeater controller monitors audio from both radios for DTMF digits so they can be received on either radio. This allows for some flexibility in controlling the system.


The µ-controller does not have CTCSS (or other squelch code) features built in so it relies on the features of the radios used. There are 2 reasons for this design decision. One, the most obvious, is cost, but it is not the key reason for the lack of the internal CTCSS tone system. The key reason is the fact the controller works through the radio's external connections. Radios are supposed to remove any sub-audible tones from the speaker output, which can make decoding difficult, impossible in some cases (personal experience). They are also supposed to remove any low frequency tones from the mike input to prevent any interference with a transmitted CTCSS tone. The degree to which the tones are removed from the external audio paths varies from radio to radio with low quality radios having little attenuation and high quality radios having high attenuation, making CTCSS detection and generation externally impossible.


The µ-controller has built in IDing functions that are user programmable. The ID can be over 70 characters long. The ID speed is fixed at 20WPM and meets FCC requirements. FCC rules state that for ham the max speed is 20wpm and for part 90 & 95 (business, public safety, utilities, GMRS, etc) the speed can be between 20 and 25wpm. The IDer tone is fixed at 1Khz, which is within FCC requirements as well (1.2Khz +-800hz). There are 3 timing (interval) options- ham (10min), business (15min), and public safety (30min). The controller actually tries to send its ID at intervals that are 1 minute less than the required timing, which isn't going to upset the FCC.

The reason for a 1minute less timing is the controller holds the ID if there is activity so it doesn't have to send it on top of someone talking. It tries to be polite. When the person drops off the ID is sent and the timer starts over. If the person talking continues until the FCC required time (1minute more) the controller sends it's ID regardless of the system activity. In normal mode this wont be a problem as the ID tones will be sent along with the re-transmitted audio. In cross-band mode it can be a problem depending on the options and transmitter activity (discussed later).
There are 2 modes of ID operation. One is the ID is sent at the selected interval even if the system has made no transmissions. The polite time of 1minute less than the FCC required time still apply. The ID will be sent every time the interval time is up, even if the repeater has not retransmitted any signals. The nice thing about this mode is it allows others to hear there is a repeater on frequency that is ready for use.
In the other mode of operation, the ID is sent only if the system has been used and actually transmitted a signal. The ID is sent at the selected interval during conversations. So, if there is a long QSO going on the ID is sent at the correct intervals. The ID is also sent at the end of a QSO. If there is no more activity (signals not retransmitted) for 82 seconds (time dictated by software space limitations) the system sends its ending ID. Of course, if the regular cycle time occurs before the 82 second end ID time the ID will be sent at the correct interval and no more IDing will take place until the system is used again.
When the system has not been used for a period of time longer than the ID interval it will send its ID on the end of the first transmission. So if the system is "kerchunked" it sends its ID as many repeaters do. If the system was accessed again before the regular interval, it won't send the ID until the regular interval or end ID (82 seconds) comes up, which ever comes first. One thing to note- If the squelch tail option is active, the system will send the start ID (if it has been idle for longer than its ID interval) as normal but it will also send the end ID 82 seconds later.
For cross-band mode there is an additional option of not IDing (inhibiting ID) on Radio1. Since in both modes (normal and cross-band) Radio 2 can act as a transmitter, Radio1 was chosen to be the one to provide ID inhibiting. In this case the system IDs itself but does not turn on Radio 1's transmitter. The reason for this option is there are situations where sending an ID on one side of the link is not required or desired.
A good example of where inhibit would be used is cross-band repeating in HAM between 2m and 70cm, which is commonly done in HTs but often not legally. The FCC considers this to be a remote base and the individual user must operate on the 70cm side (must use UHF and above for control links) and can cross-band to 2m or other lower frequencies. Since the FCC considers it a remote base the repeater does not need to ID on the lower frequency side. The user IDing themselves through the link is considered good enough for the ID of the link. The repeater must ID itself on the UHF side since it retransmits the signals of others. Since the ID of the individual operator covers the ID for the low side, the system does not need to annoy others by also IDing itself on it. Also, if the controller is used as a link connection where one side is hardwired to another controller, there is no need for it to ID on that side. If several people are using the cross band repeater, it may then be required to ID on the low side as well.

Cross-Band IDing

When running cross-band mode, several things need to be considered with the IDer. The obvious issue is that if the required (must) ID time comes up, there is a chance someone will get dropped. The probability of this depends on the options selected and how the radios have been running. The most likely interruptions will come from selecting the ID "all the time" mode with Radio1 not inhibited. Here the system will always ID at the selected interval and when it hits the must ID time, it will cause both radios to switch into transmit, send the ID and then return to their original operation. Obviously any signals being relayed through the system either direction will be dropped until the ID is complete.
If Radio 1 ID is inhibited, the signal may not be dropped depending on which direction it is being relayed. Using the example above (2M-70cm cross-band) the following will take place- if the must ID time happens while the low (VHF Radio1) side is transmitting the user will be cut off and the ID sent on the UHF side. Radio1's transmitter is turned off to prevent the ID from being transmitted and obviously nothing is being received while Radio 2 is transmitting. If the UHF side is transmitting through the must ID time the received (VHF) signal will not be dropped since there is no need to ID on Radio 1. It will continue to receive, and the ID will be sent along with the transmitted audio on Radio2. So, when cross-band repeating a 2m repeater to UHF, the signals won't be cut off every time the cross band repeater has to ID itself.
Now things get a little more complicated when we enable the ID only if the system has transmitted mode. In this mode the ID will only go out on radios that have transmitted since the last ID. If only one radio has transmitted since the last ID then the ID will only go out on that radio. In our example above where the user gets dropped (UHF to VHF relay), that would not happen if Radio2 has made no transmissions since the last ID (unlikely when linked to a 2M repeater but hopefully gets the point across). Here the ID would be sent along with the received audio from Radio2 without interrupting the link. Of course, if Radio1 inhibit is set, then no ID will be sent at all.
If courtesy beep is turned on, then IDing will occur any time the system has been used. This comes from the fact both radios transmit the courtesy beep. This means the ID will go out on both radios at the ID time. If ID is inhibited on Radio1 then we go back to the ID only going out on Radio2 so the interruption will occur while receiving on Radio2 and transmitting on Radio1. When courtesy beep is enabled, "kerchunking" the machine causes it to send the courtesy beep and, depending on which side you are listening to and the inhibit setting, the ID to be heard as in the normal mode. The difference here is that the ID will not be sent again for an end ID since squelch tail does not function in the cross band mode. If the courtesy beep is turned off, then the repeater will give no response to the "kerchunker" on Radio1 if ID is inhibited.


The controller has many options to allow it to be configured to meet almost any requirement. The controller powers up in the normal operating mode and no features can be changed, only the enable and disable DTMF codes will be recognized. To put the system into the programming mode, the power must be turned off, then the OFF/PRG button must be held while the power is turned back on (on button held for 2 seconds). The OFF/PRG button must be held until the IND LED flashes on and off at a .5second rate, indicating that it is ready to receive programming commands.
To select a feature to change, enter the DTMF code for the feature (see list). The IND LED will light while the DTMF digit is being received and then pulse the number of the selected feature, pause briefly, and pulse it again. Count the number of pulses to verify that the correct feature was selected. If the wrong one was selected, press the OFF/PRG button to return to feature selection (LED flashing at .5 second rate).
Once a feature has been selected, the LED continues to pulse the number of the feature until it has been exited or no input has been received for about 1.5minutes. It should be noted that the IND LED shows DTMF digits being received by turning on solid while the digit is received, then off for a little while before going back to pulsing indication. This allows for verification of receiving the DTMF digits. To exit a feature, press the OFF/PRG button. The IND LED will go back to .5 sec on and .5sec off flashing to indicate that the system is ready for a new command. If a feature is selected by accident (pressed the wrong DTMF button) just press the OFF/PRG button to exit without making any changes. To exit the programming mode, press the OFF/PRG button again (or don't enter anything for 1.5 minutes). The system will now go the normal operational mode and send its status.
So, a normal programming sequence is as follows- Power the unit down, hold the OFF/PRG button and power up. Continue to hold the OFF/PRG and power buttons until the led flashes. Both buttons can now be released. Send the DTMF digit of the desired feature and verify the selection by counting the LED pulses. Send the desired setting digits (observe the IND LED), press the OFF/PRG button to go back to the command mode. Select next feature by sending DTMF digit, and so on. Once all have been set press the OFF/PRG button to go to operational mode. It should be noted that in some cases it might be necessary to send the DTMF enable code to turn the repeater on once in normal operation mode.

The best way to see what the controller is really capable of is to look at its feature settings. The chart is set up where the name of the feature is listed then the number in parenthesis is the DTMF digit used to select it. As mentioned before the IND LED will flash this number (A=10, B=11, C=12, D=13) when the feature is selected. All settings are saved in EEPROM so no setting will ever be lost.

Enable code (1)- factory setting is 111
This sets the DTMF code key for enabling the repeater. Up to 15 digits can be entered and any of the 16 DTMF digits can be used in the key. Since this enables the system to transmit, it probably should be set to something long and difficult to hack.
Disable code (2)- factory setting is 222
This sets the DTMF code key for disabling the repeater. Up to 15 digits can be entered and any of the 16 DTMF digits can be used in the key. Since this turns off the system's ability to transmit, it can be set to a short easy to remember sequence to allow any user to shut it down if it is causing interference.
System mode (3)- factory setting is 2 (cross-band) for easier testing on my part.
This sets the mode of operation for the repeater.
O- (off) was included to make sure no one can turn the system on if they really don't know what they are doing. It should be noted that the programming mode must be entered and a mode selected before the repeater can become functional when mode is set to 0. The on DTMF code will also have to be sent to turn the repeater on after setting the system to an operating mode.
1- Sets the system to the normal repeater mode. In this mode whatever is receive on Radio1 is transmitted on Radio2. Nothing is ever transmitted on Radio 1.
2- Sets the system to the cross-band repeater mode. In this mode whatever is received on Radio 1 is transmitted on Radio2. Whatever is received on Radio2 is transmitted on Radio1

TX timeout (4)- factory setting is 3 minutes
This sets the amount of time the transmitter (or the input, depending on the timer mode selected) must be continuously on before timeout shutdown.
0- Disabled (no timeout)
1- 1 minute
2- 2 minutes
3- 3 minutes
4- 4 minutes
Timeout timer reset (5)- factory setting is 0 (on drop of transmit)
This sets when the timer for timeout is cleared (before a timeout occurs).
0- Reset only when the transmitter has dropped
1- Reset when input has dropped for .5 seconds (at courtesy beep)
ID time (6)- factory setting is 0 (disabled)
This sets the interval at which the ID will be sent
0- ID disabled (no ID)
1- Ham timing (10min)
2- Business (15min)
3- Public safety (30min)
ID mode (7)- factory setting is 0 (only if transmit)
This sets how the system decides if it needs to send an ID.
0- sends the ID only if there has been a transmission from the repeater. In cross band mode only the radio(s) that had transmitted will have an ID sent on them (unless ID 1 inhibit is set- where no ID will go out Radio1).
1- sends the ID at the selected interval, regardless of the system having transmitted a signal or not. In cross band mode both radios will send the ID (unless Radio1 ID inhibit is set).
ID radio1 inhibit (8)- factory setting is 0 (allow ID)
This allows the option of preventing the ID from going out on Radio 1 and only applies to cross-band mode (after all, radio 1 never transmits in the other mode).
0- Don't inhibit ID
1- Inhibit ID on radio 1 (don't send ID on radio 1)
Squelch tail (9)- factory setting is 1 second. Does not apply to cross-band mode.
This allows the option of the repeater transmitter staying up for the selected amount of time after the input has dropped.
0- no squelch tail
1- 1 second
2- 2 seconds
Courtesy Beep (A)- factory setting is 1 (enabled)
This allows the option of the controller generating a short beep .5seconds after the input has dropped. This functions in both normal and cross-band modes. In cross-band mode, the radio that was receiving will briefly switch to transmit to send the beep. This should be turned off when cross-banding to a repeater or else the controller and repeater will "play" with each other continually.
0- no beep is generated
1- generate beep
DTMF mute (B)- factory setting is 1 (mute)
This allows the option of not re-transmitting received DTMF digits. When a digit is detected any radios transmitting are turned off until 1 second after the digit is no longer received.
0- don't mute digits
1- mute digits
Xmt 2 carrier detect hold (C)- factory setting is 0 (disabled)
This allows the option of not allowing the system to transmit over others on the output frequency. This only applies to the normal repeater mode.
0- Ignore activity on radio2 receiver
1- Don't transmit if there is activity
ID programming (D)- factory setting ID (id is set to "ID")
This puts the unit into the ID programming mode. Each character (letter) is programmed one element (dit or dah) at a time with up to 7 elements per character allowed. A character is programmed by entering the elements, writing it to eeprom, then entering the elements of the next character or exiting by pressing the OFF/PRG button. The controller's EEPROM will hold over 70 characters for the ID. There are several options to aid in ID programming, such as the ability to play what is currently entered for the character, or starting the character over.
1- dit- this is entered to place a dit in the current character element position
2-dah- this is entered to place a dah in the current character element position
3-word space- this can only be entered as the 1st element of a character and takes the place of a full character. It causes the ID to pause for the period of time denoting a space between words. The play character function generates 7dahs to indicate the word space.
4-play character- Plays the elements currently entered in the character. Radio 2's transmitter turns on and the character elements are played. Once done, the system returns to waiting for data to be entered (more elements, play again, start over, write character). For a word space 7 dahs are sent.
5-re-enter character- While entering the elements of a character, this can be sent to erase what has been entered and start over. When this is entered Radio2 sends back a Morse R to acknowledge the command and let the user know that they can now start the character over.
6- write character- this writes the character into the EEPROM. Once written, the only way to change it is to start the whole ID programming over. The system acknowledges the command by sending Morse W.

Controls, Indicators, and Connections

ON Button- turns the system on. Press and hold this for a couple seconds to turn the system on. The IND led turns on and the system sends its mode setting and ID if one is programmed. The mode CW will go out on both radios if the system is in cross band mode but the ID will only go out on Radio2 if ID is inhibited on Radio1. If the system was disabled via DTMF code the system will not send anything since it is effectively turned off.
IND LED- Turns on while in normal operation. Turns off as DTMF digits are being received to give feedback that digits are being decoded. When in the programming mode the LED flashes in 1 sec intervals to indicate the programming mode. If a feature to set is selected, the LED pulses to indicate which feature is selected. The LED turns on solidly while DTMF digits are being received in this mode to aid the user in programming the features.
OFF/PRG Button- turns the system off when held for a couple seconds. Selects the program mode if held during power up. Acts as exit while in program mode.
Transmit 1 LED- Whenever Radio 1 is transmitting this LED is turned on.
Radio1 Connector- Standard 6 pin mini din (PS-2 port style) connector used for all connections to radio 1.
Transmit 2 LED- Whenever Radio 2 is transmitting this LED is turned on.
Radio 2 Connector- Standard 6 pin mini din (PS-2 port style) used for all connections to radio 2.

Radio connections

Connections to the radios are made through the 2 DIN connectors. The pin out on both connectors are similar with a couple minor differences for extra features. Standard computer PS-2 port receptacles are used to make the acquisition of connectors and the making of cables much easier. DIN connectors are available at Radio Shack (cat# 276-1474) and nicely molded cables (for the radio side) for specific radios can be acquired from TNC cable sources but can often be fabricated with parts from Radio Shack.
A 6ft male to male PS-2 cable is included for wiring the controller to your radios. The measured pin out is as follows (would be a good idea to verify your cable as the manufacturer could change their color code) Pin1- Orange, Pin2- Yellow, Pin3- Black, Pin4- Green, Pin5- Brown, Pin6- Red, Bare- cable shield. Cut the cable in half and wire in the needed connectors for your radio (usually 3/32" or 1/8 audio plugs for HTs). For many mobile radios, an 8 pin DIN mike plug (available at Radio Shack) or some other custom connector may be required. Although building your own cable isn't as clean as a factory molded cable, it works well and is much less expensive.
If the repeater radios are going to be separated over a considerable distance, regular male-female PS-2 extension cables work well. Just plug them together until the desired distance is reached.
Although there are 6 pins on the DIN connector, there are actually only 4 different connections. In most applications only 3 will be used. The pin out is as follows

1-PTT to the radio. This is a separate transmit control and is only used for radios requiring it (Kenwood, Bendix King, Etc). The output is open collector and connects to ground on transmit. If this is used it may be necessary to remove the associated resistor connecting it to the mike (used for most HTs). This is JP1 for Radio1 and JP2 for Radio2. These are solder jumper pads for connecting the PTT resistor to the radio mic. A touch with a soldering iron to the pad is usually all that is required to remove the solder jumper. Most times the resistor can be left in with no ill effects. If your radio continually transmits, then you probably need to remove the jumper (mic input load on the radio is enough to trigger the PTT on the radio through the resistor).
3- Mike input to the radio- this is the audio to be transmitted on the radio and for many radios (Icom, yaesu, Radio Shack, Etc) this also serves as the PTT line. No other connections are required for transmitting on these radios (pin 1 not connected)
5- Speaker output from the radio. This is fed to the DTMF decoder, vox detect circuit, and mike of the opposite radio.
4&6- Ground. These are all connected together and can be used at will.

Radio1 pin 2- This is a COR input for use on radios where it is required or more desirable (existing repeater radios). The COR output of a radio can be fed into this pin and the vox input disabled (remove JP4) on radio 1. The COR output must be active high (output goes high when a signal is received) and must be between 5 and 15 volts. There is no harm in connecting this pin to ground when not used (may be a good idea in fact)
Radio2 pin2- This is an external power input. The controller can be powered by feeding +7 to 20 volts into this pin. This can be used for powering the unit from radios that have voltage available on their microphone jacks or from your main power source. The controller typically draws a maximum of 12ma. Be sure to check your radio's specs for its maximum allowed current on its voltage output before connecting.

Common Connections

Icom, Radio Shack, Yaesu, (industry standard)
Radio connections- Speaker- 1/8" mono jack, mike- 3/32" mono jack.
Connecting the controller to these radios is easy and relatively straightforward. Pins 1 and 2 are not used. Pins 3 and 4 connect to a 3/32" mono plug (R.S. 274-289 or 274-290) with pin 3 connecting to the tip and 4 to the sleeve of the plug. Pins 5 and 6 connect to a 1/8 mono plug (R.S. 274-286 or 287) with pin 5 going to the tip and pin 4 going to the sleeve.

Kenwood (older)-
Radio connections- Speaker- 3/32" mono jack, mike- 1/8" mono jack
The associated mike resistor jumper should be removed (JP2 for transmitting on radio 2 and JP1 for radio 1) but try it without removing the resistor first. If the radio transmits when the cable is connected and the controller is off, then the jumper will have to be removed. Again a 3/32" mono plug (R.S. 274-289 or 290) and a 1/8" (R.S. 274- 286 or 287) are used. The speaker output on the radio is on the 3/32" jack so pin 6 connects to the sleeve of the 3/32" plug and pin 5 connects to the tip. The mike is on the 1/8" jack so pin 3 connects to the tip of the 1/8" plug. Connect pin 1 (PTT) to the sleeve of the 1/8" plug. Do not connect ground to this. Kenwood uses the sleeve of the 1/8" jack as the PTT sense and looks for a ground to be applied to this connection for PTT.
Kenwood (newer)- TH-D7, F6-
Radio connections- Speaker- 3/32" stereo jack, mike- 1/8" stereo jack

The connections are virtually identical to the above with the exception of the use of stereo rather than mono connectors. Pin 5 connects to the 3/32" stereo plug (R.S. 274-298) tip while pin 4 connects to the sleeve. No connection is made to the ring (middle section on the plug). Pin 3 connects to the 1/8" stereo plug (R.S. 274-284) tip while pin 1 connects to the sleeve. No connection is made to the ring. Again- the solder jumpers may not have to be removed. If the radio transmits continuously even when the controller is off, then the jumpers will have to be removed. Note- on the TH-F6 the radio has to be configured to use the jacks as a speaker mike jack or the system will not work.

Controller Power

The controller has its own power control system that operates with the use of momentary buttons rather than a hard on/off switch. To turn the controller on, press and hold the on button for a couple seconds. The system's indicator LED will turn on, showing that it is up and running. If a repeater mode is enabled, it will then transmit its status and ID. To turn off the controller press and hold the off button for a couple seconds until the indicator LED turns off.
There are no devices pulling power when the unit is turned off so there is no drain on the batteries. The controller always remembers its last state so if power is physically lost, it will always return to its last state (on or off). To physically power the system up, the on button must be held for 2 or more seconds. After this, the system is turned on and will always come up on when power is physically removed and reapplied. To turn the system off, the off button must be held for 2 or more seconds. After this, the system powers itself down and will remain in this state until the on button is held. It will not power up even if power is removed and reapplied.
The controller is designed to run on 7 to 20 volts. A 9 volt battery connector is supplied for easy temporary operation under battery power. An external power source can be wired to the controller using pin 2 on the radio 2 connector. The ground can be fed on pin 4,6 or the cable shield of the connector.

DTMF Enable & Disable Connections

The repeater controller can effectively be turned on and off remotely with DTMF tones. This can be done through either Radio1 or 2, or through a 3rd control radio. This allows for a great deal of flexibility in system configuration and some explanation is in order.

Radio 1- Audio from Radio1 is always connected to the DTMF decoder. Since Radio 1 is always the receiver in the normal mode, the system can be turned off or on with commands on the repeater input frequency. In some cases this may not be desirable, such as on HAM where the FCC doesn't allow the control operation of any thing on frequencies below 220Mhz. In the case of a 2meter repeater, an additional monitoring radio on UHF could be used for control. The system could still be controlled by the input frequency but doesn't have to be, thus meeting FCC requirements. Just don't send the DTMF control digits on the VHF frequency. It does give the option of shutting the system down if the control receiver fails.
Radio2- Audio from Radio2 is also connected to the DTMF decoder, which allows the system to be controlled from either input while in cross-band mode. Since the audio input from Radio2 is only used in cross-band mode, or when the carrier detect feature is used while in the normal mode, it can be used as a dedicated control input if neither of these features are used. Radio2's receive frequency could be set to an obscure frequency and serve as the control input. Another option is to feed a 3rd radio's audio into the speaker connection of Radio2 (pin5- audio, pin6- gnd). In fact, it could be paralleled with Radio2's audio. Just make sure the control receiver has CTCSS or some other squelch control so it doesn't accidentally tie up the system from noise if carrier detect hold is used.
3RD radio- An additional radio's audio input can be used for control by connecting its speaker output to J3 on the controller board. A load resistor must be added to R3 (8-16ohm 1/2w is ok) and solder jumper JP3 removed. This allows controller to decode DTMF from the third radio while not affecting the system operation. Note that you will not be able to decode DTMF from radio 2 when this is done.

DTMF Enable/Disable Control

When the system is in the normal operating mode, the IND LED will be on all the time. It turns off as a valid DTMF digit is being received and then back on when the digit is no longer detected. This helps with setting levels of the receiver(s) and can aid in system diagnostic work. While in the normal mode, received DTMF digits are checked against the programmed enable and disable codes. No other features or functions can be accessed. The system must be placed in the programming mode to change any settings.
The enable code effectively turns the system on. When the correct code sequence is received, the system sends the mode it is set to (Morse RN for normal and RC for cross-band) and then the ID if it is enabled. The repeater will now be functional. If the disable code is received the system sends Morse OF and then the ID if it is enabled. The indicator LED remains on but the system will not transmit anything. It still looks for DTMF digits for the on command and will show the digits being received. Sending subsequent on commands causes the system to send its mode and ID (can be used for a quick check) but sending subsequent off commands will not cause it to send the OF status and ID again after the system has been disabled.
Once the system is effectively turned off it will not transmit again until it receives the on code. Power cycling the system will not bring it back up. If the on code is forgotten, the controller must be put into the programming mode and a new code set and then sent while in the normal operating mode. Although this seems a little cumbersome it is intended to make it difficult for unauthorized individuals to turn on the repeater.
The enable and disable keys are decoded the same way so only one will be discussed. When a DTMF digit is first received it is compared to the first digit of the programmed key. If it is not the same as the key's, any further digits are ignored until there has been 2.5 seconds of no digits received, which brings up the point that there must not be greater than 2.5 second pause between digits when sending a valid code. The process of decoding and comparing digits proceeds for however many digits (up to 15) have been programmed into the key. If all of the digits received match the key the function (on or off) takes place and is indicated as stated above (sending status and id).


A good quality radio should be used as the receiver to minimize problems with the repeater and maximize performance. As general rule, its best to use a good quality radio that has a wide dynamic range (tolerant of strong signals at the antenna) and good mixers. The most commonly used mixer in HTs will pass anything at the antenna that mixes to the I.F. so it will be heard along with (or in place of) the desired signal (intermod). Its best to use a radio that has a tight front end, in other words, it's not a wide band scanner as well as a receiver for the desired band (these really have intermod problems). Mobile units, being larger, are a better choice for a repeater receiver, but there are HTs that work well (Radio Shack HTX-202 and 404). Avoid small, plastic cased, wide band receive HTs. These are likely to cause too many problems. Larger business band HTs (Bendix King) work well too.


Its best to use a good sized radio (especially with good heat sinks) for this job since its likely it will be operating much more than it was probably designed for. Virtually all radios are not designed to run full power transmit for extended periods of time. Its best to oversize the transmitter (i.e. if you need 5 watts, use a radio that is designed for 25 or more). If using a HT, set its power level to a lower level than its maximum. This is also a good idea when using a mobile unit. A problem, however, has turned up with some mobile units (a few Yaesus have done this) where running the mid power level actually causes the radio to fail much sooner than it would on its lowest or highest setting. The transistor that regulates power to the final takes on too much heat in the mid level setting and burns up!
If using a HT, again use a larger unit with a good metal case that acts as a heat sink. It may be very beneficial to add a heat sink externally to the case. New small plastic cased radios wonít survive long at all but the lowest power setting.
The transmitter's job can (actually should) be aided by a fan (see the fan controller circuit). This greatly helps remove heat and even allows the radio to run at much a higher output power for an extended period of time. Fans on a Kenwood TH-241 allowed it to run full power (50 watts) for over 2hrs continuously in 95degree heat. The fan system is highly recommended for any transmitter that is going to see reasonably heavy use.

System Setup

Some consideration of the radio(s) set up is in order. The first is that all special features and functions that could cause improper operation or add undesirable beeps, etc. should be turned off. This includes any CTCSS decode alerts, VOX, alarms, alerts, etc). Any auto power off functions should be disabled as well. It would not be a good thing to have the repeater up and running in a remote location and have it die because the radios turned themselves off.
The battery saver setting should be set to a reasonable time (.3sec sleep time) or turned off. If the power can be spared, it's best to turn off the battery saver. The sleep time of the saver often causes the start of signals to be cut off and weak ones to be missed all together.
Some radios have a transmit timeout built in. If the radio transmits for too long it shuts down. The timeout may or may not be user selectable (should be looked into before putting into service on the repeater). If the timeout can be turned off that is best, then the controller can handle the timeout. If the time out period is user selectable then it could be set to a value higher than that of the controller so it would act as a backup shut down. The only thing to be aware of is if the controller were set to reset on drop of input, the radio's timeout would likely keep shutting the system down unnecessarily during long QSOs.
The radio volume is the next important setting. It should be set at a level that does not cause distortion of the audio coming out of the radio. If the waveform coming out of the receiver amplifier is distorted then the audio going into the transmitter mike will be distorted. No adjustments on the repeater board will fix it. Mid volume position is usually good. The DTMF decoder can be of some help in this setting. Send digits to the receiver being set while observing the indicator LED. The LED should turn off as long as the digit is being sent. When the LED turns on then the level is too high (too much distortion) or too low. Set the volume to about mid position of the DTMF decoder functioning. It should be noted that the DTMF decoder will work with a reasonably high level of distortion so it may be necessary to turn the volume down a little more later.
Now the levels need to be set on the controller board. An easy way to do this is to override the squelch on the receiver radio(s) and listen to the transmitting radio with another receiver. Adjust the level to a point where the audio in the monitor radio doesn't increase any more than back it off a little. This should get the level pretty close to where it needs to be. With another radio send a signal through the repeater and listen to the quality. Some playing around for best sound quality can be done at this point, but it should already be good enough for most purposes. If the system is only going to function as a repeater (no cross-band) then only XMT2 level needs to be set and XMT1 level ignored. The volume of Radio 2 should be set as above if the carrier detect or control functions are going to be used with Radio2's receiver.
The beep level of the controller should be set after the radio transmit levels have been set. This can be ignored if the IDer and courtesy beep are not going to be used. The easiest way to set this is to power the unit off then back on so the system status and ID are sent. It may be easiest to remove and apply power for this rather than holding the off button then holding the on button to bring it back up. While the tones are being sent adjust the beep so it is about 1/2 the level of the audio. This should produce an adequate beep while not overriding someone talking. The FCC spec for the level is that it should be 40 +/- 10% of the maximum deviation level.

Antenna system

The antenna for the repeater is one of the most important aspects of the system. Good radios can't make up for poor antennas or location. Obviously the higher and in the clear the antenna is, the better it will work. Since this is standard for all radios we will not get into all of that. The issues associated with use on a repeater will be addressed.
There are two basic configurations for a repeater antenna system- single or dual antennas. The single antenna system requires a duplexer that allows both radios share one antenna. With a cross band repeater this is easy. All that is required is a dual band antenna (readily available) and a cross band duplexer, which is also readily available and inexpensive (about $30). With an in band repeater things get significantly more expensive and difficult. 2M ham duplexers can be expensive and are fairly large (about 15"x15"x30") to allow the radios to receive and transmit at the tight spacing of .6Mhz. 2M public safety duplexers are generally much smaller since transmit and receive separations are usually much larger (a couple Mhz or more). UHF duplexers are fairly small and are more readily available and less expensive. Obviously, the duplexer must be tuned to the frequency pair desired, which usually cannot be done without very expensive equipment. Tuning will require a visit to the local radio shop or expert with good equipment, so frequency agility is lost when a duplexer is used.
The antenna should be of good quality and have minimal SWRs on the transmit frequency. Whatever gets reflected back from the antenna the duplexor has to remove, making its job that much more difficult, and probably causing weak signals on the input to be lost. The cable should be good quality to keep loses low and the connectors on the cable can be an issue. BNCs have proven (at least in my experience) to be very poor connectors for repeaters. They can have slightly higher than 1:1 SWR and cause desense in the receiver (can be heard by wiggling the connector while the repeater is receiving a weak signal). Often times its necessary to do some work on the BNCs (flaring the ground fingers on the male side and squeezing the pin connectors on the female) to get them to behave.
The cheapest antenna system for a repeater is the dual, where each radio gets its own antenna. Again, cross band is the easiest and probably will present few problems. It's likely that 2 HTs can be placed next to each other and function OK. Of course there could be some issues of RF getting into the circuits of the opposite radio but that will usually be solved by a little separation of the radios from the antennas or each other if rubber ducks are used.
Again, the real difficulties come in with the in band system. The better quality the receiver (its tolerance for close by signals) the easier implementing a 2 antenna system will be. There are two choices for the antennas, separate them vertically or horizontally. Vertical separation is much more effective than horizontal as horizontal separation can easily require 50ft or more between the antennas before the repeater will hear reasonably week signals.
For vertical separation, 1/4 wave distance between the antennas is a good place to start, but more distance will probably be required. Some experimentation will be required to find the ideal separation distance. There will be nulls where the signal strength from the transmitter is significantly less (usually at 1/4 wave increments) and will allow the receiver to hear better. Using a scanner or HT set to have its local oscillator on the desired receive frequency can help in finding the ideal location. This is done by setting the scanner to receive a frequency calculated by- receive frequency = desired reference frequency + or - the scanner's I.F.. Whether + or - is used depends on how the scanner works- if its local oscillator is above or below the receive frequency. Some experimentation will be required, but if it doesn't work one way try the other. This will give a very good weak reference signal for experimentation. If using a HT for the signal source, be sure to turn off battery saver or open the squelch completely so it doesn't go to sleep.
Although it is more desirable to have the repeater receive antenna up as high as it can go (the top antenna) so it can hear weak signals, it may be best to have it the low antenna. The reason for this is the transmitted signal may get into the receiver cable as it passes by the transmit antenna and cause interference if itís the low antenna. Having transmit the high antenna may allow the output power to be reduced for good coverage, thus reducing potential interference to the repeater receiver. Obviously good quality cable is order to prevent any cross talk between the two. Poorly shielded cables will cause cross talk!
For in band repeaters the output power will play a role on how well the repeater hears weak signals. The lower the output power the lower the potential for desense. It is a good idea to run the repeater transmitter at as low of setting that gets the job done. Consider 1watt versus 10watts. 1 watt is 30Ddm and 10 watts is 40Dbm. Running 10 watts means the system (separation or duplexer) must remove 10 more db of potential transmitter interference to the receiver to hear an equally weak signal. 50 watts adds another 7db to the problem. Adding more power may allow the repeater to be heard better but may make it hear less, thus reducing the functionality of the system. If high output power (50watts +) is required then great care will be required in the setup of the antenna system.


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