Tag Archives: amateur radio

How to build a tunable repeater on the cheap (Part 3)

In the last post, we got the COR circuit working between the Baofeng and the repeater controller.  In this post, we will continue with wiring up the Baofeng to the input side of the repeater and getting wiring looked at for output to the D710.

Byonics htkp Cable Diagram
I am using the Byonics HTKP series HT cabling for getting audio out of the Baofeng UV-5R, and providing power to the repeater.  In this case, I have the Powerpole connector on the cable.  I have a DB9 female connector with pins 5, 6 and 7 passed through (the rest are unconnected).  Pin 5 is the speaker audio, Pin 6 is Ground (linked between the shield on the headphone and the negative line on the powerpole), and Pin 7 is the +7 to +18V positive from power (red on the power pole).

The pinout on the ID-O-Matic IV has the pinouts as follows:

PIN 1 Ground
PIN 2 Power Input (6 to 20V)
PIN 3 PTT Out (keys the transmitter in FM repeater applications)
PIN 4 CW Out (on/off keyed Morse code output, NOT audio)
PIN 5 Beacon Indicator output (active when beacon is being transmitted)
PIN 6 Reset (ground to reset the ID-O-Matic IV)
PIN 7 COR Input
PIN 8 Receiver audio input
PIN 9 ID Indicator (active when Morse ID is being transmitted)
PIN 10 ALT MSG input (selects the alternate CW ID transmitted)
PIN 11 Audio Out (Morse ID and Tone output)

I put a 1K resistor between the pin 2 and 7 on the ID-O-Matic, then brought in the COR line from the Baofeng to PIN 7.  The ID-O-Matic is now setup to receive power and audio from the Baofeng and Byonics cable.

Now, to get audio out of the repeater to the D710 is pretty easy.  The D710 has a documented information about its microphone port.  It is RJ45, which makes it pretty easy to come up with a cable for.

On the Kenwood RJ45 connector, Pin3 is Ground, Pin4 is PTT, Pin5 is Mic Ground, Pin6 is Microphone input.  Output from other audio sources should have a register on the mic line of the value 470.  It should also be shunted to Pin5 via a resistor of value 3.9.  I get these values from the Sky Commander manual for the D710G.  With this fairly simple wiring, we have the following:

PIN 11 (Audio Out) PIN 6 (MIC)
PIN 12 (Ground) PIN 5 (Mic Ground)

Once these are all hooked up, the repeater should work.  The kenwood will key up when the green LED turns on with the baofeng.

I ended up moving all of this to a board with solder on plug connections from Sparkfun for the RJ45 and DB9 Connectors I am using.  Here is the board while being created:

Radio interface module for ID-O-MATIC by N3BBQ

This allows me to put the repeater in a small box and supply power / control lines to the radios via standard connectors which are already on my cables.

Stay tuned for information about duplexers in Part 4.

How to build a tunable repeater on the cheap (Part 2)

In my last post, I went over the basic parts of a repeater, and said the parts I selected for our build.  I will go into the choices further and give some information about getting the baofeng working with a COR output.

The radio I selected was the Baofeng UV-5R.  Its schematics are available online, and I found that the radio only lights up its green RX LED circuit when the PL circuit breaks squelch when using tones (unlike other handsets that show receive, even though they don’t break squelch). This seemed like the perfect place to add a link from the hand held to the controller.


The transistor shunts the circuit to ground (with the battery on the other side) when a signal comes from the radio’s PIC.  So we will have to keep a positive voltage on the COR line with a resistor so that when it shunts to ground, we can have the COR circuit go low when active (ACTIVE-LO polarity on the I/O menu of the ID-O-Matic).

So, I took the UV-5R apart (instructions are already on the web, so I will not duplicate them here), and found where the circuit physically is. It is by the PTT button, and wraps around the VFO-MR orange button.

UV-5R RX Led Circuit

You do NOT need to remove the LCD screen for this mod.  But you should remove the speaker from the board connections, and the case, so you have room to route the wire out.  I drilled a hole in the case on the opposite side (where in front of where the mic/headset plugs are).  I soldered it directly to the bottom of the two transistors (the correct circuit in this case).

Here is when I was testing the circuit before I added a ground between the two (this will be added permanently when I add my Byonics HTK2P cable that will power the controller, and give me the speaker output all at once).

Once I verified that COR was working correctly, I packed it all back into its casing with the cable done in such a way that it could be used in the future.  The Baofeng is now modded to be used as a Receiver radio with the ID-O-Matic.

Stay tuned for more information on how to build a tunable repeater on the cheap!

How to build a tunable repeater on the cheap (Part 1)

I recently set off on a small quest of building an inexpensive same band repeater for portable and special uses where there are no current repeater coverage.  I wanted something low cost, portable, and tunable without special software.

I finally settled on using some parts I already had, and other parts which I could build.  Lets take a look at what the main components of a same band repeater are:

  • Receiver Radio
  • Controller
  • Transmitter Radio
  • Duplexer

Most people know what Receiver and Transmitters are.  This isn’t a repeater that is going to be used much, maybe one weekend a year.  Therefore, I decided to use the Baofeng UV-5R I have as the receiver radio since I will not be transmitting with this radio.  The Baofeng is what I consider a disposable radio, coming in at under $50 most of the time.

For the Controller, I selected the ID-O-Matic IV by Ham Gadgets with the additional Voice Module.  This kit cost me $49.  It does Time Out Timer (keeps the repeater from being keyed up too long), morse ID, and a voice ID.  It has a simple USB (serial) interface to change settings and update firmware.  The only problem with it and the baofeng, is that it requires a COR input to know when the receiver is receiving (and to PTT the transmitter), and the baofengs (and most hand helds) do not have this output.  Also, some controllers deal with the PL codes.  However, we will be using the PL decoder/encoder on our radios, so these can easily be changed in the field.

The Transmitting radio is where you would want to spend money.  I am using a mobile Kenwood TM-D710G as my transmitter radio.  Normally, this radio can do crossband repeating by itself (and even do ID when in this mode), but we are going to just be using 1 side of the radio for this project.

Finally, the all important Duplexer.  This is the hardest part to come by cheaply.  The Duplexer / Cavity filters are important so you can use one antenna between both antennas, but not have the transmitter desensitize the receiver.  These need to be tuned, so they only allow the two frequencies you want out of the duplexer for each radio.  Cheaper duplexers you can find on Ebay from china can work, but you must make sure they are tuned correctly!.  I selected a Chinese made UHF 6cavity duplexer, and requested them to tune it to specific frequencies for me.  This included a +5Mhz offset, like normal repeaters use.

Of course, there are other things that will need to be looked at, like power, and maybe a GPS unit to supply time to the controller, but those are generally things that you can build / pickup cheap locally and use for other projects too.

In Part II, I will be writing about adding the COR circuit to the Baofeng UV-5R, and getting the repeater wired up to the receiver correctly.

How to build a tunable repeater on the cheap (Part 2)


Setting up crossband repeating on a Kenwood TM-D710

Setting up crossband repeating is pretty straightforward with this radio. In this version I use a TM-D710A with the Greenlight labs GPS module to set up crossband repeating and test it with my TYT-UVF1 handheld.

There are a few little things that are not obvious in previous instructions I found on the internet, so here is my attempt to explain it.