|A while ago, I acquired about 20 radios that were destined for the dumpster, because of the FCC mandate for narrow band systems on the business bands. These radios, Kenwood TK-722R(H),appeared to come from a school district in the San Fransisco area.|
After much research, and digging through the service manual, I have a stack of radios that I can give to those that need one, and also rebuild a local repeater. I wanted to share what I did, in case someone else finds a stack like I did, and could benefit from what I did and learned.
This is a finished product that I will be donating to the local club for its annual banquet. It is destined for someone that doesn't have a radio but is licensed, so they can get involved in the hobby.
|First, I removed the aftermarket tone board on the top of the radio, it produced an annoying "Chirp" at the end of each transmission. Then I programmed the radios. Note: The removable chip on the board is for Tone Frequencies only. The same kind of chip is used for the Frequencies, but is access through the vertical port on the front board. This makes programming cumbersome because you have to use the external cable for the Frequencies, and play musical chips for the tone boards. To make it more interesting, you have to have the radio on to program the freqs, and you have to remove the tone chip and program it on the programmer unit directly (KPT-20). Also, the programmer can't do two chips at once, you have to clone each type independently.|
Once programmed, I turned the RF Output down. These radios will push up to 125 watts if you let them, so I tuned them down as far as they would go, at 35 watts. The adjustment is the port on the heat sink on the top of the radio, as shown in the picture.
|According to the Service manual, I adjusted the voltages for the Common PLL (Ref: TP1) and the TX PLL (Ref: TP2) to as close to 6.0 Volts as I could while tuned to the highest frequency the radio was to be setup for. I tuned to 147.770 MHz. Some radios wouldn't get all the way to 6.0 volts, so I adjusted it as high as they would go according to my voltmeter. These are pretty old radios, but they seem really stable.|
I found it helpful to listen to the transmission on another radio while adjusting the TX side and observe the watt meter, because you can hear the circuit collapsing, and the power output drop when the voltage was to low.
The last part was to adjust the TX Audio. The Mic audio seemed a bit low, so I boosted "MIC VR1" until I had more audio without over deviation.
The orange wire shown here is where I pulled the discriminator audio from. It is right from the tuner, before it hits the amplifiers. This row of wires I tapped into runs up to the Tone board on the top side of the radio, where it is filtered, and then returned to be amplified without the tones embedded in the signal. I ran this to the molex connector on the back of the unit for easy access. Here is the pinout of the Molex connector on the back of the radio unit.
I took apart the head, and shorted out the pads marked in the picture, and that enabled the "Talkabout" feature. Basically, when you tune to a repeater channel, and push the AUX button, it will go to simplex mode, and transmit on the repeater output frequency. I found this useful when I broadcast the ARRL Audio News, and I couldn't justify transmitting 35 watts, just to be repeated by 10 watts.
|This is the Frequency Chart I made for these radios before cloning the whole stack. I wanted these radios to be useful in my area, as well as other areas in Southern California. I attempted to verify all of them before programming, and most of them worked. I added the PL function on the simplex frequencies in case someone wanted to link it somehow, and didn't want the radio breaking squelch all the time. |
Note: If you ground the metal plate on the back of the microphone, the radio will not break squelch unless the PL for that frequency is detected. The only exception is when the Monitor button is pushed in, or that channel number doesn't have a PL.
Overall, I am pretty happy with these radios. The only thing I wasn't able ot figure out was how to get the SCAN and the ADD/DEL buttons on the control head to do anything. This might have something to do with either the type of tone board, or how it is programmed. I thought it would be handy to scan the local repeaters, but I can't complain.