Adding ALC (auto level control) to the transmitter on DMK URI using a cassette tape recorder
When I had discrete radios for my repeater's transmit and receive, I used 3.5mm phone jacks and plugs for the radio connections. This allowed me to connect an ALC device to the transmitter easily. I used the tip for audio, and the middle ring for PTT or COR, and the sleeve for ground.
Since I had the URI to Quantar repeater interface specially made, any access to those lines would be very difficult.
I've since found a way to get around that. It involves bringing the ALC in and out of the URI rather than the radio interface. This is accomplished by removing the R15 resistor from the URI and soldering in two 1K resistors and two 3.5mm audio plug pigtails to the bottom of the URI board.
The leveller: The way it works is that a cassette recorder encounters a wide range of input levels. To make it sound good, the ALC circuit in a cassette recorder has a very wide dynamic range of input. The speaker out jack usually serves as a monitor jack with a line level output while recording. If you find one that turns off output to the speaker-out jack while recording, find another one. To test, plug in a computer speaker to the external speaker jack and put the unit on record. If you hear what's going into the mic, you're good. The only other thing that you need to do is to disable the motor so that it doesn't wear out all the mechanical parts. Do this by inserting an open circuit 2.5mm plug into the remote jack (the smaller hole next to the mic jack) or cutting the wire to the motor.
A URI connected to an Allstar node, turned up to 999 on the transmit level (maxed out) which is on the susb-tune-menu, will just barely be an acceptable level for a line level input on a cassette recorder. It works, but any signals with very low audio coming in won't be amplified enough. Plugging in to the mic jack with the level on the Allstar menu turned all the way down, is still too high, and because the recorder isn't always shielded properly, the impedence mis-match causes un-wanted hum and other noise because of the sensitivity of the mic input.
Purchasing a Line to mic level adapter won't solve it either, as you're just back to standard line levels.
The fix is to place a resistor network on the URI board (this reduces the audio to MIC levels and lowers the impedence), and connect it to the MIC input on the recorder.
After doing this, any noise gets shunted to ground, and the signal left is very clean. Setting the Allstar menu level to 500 is just perfect.
Below is a schematic diagram of what needs to happen. In my installation, the white wire connects to the tip of the plug, the red to the middle. I tied the red wires together in case they need to pass PTT or COR. I left the connections exposed for clarity. I use a stereo barrel connector to test for original behavior to make sure I didn't mess anything up. Also it's good to note that the output from the ALC may or may not be adjustable with the tape recorder's volume control. If it is, you're in luck. Mine wasn't. In this case you'll need to adjust the deviation control in the radio or do like I did and put in a trim pot to adjust the level going into the repeater. Fortunately I already had an external volume control using a 10K audio Pot. You can see it in the image, the small black box just to the left of the tape recorder.