CBWI September 2001 The RF Limited UTB-1

The RF Limited UTB-1

The Universal Talk-Back Board is what the name suggests, a talkback PC board that installs into any CB or 10-Meter transceiver and produces adjustable talkback. It’s the first talkback board that incorporates an on- board audio amp. This allows talkback, which will work on all modes of communication, to be installed in any radio. This board does require more work for installation than other units, but the clear talkback is worth it. It doesn’t have a switch to turn it off, but with the talkback volume control fully counter-clockwise, the talkback level is zero. The on-board amp is a low power amplifier. To use a high power amp would be too costly and the only accomplishment would be to create louder feedback. The amp is more than sufficient for talkback purposes. In addition, a higher wattage amplifier would be larger and require more associated components, requiring a larger PC Board. With all the add-ons and with what’s in some of these radios already, for example, the Galaxy DX99V, the smaller the talkback board the better.

The UTB-1 kit comes with instructions that will allow anyone with some basic electronics and soldering experience to install this board easily. There is technical update and a diode included with every board. This update is for radios that won’t allow the UTB-1 relay to release after a transmission is completed. These radios hold the TX line down to 8 volts or lower leaving 4 volts or more across the relay. This wasn’t a problem on the prototype boards, because the original design in used a 5-volt relay and a resistor in series with relay in the circuit. The relay was changed to a 12-volt unit and the resistor was eliminated because factory had an abundance of 12-volt relays and at the time, and no one envisioned a problem using them. However, the issue became clear as soon as techs started to install them and call with complaints. See the diagrams below for the technical update.

RF Limited UTB-1 Universal Talk-Back Board Box

RF Limited UTB-1 Universal Talk-Back Board And Adjustable Control

Typical Cobra/Uniden 4 Pin Wiring

Typical Cobra/Uniden 5 Pin SSB Wiring

This talkback works well in radios that have none adjustable talkback too. The talkback in most radios is a crude setup. What is done in the circuit is to eliminate the switching that occurs during transmission that eliminates the RF modulating the audio amplifier via the supply voltage. Many of these radios do not have an audio input to this amplifier; it’s just the RF and fluctuation of the supply voltage to that amp that causes talkback. If you ever noticed on these radios that the talkback on sideband sounded like listening sideband on AM, this is why. Also in these radios the talkback won’t work on FM. There is no fluctuation in supply voltage during FM transmission. Some of the later radios that include an adjustable version apply the audio through a potentiometer to the audio amplifier. These work better, however some still have the supply voltage problem, resulting in low level distortion when the control is set low or off.

Typical Diagram Of Installation

The UTB-1 generates a clear version of talkback that in most cases works independent of the mic gain control. There’s no need to reset the talkback every time the mic gain is adjusted. One trick to getting clean audio talkback form this board is in the ground placement. Moving the black wire to different ground locations produces better audio. This should be kept in mind when making an installation. Another tip, don’t connect the shielded portion of the gray input cable. This will increase the instance of distortion. It can be covered in shrink sleeve tubing or cut off. Bob F

September 2001 Web Edition