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.
| Typical
Cobra/Uniden 4 Pin Wiring |
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| 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 |
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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
You can find them at: http://www.bobscb.com/kits/tr_kits.htm
