FAQs

Q: I am using the Duo Talkback unit in a new studio which is a lot noisier than the last one. I am having a problem with the audio level. Is it possible to adjust the Audio level in the Duo to give me more volume?

Yes.  There are 2 ways of adjusting the volume. You can either increase the microphone gain or increase the received audio volume.  Below are the adjustments required

Microphone Gain Setting

RV5 and the link PL11 are used together to set the microphone input gain. Note that

microphone gain is not as critical as for standard two way radio equipment due to

inclusion of audio soft limiter circuitry in the Duo. However, careful adjustment will give optimum audio quality with the minimum of extraneous background noise. PL 11 is used to select between high and low microphone gain modes as follows:

 PL11 Fitted Low Mic. Gain

PL11 Removed High Mic. Gain

 RV5 Fine Adjustment of Input Gain

Note that almost all microphones so far tested (both dynamic and electret) have provided sufficient output to be used in Low Gain mode (PL11 fitted.)

RV5 should be moved clockwise to increase input gain or anticlockwise to reduce input gain. Take care to avoid the "dead spot" between the clockwise and anticlockwise extremes of travel. The correct setting of RV5 depends both on the microphone type and on the position in which it will normally be worn. The most reliable setup method is to talk normally into the microphone whilst observing the TX output on a modulation meter (or Radio Communications test set). Start with the control fully anticlockwise and advance clockwise until normal speech gives a peak deviation of around 3kHz (25kHz radios) or 1.5kHz (12.5kHz radios). Do not advance RV5 further clockwise than necessary as this will lead to excessive background noise and may lead to acoustic feedback when used with a base station.

 Receive Gain Setting

The link at PL13 is provided to allow adjustment of the RX AF gain. Under normal

circumstances, a jumper is fitted here, and the gain is such that peak system deviation will drive the headphones to maximum output with the volume control set at maximum. With PL13 removed, an extra 20dB of gain is added in the audio path. This is useful when the radio is being used with a base station which is set up such that under normal circumstances it provides a deviation much lower than the peak system deviation. Note however, that operation in this manner inevitably compromises the received audio signal to noise ratio.

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