Sidetone Adjustment of RTS BP325

Fauly Beltpack? Is the call signal only partially functioning and the audio all over the shop?

Want to see if your trusty "comms engineer" has made a few onsite adjustments?

Compare the positions of the sidetone pots on a good working beltpack with one that is playing up. Any difference and you may have found your cause and saved yourself a repair bill.


Sidetone on a BP325 beltpack is the volume of one's own voice heard in your own headset when talking on an RTS channel. When talking on both channels simultaneously the sidetone volume doubles.

By default| sidetone volume is pre-set to about 10dB below the typical received level per channel; this is to confirm the 'transmission' and remind the user that the mic is live.

In very noisy environments| operators occasionaly request or reduce anyway the sidetone by means of the preset 'Balance' adjustments on the main circuit board of the belt pack.

Alternative solutions at reducing ambient noise include using ear defending headsets with good noise cancelling mics.

However the Balance adjustments are not simply sidetone volume controls| they adjust the hybrid balance and should be used with CAUTION. Incorrect settings can cause malfunction.

These controls are delicate| use a screwdriver with blade width between 2 and 2.5mm. The preset control nearest to the control panel is for Channel 1.

Select "Talk" to a channel and rotate its Balance control fully anticlockwise (the sidetone will usually increase).

Blow evenly or talk into the headset mic and rotate the Balance control slowly clockwise until sidetone is at the desired level (usually minimum). Do not rotate the control further than approximately half way. The sidetone will not reduce further and the hybrid circuit may not function correctly after this point. Repeat the operation for the other channel if necessary but only select and adjust one channel at a time.

Note that the balance (and therefore sidetone) is affected slightly by ring circuit impedance i.e. the number of belt packs (or other user stations) on the ring and the total length of interconnecting cable. Adjustment may need to be made under typical operating conditions rather than 'on the bench'.

Thanks to Chris for the tecnical info 

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