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Baofeng UV-5: Squelch Tail Elimination

Baofeng UV-5 radios can (mostly) eliminate the loud hiss heard at the end of a transmission before the squelch kicks in after the received carrier drops: Menu → 34 STE → ON. A detailed description of the option suggests it’s a 55 Hz subaudible tone sent for 250 milliseconds after the sender releases the PTT and before the transmitter stops sending, with the receiver muting its audio during the tone. Obviously, this requires a Baofend radio at each end of the conversation, which applies to our bikes.

Saying “laaaa” while kerchunking (into a smaller dummy load than the hulk) with STE OFF:

Baofeng - STE OFF - laaaa

Baofeng – STE OFF – laaaa

Compared to the received audio, the squelch tail hiss is really really loud.

Then with STE ON:

Baofeng - STE ON - laaaa

Baofeng – STE ON – laaaa

You can see the STE tone reception start about 250 ms before the audio cuts off, although it’s not at all clear the audio is muted on either end. In any event, there’s no squelch tail worth mentioning, even if there’s an audible tick when the STE tone starts.

Saying nothing with STE ON:

Baofeng - STE ON - silent

Baofeng – STE ON – silent

It’s unlikely the audio output would include the subaudible tone, but you might convince yourself something happens in the 250 ms between the STE blip near midscreen and the final pop (now clipped) as the audio drops.

All in all, a definite improvement!

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  1. #1 by david on 2018-08-14 - 22:49

    Only Baofang could fuck up something that’s been completely standardized since literally the days of tuned mechanical reeds for squelch coding… sigh. http://www.repeater-builder.com/micor/reverseburst.html

    • #2 by Ed on 2018-08-16 - 07:35

      I wonder how much DSP you’d need to detect the phase reversal? Probably more than you can stuff in a $25 radio.

      Obligatory XKCD

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