Measuring PL-380 Soft-Mute


Hi All,

It has been debated occasionally whether the PL-380 has
soft-mute. The short answer is: mine does (PL-380 2009.9 ver 1)
and it's fairly easy to measure. The procedure is to tune a
strong, steady station, measure its average audio level, then
off-tune by 1kHz, and finally remeasure its level.

To measure the average level, use a free computer recording
program. I think many of you have Audacity and, while it's not
my favorite, it works fine for this purpose. Here's what I did:

1) Install Audacity and launch the program.
2) Attach an audio cable from your PL-380 to the computer's
mic or line input.
3) Turn the radio on, tune in a strong station with good
SNR, and set the radio's volume control to 7 or 8. Also,
set the IF filter to 6 kHz.
4) Back in Audacity, locate the input meter (rightmost), and
click on meter to start monitoring the input. (Stretch the
meter toolbar out to see the levels better.)
5) Next, you'll have to locate your system's recording mixer
and adjust the recording level. I can't tell you the
specifics, since this depends on your sound card. If you
are using a 'mic' input, try to turn off its 'boost'
setting. Adjust the mixer level until the average signal
shows about -15 dB or so on the Audacity meter.
6) Now monitor the signal's running peak (a dark-red
vertical line on the meter). Determine a where this peak
sits for a particular talker's voice or song. For
example, I'm seeing about -12 dB on my meter now.
7) Tune the radio off-carrier by 1kHz. Even for strong
signals, this causes the radio to indicate and SNR of 0 dB
which kicks-in the soft-mute function. Measure the peak
level again. I see about -18 dB now. So my conclusion
is that my radio has about 6 dB maximum soft-mute.

The conclusion is, PL-380 2009.9 ver 1 radios have about 6 dB
soft-mute. This probably also means that the soft-mute
threshold is 6 dB, but that is not certain. We can also
conclude that Tecsun is setting this deliberately, since it does
not match with the Si4734 defaults (neither firmware 2.0 or
4.0). Perhaps one of you with a 'new' model can test if the
settings have been changed.


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