Re: Measuring PL-380 Soft-Mute

jim_kr1s <jkearman@...>

--- In ultralightdx@..., "sdwillingham" wrote:

> This suggests one way to defeat the effect: just off-tune
> from the carrier by 1 kHz, which engages the soft-mute.
> Then turn your volume knob up by 2-clicks (PL-380) or
> 4-clicks (PL-300). As long as you can live with the offset
> filtering, this should get rid of the pumping effect. Since
> you are already dealing with low-SNR signals, this technique
> should not further degrade reception.


This is true if there is only one steady signal, or at least no phase difference between multiple signals. When two signals on the same frequency are out of phase, when they cancel each other, the drop in volume is quite a bit more noticeable on the G8/PL-300wt than on the PL-380, even when tuned to the carrier frequency.

You can raise the audio floor by turning up the volume, but then the audio ceiling is increased by the same amount, so the effect is unchanged. This is what I would call pumping: the rapid periodic rise and fall of audio level caused by phase shifts, due to stations either slightly off frequency or ionospheric Doppler shift.

These effects are common on MW, especially around sunrise and sunset.  I've also observed them on SW, when ionospheric effects cause a single signal to flutter.


Jim, KR1S 

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