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[TenTec] Weak Sig/Filter BW [was:Ten-tec noise and RXquestions}

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Subject: [TenTec] Weak Sig/Filter BW [was:Ten-tec noise and RXquestions}
From: pklein@2alpha.net (Peter A. Klein)
Date: Wed, 27 Oct 1999 22:47:03 -0800
[TenTec] Weak Sig/Filter BW [was:Ten-tec noise and RX questions}

>My opinion on the narrow bandwidth/noise/weak signal phenomenon is that when 
>trying to copy a weak sig out of the noise, narrower is worse(er).  The 
>reason being, the noise is limited to a frequency bandwidth that is *really* 
>close to the frequency [say, 600 Hz] that you are trying to copy.  It's 
>harder for your brain to distinguish that.  Broaden the filter, and the weak 
>signal is easier to copy because the adaptive filtering in your head can
>out as 'noise' all the garbage that is occuring in a wider [say 2,4 kHz BW] 
>filter, even the stuff close to that 600Hz tone you are trying to copy.

One trick you can try is to put the signal near the edge of the filter
passband.  That makes the signal a different pitch than the apparent
resonant frequency of the noise through the filter, allowing your brain to
do its adaptive filter thing.  

In other words, if you have the 250 Hz filter and your normal sidetone/CW
frequency is 600 Hz, tune a signal to 600 Hz pitch by matching it to the CW
sidetone.  Then rotate the PBT so the noise appears to lower in pitch, and
do it until the signal just disappears. Then back off the PBT until the
signal just reappears again.  Hear the difference?  You can also set the
noise higher in pitch than the signal, but I think most people would prefer
it lower.

Another way to do it is to offtune the signal with the RIT.  Offtune the
signal until it just disappears, then back off until you hear it again.

FWIW, I find the stock TenTec 250 Hz filter for the 6.3 MHz IF very good
for weak signals more often than not.  The trick above doesn't work on the
very weakest of signals, which need every bit of gain you can get.  But for
most operating, it increases my comfort level.

73 from KD7MW,

--- Peter
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