[Lowfer] narrow filters

[jrusgrove at comcast.net]

Doug

It's been my experience that narrow selectivity in the receiver i-f offers no improvement when using 
FFT programs ... unless you are trying to remove an interfering signal. Narrowing the receiver i-f 
bandpass can actually be counterproductive in the presence of QRN as narrow filters tend to stretch 
the impulse noise. I typically run the widest i-f bandwidth available unless interfering signals are 
present. The improvement using wider i-f bandwidths is more noticeable during the summer months with 
higher QRN levels.

Listening by ear is a different animal.

Jay W1VD  WD2XNS  WE2XGR/2


----- Original Message ----- 
From: "Douglas D. Williams" <kb4oer at gmail.com>
To: "Discussion of the Lowfer (US, European, &amp,UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Sunday, October 31, 2010 8:06 AM
Subject: [Lowfer] narrow filters


> Since LF activity really seems to be picking up, I went ahead and
> ordered the 250Hz 455kHz IF filter for my R75. This, combined with my
> current 500Hz, 9MHz IF filter, should give the receiver good
> selectivity. In your opinions, would I see any additional benefit in
> getting an even narrower external audio filter? Some of the DSP units
> can provide selectivity down to 20Hz! I'm not sure if this amount of
> selectivity would help when trying for QRSS signals. I suppose it
> could be of benefit when listening for NDBs. Opinions?
>
> -Doug KB4OER
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