Message-ID: <008401bf0ab3$17e3ebe0$16fbabc3@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
Subject: LF: re Toni's comments on the 7030 and filters
Date: Wed, 29 Sep 1999 20:10:23 +0100
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Hi Toni, thanks for the comments....yes I know what you mean, it is a very
fiddly rig to operate. I am finding ways of dealing with that and am not
having too much trouble. I think I agree with your comments on filters in
part.

I have found that, after installing the 500Hz filter, I did not get the
advantage I expected. It does make copying weak stations a little easier, I
can maybe copy about 3dB weaker signal than in the SSB 2.5kHz filter. I
would have expected nearer 7dB for a reduction in bandwidth of 5 times.
Maybe I am too optimistic! The problem seems to me to be that as the signals
approach the noise level the bandpass peaked noise does tend to mask the
signal. Not being an experienced CW operator, and as a result probably not
having quite so good a filter between the ears,  I have learned a few tricks
like placing the wanted signal on the shoulder of the filter resonse to make
the tone stand out a little more from the filtered noise. Also the use of an
acoustic multipath 'filter' on the speaker. I have conventional audio
filters at between 150 and 70Hz but find they do not improve the readability
of weak signals at all. The DO help if there are other signals in the
passband, but only if the QRM-free signal would be readable without the
audio filter. Even then I find a notch is often better than a peak.

I certainly would like to try a narrower filter for the AOR...so far I
cannot find one. Are you aware of a 455kHz filter with a bandwidth of 300Hz
or less I could use?? I am quite willing to kludge anything in. I buy kit
for keeps and don't care about resale value if it works well. I suspect at
this IF I may have to have a little more amplification to counter the
insertion loss of a really narrow filter. That probably means I may have to
build a small daughter board to drop into the spare filter slot. Filter
alignment is by software and automatic, so even if the frequency wasn't
quite right, it may not matter too much.

73 de Alan G3NYK
Alan.Melia@btinternet.com