As noted in a previous email, I received my new 250Hz low offset filter
yesterday. Last night I removed my 9MHz 500 Hz filter and replaced it with
the new filter. My first impressions were disasterous, noting a sharp
decrease in signal strength when I used the new filter. Looking at the
filter specs, you see that the original 500 Hz filter has 7.5Db insertion
loss and this new filter has 14.5 Db loss! Initially rather discouraging
since one of the reasons you would want this filter is to help pick out weak
signal stations!
After 'playing around' with my Omni 6+ for a while, I found out that if
I used the 2nd IF 500 Hz filter in combination with the 1st IF 250 Hz filter
(the new one), signals seemed to pop out of the noise and QRN on 40 mtrs
last night. Not only was noise and QRN reduced, my practically useless DSP
now seems to work much better in that it now seems to really pull the weak
signals up to where they are very readable in the presence of QRN.
After comparing my Omni 6+ to a very good Icom IC-781, A/B switching the
same antenna over a six months period, I concluded the AGC in the Omni
'handles' QRN significantly better than the IC-781 (my opinion). My
impression (note: after only about an hour's use) now is the addition of
this 250 Hz low offset filter provides a significant improvement to the Omni
6+ in terms of it's ability to handle QRN. I will be very interested to
read others experiences as they install and use this filter.
Has anyone tried replacing the 'standard' 2400 Hz 9Mhz filter with a
1800 Hz filter? I'm tempted to try it, especially for CW DX contest. In the
first IF, the 2400Hz, the 1800 Hz, and the 500 Hz filters are 8-pole
filters. Replacing the 2400 Hz filter with a 1800 Hz filter would
effectively give you a 16-pole 1800 Hz filter in the 1st IF, which hopefully
may improve the stopband characteristics somewhat. Any opinions on
replacing the 2400 Hz filter with an 1800 Hz filter? I understand SSB will
be somewhat affected, but I'm primarily interested in a little rcvr system
performance improvement during CW DX contest.
Chester Alderman
chestert@pressroom.com
Tom - - W4BQF
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