[Elecraft] filters and contests and interference question/opinions

[Bill W4ZV]

goldtr8 wrote
> 
> Currently I have a 2.7, and 2.1 filter plus the narrow ones for digital.
> 
> My brain is starting to tell me to stop using the 2.1 and get either a 
> 1.8 or even a 1.5 or possibly both.   My thoughts are that the dsp would 
> work much better if some of the interference can be directly blocked out 
> by the filter.   These thoughts are guided by past readings on the list 
> that this is the case.
> 
> What is the collective wisdom of these filter changes I am thinking 
> about.   I am curious about others who may have tried these and if they 
> kept them or if they thought it made no difference at all.
> 

The answer is...it depends.  :-)

I believe you're fairly new to radio and contesting.  Therefore I'm assuming
you mostly tune for DX stations and call them rather than running a pileup
yourself, which requires good antennas and high power on SSB.  For DXing or
Search and Pounce (S&P) contesting, you normally have plenty of time to tune
in stations carefully before calling.  In this case narrow filters (either
XFIL or DSP) will work even with bandwidths down to 1.5 kHz.  BUT...this
assumes you have time to carefully tune in the station you want to call.

In the case of someone running a pileup at fairly high rates (e.g. 150-200
per hour), it's a different situation.  You want to copy callers correctly
the first time without any tuning, send your exchange and get his exchange
in the space of 15 seconds and go on to the next one.  The problem with
extremely narrow SSB filters is that many callers will be slightly off
frequency (e.g. 100 Hz) which renders them unintelligible when using narrow
filters.  With a little wider filter, your ears can still copy the
off-frequency guys without needing to touch the VFO.  

I had a 1.8k filter in the CQ WW last October and gave up using it because
of this problem...and a 1.5k would be even worse.  Instead I found myself
using a DSP setting of 2.0-2.1k with the stock 2.7k XFIL, so after the
contest I traded my 1.8k XFIL for a 2.1k.  Unfortunately conditions on my
favorite SSB band (10m) have been so poor that I opted not to enter the ARRL
DX SSB or CQ WPX SSB and really haven't had a chance to try it under fire,
but I believe it will be better than the 1.8k for my purposes. 

As Don said earlier, the major advantage of a narrow XFIL is to prevent AGC
pumping from strong stations nearby.  In extremely crowded contests this can
be a major problem.  However a narrower filter WILL NOT remove the splatter
from nearby stations...nothing can do that short of using phased antennas to
null their signal.

73,  Bill




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