[PCR-1000] Filter Modifications for CW

[Martin Francis]

Hi there,

this is my first posting to this list (I am an active member of the 
ndblist), and having read through your archives and been unable to answer 
my question that way, I wondered if any of the list members might be able 
to help me with this query:

I'm using my PCR-1000 for logging NDBs in the range 198 - 430KHz. NDBs have 
a channel separation of 1KHz and I would like to fit a much narrower filter 
to deal with this (perhaps 250Hz or even less). Presently I'm tuning to the 
carrier frequency, switching to either LSB or USB (Canadian beacons are 
generally only LSB), then using audio DSP filtering to try and isolate the 
tone I'm looking for.   Problem is, if there's a local station on an 
adjacent channel, the AGC pulls right down and it's very hard to hear the 
DX.   With a much narrower filter I could use CW mode instead and tune to 
the mod offset frequency (e.g. for 1020Hz modulation this would be + or - 
1020Hz on nominal carrier)

Does anyone have any experience of fitting a narrower (e.g. crystal) filter 
to this set?   Is there any easy way to change the third IF frequency from 
450KHz to 455KHz, for which filters are more widely available (can this be 
done through slight adjustment of firmware variables?)

Would it make sense to apply narrower filtering to the 10.7MHz stage as 
well, and perhaps reduce some of the AM BC breakthrough I often have to 
deal with on LF?   Please note I'm already using a low pass filter between 
set and antenna

Can anyone help?


Best wishes,

Martin Francis

=======================================================
 Martin Francis

 NDBList:   Official Mapmaster + Country Co-ordinator
 Location:	Richmond Hill, ON, CANADA
 Lat / Lon:	43.53'08"N / 79.27'30"W / FN03GV
 Beacons:	312 received since May 7, 2003

 Antenna:	Twin K9AY 85' loops on 300 feet of coax
 Receiver:	ICOM IC PCR1000 with 2.8KHz filter
 Software:	NDBWebLog / WWSU / Argo / SR5 / Goldwave
 Web Site:	http://www.classaxe.com/dx
 NDB Log:   http://www.classaxe.com/dx/ndb/log
=======================================================