[INRAD] Filter Board

[steve.root@culligan4water.com]

A "Roofing filter" is a crytal filter that is used in the 
first IF.  My understanding of the problem is that the 
decision to include general coverage reception dictated a 
first IF frequency in the VHF range, like 70 Mc.  Until 
fairly recently it was difficult to make a narrow filter that 
operated at these frequencies.  The first IF stage was pretty 
broad, on the order of 12 Kc wide.

I have a lot of time in with both the FT-1000MP and the FT-
1000D before and after adding the roofing filters.  The 
differences are immediately apparent.  The MP in particular 
was much improved.  During periods of heavy activity like a 
CW contest I usually ran the MP with the pre-amp off and 6 or 
12 db of attenuation in line to keep the receiver 
from "crunching".  After adding the roofing filter the 
attenuation wasn't necessary as stong signals outside the 
passband were eliminated by the filter.  In a word, it's 
great!

73 Steve K0SR