[INRAD] Filter Board

[Charlie Mazoch Jr.]

Hi Steve:
I'm waiting with baited breath for Inrads roofing filters to arrive. One 
of the rigs I plan on modifying with their roofing filters is an Icom 
756. I may have enough room to add a cascade filters circuit to the 
second IF. This should make an old radio shine. The other rigs in mind 
for the first IF filters are a Yaesu FT-980, (still a great rig) and a 
Yaesu Ft-847. I'm impressed with your comments on the Inrad Yaesu 
roofing filters. The problems with OEM first IF filtering are as you 
mentioned, width of pass band and using an inadequate number of poles to 
sharpen and deepen the skirts. Two poles of filtering at 15 to 20 Khz 
width is not enough.
Charlie W5VIN
steve.root at culligan4water.com wrote:

>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 
>
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