[1000mp] MP Roofing Filter from INRAD

[Joe Subich, K4IK]

> When I visited the INRAD booth at Dayton, I learned from 
> George, W2VJN that the roofing filter is installed ahead 
> of the IF---in place of the IF "hiss filter" mod that many 
> have installed presently. It is apparently an "either-or", 
> so that those with the IF mod will need to choose between a
> quieter RX for weak-signal work or more-robust strong-signal 
> performance for contest work. 

That is correct.  the weak point of the FT-1000MP/MKV/Field 
is the second mixer ... its IMD3 is what sets the narrow 
IMD dynamic range.  The "hiss filter" mod reduces the close 
in dynamic range by more than 10 dB. 

I suspect, but did not have time to question George on the 
matter, that the 2 dB gain figure was a compromise between a 
little noise reduction and IMD.  I figure that one can use 
the radio's DSP or an external filter (even a relatively 
simple passive analog filter) to remove the hiss if it is 
too objectionable.  There is no way to remove the IMD once 
the second mixer gets crunched. 
 
73, 

   ... Joe, K4IK