[1000mp] 4 kHz roofing filter

[Joe Subich, K4IK]

> So as I understand this new roofing filter would be a direct 
> replacement of the existing 70 mhz IF mod board?

Yes, it is a "plug in" replacement for the INRAD 70 MHz board 
in the FT-1000MP (installation is different in the TenTec). 

> Does the new roofing filter replace the 70 mhz MOD board and 
> it's benefits along with the improved selectivity from the 
> 4 khz filter?

The new board has 2 dB of excess gain vs. the 8 dB of gain in 
the "noise reduction" modification.  Others have shown that 
the existing "noise reduction" mod actually reduces the close 
in IMD dynamic range since the limiting factor is the overload 
point of the second (70 -> 8 MHz) mixer.  

The noise reduction modification adds 8 dB of gain (to every 
signal in the 14 KHz 70 MHz passband) in front of the "weak" 
mixer.  That gain can (and does) reduce the close in dynamic 
range by 16 dB (8db + 8 dB).  

To directly answer your question - no.  The 2dB of excess 
gain will not provide the same noise reduction as the 8dB 
gain of the previous mod (you will need to turn the IF gain 
back up somewhat).  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. 

If the noise is bothersome, consider using the radio's DSP 
and/or an external audio filter like the Idiom Press SCAF. 

73, 

   ... Joe, K4IK