[INRAD] Roofing filter and IMD?

[Randy Farmer]

>With 3 dB more signal from each tone, the IMD will be
>proportionally larger (memory wants to say the sum of the
>increase in each signal plus 3 dB but I'm not sure).

Actually, for 3rd order IMD the rule is 3 dB for every 1 dB of tone 
power increase (a 3:1 slope on a log-log plot). Thus, 3 dB more power 
(per tone) into the nonlinear device would increase the IM power by 9 
dB. The roofing filter board amplifier should provide only enough 
gain to recover from the additional loss incurred from the filter 
substitution. That is, if the new roofing filter has 2 dB more loss 
than the original filter the amp should have 2 dB gain to bring the 
signal level up to the same as it would have been with the original 
filter. More gain at this point in the receiver lineup does more harm 
than good.

73...
Randy, W8FN