[1000mp] Sub receiver filter question

[Joe Subich, K4IK]

Bruce, 

>     I'm thinking of changing out an INRAD 703-C (400 hz) 
> filter in the sub receiver for a 704-C (250 hz) or 712-C (300 
> hz) filter.
>     Any opinions, or expressions of experience would be appreciated

I had the same question a couple years ago when I got my Mark V.  I 
asked George at INRAD a series of questions about filter options (I 
had some stock Yaesu filters from another radio).  Here is his answer 
about using a 300 Hz fitter in the sub-receiver: 

>>2) Put the Yaesu (factory) 500 Hz filter in the main receiver paired 
>>   with the stock 500 Hz 2nd IF unit.  Purchase a 300 Hz Collins unit 
>    (Inrad) for the sub receiver.

> The 300 is too narrow for use in the sub rcvr.  You want wide skirts 
> to hear off channel signals when searching the pile up.
 
The Yaesu (factory) 500 Hz filter was a 500 Hz crystal filter ... I 
ended up with the 500 Hz crystal filter in the main receiver and a 
500 Hz collins filter (the INRAD) in the sub receiver.  One of these 
days I may swap the two (or get a 400 Hz filter for the main receiver 
and move the 500 Hz crystal filter to the subreceiver).  

The cascaded bandwidths of the stock 2nd IF filter and the INRAD 400 
Hz crystal filter are 410 Hz at -6dB and  700 Hz at - 60 dB.  The 
stock 2nd IF filter and the 500 Hz Collins filter (INRAD or Yaesu) 
are  490 Hz at -6 dB and 870 Hz at -60 dB according to George.  This 
was before INRAD offered the 500 Hz crystal filter at 455 KHz so he 
could not give me numbers for a 500/500 HS configuration using the 
crystal filter in the 3rd IF slot.   

73, 

   ... Joe, K4IK