[1000mp] 4 kHz roofing filter

[Joe Subich, K4IK]

> Very interesting news concerning the new Inrad roofing filter. 
> I will certainly install one in my Field, however I don't see it 
> advertised on Inrad web site. 

It is not currently on the web site.  George told me they would 
update the data after they returned home (a leisurely trip back 
to the west coast in their RV).  Look for the data in a couple 
of weeks. 

> There is a problem though: in case the first LO is not
> shifted when changing modes (and why would it with a 12 kHz 
> roofing?) then one must also give up 2.4 kHz SSB in addition 
> to FM and wideband AM. 

The first LO is shifted ... the second IF filters are nominal
center frequency and the LO must shift +/- 1.5 KHz to select 
USB/LSB.  Thus with the INRAD roofing filter, one has a 4 KHz 
"window" around all of the second/third IF filters.  In SSB 
one should be able to shift +/- 1.5 KHz before hitting the 
roofing filter ... with narrow CW filters, the roofing filter 
will probably not impact shift/width operation in the least.  

> Anyone having more detailed information? Perhaps some info 
> concerning insertion loss? (normally should be bigger when 
> reducing the bandwidth)

The filter comes on a board that installs in place of the 
70 MHz IF mod.  The board includes impedance matching and 
a post filter amplifier that has about 2 dB of excess gain 
(gain in excess of the filter loss).  

Performance specs (Dynamic Range) are: 

            Signal spacing            Dynamic Range 
               10 KHz                    107   dB 
                5 KHz                    100.5 dB 
                3 KHz                     97.5 dB 

This compares to an unmodified 5 KHz dynamic range in the 
mid-80 dB range (from memory).

Price will be $165 ... deliveries are scheduled to start in 
four to six weeks.  INRAD also has a roofing filter for the 
TenTec Omni VI series and are working on roofing filters for 
the IC-765/IC-781.    

73, 

   ... Joe, K4IK