[INRAD] IC-746 Roofing Filter

[Charlie Mazoch Jr.]

Hi Perry:
  I do not own a IC-746 but have noted it's roofing filter is the same 
frequency as the IC-765 and IC-775. I added one of INRAD's filters to an 
IC-756 and it worked fine. It was a cut and solder task as yours would 
be. It's posted at dk.mods.  The area I'd consider is between L215 and 
L231. On INRAD's board you'd have to lift R7 off ground, tie it to J1 
and bypass it with a 0.1 uF capacitor. The output is configured in this 
same manner. The only other area I saw to utilize the filter is between 
L241 and D251 which would be more involved. Instead of switching into Rx 
using a DC path between Q241 and D215 you'd use the INRAD  output 
circuit to do this. R249 would be eliminated and a Rx switched voltage 
would be applied to either the bypass or INRAD amplifier leads thus 
switching the filter in or out. The filter would be utilized in only the 
Rx side in either location. The other half of D251 is the Tx side. 
George is the Rf engineer so you may inquire as to what his opinion is.  
73's  and  Merry Christmas        Charlie  W5VIN