[ICOM] IC-765 compared to a PRO-III

[Bill Tippett]

N0JR wotte;

 >I don't have an Orion, but I wouldn't hesitate to
bet $100 that the thus-modified 775 matches or
exceeds the third-partry published receiver ratings
for that no. 1 radio.

         I'll take your bet Jan...but here's why you
don't want to take me up on it:

1.  Inrad's roofing filter for the 775 is 5 kHz.
2.  Orion I with an Inrad 762 or Orion II with
the TT 2001 both use a 600 Hz roofing filter.

In simple terms, this means very close-spaced
CW signals (such as you typically have in contests
or big pileups) will appear within the 775's roofing
filter, but fall outside Orion's 600 Hz BW.

         From page 5 of Inrad's own roofing filter paper:

***********************************************
1. What can you expect from this mod?
Less IMD in crowded band conditions, particularly from stations at
offset frequencies of 2 to 10 kHz either side of the operating frequency.
***************************************************************************
http://www.qth.com/inrad/roofing-filters.pdf


         While the mod greatly helps the stock 775's
performance down to ~2 kHz spacings, it does nothing
for interfering signals which appear within the 5 kHz
bandwidth of the roofing filter.  With a 5 kHz bandwidth
(+/- 2.5 kHz from center) a 2 kHz spaced interfering
signal appears well inside the 775's 5 kHz roofing filter,
but will fall far outside Orion's 600 Hz roofing filter.

                                 73,  Bill  W4ZV