[ICOM] IC-775 filters (Was Icom 781 vs. 756 Pro 3)

[Adam Farson]

Hi Anders,

Many thanks for the recommendation!

http://www.ab4oj.com/icom/main.html

For SSB, I normally recommend retention of the FL-80 and replacement of the
stock FL-96 with an Icom FL-44A (now quite rare) or an Inrad 109. The FL-96
is 2.8 kHz wide; as a result, the Twin PBT is rather sloppy with this
filter. The FL-80/FL-44A pair is probably the best filter combo Icom ever
made.

I agree that "perfect" filter symmetry can be achieved only with IF-DSP, as
in the radios you mentioned. This is shown rather dramatically here:

http://www.ab4oj.com/icom/passband/main.html

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Anders Janis SM4RNA
Sent: 07 December 2006 13:54
To: ICOM Reflector
Subject: Re: [ICOM] IC-775 filters (Was Icom 781 vs. 756 Pro 3)

I am afraid not. All filters are individuals. You must figure out by your
self what filter or filters that "needs" to changed. Also no matter what you
do you will be able to make make it to sound 100% alike. To do that you need
to go DSP, like 756PRO, 746PRO or 7800.

Icom has no 2,1kHz SSB filter.

In the 455kHz filter bank the 2,7 kHz can be changed to Inrad 2,4 for best
selectivity together with the 2,4kHz wide FL-80 in 9MHz. If you have the
option SSB narrow filter in 455 kHz installed, the 1,8 kHz filter it can be
replaced with a 2,0 or 1,8kHz Inrad at your choice.

In the 9 MHz IF the Inrad filters is not plug in. They need to be wired in
with coax. It has pros and cons. The 9 MHz filters are not so sharp as the
455 kHz filters. Try changing the 455 kHz filter at first and then with the
fact that it will never be 100% alike in mind, and than take the dession
upon if it is worth wireing filters.

Also see Adam Farsons homepage. You can find informaton om the diffrent
filters and also about the FL-80 + Inrad 109 combo. Also tha manual
belonging to the 775 and a blockdiagram can awnser som questions.

Also I had a defect 250Hz filter for 9 MHz from Icom that was so bad it
generated 10 dB additional attenuation than a normal filter. SO filters van
apparently be bad.


de Anders



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