[INRAD] IC775 Roofing filter +

[Giancarlo Moda]

Hi all,

Charlie, W5VIN, sent me part of the IC775 block
diagrams.  These are very interesting and I would like
to share with you what I commented  to Charlie.

***
It is strange but both RX have the 1st IF in
common.... a cheap solution certainly selected by
financial people and not engineering to save a few
dollars.

I do understand the Inrad filter is positioned
similarly to the FT1000MP after the 1st IF and in
front of the 2nd mixer.

I can see two possible mods to really inprouve the
IC775:

1) replacement of the 2nd mixer IC34 (uPC1037) with an
H-Mode Mixer. This is one of the most critical part of
the IC775. Signal entering the roofing filter
(original or inrad) will generate IMD at this stage.

2) modify the 1st IF having: 
a) the inrad roofing filter with a strong post filter
amplifier serving the main RX; 
b) using the original roofing and post amp as the 1st
IF for the sub RX.

I do not know if there is space to fiddle inside the
IC775 to apply such mods.
I have replaced the 2nd mixer in an FT1000MP and the
performances are really up ... there you discover that
the following problem is now the 3rd mixer.

I do not know if the IC775 inrad filter is ready but I
am sure the quality is as reported. 
I have seen the one for the IC765 and probably it will
be better positioned than in the IC775 being after the
1st mixer, the real place.

I may have friends interested in such mods (Inrad and
mine) so I will see if they volunteer....hi

*****

73

Gian
I7SWX


		
__________________________________________
Yahoo! DSL – Something to write home about.
Just $16.99/mo. or less.
dsl.yahoo.com