[INRAD] IC775 Roofing Filter

[Giancarlo Moda]

As already explained by other members you are loosing
bandwidth with the narrower roofing filter. This is
part of the roofing filter to help CW and SSB signal
getting less ineterferences by nearby stations.
I have not understood where the IC775 roofing filter
is inserted in the front end. Is it after the mixer
and before the 1st IF? I have no circuit diagram of
the 775.

I have looked at the Inrad circuit diagram and it
seems to me easy to add a small circuit for those
interested to operate in AM and FM.
There will be some cut and soldering to do. What it is
necessary is to arrange a simple circuit when FM/AM
are selected the +8R is disabled and the +8T is
selected. You will have to arrange that there are no
problems of voltages retun to the +8T and +8R lines in
the receiver.
It should not be difficult to trace the AM and FM
control lines inside the IC775.

I have designed a roofing filter selection circuit for
the FT1000MP/MKV (see www.mods.dk) but for the IC775
there are no switching relays to be added.

73

Gian
I7SWX

Message: 1
Date: Wed, 23 Nov 2005 04:03:46 +0100
From: "Anders Janis SM4RNA" <sm4rna at telia.com>
Subject: [INRAD] Roofing filter for the IC-775DSP
To: <list at inrad.net>
Message-ID: <09e201c5efda$857d0840$6400a8c0 at ham>
Content-Type: text/plain;	charset="iso-8859-1"

701-B and 701-CI have found a thing that I finde
strange in "IC-775 
ROOFING FILTER INSTALLATION INSTRUCTIONS?"

"This may degrade the audio bandwidth for AM and FM
reception somewhat. 
Those modes will still be available for reception with
the sub 
receiver."

Is this really true?



/Anders




		
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