[ICOM] Fwd: Re: Hope to see a roofing filter for the IC-775DSP

[Adam Farson]

hi Durwydd,

The roofing filter is the first IF filter immediately following the first
mixer. In an up-converting receiver architecture with a first IF above the
highest operating frequency, the roofing filter is at a VHF frequency such
as 45, 48, 64 or 70 MHz.

The main purpose of the roofing filter is image rejection and limitation of
the first-IF bandwidth to eliminate strong signals well outside the IF
passband. Normally, the roofing filter is sufficiently wide to pass the
widest emission in use (typically 15 kHz to accommodate FM).

A narrower roofing filter will reduce the statistical probability that
unwanted signals close to the desired signal will enter the IF chain and
cause overload, intermod or cross-mod.  Inrad has been offering narrower
roofing filters for the FT-1000MP series. The question was whether they
would develop one for the IC-775.

Please refer to:

http://www.qsl.net/ab4oj/icom/ic756pro_notes.html#roofing (a discussion of
the roofing filter in the IC-756Pro/Pro II).

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 Durwydd MacTara
Sent: Saturday, September 11, 2004 17:51
To: icom at mailman.qth.net
Subject: RE: [ICOM] Fwd: Re: Hope to see a roofing filter for the
IC-775DSP


What is a "roofing filter" and why are they desireable?



  "Carpe` Diem!"
             Durwydd MacTara


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