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

[Jan C. Robbins]

A true roofing filter is, I'm sorry to say, not in the first IF.  It is 
AHEad OF THE FIRST IF.

Adam Farson wrote:

> 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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