[INRAD] Filter Board

[N5IET Bob]

So the answer to the original question "what is a roofing
filter" is that it is a filter that puts a roof or limit
on what the rest of the IF's have to handle is that
correct.

They limit the work for the rest of the radio. By placing
a sort of top (roof) on the first incoming signals.

 73 fer nw,
Bob N5IET

10X# 37210, FP#-1141, SMIRK#-5177
http://www.n5iet.com/
Code may be taking a back seat for now,
but the pioneering spirit that put the code
there in the first place is out front of it all.


> -----Original Message-----
> From: List-bounces at inrad.net
[mailto:List-bounces at inrad.net] 
> On Behalf Of Tommy-W4BQF
> Sent: Tuesday, October 25, 2005 8:33 PM
> To: list at inrad.net
> Subject: Re: [INRAD] Filter Board
> 
> 
> I think Steve is close to correct, however a roofing
filter 
> normally is installed before the first IF, in some rigs,

> right after the first mixed. And yes, because most rigs
have 
> the ability to receive FM (why?), the 'normal' filter is

> something like 20 kc wide. With that your first IF has
to 
> handle signals and noise in a 20kc wide spectrum.
Install a 
> 600 hz roofing filter, and your IF stages have to handle
a 
> bandwidth of only 600hz, meaning both strong signals
close to 
> your QRG plus the noise, are both greatly reduced.
> 
> In the Ten Tec Omni 6 Plus rigs, the improvement is
astounding!
> 
> Tom - W4BQF
> 
> ----- Original Message ----- 
> From: "Dick Powers" <powersharp at juno.com>
> To: <steve.root at culligan4water.com>
> Cc: <list at inrad.net>
> Sent: Tuesday, October 25, 2005 9:19 PM
> Subject: Re: [INRAD] Filter Board
> 
> 
> > So it's kind of like a funnel right in the front end
to 
> eliminate the 
> > unwanted stuff right off the bat I guess, huh? Thanks
Steve (Boy I 
> > haven't seen the term "kc" used in awhile.) Dick
WB9PWQ 73
> >
> > On Tue, 25 Oct 2005 20:37:46 -0400
<steve.root at culligan4water.com>
> > writes:
> > > A "Roofing filter" is a crytal filter that is used
in the 
> first IF.  
> > > My understanding of the problem is that the decision
to include 
> > > general coverage reception dictated a first IF
frequency 
> in the VHF 
> > > range, like 70 Mc.  Until fairly recently it was 
> difficult to make a 
> > > narrow filter that operated at these frequencies.
The first IF 
> > > stage was pretty broad, on the order of 12 Kc wide.
> > >
> > > I have a lot of time in with both the FT-1000MP and
the FT- 1000D 
> > > before and after adding the roofing filters.  The
differences are 
> > > immediately apparent.  The MP in particular was much
improved.  
> > > During periods of heavy activity like a CW contest I

> usually ran the 
> > > MP with the pre-amp off and 6 or 12 db of
attenuation in line to 
> > > keep the receiver from "crunching".  After adding
the 
> roofing filter 
> > > the attenuation wasn't necessary as stong signals
outside the
> > > passband were eliminated by the filter.  In a word,
it's
> > > great!
> > >
> > > 73 Steve K0SR
> > >
> > >
> >
> >
> > Dick
> >
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