[INRAD] Filter Board

Tue Oct 25 22:29:17 CDT 2005

You know it is funny that you would mention the
atmospheric noise thing Tom.

This may sound a little overboard to some but I am going
to say it anyway because I mean it just that much. 

As of two days ago from now, at this radio room, a lot of
what goes into picking a rig in the future, will be
determined by whether it will take an INRAD board. IT
MAKES THAT MUCH DIFFERENCE.

INRAD IS TOPS AT THIS SHACK :0)

Here is one of the main reasons for this decision.

I love working DX especially weak signals.

I have really been discouraged on 40, 80 and 160 until
now.

Since the colder weather has arrived and the bands have
quietened down a bit here as far as atmospheric noise is
concerned now that I had the FT-920 I thought surely I
would at least be able to hear the dx stations on 160, but
no luck.

I would see dx spots in my logger32 logging software and
click on the freq to go there and see if I might get lucky
without co phased towers, arrays ect (just my little
dipoles here) and work a dx station (no Canada is not
included in the list).

Heck I couldn't even hear them, much less work them.

I could only could hear the stateside stations sending to
them. So I was about ready to give up until I could afford
a co phased tower arrangement or at least one tower with
enough height to support a 1/2 wave sloper for 160.

What I didn't realize is that they were in there all the
time, it wasn't about more gain it was about less noise.

They were there, but under my noise floor.

Now that I have my little INRAD CW cascading filter board
installed (400hz and 250Hz), I can hear them and there are
plenty out there Hi Hi

All of a sudden I am hearing many dx stations on both 80
and 160 and even a few between the broadcast stations on
40  -- now that I can get in between the broadcast
stations on 40.

Heck I am *once again* actually looking forward to going
to my rig NOW instead of dreading all the noise
sidebanders, broadcast stations, ect and doing it because
"I need another one for DXCC". 

I just enjoy doing it again.

Haven't worked one on 160 
<<bold type>>  YET  <<bold type>>
But at least I can hear them now.

However, I did snag CU2/OH1VR/P (Azores Islands (SanMiguel
Isle) who I would have never heard on 40 without the
narrow filter activated on the filter board. 

He was just above the NEW LOW NOISE FLOOR and copied me
fine.

 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 9:52 PM
> To: list at inrad.net
> Subject: Re: [INRAD] Filter Board
> 
> 
> Yep! And a good way to look at it Bob. A roofing filter 
> limits the amount of bandwidth the remaining circuitry
has to handle.
> 
> On my Omni 6 Plus, it originally had a 20kc wide filter 
> before the first IF, so the IF would have to handle all 
> signals in that wide bandwidth, up to the IF filters 
> themselves. Included, of course, in that 20kc is
atmospheric 
> noise (static, QRN, lightning crashes, etc.). With a 600
hz 
> filter BEFORE the first IF stage, now any signal outside
of a 
> 600 hz bandwidth, is reduced and the IF stage(s) now
have to 
> handle the atmospheric noise contained in the 600 hz
bandwidth.
> 
> For example, on 80m with no roofing filter, my Omni 6
Plus 
> may read +20 dB of noise plus weak signals. With the 600
hz 
> roofing filter, the noise drops to S-5 - S-7, BUT the
weak 
> signal your trying to hear does not drop in strength at
all. 
> A big improvement for both your radio and your ears!!
> 
> Tom - W4BQF
> 
> 
> ----- Original Message ----- 
> From: "N5IET Bob" <rtnmi at sbcglobal.net>
> To: <list at inrad.net>
> Sent: Tuesday, October 25, 2005 10:29 PM
> Subject: Re: [INRAD] Filter Board
> 
> 
> > 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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> >
> >
> >
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> 
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