Thanks Bill.
73,
Bernard, WA4OEJ
----- Original Message -----
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <tentec@contesting.com>
Sent: Thursday, August 05, 2004 9:39 PM
Subject: [TenTec] Orion Roofing Filter Cut In
> Bernard, at your invitation I quickly looked over your
> discussion and have to agree with Steve that Orion's design
> is not new. However I disagree with Steve in that the term
> "roofing filter" is also not new. In fact, Sherwood Engineering
> used this term in the 1970's to describe their "600 Hz Roofing
> Filter Mod" for the Drake R4C. In many respects, Orion is
> simply a modern version of the R4C design...ham band only,
> relatively low down-converted First IF at 9 MHz (R4C used
> 5.6 MHz) and narrow roofing filters like Sherwood's for the R4C.
>
> >I was just looking at the schematic diagram of my FT-1000 to see if
> I could determine the filter bandwidth going into the receiver front end.
I
> didn't see it called out on the set of diagrams that I have in the user's
> manual. However, I strongly suspect that it would be something on the
order
> of 20 kHz or greater. Maybe someone one this thread can tell us what it
is.
>
> I'm not familiar with the FT-1000D but the MP uses a 12 kHz
> roofing filter.
>
> >This first stage is where the TenTec roofing filters are. And,
> selective roofing filters at this stage is something that we haven't seen
in
> ham rigs (at least in quite a while).
>
> Not true. Elecraft's K2 also uses a narrow roofing filter since
> it is a
> single conversion design and only has one IF. I'm not really familiar
with
> other other Ten-Tec rigs but I believe most use down-conversion and have
fairly
> low First IF's...some of the Omni guys may know the answer to this. If
they
> don't have narrow roofing filters now, they soon will because Inrad
announced a
> filter mod for the Omni VI at Dayton (and BTW, I just got a note from
> George W2VJN
> at Inrad which said the assembled 4-pole 600 Hz #762 is NOW AVAILABLE for
> Orion).
>
> >Anyhow, my point was that the way the Orion is set up, I think that
> they should eliminate the 1.8 and 2.4 filters because they don't kick in,
in
> the automatic mode, until the signal bandwidth is much too low for some
> (many) of us to understand the SSB. I still think that a 3.5 kHz filter
in
> place of the 1.8 and 2.4 filters would have been a better all around
> selection.
>
> As I said elsewhere, I can comprehend SSB down to 15-1600 Hz BW,
if I
> do some tweaking of PBT settings. This is not armchair ragchewing but
heavy
> duty contesting under extremely crowded conditions. The 2.4 is ABSOLUTELY
> necessary for these conditions and I personally would not be without my
1.8
> for SSB contests.
>
> Ten-Tec has designed Orion so we can all have what we want. If
> you like
> wideband SSB (which is what I consider anything above 3.0 kHz) or AM for
rag-
> chewing on a quiet band, the 6000 Hz roofing filter works fine. You can
still
> set DSP to 3.5 kHz if that is what you like. But if you tried that in a
> contest,
> you would have not one but 3 or 4 signals within your First IF which would
> create all kinds of havoc before getting to the 3rd IF DSP! Maybe you are
> confused because Icom and Yaesu announced 6 and 4 kHz roofing filters.
The
> reason they didn't go lower was not because they didn't want to, but
because
> narrower filters are simply not available at the 45-65 MHz IF's these rigs
> use. Believe me, if it was simple to obtain a 2.4 kHz filter at that
> frequency,
> they would certainly have done so. Of course 1000 Hz or 600 Hz is totally
> out of the question for such up-conversion designs using 45-65 MHz IF's.
>
> Hopefully this answers some of your questions.
>
> 73, Bill W4ZV
>
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