[TenTec] Orion Roofing Filter Cut In

[Carl Moreschi]

All the Omni series receivers had a 9 mhz first IF just like the Orion.
That's why you can use the Omni filters as roofing filters in the Orion.
The difference is the Only filtering is still very sharp even without the
optional roofing filters.  This is not the case with the Omni's.

Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <tentec at contesting.com>
Sent: Friday, August 06, 2004 2:39 AM
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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