[TenTec] Orion Roofing Filter Cut In

[Bill Tippett <btippett@alum.mit.edu>]

        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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