I think Bernard's comments about the point the roofing filters are kicked in
is a very good one. I was just doing some listening on SSB with the 2400
hertz DSP filter and switching back and forth with the 6 and 2.4 khz roofing
filter. My conclusion is the shape factor of the 2400 hertz DSP is much
sharper than the 2400 hertz roofing filter. In fact, I previously measured
the 2400 hertz DSP shape factor as an outstanding 1.06 to 1 ratio. The 2400
hertz crystal roofing filter has a shape factor in the order of 1.5 to 1.
This being the case, I see no justification whatsoever for automatic mode
not engaging the 2400 hertz roofing filter when the DSP filter is 2400. The
present 1700 or so just seems wrong. Also, the 1800 hertz roofing filter
should come in at the 1800 DSP setting and so on. The roofing filters are
no where near as sharp as the DSP filters so there would be nothing lost by
doing this. The way it is now, unless you manually engage the 1800 hertz
roofing filter for SSB, it is useless and only helps for CW. I would expect
TenTec will eventually change this in the firmware unless there is something
here we are all missing.
Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Bernard(wtrone)" <wtrone@comcast.net>
To: <tentec@contesting.com>
Sent: Friday, August 06, 2004 1:41 AM
Subject: Re: [TenTec] Orion Roofing Filter Cut In
> Steve:
>
> 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.
>
> 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).
>
> 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.
>
> 73,
>
>
> Bernard, WA4OEJ
>
>
> ----- Original Message -----
> From: "Steve N4LQ" <n4lq@iglou.com>
> To: <tentec@contesting.com>
> Sent: Thursday, August 05, 2004 8:15 PM
> Subject: Re: [TenTec] Orion Roofing Filter Cut In
>
>
> > Bernard:
> > I am refering to the basic block diagram of the receiver section. Yes,
the
> > Orion does have DSP as I mentioned however, the RF chain ahead of the
DSP
> > unit is the same basic superhetrodyne receiver that we've seen for 30
> years.
> > Sure the schematic is different but not the scheme.
> > Furthermore, we are now seeing direct conversion make a come back as in
> the
> > SDR radio by Flex Radio and DC goes back further in history than
Superhet.
> >
> > Steve N4LQ
> > ----- Original Message -----
> > From: "Bernard(wtrone)" <wtrone@comcast.net>
> > To: <tentec@contesting.com>
> > Sent: Thursday, August 05, 2004 9:05 PM
> > Subject: Re: [TenTec] Orion Roofing Filter Cut In
> >
> >
> > > Steve:
> > >
> > > All I can say is that you are wrong. Please review the Orion
> > > diagrams and schematics. They not the same as what we were used to 30
> > years
> > > ago. Period!
> > >
> > > 73,
> > >
> > >
> > > Bernard, WA4OEJ
> > >
> > >
> > > ----- Original Message -----
> > > From: "Steve N4LQ" <n4lq@iglou.com>
> > > To: <tentec@contesting.com>
> > > Sent: Thursday, August 05, 2004 6:32 PM
> > > Subject: Re: [TenTec] Orion Roofing Filter Cut In
> > >
> > >
> > > > I disagree. Roofing filers serve the same purpose, are located in
the
> > same
> > > > place and are even the same physical part they have been for the
past
> 30
> > > > years. Roofing is simply a new term invented to describe a filter
> needed
> > > to
> > > > overcome the shortcomings of DSP. With adequate "roofing filters"
> there
> > is
> > > > little to be gained from DSP in the cw realm. They have nothing to
do
> > with
> > > > the "front end". They are in the IF chain as they have always been.
> The
> > > > Orion is a superhetrodyne receiver which was invented 70+ years ago.
> It
> > > has
> > > > a first converter, IF and detector. The roofing filter is located in
> IF
> > > > stage just like it has always been. The IF is downconverted to a
very
> > low
> > > > frequency (still considered an IF) and fed into the "DSP" system we
so
> > > > highly revere. The DSP provides, amoung other things, a detector and
> agc
> > > > system. If the roofing filter were narrow enough, the DSP would not
> have
> > > > much to do on cw. After all, once the filters have removed the QRM
> from
> > > both
> > > > sides of a signal, all we need is a product detector to convert it
to
> > > audio
> > > > so we can hear it! Shucks, cw is just a tone! What is the point of
> > > > converting it to digital pulses then trying to reconstruct it into a
> > tone?
> > > > Now with SSB were we must wide wide wide filtering like 2.4khz just
to
> > > > understand the stuff it's a different story. Now we can use the DSP
to
> > act
> > > > as an automatic notch filter and eliminate cw tones which BTW mostly
> > exist
> > > > on 40 meters. DSP is also used in the transmitter's circuit to good
> > > > advantage to intregate voice procession etc.
> > > > There has been some talk about DSP filtering "not ringing". This is
> very
> > > > true in the JA imports but TenTec's filters seem imune from ringing,
> > even
> > > > the narrow 250hz filters sound very natural. If you want to hear
some
> > > > ringing, fire up a PROII with a 50hz filter and tune across 80
meters
> at
> > > > night. A little time spent with that in your headphones should send
> you
> > > > running for a quiet spot.
> > > >
> > > > "I noticed the same thing as I started getting to know my new Orion.
> I
> > > > think that part of the confusion is that the roofing filters are not
> the
> > > > signal bandwidth filters that we are used to seeing advertised in
> other
> > > > rigs. The roofing filter sets the overall operational bandwidth
that
> > the
> > > > receiver front end sees. The signal bandwidth is set using the DSP
> > > > bandwidth control."
> > > >
> > > > Steve N4LQ
> > > > ----- Original Message -----
> > > > From: "Bernard(wtrone)" <wtrone@comcast.net>
> > > > To: <tentec@contesting.com>
> > > > Cc: <ditsnbits@tentec.com>
> > > > Sent: Thursday, August 05, 2004 5:53 PM
> > > > Subject: Re: [TenTec] Orion Roofing Filter Cut In
> > > >
> > > >
> > > > > I noticed the same thing as I started getting to know my new
> > Orion.
> > > I
> > > > > think that part of the confusion is that the roofing filters are
not
> > the
> > > > > signal bandwidth filters that we are used to seeing advertised in
> > other
> > > > > rigs. The roofing filter sets the overall operational bandwidth
> that
> > > the
> > > > > receiver front end sees. The signal bandwidth is set using the
DSP
> > > > > bandwidth control.
> > > > >
> > > > > Having said that, I think that TenTec confused the situation
by
> > > using
> > > > > 1.8 and 2.4 kHz values for their "SSB" roofing filters. Plain and
> > > simple,
> > > > I
> > > > > think that these filters are a mistake for those of us who enjoy
> > mostly
> > > > > using SSB! Why? They are too narrow.
> > > > >
> > > > > I think that it is reasonable and prudent to have a roofing
> filter
> > > > that
> > > > > is somewhat wider than the desired signal bandwidth. How much
> wider?
> > > > 20%?
> > > > > 50%? 100%? I don't know, but I suppose that there are
performance
> > and
> > > > cost
> > > > > trades that establish the optimal range.
> > > > >
> > > > > I don't know about the rest of you, but I have great
difficulty
> > > > copying
> > > > > SSB with a bandwidth less than 2.0 kHz. I have had rigs with 1.8
> and
> > > 2.0
> > > > > kHz signal bandwidth filters and I just didn't use them. They did
> me
> > no
> > > > > good. I normally set my Orion signal bandwidth between 2.1 and
2.8
> > kHz
> > > > > depending on the band conditions. On automatic filter selection,
I
> > just
> > > > > don't use the 2.4 kHz roofing filter. It is too narrow. I could,
> of
> > > > > course, select it and lock it.
> > > > >
> > > > > So, back to the TenTec mistake, IMO. I think that they should
> > have
> > > > > selected a "SSB" roofing filter of about 3.5 kHz and forgotten
about
> > the
> > > > 1.8
> > > > > and 2.4 kHz filters. A 3.5 kHz roofing filter probably would have
> > > allowed
> > > > > DSP bandwidth settings of 2.8 kHz or less. I think that would
have
> > been
> > > > > "ideal" for us SSB operators. The 6.0 kHz filter, IMO, is a
little
> > too
> > > > wide
> > > > > for DX who are using a 5.0 kHz split. We need something narrower
> for
> > > the
> > > > > heavy QRM.
> > > > >
> > > > > I do have a question for any of you who have both the 1.8 and
> 2.4
> > > kHz
> > > > > filters. Have you tried setting the DSP bandwidth at 1.75 kHz or
> so,
> > > and
> > > > > then tried both the 1.8 and 2.4 filters on various SSB signals?
Did
> > you
> > > > > hear any difference?
> > > > >
> > > > > Don't get me wrong, I really like my Orion. I just think that
> > > TenTec
> > > > > selected the "wrong" SSB filters. I suppose that they were more
> > focused
> > > > on
> > > > > CW operation.
> > > > >
> > > > > Just one man's opinion.
> > > > >
> > > > > Comments??
> > > > >
> > > > > 73s
> > > > >
> > > > > Bernard, WA4OEJ
> > > > > ----- Original Message -----
> > > > > From: <K4IA@aol.com>
> > > > > To: <tentec@contesting.com>
> > > > > Cc: <ditsnbits@tentec.com>
> > > > > Sent: Thursday, August 05, 2004 8:42 AM
> > > > > Subject: [TenTec] Orion Roofing Filter Cut In
> > > > >
> > > > >
> > > > > > I am confused by the scheme used to automatically cut in the
Orion
> > > > roofing
> > > > > > filters.
> > > > > >
> > > > > > Why does the filter not cut in until the DSP bandwidth is
> > > substantially
> > > > > less
> > > > > > than the filter?
> > > > > >
> > > > > > For example, the 2.4 filter doesn't switch in until the DSP is
at
> > > 1.990.
> > > > > >
> > > > > > The 1.8 doesn't engage until the DSP is at 1.400 This is way
too
> > > narrow
> > > > > for
> > > > > > SSB - thus there is no effective roofing filter for narrow SSB
and
> > one
> > > > > could
> > > > > > argue this roofing filter is useless for SSB. Yes, I know you
can
> > set
> > > > the
> > > > > > passband for +150 and still be able to decipher SSB at that
narrow
> a
> > > DSP
> > > > > setting,
> > > > > > but speech is very difficult to understand.
> > > > > >
> > > > > > The 1.0 comes in at .740 Is this one of the reasons some have
> > > switched
> > > > > out
> > > > > > the 1.0 in favor of the INRAD 600 in this position?
> > > > > >
> > > > > > The 500 is at 350. I don't have the 250 so I can't comment on
> that
> > > one.
> > > > > >
> > > > > > Wouldn't it make more sense to have the roofing filter match the
> > DSP?
> > > > > >
> > > > > > Would it make sense to have the roofing filter kick in "early"
as
> > the
> > > > > INRAD
> > > > > > 600 does when placed in the 1.0 position?
> > > > > >
> > > > > > Radio k4ia
> > > > > > "Buck"
> > > > > > Fredericksburg, Virginia USA
> > > > > > _______________________________________________
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> > > > > > TenTec@contesting.com
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> > > > > >
> > > > >
> > > > >
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> > > > >
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> >
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