[TenTec] Orion Roofing Filter Cut In

Bernard(wtrone) wtrone at comcast.net
Thu Aug 5 21:05:38 EDT 2004 

    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 at iglou.com>
To: <tentec at 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 at comcast.net>
> To: <tentec at contesting.com>
> Cc: <ditsnbits at 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 at aol.com>
> > To: <tentec at contesting.com>
> > Cc: <ditsnbits at 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
> > > _______________________________________________
> > > TenTec mailing list
> > > TenTec at contesting.com
> > > http://lists.contesting.com/mailman/listinfo/tentec
> > >
> >
> >
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> >
>
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