John
First, tnx very much for a thoughtful detailed response.
I *do want to listen to regional ragchews and local ground wave nets using
a wide filter but I also want to be able to do semi serious, fairly casual
contesting and listening to weak DX signals . I hope I don't have to own 2
separate radios and dedicate one to contest/DX and one to ragchewing?
I may misunderstand what the possibilities are. You state:
"Remember that the wider fixed 9 MHz filter will allow more strong signals
inside the passband...<snip>...I'd think twice about opening up the
bandpass beyond 2.4 KHz...in fact I wouldn't do it.
John,
I don't want to open up the bandpass *permanently - I want the flexibility
to open up the bandpass for local ragchews when there is little QRM and
then be able to close it back up for contesting. I want to be able to
cascade two 1.8 filters for ssb contesting. I think one 500 Hz filter
cascaded with one 1.8 filter would suit my casual cw operating. I do not
want my 2.8 filter(s) to degrade my 1.8 and 500Hz filters.
For a combination of ssb ragchewing, ssb contesting and casual cw operating
I thought that the following combination of filters would work *without*
degrading the narrow filters.
6.3 MHz: 2.8, 2.4, 1.8
9 MHz: 2.8, 2.4, 500Hz
Would other combinations work better for the objectives I stated? Or am I
misunderstanding something?
I currently have access to a TS 690 with cascaded filters, and would like
to try tuning it according to your directions. I understand most of your
directions but I'm confused by one statement. What do you mean by "tune the
signal so that it lies just within the slope of the filter within either
the upper or lower boundary"? How do I do that? How would it sound?
tnx & 73
Bob KB1CIW
> [Original Message]
> From: John Clifford <johnclif@ix.netcom.com>
> To: tentec <tentec@contesting.com>
To: <tentec@contesting.com>
> Date: 11/26/02 1:11:24 PM
> Subject: RE: [TenTec] cascaded filters was Omni V audio
>
> Re wider filters and SSB quality... I have listened to SSB on my Drake R8A
> with 4 kHz and 6 kHz filters. Sure, SSB sounds 'nicer' with a wider
filter
> but this affects aesthetics more than readability. In fact, at wider
> bandpasses QRN and QRM can make copying harder due to interference, and a
> fixed wider filter will make PSK operation on a crowded band more
difficult.
> Remember that the wider fixed 9 Mhz filter will allow more strong signals
> inside the passband and thus your receiver will be desensitized in the
> presence of strong signals within that wider window. If I were going to
use
> the rig for HF digital modes I'd think twice about opening up the bandpass
> beyond 2.4 kHz... in fact, I wouldn't do it.
>
> I find that with the Omni VI I rarely need to cascade filters, but when I
do
> it sure lets me zero in on a signal.
>
> It's my experience that the ability to cascade filters doesn't give you a
> 'sharper' filter (one with a more abrupt cut-off at the high and low end),
> but instead gives you the ability to dynamically narrow your effective
> filter.
>
> In the Omni VI, the 9 Mhz filter is 'fixed' in the receiver's passband,
> while the 6 Mhz filters 'move' up and down the band as the pass-band
tuning
> knob (PBT) is rotated back and forth. Think of your bandpass as a window
> thru which you 'view' a section of the airwaves. A single filter is
similar
> to closing curtains to 'narrow' the window. The cascading filter is like
> partially closing a shutter and then moving the curtained gap to eliminate
> even more daylight.
>
> Here's an example of how they would be used to fight QRM:
>
> - using the tuning knob (VFO) the desired signal is tuned so that it lies
> within the bandwidth of the narrow filter
>
> It is best to tune the signal so that it lies just within the slope of the
> filter at either the upper or lower boundary. This allows for the most
> 'narrowing' of the cascaded filter.
>
> - switch in a narrow 6 Mhz filter, and then adjust the PBT so that any
> offending signals are eliminated and only the desired signal lies in the
> common bandpass.
>
> Rigs with digital filter capabilities, e.g., the Jupiter and Pegasus, give
> the operator the same flexibility as does cascading filters, yet they are
> easier for most operators to adjust and generally don't have the problems
of
> narrow crystal filters such as ringing. However, since the digital filter
> is fairly late in the receiver chain, strong signals can affect the
> receiver's AGC even though they appear to be filtered out.
>
> The Orion looks to be combining the best features of both digital and
> hardware filtering, using crystal filters to limit the bandpass and then
> allowing digital filters to really narrow the bandpass and allow the
> operator to 'zoom in' on the desired signal. I'm looking forward to
hearing
> how effective the implementation is.
>
> BTW, crystal filtering (as in the Omni V/VI) is a very nice feature for HF
> digital enthusiasts (PSK31, etc.). It's easy to bring a weak signal out
of
> the noise and into 100% readability no matter how crowded the band gets.
> Ten-Tec deserves a pat on the back for allowing the operator to use any
> filter in any mode (unlike many Japanese rigs).
>
> In summary... wider filters are great if you envision ragchewing with your
> regional buddies who all run a lot of power, and you don't envision
> operating a lot of DX or digging out weak signals on crowded bands. My
vote
> is to stay with the current filter WIDTHS offered by Ten-Tec, even if you
> choose to go to Inrad for higher quality.
>
> - jgc
>
> John Clifford KD7KGX
>
> Heathkit HW-9 WARC/HFT-9/HM-9
> Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
> Ten-Tec Omni VI/Opt1
>
> email: kd7kgx@arrl.net
>
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--- ROBERT STEPHENS
--- bstephens1@mindspring.com
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