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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