[this is a *long* quasi-review, but may prove useful to some folks]
Steve Ellington <n4lq@iglou.com> said:
> Where dsp helps is when you have some old boatanchor radio with
> a 6kc wide I.F. and hang the dsp on the audio output. For rigs with
> filters like the Omni VI, dsp only makes things sound weird. On SSB with
> the dsp turned on you will hear all kinds of spooky little sounds in the
> background. I find these more distracting than QRN!
> Yes. Why should I want to listen to audio that has been chopped up,
> processed and converted when I can listen to the real thing? Sorry if
> I got carried away. Maybe I should be.
Bet you have Macintosh tube amps for your stereo system, right? :-)
Chester said:
> > >>the auto notch is great for the phone operators, but I have yet
> > >>to find a signal that I can copy with the dsp, that I can't copy
> > >>without. I guess it could be considered a nice toy, but not of
> > >>great help in serious dx chasing.
Here are my observations after a couple of weeks playing with the Option 1
upgrade. Note that reactions to DSP are *very* subjective. Every signal
is different, there are many types of noise, and every operator has
different ears and brain "wiring." So your milage may vary.
* BACKGROUND *
I have owned a Timewave 59+, and currently own a Timewave 599zx. I'm not
selling the Timewave, despite getting the Omni noise reduction feature
with my Option 1 upgrade. I'm also not sorry I upgraded my Omni.
I am a satellite operator, and DSP noise reduction (NR) on VHF/UHF *can*
mean the difference between copying and not copying. DSP is better at
removing the "white noise" of VHF+ than the more variable noise sources on
HF. So on HF, DSP NR is less of a make/break feature, but it can
significantly decrease operator fatigue.
I don't have an HF beam. So my S/N ratios may be lower than those of you
with beams, and noise reduction may be more critical for me. I know that
once I got my Timewave, I couldn't imagine living without DSP.
* IF FILTERS VS. DSP *
Both my Omni 6 and my most recent other HF radios (Icom 745 and 751a) have
had pairs of 2400 and 500 Hz filters. I've never owned 1800 and 250 Hz
IF filters. What I have heard from almost everyone is that DSP filtering
to get more audio bandwidths is a perfectly good substitute for extra
filters *if* the adjacent signals aren't so strong that they capture the
AGC or cause IMD.
My own experience confirms this. On satellite, for example, I almost
never bother with a CW filter at all--I just narrow the Timewave
bandwidth. Everybody's weak to moderate anyway, so where the filtering
occurs doesn't really matter much. On HF, I just use 2400 Hz for SSB and
500 Hz for CW. If that's not enough, I use either PBT or kick in a
narrower bandwidth on the Timewave. It works most of the time.
Now hard-core DXing and contesting are different animals altogether.
There, you want to copy the weak, watery 9N1 who's 50 Hz from the
60-over-9 "California Kilowatt" with key clicks :-) That's probably why
many of you got your Omnis in the first place, right? Under those
conditions, DSP won't do much, and those extra filters are the way to go.
There are a few occasions when *both* DSP and IF filtering are needed.
Let's say that even with your best IF filtering, a strong adjacent signal
is in your skirt. He's not pumping your AGC, but he's still quite audible
and interfering with copy. A DSP bandwidth filter can provide a "brick
wall" audio cutoff--almost a 1:1 shape factor--something no xtal filter
can do.
* NOISE REDUCTION *
The Timewave and Omni DSP noise reducers are very different. The Omni NR
is fairly conservative--it corresponds, roughly, to a very low
"aggressiveness" setting on the Timewave. But even at its lowest
setting, the Timewave NR often removes more noise than the Omni, along
with somewhat more signal.
Actually, a *little* noise is not a bad thing, and it actually can *help*
copy of weak signals. This is just how the brain works, and it's been
confirmed by scientific studies. Whoever designed the Omni noise
reduction seems to have understood this. They designed the algorithm for
that "sweet spot" where it would increase intelligibility and reduce
fatigue under most HF conditions, most of the time, without adding too
much distortion. This may also coincide with how much processing can be
done in the rig, as opposed to in a dedicated box. Whatever the case,
they did a wonderful job!
The result is that the one-button Omni NR is more pleasant-sounding, and
may be more effective under most conditions, even if the raw dB reduction
is less than the Timewave. The Timewave is more effective under really
cruddy conditions, but you have to really know it well and tweak it to get
the most out of it. Many will prefer the one-button solution.
All DSP noise reduction adds some hollow "in a barrel" or frying quality
to the signal, and a bit of "space alien" quality to processed and reduced
background noise. The Omni NR is pretty good, but DSP is DSP.
The Omni noise reduction is *very* good at pulling a marginal CW signal.
out of the noise. It seems to just pop out of the noise--more so than the
Timewave. Even when you're using narrow CW filtering. With the Timewave,
I have found that if there's no QRM, it's often better to use a voice
bandwidth and NR. Somehow the algorithm works better that way.
The Timewave has an audio AGC button that can really work wonders on weak
ones, especially when combined with noise reduction and narrow filtering.
It also supplies some additional gain, which is often better than just
cranking up the volume.
The Omni NR almost sounds like it has some kind of audio AGC built-in. It
may just be that the DSP algorithm digitally mimics AGC characteristics as
it peaks the desired signal frequencies.
I have had easy CW QSO's using the Timewave on signals so weak that I
could barely hear them without DSP. The trick is to use slow CW (about
10-15 wpm) and *very* narrow filtering, 75-150 Hz bandwidth. Combine it
with the AGC and noise reduction if that helps. This works best on the
higher bands where noise is more "white," but I've done it on 40m at
night, too. The Omni DSP can't compete here.
Often (but not always) narrow filtering is much more effective than NR on
CW, *if* your filters don't ring. If there is so much noise that the noise
resonates in your filters louder than the signal, DSP NR may be better.
Both DSPs are more effective on CW than on SSB. I would give the Omni DSP
a slight edge over the Timewave on SSB, under average conditions. When
things are really bad, the Timewave makes SSB listening more bearable than
the Omni, at the expense of audio fidelity.
The Omni NR has much less of a tendency to overload. With the Timewave.
I'm constantly adjusting rig's AF gain for proper audio input level,
changing the Timewave's AF gain to compensate. The Omni NR seems to work
well except on very strong signals, where it does overload unless the
volume is turned WAY down. For a signal that strong, set the AGC on slow
and forget noise reduction.
I must agree with Ten-Tec's advertising. The Omni 6 Plus (or upgraded 6)
has "just the right amount of DSP" for most circumstances. If you have
all the accessory filters, you won't need a DSP box--most of what you'd
buy a DSP box for is already in the radio. The internal noise reduction
is set up very nicely for many HF situations. If you want to get away
with just the stock 2400 Hz filters and one 500 Hz filter, an external box
will help. Under som very severe noise conditions, an external box may
work better. If you're a hard-core competitive operator, you've probably
bought every filter you can fit in the rig anyway, and DSP won't help you
that much.
* OTHER DSP OBSERVATIONS *
DSP is best at killing whitish noise below or near the signal level.
Noise blankers are best at impluse noise whose peaks are above the signal
level. Nothing really helps power-line noise that much, except a JPS
ANC-4, and you have to tweak that a lot. NR and notch filters can
sometimes make a dent in power line noise. Sometimes.
The Timewave's auto-notch is a little bit deeper than the Omni's.
However, the Omni's auto-notch will partially knock down a digital signal
that the Timewave's passes.
The manual notch doesn't quite go up to the passband limit--the notch just
stops working at about 2.2 kHz, even though the pot is only at about the
3:00 position. A higher tone of 2.2-2.4+ kHz must be knocked out with the
PBT, which is probably better, anyway. This upper limit on the manual
notch is in the specs. A little disconcerting when you first discover it,
but not a problem.
When NR is on, the green decimal point next to the green 10Hz digit
lights. Undocumented, but a nice touch. I wish Ten-Tec had done
something similar for the lowpass filter. I occasionally forget that it's
on while using voice or AFSK, with amusing results. I almost wish it
could be set like it was before the upgrade--LP enabled on CW, and off for
everything else. All this is only a problem for Option 1 people. On the
factory upgrades, NR and LowPass buttons are moved one column to the left,
where there are LED annunciators.
Hope all these ramblings are useful to somebody.
73,
Peter (KD7MW)
Peter A. Klein (pklein@seattleu.edu) : -----==3== --- ---
Network Administrator, LAN/WAN/Novell : | | | | | | | |
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