manfred sez...
Now if the radios you mean happen to use low quality second sideband
filters, with slopes that aren't steep enough, and with poor stopband
rejection, then of course there will be more splatter. But that's a
problem of cheap implementation, not of the principle.
## The DX engineering RF clippers used on my old drakes used
tiny filters, think they were 4 pole units. Best version was the
rob sherwood unit, that used real 8 pole filters, one for each sideband.
With current DSP technology pretty sophisticated and clean speech
processing can be implemented, at very low cost. Good speech processors
in DSP often shift the audio signal to some low RF (which is the same as
passing it through a balanced modulator and sideband filter in the
analog world) and then apply the compression and limiting, precisely to
move most of the artifacts out of the passband and then filter them away.
### Which xcvrs do that ? On paper it would work...provided you could
use a DSP filter to filter out the DSP artifacts. I havent see any version of
a digital DSP based
clipper, only limiters and compressors.. but that is not at low RF freqs...
just 20-20k audio.
I have dsp 6 x band audio compressors, but they are for a different
application.
When I started writing this post, I intended to question that remark -
but now, after having looked closely at all those ALC implementations, I
see your point. Let's be kind and think that amplifier manufacturers
provide ALC outputs tailored to specific radios. Obviously those
manufacturers that make the amps as accessories for their own radios
will tailor them to these radios, but I wonder what the amplifier-only
manufacturers have in mind, when defining their ALC outputs... Maybe
some specific, widely used radio? Or the radio the company's boss
happens to use?
#### You just nailed it, there is no standard, hence the incompatibility
issues.
And broadcasting is very different from ham operation, too. In
broadcasting, you set up the transmitter on one frequency, then usually
run it there, 24/7, for years. Or at least for hours, in shortwave
broadcasting. You have no frequency changes, and no thermal drifts from
circuits heating up and cooling down. In ham radio instead you change
frequency often, you also might change bands every now and then, and
your transmitter stages are all the time changing temperature, due to
the RX/TX cycling. So there is far more need for ALC than in broadcasting.
> VE7RF does extensive audio processing in his station.
### Even if the xcvr in question has overshoots, its still not an issue.
Either develop the ALC voltage externally, or limit the audio...b4 it
gets into the xcvr.
Audio processing in ham stations, using external consoles with
compressors, AGC, equalizers, etc, seems to be all the rage at present.
Some hams indeed produce excellent transmission in that way. Others not
so much. I keep hearing hams with lousy signal quality, bragging about
their studio mikes and all the audio equipment they are running to
process their audio signal. Some even add cathedral-style echo effects,
like those CB operators of 30-40 years ago! :-)
## ESSB has been going on since late 90s. Its a very tricky setup
depending on what gear is used, and how things are configured.
If I know the station on the other end is using narrow band RX, like
300-2700 hz, I have to configure entirely differently vs a station that
has a wider RX BW... like say 100-3900 hz. Wide band TX ssb will never
sound correct on a narrow band RX, it just doesnt work. The EQ
setup on TX is such that it wont sound right unless the RX BW at the
other end is the same BW..or wider. Even if you play with the shift control
on a narrow band width RX, it still wont sound right. You get either the
bottom,
middle, or top end, but you can never get all of it at once. When a bunch of
wider band
ops all of a sudden all get lousy audio reports from a fellow using narrow
band RX..and
also a 2 inch diam speaker built into the top lid of his icom, we have a bw
issue.
For all intensive purposes we are transmitting a mode that the narrow RX BW
station
cant copy.
manfred sez...
The funny thing is that so many hams use this sophisticated audio
processing on HF SSB, where HiFi audio makes little sense, due to all
the usual QRM and QRN and the intrinsic limitations of SSB. It would be
far more logical to strive for excellent audio quality on VHF and UHF in
FM, but that's something no ham in my area does.
## Not true. It works superb on HF..it also works superb on VHF.
On HF, I have not used phonetics since 2001, even on a real noisy
80m band, during the summer months..with ssb signals buried in the noise.
Several of us ran thousands of exhaustive tests on intelligibility vs BW.
The results are jaw dropping to say the least. On most tests the bottom
end was cut off at 300 hz. The top end was cut off initially at 2700 hz,
then
incremented slowly upwards in small steps to aprx 4000 hz. Slight changes in
the digital tx eq had to be tweaked in as this is all going on.
Once u hit aprx 3600 hz at the top end, the clarity comes alive.
3600-300 = 3300 hz BW.... which is not much wider
than ur typ ham xcvr. With the top end at 3900+ hz, its razor sharp. You
can easily
go from Q3 to Q5. I recorded a fellow doing the above tests on my sony rack
mount
mini disc setup, and it still astounds me to this day. Then the above tests
were done
again, but TX po reduced such that signals were right at the noise level.
Same deal, but
even more pronounced effect. Then a bunch of similar tests done with dx
stations that
were also essb equipped. We tried everything from 300-2700.....all the way
up to
300-5800 hz. Intelligibility increases every time the top end was increased.
Turns out we just
re-invented the wheel, as the BW vs intelligibility is well documented in
tech references, like
SSB systems and circuits.... written by collins engineers. They have already
graphed it all out,
with supporting documentation. They used standardized tests, which also
included using
non sensical random word groups.
## BTW, the audio eq setup used for say a 300-3000 hz tx BW is not even close
to what is
used on say a 300-4100 hz setup. Its not just the extra top end either. The
lower and middle portion
is tweaked quire a bit differently. Hence when a RX station listens to wide
band ssb.... on his narrow band
RX, it sounds bad.
Its all fine as long as no QRM, and no contest is on. Its not like there is
loads of wide band ssb signals strewn across each band. They typ congregate
on one or two freqs on each HF band. Typ what happens is even if I tx with a
top end
cut off at say 3900 hz, I will RX with a top end of 5800 hz....so I can listen
to both
wide..and wider ssb stations. Not to harp on the subject, but some of us
have experimented
with audio processing on RX. Everything from gentle downward expansion on RX,
to extensive
digital eq-ing. I also tried adding artificial harmonics to the RX audio, to
widen the BW, then
eq-ing the added harmonics...with great success. I 1st tried that stunt when
listening to a KH6
calling cq in a contest..on 15M...just as the band was about to pack it in.
That was beyond an eye opener.
Jim VE7RF
Manfred
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