Hi Joe,
How would you then explain that this "phenomenon" is not heard or
perceived as carrier on a normal SSB signal when tuning the signal lower
in frequency than where the carrier is. This converts the frequencies
present to even lower frequencies than they actually are. Simulating
enhanced base but not of the proper frequency for demodulating into
intelligence of course.
There are a lot of phase shifts going on in an SSB signal just by the
nature of the signal.
I don't know that you will be able to see this stuff on a regular
spectrum analyzer. Wonder what you have?
73
Gary K4FMX
Joe Isabella wrote:
My rig uses DSP generated sidebands. It would be very difficult to create the
kind of situation
you suggest. But as you have audio content closer to the carrier point, the
receiving station
percieves it as a carrier while tuning through because of relative closeness of
this content to
it.
However, I will take a closer look at my transmitted signal and see what it's
doing on the spec
any...
Joe,
N3JI
--- Gary Schafer <garyschafer@comcast.net> wrote:
The "carrier" that you hear on these signals is probably not carrier but
inband IM products from the low frequency audio signals. Listen closely
and you will see that it is only present with modulation.
As to opposite side band suppression, with a filter, the low frequencies
are not attenuated by the filter as much as the higher frequencies.
Because they are closer to the pass band of the filter. Not as far down
the skirt. So more get through on the unwanted side band. Especially
when the base is boosted.
With a phasing type of side band generation the problem comes from
inadequate phase linearity at the low frequencies. Then add in the
inband (audio) IM products and the apparent side band suppression really
gets bad.
No I am not an advocate of limited bandwidth either. Experimentation is
great. There are more "better" sounding stations on the air as a result
of the experimentation. It has a ways to go as far as being "clean" but
it is no worse sounding than some of those awful appliances with
"special" microphones designed to "cut through the qrm". They can make
your ears bleed.
73
Gary K4FMX
Rob Atkinson, K5UJ wrote:
Not at all. Why? A. the > 3 khz guys are almost all using digital
phase cancellation methods for sideband generation therefore there is no
carrier and no opposite sideband to suppress.
B. The few who are using 6 khz xtal filters (actually a little
less--5.8 khz) and analog method are using rigs with front panel
adjustable microprocessor controlled carrier set points that allow them
to place the carrier at least 200 hz below the -6 db filter skirt point
so it is way way down the skirt; the opp. s.b. even farther away. Oh
sure, there may be a few hams who are attempting this with the wrong
gear and don't know any better. Anything's possible. Are mistakes,
booboos and a learning curve now forbidden? I guess it's time for all
rigs to be contained in solid epoxy blocks before being sold to us.
Didn't know experimentation was taboo.
Rob/K5UJ
<<<Having bass that extends well below 100hz will cause a SSB signal to
be wide by modulating too close to the carrier point, crossing over
onto the other sideband, and virtually turning into a DSB signal If you
don't believe this just try tuning a "hi-fi" guy in on using the AM
mode. The signal will be 100% intelligible!! You can even hear the
carrier when you tune across one of these signals. Plus the fact when
one tries to force over 10db of extra energy at very low or very high
frequencies the IMD is terrific and that also contributes to the width
of the signal.
WY3D>>>
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