[QRO] ssb refresher course needed

[Robert Lay]

> I need a brief refresher course in HF SSB.  It's been awhile now since
I've
> been into this stuff....
>
> Assuming a modern, commercially produced SSB final amp is operating in
> linear mode, is not overdriven by audio or rf gain on the input side, and
is
> not distorting, can the transmitted signal still be wider than the 3khz
> standard?
>
> Based on the above conditions, if an amp is putting out a SSB signal that
is
> too wide, what practical means are there to narrow the sideband down?

Based only on fundamental concepts, there would be NOTHING about a
commercially produced linear amplifier that would limit its bandwidth to
anything less than the tuned circuits involved - which are inherently much,
much wider than your specified 3 kHz. [also note that I do NOT use the term
"SSB", or "final amplifier", since the commercially produced "linear"
amplifier would not be so restricted. A linear amplifier is a linear
amplifier - use it how you wish!]

If the exciter is modulated such that the drive to the linear has 5 or 6 kHz
of audio bandwidth (not impossible, at all), then the linear would reproduce
that reasonably well.

So, what I am suggesting is that under your constraints of proper RF drive
level from the exciter AND not over-modulating the exciter with too much
audio, the only thing left that would cause a wide signal is the bandwidth
character of the audio through the exciter. I can design an exciter that has
audio fidelity out to 10 kHz with ease. Whether you would find such
capability among ham transceivers or not is questionable. Whether you would
find such a problem in ham transceivers as a design defect is also
problematic but could certainly happen.

The final quesion of how to narrow the bandwidth is answerable only if we
know for sure WHERE the problem originates. IF we take all of the
constraints you mentioned on faith, then it HAS to be that the audio
passband in the exciter is the reason for the wide signal and the
BEST way to limit that is to correct the implementation in the exciter so
that it cuts off the bandwidth, sharply, at 3 kHz. If the system from that
point
on is linear, then you cannot be generating a broad signal.

[note that we are NOT even considering the question of whether or not the
supposedly wide signal is in fact too wide. We are taking that on faith -
which is a big fish to swallow.]

Bob Lay (W9DMK) in Dahlgren, VA
http://www.qsl.net/w9dmk