An interesting point from Tom re SSB modulation added problems.
A really informative website re "plain old RTTY" is
http://www.frontiernet.net/~aflowers/k3rtty/k3rtty.html
and is a good introduction to the technical complexity of digital
modulation systems and what to do to make "better" RTTY signals.
The W7AY work is referenced w7ay.net but the site was not available when
I tried it.
Is there any good testing posted for other modes and on other radios and
software generators?
Grant KZ1W
On 12/31/2013 7:13 AM, Tom W8JI wrote:
Well, I certainly have to agree, Tom, if the signal on the desired
sideband
is just a single shifting tone. Might get messier if an sudio stage
or A/D
is driven into limiting and producing harmonic distortion at audio, I
guess.
The entire thing for digital modes was poorly planned. I'm surprised
no one objected to the frequency choices (of Europe), because they are
technically always going to be a long term problem. The frequency
range really could not have been more poorly planned for future
long-term band use.
Any digital mode piped into the SSB transmitter system, like it or
not, is really SSB modulated. It has all the noise, carrier, and
opposite sideband suppression issues, as well as sensitivity to
levels. If they transmit 1835-40 using USB on the radio, the opposite
sideband falls in the 1832 and upward range. IMD can be anywhere, if
it is a multiple tone at the same time mode. Harmonic distortion is
upward from the carrier on USB.
Collins got burned by this. They tried running a pure audio tone into
the SSB transmitter of the early S line to generate CW. The FCC (back
when they did enforcement) starting handing out pink slips left and
right to Collins owners. Any carrier, noise, or harmonic distortion at
all resulted in an FCC citation, so Collins had to convert
transmitters back to a keyed carrier.
Anything converted to RF in a SSB transmitter system really belongs
off by itself, well away from other operation. It's really a technical
issue that will always exist, because the basic RF generation system
or idea is flawed.
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