On May 16, 2007, at 11:53 AM, Edward Dickinson, III wrote:
I'm not exactly sure we are talking about the same thing.
http://www.aorusa.com/ard9800.html
Yes, we are talking about the same thing. They take the voice and
digitize it and then put the data stream into multiple PSK carriers
that fill up the entire voice bandwidth (2.7KHz).
I would take their claim of, "The digital signals may require LESS
SIGNAL than analog throughput making operations possible under
adverse band conditions," with a grain of salt as not too long
thereafter they say:
"Your duty cycle will be more intense. This is important to users of
amplifiers. Because the digital signal makes full use of the SSB
audio bandwidth, you should consider that you will be transmitting at
the maximum power output you have selected. At maximum power
settings, this will likely result in your transmitter consuming more
power and generating more heat. If you transmit images or large data
files, your "key down" time could be three minutes or more."
This tells me that they are transmitting with higher average power so
of course more power reaches the destination. I think they are
counting on a much smaller peak-to-average ratio than SSB so S:N is
more consistent.
Time to become familiar with the term Eb/No.
But this is not really SSB, at least, not as we think of it. They are
generating the digital signal at what would be a very low IF (300Hz -
3000Hz). We think of that as being audio but it is really just a
very, very low IF. They modulate a number of carriers in that
spectrum and then use the SSB transceiver to translate that up to the
final RF frequency. The SSB transceiver is being used as a linear
translator. PSK31 and AFSK (RTTY) work exactly the same way.
73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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