Keep in mind that the spurs generated will probably [produce a signal that
will exceed the 2.7 Khz bandwidth! Especially with operators who are not
that technically inclined. To digitize the signal really won't gain you a
whole lot! As more and more people try it, I fear the noise floor will rise
with more and more use of it.
73,
Sandy W5TVW
----- Original Message -----
From: "Brian Lloyd" <[EMAIL PROTECTED]>
To: "Edward Dickinson, III" <[EMAIL PROTECTED]>
Cc: "Elecraft Discussion List" <elecraft@mailman.qth.net>
Sent: Wednesday, May 16, 2007 5:42 PM
Subject: Re: [Elecraft] Digital SSB..?
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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