[Elecraft] Digital SSB..?

[Sandy]

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" <brian-wb6rqn at lloyd.com>
To: "Edward Dickinson, III" <softblue at alltel.net>
Cc: "Elecraft Discussion List" <elecraft at 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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