Re: [officers] Re: [amsat-bb] "Two Hundred Meters and Down," 2003edition

[Phil Karn <karn@xxxxxxxx>]

Jeff Davis wrote:

> And yet, there is a certain sweet irony that while all the no-code forces in 
> the universe worked their tails off to eradicate CW from amateur radio the end 
> result may very well be that the only mode that can survive BPL is ... CW.

Have you paid any attention to the results of the FEC mode that was 
recently added to AO-40's telemetry? A friendly rivalry seems to have 
developed to find the crappiest receiving system that can still copy the 
FEC telemetry from apogee. Simple S-band ground planes and dipoles, bare 
feeds, off-pointed dishes, noise generators and attenuators have all 
been used. They produce a signal that often can't even be detected by 
ear, yet can be reliably decoded with a garden-variety PC.

And while FEC definitely helps with a weak but stable signal from 
apogee, it doesn't *really* shine until the signal is fading deeply 
and/or is impaired by impulsive interference. I've noticed occasional 
pulsed interference on the AO-40 beacon frequency that is believed to 
come from local cordless phones, and it often impairs reception of 
uncoded telemetry even when the average signal strength is very high. 
But FEC makes short work of this kind of interference, especially when 
you have a good noise blanker in your receiver.

Judging from the ARRL's recordings of BPL signals on HF, a well-designed 
digital mode with FEC should be extremely effective against this kind of 
interference as well. But having said that, I do oppose the deployment 
of BPL if the interference levels are as high as indicated. Broadband 
connectivity is important, but there are several good alternatives that 
don't impair so much of the spectrum.

Phil

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