[RFI] RE: Another "no interference" conclusion. . .

Cortland Richmond ka5s at earthlink.net
Wed May 14 12:20:38 EDT 2003

Ed, the first-generation ADSL I worked with (and helped get to deployment)
used a "carrierless" modulation which sounds rather like this. The good
news is, even "up close and personal" I had problems detecting it with a
narrowband receiver.  However... it was _extremely_ susceptible to impulse
noise, and Discrete Multi Tone (DMT) ADSL has replaced it. 

DMT monitors the SNR on each tone, and marks out of service tones with poor
SNR. This is how, I believe, the PLC folks intended to put Amateur-band
notches in their signals.  I do not see any notches for broadcasting,
however, and that too is a service the FCC is _supposed_ to protect.  


> [Original Message]
> From: Hare,Ed, W1RFI <w1rfi at arrl.org>
> Subject: Another "no interference" conclusion. . .
> the potential of interference to radio users, thanks to a decrease in =
> transmitted power spectral density. The OFDM modulation spreads the =
> signal over a very wide bandwidth, thus reducing the amount on power =
> injected at a single frequency. Field trials of PLC technologies carried =
> . . . 
> It is easy to report "no interference" when the interference potential =
> has not been studied by the industry and the interference studies done =
> and reported by amateurs are not considered in reaching the conclusion. =
> :-)  Right now, I don't know of any industry interference study, but if =
> any of you can point me to one, I want to include it on the ARRL web =
> page for completeness.

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