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

[Hare,Ed, W1RFI]

To date, DSL has not caused hams any problems, but it stops a 1.1 MHz, though it will soon be going higher.  But twisted-pair telephone wiring is a much poorer antenna than overhead power lines, so the amount of notching that BPL would need would be unworkably high. I know hams who can literally hear a neighbor a mile away turn on a computer power supply.  How do we protect that capability?  How about apartment dwellers who aren't allowed outside antennas? Do we "write off" that aspect of ham radio?

By my calculations, about 70 dB of notching would be necessary to protect against BPL interference in quiet environs with antennas located about 100 feet from a radiating power line, with more needed for the circumstances I described above.

The bottom line, IMHO, is that signals much stronger than the present conducted emissions limits should not intentionally be put onto power lines.

73, 
Ed Hare, W1RFI
ARRL Lab
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: w1rfi at arrl.org
Web: http://www.arrl.org/tis

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> -----Original Message-----
> From: Cortland Richmond [mailto:ka5s at earthlink.net]
> Sent: Wednesday, May 14, 2003 2:21 PM
> To: Hare,Ed, W1RFI; rfi
> Subject: RE: Another "no interference" conclusion. . .
> 
> 
> 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.  
> 
> 
> Cortland
> 
> 
> > [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.
> 
> 
> 
> 
>