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

Hare,Ed, W1RFI w1rfi at arrl.org
Wed Jun 11 18:14:35 EDT 2003

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.

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

ARRL is the National Association for Amateur Radio.  It is supported by membership dues, individual contributions and the sale of  publications and advertising. For more information about ARRL, go to http://www.arrl.org/news/features/inside-your-league.html. For more information about membership, go to http://www.arrl.org/join.html.  Your contribution can also help support ARRL's ongoing efforts to protect Amateur spectrum. Go to https://www.arrl.org/forms/development/donations/basic/ to learn more about the ways you can support the ARRL programs and activities of most importance to you. You can help ARRL protect Amateur Radio for you and future generations to enjoy.

> -----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.

More information about the RFI mailing list