[Fwd: LF: Power line interference]
Tue, 26 Jan 1999 17:36:30 -0500
> Comments on part of the message from Mike Dennison:
> > However, I have found some lines to be extremely noisy - including
> > the one adjacent to my Welsh holiday home. These are usually
> > relatively low voltage, 11kV - 400V, and I assume the noise has
> > more to do with a fault than design as most of these are noise free.
> > The noise tends to radiate for 50 yards or so, but no more.
> For low voltage power lines I believe the worst noise is actually
> generated in consumer appliances, namely switch mode power supplies, and
> is spread by conducting back into the mains distribution. Mains filters
> become increasingly ineffective at lower frequencies as (safety)
> regulatory limits on capacitance from phase or neutral to earth of some
> 0.005 uF is simply insufficient to do a decent job of filtering at LF.
> Tests done by Andrew ZL2BBJ using a sensitive portable receiver (battery
> powered) showed a dramatic reduction in mains borne LF noise for
> separations from mains wiring of only 5 metres or so.
> Amateur reception on LF can be "fairly noisy" when using a transmitting
> antenna for reception. A separate receive only active whip with
> suitably low noise figure located "down the back yard" can yield better
> S/N, but care is needed with power supplies to decouple from mains borne
> noise (use split core double insulated transformers and a separate RF
> ground for the antenna). Andrew ZL2BBJ supplied the information on this
> for the latest ARRL Antenna Book (18th edition, page 6-35, figure 65).
> Note that some production errors crept in to the circuit diagrams, but
> the isolation idea is shown correctly.
> Bob ZL2CA