[Fwd: LF: G3XDV/ON7YD comments]
Tue, 09 Jun 1998 10:27:17 -0400
Walter Blanchard wrote:
> Earth losses - Yes, you might get up to 50-100 ohms
> if you just stick a stake in the ground but even an
> elementary effort to get out a few radials will bring this
> down. The figures I used were from actual measurements
> we (Decca) made some years ago when attempting to see
> how small a ground plane could be got away with
> using our 15 m pole at 127 kHz - we were trying to make
> a reasonably portable system.
> The results were summarised in an internal Decca memo
> that had over 100 graphs but in general it showed that
> (unsurprisingly) the worse the soil the more radials and
> length required - you are simply replacing the poor soil with
> more wire. What this meant in practice might be surprising.
> Example: in damp rich soil (10-13 mhos/m) there was very
> little difference between 18 and 72 radials and very little to
> be gained by going beyond 200 ft lengths.
> We measured 0.8 ohm loss resistance for the 72-wire system.
> But in very poor ground (sandy, 10-15 mhos/m) to get down to
> 1 ohm or so it was ESSENTIAL to use either 150 radials
> of 500 ft length or 50 radials of over 1000 ft.
> Hardly a backyard system even if you can afford the cost!!
> In reasonable average UK soil it was fairly easy to get down to
> 15-20 ohms simply by running out 8 or 10 100 ft lengths and
> burying them a few inches (laying them on the surface meant a
> lot more wire).
> My own "soil" here is neat greensand so I'm in the 10-15 mhos/m
> category and would be delighted to find some way of doing away with
> an earth.
> Walter G3JKV.