[Fwd: LF: What! Loops again!]

André Kesteloot akestelo@bellatlantic.net
Mon, 15 Jun 1998 10:19:42 -0400

Peter Martinez wrote:

> >From Peter Martinez G3PLX Kendal Cumbria.
> I didn't include the N-squared term in the loop radiation-resistance formula,
> because the formula is for the loop itself, not for the wire wound round it. If
> that sounds like I am trying to wriggle out of Andy's criticism, consider the
> following:
> Make a two-turn loop, but with separate turns so that there are four ends.
> Wire them to a switch so that in one position of the switch the turns are in
> series and in the other they are in parallel. Analyse what is happenning.
> Clearly, with the switch in the series position, the impedance presented to
> the transmitter (from radiation resistance and from losses) will be four
> times what it is in the parallel position, but if we take this into account, the
> radiated power and the losses are the same. If we compare either of these
> with a single turn loop of the same wire, we can see that the two-turn loop
> (series or parallel) is less lossy than the single-turn loop.
> The N-squared term therefore is really telling you something about the
> transforming action of the multi-turn coil and not trying to say that there is
> something magic about a radiating properties of a multi-turn loop. Andy's
> work showed that N parallel turns give the same improvement as N
> series turns, confirming my series/parallel switch experiment.
> The essential point is that the efficiency of a loop increases as you
> increase the quantity of copper in it regardless of whether you do that by
> using longer copper or thicker copper. To choose between one or the other
> will involve considering things like the lossy voltages between turns and to
> ground, skin effect, etc. My vote goes to a single-turn loop consisting of as
> many parallel wires as you can afford.
> 73
> Peter