On Nov 21, 5:38*am, Wimpie wrote:
On 21 nov, 04:47, Steve wrote:

I've seen several programs that will help you calculate the precise
dimensions of a single-turn loop, given the composition of the
radiating element, its thickness, and so on. However, none of these
programs are written to cover the case of a two or more-turn loop.

Does anyone know of a program that will offer guidance in the
construction of a two or more-turn loop?

Thanks,

Steve

Hello Steve,

You probably did some loop calculations and found that in a transmit
case the voltage across the tuning capacitor is very high (and
bandwidth is limited). Also for small loops, most input power is lost
as heat due to copper resistance.

When you make a two turn loop, the radiation resistance will increase
with factor 4. So with half the current through the loop, the radiated
power is same (as for a single turn loop). *When the 2 turns of the
loop are relative close together, the inductance increases with factor
4, hence the reactance.

The current has been halved, but because of the reactance, the voltage
across the tuning capacitance will be 2 times the value for the single
turn loop with higher probability on corona effects. *An advantage can
be an almost 4 times smaller tuning capacitor.

One may expect that the loss resistance due to heat of a two-turn
inductor will be twice as high (w.r.t. single turn case). This is not
true; the loss resistance will be more then twice as high because of
proximity effect. The current will not equally distribute along the
circumference of the tube/wire. *So the efficiency of the loop will be
less then twice as high (w.r.t. single turn case).

When the turns are far apart (with respect to wire/tube diameter),
inductance will not be 4 times higher and proximity effect will be
less. You will get better performance than the single turn loop made
of same diameter tube/wire. The result will be the same as when you
place the two turns in parallel. Inductance will decrease somewhat
(hence lower voltage across capacitor), AC resistance also, hence
radiation efficiency).

There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: *1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. * The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. *Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).

Off course for the receive-only case, a multi turn loop can be helpful
as you can use a smaller tuning capacitor.

Best regards,

Wim
PA3DJSwww.tetech.nl
In case of PM, don't forget to remove abc.

Seems to me you are recommending the "?slinky" !
Is that correct?
Art