Roger Wheeler wrote:
> I am trying to quantify the efficiency of trapped h.f. antennas
> references tell me that -traps are lossy and trapped antennas are
> inefficient.I cant find a reference to the typical efficiency, is it
> 20% ,40% or is it 90%?
> Any ideas on measuring the loss resistance of an hf trap.?
Hello Roger,
There has been lengthy discussions on the Towertalk reflector
on efficiency of traps in the context of tri-banders v. full size
yagi antennas.
Reductions in tribander performance include the effects of:
1. Shortening of the elements
2. Compromises of element spacing on 20/15/10m
3. trap losses and loading coil losses.
Roger Cox of Hygain has published some typical trap data
for L, C and Q as an aid to building more accurate models.
Traps serve different purposes, so you may need to be more specific
in your area of interest:
* A 15m trap acts as a parallel tuned circuit to be a
band stop on 21MHz. But on 14 Mhz it acts as a lumped L to
shorten the 20m half element length. I imagine the losses are
not the same on both bands.
* The CC 40-2CD uses loading coils to reduce the element
half lengths. These are not traps as such (they don't trap anything!).
But you may wish to include them in your study.
If you contact LB, he may be able to assist.
Regards,
Martin ZL1ANJ
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