Nice antenna!
papabravo said:
I certainly would be interested in seeing a return loss plot of that configuration. I'll have to take your word for it.
Inspired by this comment I did some experimentation using a home made Return Loss Bridge (RLB), and the results were both interesting and confusing in some areas.
From memory, (I am away from home at the moment):
1/ Connecting the 1metre wire (straight line) to the
Unknown port of the RLB and just the cables to the signal source and detector, I could not find a sensible resonance between 30 and 100Mhz. A very poor result.
2/ Connecting the 1metre wire (straight line), and mounting (a soldered connection at two points) the RLB onto the middle of a strip of copper, about 7cm wide, 1.2m long and 0.2mm thick, I found a good dip in return loss (>20dB) near the expected resonant frequency of the antenna (73Mhz). A good result.
This is what I would expect, the antenna will not give good results without a reasonable earth plane to work against, just like in the model areoplane, where the only earth plane is the reciever chassis and power wiring.
3/ Winding the antenna wire into a helix, about 3cm dai and 30cm long, and connecting it to the RLB as in 2/ above.
I could find a resonance at some frequency, but it was up at about 200Mhz (from memory).
4/ Winding a second antenna from 3 metres of wire (helix 3cm dia, about 80cm long), and connecting as in 2/ above.
I could find a resonance at about 45Mhz (again, from memory).
Some strange results, not quite what I would have expected, from tests done under far from idea conditions.
Another test I did was to measure the relative response of the straing wire and the same wire wound into a helix.
The helix gave 10 to 15dB less signal.
Again I emphasise that the test conditions were far from ideal (verging on a joke).
Relating all this to the practical situation of jpanhalts' model plane, his helix although probably far from ideal, provides a working solution for him.
He is working line of sight to the plane and there will be plenty of signal from his controller with its 200mW transmitter and better mounted antenna.
JimB