Friday, May 3, 2019

Cheap reversible beams

A half wavelength dipole is a cheap antenna that can be made and erected by one person in an afternoon. 

A rotary beam is a major undertaking that requires concrete, a strong metal tower, rotator, a heavy antenna assembly and probably several people to safely erect it. 

The latter gives you superior performance in all directions. But at a cost that not everyone can or is willing to pay. 

Between those extremes is the reversible beam. You get good performance but not in all directions. But you do get it in two. If you have it set up for a particular area with a high ham population it will do much better than a simple dipole and reject QRM off the side and rear. And the reversing (which can be electrical or physical) allows you to compare long and short path instantly (no need to wait for a beam to turn).

The late Les Moxon G6XN in his book HF Antennas for All Locations (which you really should buy) describes two loops, each with tuned feeders coming into a shack via a switch box. To change direction you swap the feeders and tune the parasitic element via the unenergised feedline.   

Reversible beams are often light and made of wire. If they're in the right places they could even be slung in or between trees. Both yagi or quad loop versions are possible. If you have a three element design you might have the driven element in the middle and use relays to switch around the reflector and director.

Anyway here are some ideas from others who have succeeded with them. 

* Rick C's reversible yagi for 20m
* AA2NN's reversible yagis or 40m
* AC0C wire phased v-beam for 40m
* M0MCX bidirectional switchable wire yagi
* N4JTE 2 element reversible quad
* N4JTE reversible string beam
2 element fixed reversible yagi for 20m
* W4RNL's antenna options - 14 Reversible wire beams for lower HF use (pdf)

PS: Wish to explore other aspects of amateur radio? This top selling book is full of ideas. Available for $US 5 in electronic form with a paperback edition also available it's ideas for both the beginning and experienced ham. Find our more here.

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