Turnstile antennas are provide circular polarization straight up and at large angles from zenith. Originally I was going to just connect the two antennas together at my switch so I could select one, the other or both. The electrical delay would be provided by one longer feed line. However, one attribute considered essential by the scarce resources on the Internet insisted on switchable polarization: RHCP to LHCP and back by simple inverting the connection to ONE of the antenna feed lines.

With these thoughts I changed the plan a bit. Instead of using my switch and two very long feed lines, I now have one single feed line from the switch to the base of my 50 foot high antenna mast. Here I will provide a relay box with three relays, one coaxial cable in and two coaxial cables out. The two output coaxial cables will each feed one 75 meter dipole on the antenna mast. One cable is ninety electrical degrees longer than the other.

Here is a schematic of the relay box…

Schematic Diagram for Relay Controller

All this will be going into a weather proof enclosure with cables directly connected to the relays where noted.

What about perfect matching John?

I am not too worried about the perfect 1:1 SWR for this setup. In fact I don’t worry much about SWR under 3:1. The impedance presented to the radio side coaxial cable will be the two antennas in parallel although I admit I am not quite sure how these signals combine if they are ninety degrees different in phase. I forgot to look at that in EZNEC. I do remember it was not too high.

In another post I will show some photos of the resulting assembly.

A particular thread on one of these lists spoke of ways to disconnect coax, rotator control lines, etc. at or near where they come into the building. One implementation described by some fellow used relays to disconnect things so he could through one switch and instantly isolate his radios from the antennas.

The problem with this is obvious as the gap between the open contacts of a relay are easily breached by the enormous energies associated with lightning events.

The reason why can be understood with the following value of the breakdown potential of a air gap…

Translate this to, say, a 1 mm gap between the open relay contacts results in only 3,000 volts before breakdown begins.

3,000 volts sounds like a lot, but to a lightning surge it really amounts to nothing. Remember lightning travels far more than that small gap to get to ground and won’t have any problem making the final jump.

So, really, the best approach to disconnecting your equipment remains detaching coaxial cables and ensuring they are far away from the connectors.

Of course designing in good lightning protection devices on a good single point ground (SPG) is still urgently suggested.

You spent good money on your Icom, Kenwood, Yaesu, Ten-Tec, Elecraft radio… probably a lot. No ham shack is complete without spending, say, another 10% of the radio cost on lightning protection from PolyPhaser, Alpha, etc.

Consider good lightning protection cheap insurance for your radio investment. Don’t be cheap.