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.

Some have the big bad beam high in the sky with an 80 meter dipole added.

Others have smaller beams and more wire antennas.

Others go mobile on VHF and HF.

Still others go expedition and construct antennas that lend themselves towards portability.

I am considering added a 75 meter turnstile antenna to my station.

My club is very active in the Virginia QSO Party. All members have supplied their logs for analysis with Cabrillo Analyzer resulting in these graphs of QSOs over time categorized by band…

VAQP QSOs 2006

VAQP QSOs 2007

VAQP QSOs 2008

80 meter contacts are shown in dark purple. It is quite obvious the band that brings in the points is King 80.

During our sunspot minimum we figure concentrating on 80 and 40 antennas for VAQP 2009 is essential. 20 and 15 are important too. 10 is almost pointless except for some local contacts.

Last year my 75 meter inverted V worked just fine. The apex was about 50 feet up with the wire tips dropping to within ten feet of the ground. This plus several other antennas worked OK. NVIS was most certainly the rule for 80 and 40 this contest.

For 2009 I am wondering if there is something more I can do with 75 and 80 meters. I read some notes about ionospheric sounding techniques that sometimes uses turnstile antennas to transmit their ping upwards and most always use turnstile dipole sets to receive the reflected ping from the ionized layers.

Is this a technique I can use to improve my 75 meter antenna’s performance?

If I create two inverted v antennas arranged orthogonally in EZNEC, but not quite touching at the top…

75 meter dual inverted V

.

…and feed feed each like a normal dipole with 90 degrees phase difference between them…

…we get…

75 meter CP pattern for turnstile

Research on the Internet reveals little information except for the occasional “Wow, so and so was sure loud with his 75 meter turnstile.” This is enough for me to at least try this.

The ionosphere folks suggest providing a way to switch the handedness of the polarization by simply inverting the connections of one of the feeds. If I have enough time I will put together a relay box that can select one, the other, both in RHCP or both in LHCP. It will be an experiment.

Listen for kx4o during the weekend of March 20 on 80 meters and tell me if you think my turnstile antenna is worth the effort.