Hi Brady,

My quick three cents:

first penny) The coax relay at the feedpoint method is feasible and is how the M2 Antennas Inc. switchable polarization sense feedpoints work. I have no personal experience fabricating these, but we use them in the VT Ground station to switch between LHCP/RHCP. M2 Antennas documentation warns of a slight VSWR increase with this technique, but so far (couple years now) they have performed great for us.

second penny) While you might not have to cut phasing lines with the 1/4 wave offset technique, you will likely need to cut 1/4 wave impedance transformation lines. If your two feedpoints are 50 ohms each, then a 1/4 wave transformer of 75 coax will be needed (transforming to 100 Ohms) so that when they are placed in parallel (via a splitter/combiner) you present 50 ohms to the feedline/radio. This link has a lot of good info on this:

http://www.qsl.net/sv1bsx/antenna-pol/polarization.html

third penny) There is a great section in the ARRL Antenna Book (I think in the Antennas for Space Communications chapter) about using a coax relay and a pair of 50 ohm feedpoint yagis to achieve circular polarization. The coax used in that example is both for phasing and impedance transformation in one, though requires 100 ohm (or close to that) coax (which last time I checked was available at the RF connection, who can also fabricate properly phase calibrated cables for you). Also the relay in that example was not at the feedpoint of the antenna. So it does exactly the opposite of what you are trying to do (antennas are not offset, and you need phasing/impedance transformation lines) but in my experience I found it easier than trying to crack open a (potentially expensive) coax relay and integrate it into a feedpoint (I left that to the pros at M2 Antennas).

Good Luck!

73s,

Zach, KJ4QLP

Research Associate Aerospace Systems Lab Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305

On 4/12/2017 6:51 PM, Richard Tejera wrote:

Brady,

Domenici, I8cvs SK had published a pair of articles on making a switching relay between vertical, Horizontal, LHCP & RHCP. he sent me PDF's, which are in my to do someday folder.

Contact me off list (email is good on QRZ), and I will send them to you. They are for 70cm, but certainly can be adapted for 2m easily enough.

Rick Tejera K7TEJ Saguaro Astronomy Club www.SaguaroAstro.org Thunderbird Amateur Radio Club www.w7tbc.org

On April 12, 2017, at 14:11, Brady Gordon ac0xr@lowswr.com wrote:

Hi Everyone,

I'm working on building a pair of crossed yagis for 2m and 70cm, and I have some questions. I apologize if this has been discussed before, but I couldn't find answers online so I was hoping you all could help me out.

First, it seems easiest to me to build an antenna system that can either switch between vertical and horizontal linear polarizations, or between right hand and left hand circular polarization. Which would be more useful? And is it worth the extra effort to build an antenna system that can switch between all four polarizations?

Also, I've been looking at the different ways of achieving circular polarization. I like the idea of using mechanical 1/4 wave separation between the two yagis so I don't have to cut phasing lines. Would it be possible to switch polarizations by putting a relay at the feedpoint of one of the yagis and switching which side of the driven element the center conductor and shield of the coax goes to? I've never seen this done before, but it seems to me it would work. Any thoughts?

Thanks and 73, Brady AC0XR _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb