Polarity change for EME

Discussion in 'Satellite and Space Communications' started by N8SAN, Dec 2, 2021.

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  1. N8SAN

    N8SAN Ham Member QRZ Page

    Hey everyone!
    Well after many years of parts collecting I finally got my first EME (and 2nd) qso these past few weeks!
    SUPER excited!
    Number one was Franco, I2FAK. If anyone is moderately into EME, you've probably worked him. Massive station.
    I was just CQ'in into the dark. No forums or SKEDs. Just skipping off the Sea of Tranquility and he came back to me! Said he saw me on MAP65.
    Number 2 was Earl WB9UWA. That was sorta setup on JT65 EME chat.

    My QSO with I2FAK was the Friday before the EME contest. I heard a few stations that weekend but did not work a soul. I2FAK emailed me later to tell me he saw transmissions answering the to CQ's at -22 to -24 (or so).

    Questioning why no one heard me. I had forgotten all the stuff I had learned during my parts collection phase. Spatial rotation, Faraday rotation, etc.
    In light of that I thought about adding some capability by being able to change polarity.
    I can "easily" -read cheap- make the antennas rotate 90° to vertical and back to horizontal.
    Which could theoretically "double" my capability. I say double in the sense that I would be able to change polarities.

    My current setup is 2 M2 2M9SSB's horizontal on a fiberglass boom.

    I'm mentally envisioning some spring hinges and some sorta motor/pulley arrangement to make the event happen.
    I don't really want to use limit switches so I'd have to have some sort of travel limiter. (Or a stop on the hinge) Which would be easier with linear actuator. But a small rotational motor would be easier to make it work.
    I would use exterior door spring hinges. So the motor would only have to work in one direction and the springs would always keep the line in tension. (But I don't know if the metal hinge will effect my performance. It wouldn't be in direct line of the elements.)
    I'd just use whatever actuator to lower the tension on the line and the spring would move the antenna to the desired polarity. And so on.

    Something like this.


    I feel like I've seen something out there like this, but I cannot find again.

    Any feedback is appreciated.
    N3RYB likes this.
  2. K6CLS

    K6CLS Ham Member QRZ Page

    Aha! In North America we need to run vertical polarization to QSO with EU stations.

    Loosen the u bolts and turn the antennas 90°. (Make sure they are both the same 90, with the baluns on the same side, ha!

    I found on 70cm vertical usually worked better, horizontal rarely.

    Can you reach the boom easily? If you left the u bolts slightly loose, could you run over and rotate quickly if you had to?

    Some folks have made polarization rotation jigs, and they seem to work ok, but frankly I'd rather just get 4 longer X pol M2 antennas...
  3. N8SAN

    N8SAN Ham Member QRZ Page

    I mean that can't be a hard and fast rule, is it? It seems to be one of those things the can move.
    Not questioning you, just wondering.

    Now that's interesting. I wonder why?

    I did not. They are snug. But I can get to them rather simply. Just would have to get on the roof.
    The reason for the jib is obviously, to be able to adjust while at the control point and see if it help.

    What issues did people run into with rotation jigs? Seems rather straight forward.

    I tend to agree. That X pols with more elements are better.
    But off the bat-
    4 antennas, H frame, 4 conductor power divider, polarization switch, coax....That's what? 3k new? 2500? That's probably more than I have in my whole EME system. Including the IC9700!
    I'm talking about 65$ to try this!

    While I DO know that this isn't something you typically try to see what you get away with the least possible stuff. But this is what being an amateur operator is all about. :D
  4. K6CLS

    K6CLS Ham Member QRZ Page

    Ha! Yep. Definitely feels like a win setting up a simple inexpensive jig that works.

    The reason vertical from NA works with horizontal in EU is the geometry of the path. Get a couple balls, for the earth and moon, and a couple toothpicks, to represent the polarization of the E field.. Take a look at the polarization on both sides of the path.

    ... Except for Faraday rotation! Can be so confounding. Might be what happened on your second night? So yeah, rotatable polarization is really handy.

    On 70cm I've had some weird nights. TX on horizontal (ground gain with rising moon low), but I needed to rotate the antennas to 60° for best RX. Stayed like that for a couple hours. Good way to stay warm, running back and forth outside every minute! But climbing on the roof, no thanks!
  5. W1VT

    W1VT Ham Member QRZ Page

    NC1I has 48 rear mounted Yagis. The rear mounting allows rotation of the entire array!
    Steve K1FO (SK) figured out how to do this and Frank built a much bigger array than Steve's invention.

    With a large dish one can rotate the feed to allow polarity rotation.
    N8SAN and KD2HAM like this.
  6. N8SAN

    N8SAN Ham Member QRZ Page

    Right. I gotta believe adding polarization capability won't go unutilized! As you said, sometimes, it's between the V and H where you get best RX. I want that capability.
    I'm not willing to throw multiple grand at antenna upgrade right now.
    IF anything I would add 2 M2 and make an H frame and get the power divider. But I feel for now, getting the antennas to move between V and H is probably the next best step for me.

    HAHAHAH yeah! I'm sure you kept warm running back and forth. I don't want to do that. I like being able to control stuff remotely.

    HOLY CRAP! I just looked up his farm. He has more antennas than DX ENG has in stock.
    His array is INSANE!! I love it!!
    I'm not looking to get into the structural requirement for rear mounting. Not even close. But that's killer.

    That does however make me think of something.

    What about a clamshell type bearings (think crankshaft-connecting rod) that I could capture the boom in. Couple of set screws to keep the boom from moving fore and aft. And then just rotate the boom in in the bearing without a hinge. The only thing with this arrangement, it would need push and pull capability. But would keep the antenna boom in the same place. For spacing reasons.
    K6CLS likes this.
  7. VE3CGA

    VE3CGA XML Subscriber QRZ Page

    thats a good idea with bearings
    you might want to go to the autowreckers and look for a 12V window motor. they might have limit switches builtin and some I've seen only go 90 degress with the crank arm already there
    the connecting rods out to each antenna boom could be those fiberglass laneway markers I think they are 4' long
    Plastic or nylon offset arms out on the antenna booms, cheap relay or transistor switch for reversing the motor
    We used small 24vac motors to open and shut large air handler intake and exhaust dampers simultaneously for smoke exhaust
    in the event of fire. All were 90 degree movement with connecting rods and crank arms
    One connecting rod on each damper, crank arm offset at 45 degrees, then moves 45 degrees the other direction for 90 degrees movement
  8. N8SAN

    N8SAN Ham Member QRZ Page

    I ordered a single linear bearing yesterday to see if it'll work. I think that it might.
    They only had 1 in stock. So I'll have to wait 1-3 weeks if I order another! hahah OR pay 3x the price.
    The only thing I'm sorta concerned with is having more metal on the centerline of the boom. How will that effect the antenna? Maybe not at all.

    Was going to use these. 1.1' each push pull rods. 4mm but light and pretty sturdy.


    I do like your idea of the laneway markers. My father in law has 6' ones for plowing. I might use that.
    I liked the push/pull as they have threads on the end. BUT the specific length might be a problem in the end.

    Auto door window motors know the travel limit by an increase in current when they stall. That's how they shut down.
    I think I might use a 1/4 scale boat rudder servo. A coreless servo has massive torque and staying power. Meaning wind won't be able to move the servo via the antenna.
    They're about 120$ though....didn't want to get that pricy.
    That said, with a servo I would be able to easily dial in any degree between H and V.

    More thinking.
    VE3CGA likes this.

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