Differences

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--- 2m0iig-satellite-yagi [2022/08/25 21:18] – [Build Process] mm3iig
+++ 2m0iig-satellite-yagi [2022/12/08 19:34] (current) – [2/70 Direct-Fed Satellite Yagi (work in progress)] 2m0iig
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-====== 2/70 Direct-Fed Satellite Yagi (work in progress) ======
+====== 2/70 Direct-Fed Satellite Yagi ======
 ===== Introduction =====
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 ===== Parts List =====
-{{ :1_materials.jpg?direct&300|}}
+{{:1_materials.jpg?direct&300| }}
   * 1m section of 20mm rigid PVC conduit
   * 3 x 20mm conduit spacer bars
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   * Something to make marks with (sharpie?)
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 {{:4_elements.jpg?direct&300 |}}The antenna elements themselves were mounted on the pipe spacer bars with some long M3 screws to fit the antenna elements. The key is to insert the screws the other way up from how they are meant to be used (screwhead down). Luckily the screw holes in the spacers were juuuust about M3 size. Nothing some extra force didn’t solve.
-The bottom of the top two spacer bars on the boom have small lengths of solid core wire joining the two sides, wound around the screw threads tightly before screwing the screws down as far as I could. Check the continuity at this point! The two sides have to be joined together to make a continuous half-wave radiator.
+The bottom of the top two spacer bars on the boom have small lengths of solid core wire joining the two sides, wound around the screw threads tightly before screwing the screws down as far as I could. Check the continuity at this point! The two sides have to be joined together to make a continuous half-wave radiator. The bottom, driven elements have to remain separated, so just wrap the coax centre and shield - one around each thread - and screw those tightly too.
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 Initially I used some tape to hold the spacer bars in place while I tuned the antenna on a VNA. I used the dimensions Adam gave as a starting point and retracted the telescopic lengths until I had a decent tune on both 70cm and 2m. I then slid the spacer bars a tiny bit back and forth and checked the tune. After dialling it in well I drilled a hole in the middle of each top clip and used some self-tapping screws to firmly secure the bars to the pole section.
-And that is basically it. Keep the M3 bolts tightened (this will annoy you, they are joined at only one place so things will rotate when you don't want them to or when travelling etc) and make sure you don't bend any of the telescopic elements. The more you do that the more out-of-plane they'll become. For the best efficiency and radiation pattern your Yagi elements all need to be in the same plane.
+And that is basically it. Keep the M3 bolts, nuts, and wingnuts tightened (this will annoy you, they are joined at only one place so things will rotate when you don't want them to or when travelling etc - is there some sort of locking nut you can use to stop this?) and make sure you don't bend any of the telescopic elements. The more you do that the more out-of-plane they'll become. For the best efficiency and radiation pattern your Yagi elements all need to be in the same plane.
 The elements will, of course, bend at the right-angled join, meaning that you can store the antenna stowed, attach it to a rucksack, etc. Or you can fully disassemble and reassemble each time. Bring a spanner! And maybe a small screwdriver.
 {{ :6_stowed.jpg?direct&900 |}}
+===== Improvements =====
+There’s loads of ways you can improve this design. A foam grip or pistol grip would be good for the wrist - these antennas do get a little heavy and cumbersome after a while.
+I’ve also considered adding a reflector behind the driven elements. There’s room for it, and it may improve the UHF downlink receive which is the only downside of this antenna (hence it only really working to 40ish degrees). I will run the model for this in MMANA-GAL and see how it helps. It may ruin the 70 cm match though.
+I think the original design with arrow shafts (used on the, er, Arrow too) are a better idea for better rigidity and keeping everything aligned right. But I don’t really have much in the way of tools or skills, so drilling holes for threads and inserts scares me. But seriously, if you are okay doing that kind of work then definitely do it - it’ll be much better than my build.
+A split boom somehow would also be good, just to keep the size down. How to attach the two halves together is something I’d need to think about.