This summer I attended the TI-2 Space workshop put on by the ARRL and DARA in Dayton, OH. We spent 4 days learning how to make contacts with orbiting satellites like AO-27, AO-51 and the International Space Station, just to name a few. The antenna we used was the dual-band Arrow II Antenna. I've owned one for years and really like it. I wish more people had them, but I think most people think spending $140 for an antenna that can only handle 10W is a bit much.
My aim was to make a cheap alternative to the Arrow that is easy to break down for transport and storage. I really like the idea of using aluminum arrow shafts for elements; they are lightweight, straight, weather resistant, and fairly inexpensive. Another nice feature is the #8-32 threaded insert for broad heads that almost every arrow comes with.
I spent a couple of hours reviewing all the "cheap" and "ugly" yagi designs, as well as others like the "tape measure" and even a new-to-me "backpacker" design. They each have their own advantages and loyal followers.
I finally based my antenna design on one found in the ARRL Handbook from 1999. While not an exact replica, my design is very similar. I had decided to go with the through-boom design like the Arrow, as opposed to side-mounted because it is, in my opinion, cheaper. After buying 6 arrows and a quick trip to Lowe's I had a length of #8-32 all-thread and a piece of 3/4" conduit to use as the boom. I marked a straight line down the center of the boom to give me a point of reference, measured out the spacing holes, made sure I was drilling square and level and got to work. After the 3 holes were drilled, I cut 2.5" lengths of all thread for the director and reflector. Since I was going with the split driven element design of the IDX yagi, I would not need threading for the Driven Element, I'd use machine screws for that. Originally I planned to use nylon 8-32 all-thread to go through the boom for the driven element, and feed each side independently similar to the Tape Measure Yagi, but I couldn't find nylon all-thread, and the longest nylon screws to be found came up an inch too short.
I cut a length of RG-58 cable and soldered on two o-ring connectors to slip over the machine screws before screwing on an arrow.
Lastly I cut each arrow to the appropriate length, which worked out to:
- 19 5/8" for each Reflector arrow
- 18 1/8" for each Driven arrow
- 17 1/8" for each Director arrow
The measurements came from IDX's lengths, subtracting 3/4" (for the boom) and then divided by 2 to give me the necessary length for each arrow.
I used a cutoff wheel and my air compressor to cut the arrows to length instead of a hacksaw. The cutoff wheel leaves a clean cut as opposed to sawing.
After putting my MFJ-269 analyzer on the yagi, I found the lowest SWR to be about 1.4 right around the target frequency of 144.490 MHz. Not too shabby for a first yagi.
For those taking my lead, I found it helpful to feed the yagi as perpendicular to the boom as possible. It is also somewhat important for the O-ring feedline connectors to be on the same side of the boom as the arrow.
Here's a pic of me holding the 2m yagi. It's a bit larger than the commercially made Arrow.
update: I've been asked by more than one person why the split driven element. As you read above, it was semi forced on me by necessity. I needed it to be split for mechanical reasons. the screws going through the boom serve as a match, negating the need for the "hairpin" match from the tape measure yagi or a gamma match. The driven elements being split probably do affect the radiation pattern in the long-field, but perhaps only skew the pattern more in one direction.
(TLDR: it's easier that way and it just works!)
update #2: Hello Hack-A-Day! Yes, you can talk to the space station and many other amateur radio satellites.
update #3: Okay, for those that are interested, I'll be putting together kits if you want. Price to be determined based on what you want/need. You can email me at firstname.lastname@example.org for more info.