Sunday, July 20, 2008

My first beam - Part 1

It finally happened. I finally have an antenna that can be pointed (where pointing actually has an effect on the radiation pattern.)

Until now, all the antennas that I've had have been (more-or-less) omnidirectional, which means that they work equally well (or equally badly, depending on your point of view) in all directions. After several years of begging discussions with Sharon, she's agreed that it'd be OK if I put a small beam up on the roof. I felt that even a relatively small HF beam was a bit bigger than what I wanted to start with, so I figured that I'd go with a small 6 meter beam. I chose the M2 6M3 (a 3 element beam) based on the specifications compared with similar beams and on recommendations from friends. I really would have liked the 6M5X, a 5 element beam which has better gain, but the 18 foot (5.5 meter) boom seemed a bit much for what I wanted to do. (The boom on the 6M3 is 6.75 feet [2.06 meters]).

I did some price shopping, and found that Gigaparts had it listed for about $30 less than I could find it elsewhere, with the caveat that it was out of stock and the discount only applied while it was out of stock. It turns out that the out of stock condition lasted a lot longer than I (or they) expected, so instead of the antenna arriving in June (I ordered it on May 31), it finally showed up on July 11. Sharon and I were out of town taking a mini-vacation then, and with Justin's surgery coming up when I got home I was very busy, both at home and at work, trying to cram a week's worth of things into about three days. As a result, about all I had time to do was to open the box and take a look at the instructions.

The first thing that I noticed in the instructions was that it referred to the "N" connector on the T-Match. (The T-Match is where the antenna connects to the feedline.) "N" connectors are normally used at ultra high frequencies and above (they were originally designed to be used at microwave frequencies) or sometimes at VHF frequencies when it's critical minimize any signal loss. Normally though, antennas of this type use the more common UHF (or SO-239/PL-259) type of connectors. All of my feedline terminates in PL-259 connectors, so I needed to either obtain a male "N" connector and fabricate a cable, or use an adapter. The adapter route seemed easiest, and fortunately, my friend Matthew, K2NUD, had a spare that he was able to lend me until I could purchase my own.

As it turns out, the instructions were wrong; the connector on the T-match was indeed an SO-239. I didn't discover this until after I finally started building the antenna. So, I'll return the adapter to Matthew, and figure out to do with the other four adapters that I got from ebay when they get here. (Fortunately, they were relatively inexpensive.)

As I mentioned, Justin had his surgery this week on Thursday. I worked Monday through Wednesday trying to cram all my regular weekly activities into three days, and that, along with other "family matters" kept me from looking at the antenna again for the remainder of the week. The really good news is that Justin's surgery appears to have been successful. His back and leg pain have been significantly reduced, and while he's got a fair amount of physical therapy ahead of him, all of us are happy with the results so far.

We brough Justin home from the hospital on Saturday afternoon, and got him settled with his laptop (of course) in front of the TV. After spending a while catching up on some of my emails, I decided that I'd take a crack at putting the antenna together and making making a few QSOs. As it happened, this weekend was the CQ WW VHF Contest, but because I knew I'd be tied up with Justin, I figured that I wouldn't really participate at all anyway, so putting the antenna together seemed like a good idea. If it had been a nice comfortable summer day, I would have gone outside and used the backyard table as a workbench. Unfortunately, it wasn't exactly comfortable. It was about 95+ degrees F (about 35 C) and humid outside. It seemed to me that indoor assembly made a whole lot more sense.

The first problem was finding enough space in the house, and making sure that once I got the antenna assembled, that I'd be able to get it out of the house. The assembled antenna is about 6.75 feet (2m) long and over 9.5 feet (almost 3m) wide with the elements attached. Fortunately, a few years ago we put an addition on the house which we call the "great room" that had a good amount of space, and a sliding door directly to the outside. The first order of business was to roll the area rug up since when I handled the aluminum tubing I realized that my hands were covered with what looked like aluminum powder, presumably from the manufacturing process. Getting that on the area rug would have been A Bad Thing.

The smaller parts (the various nuts, bolts, and washers) all come in sealed plastic bags, and I've had enough experience putting things like furniture from Ikea and kids toys together to know that I need a place to keep the parts after I've opened the bag. Without that, there's some law of physics that comes into play that says something like "any unsecured small part will roll to the most unreachable location possible, assuming that it is not possible for the part to be lost entirely". A set of Tupperware bowls served double duty to not only keep the parts handy, but to the antenna off the floor. I got all the parts together, re-read the instructions, and got started.

To be continued ...

1 comment:

  1. Great post and I'm looking forward to your series. I just checked out the price tag on the 6M-3SS 6-Meter Starter Antenna and its very budget friendly. Total shipping weight is 6 pounds that is incredible. And the beam looks like a good fit for CC&R ham radio operators as well. Likewise, M2 Antenna Systems is almost just up the road, in Fresno. Thanks again David!

    73
    Scot KA3DRR

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