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Saturday, January 13, 2024

It's Antenna Season!

It's a long running cliché of mine that all of my antenna projects begin with the words, "when it cools off..."  Well, it's antenna season! 

The truth this year is I don't have anything I've been planning to do for months or a new antenna to add, so it's just a matter of doing regular checks, any maintenance, or things that I figure would be good to look at.  Except for a totally unplanned, unanticipated bit of fix that had appeared about two weeks ago.  

I have two beam antennas on my small (20 foot tall) tower.  For those who care and don't already know, there's a small HF Log Periodic Dipole Array (LPDA) from a company called Tennadyne, (an older model of theirs called a T6) mounted at 20' above ground, and a VHF (6 meter) yagi from a company called Directive Systems & Engineering (their model DSEJX5-50) mounted above it by not quite five feet.  

About two weeks ago, I glanced up and noticed that the driven element of the 6m yagi had suddenly tilted quite a bit.  We've been having crappy weather this winter, and it's possible that one of the days with 40mph wind gusts did it, but the fact that nothing else had moved made me think that perhaps it was just that an unusually fat bird decided to land on it.  Or a normal weight but bigger than average bird tried to perch on it and it was just more load than it could take.  While it's a bit difficult to see accurately from the ground, this is what it looked like:

Look at the top antenna, toward the right, and you'll see "one of these things is not like all the others."  There's a loop of wire to its right, that'll tell you it's the driven element.  Compare it to the one just to the right of that loop of wire and you can see the end of the driven element is very different from the one to its right.

So "all ya gotta do" (among the most terrifying phrases in all of engineering) is crank over the tower, reposition that element and crank the tower back up.  Easy peasy, right?  Long time readers might recall that through the end of '22 (after Tropical Storm (here) Ian) and all the way to last June, I had to rebuild my method of anchoring my tower.  Instead of bolting it to the eaves of the house, as I had since the 1990s, I designed and built a system using aluminum channel stock, bars and stainless steel hardware.  Some background here, which links to a bigger set of pictures here.  

Something I never did through that was test out cranking over the tower. Another thing I meant to do but didn't (summer is way, way past the end of antenna work season) was replace some galvanized fasteners I used with stainless hardware.  I even bought the hardware but never got around to replacing the old fasteners. 

That became today's job.  It was in the mid-60s, cloudy with mild breezes all day, really good weather for being out doing this stuff.  The tower mounting hardware came apart easily; instead of removing two lag bolts holding the outside half of a split, pressure-treated 2x4 to free the tower, I had to take two nuts off two separate 3/8" u-bolts.  Everything else went like the last times I cranked the tower over to work on stuff.

While getting the driven element rotated and spaced properly to the elements in front of and behind it was tedious, along with making sure everything else appeared to be aligned properly, it didn't take as long as it felt like.  Probably an hour.  The whole job took from around 2 to 5 PM, including replacing the galvanized hardware and dragging all the tools out of and back into their places in the shop.  The final antenna came out like this (now pointed about 20 degrees off vertically at the ground).

There are two pieces of metal visible below and behind the one I was working on curving downward the farther to the left you can see; those are parts of the T6 log periodic.

The ease with which it all worked left me feeling optimistic that I can continue to handle this for a good long time, barring those accidents and other nasty things that can happen.  The most useful thing I could do to improve my station would to replace the tower with something taller.  That's probably in the "too expensive" category, but sometimes we luck into things.  Another aluminum tower or some other way of getting the 6m yagi from 25' to closer to 50' would be the most dramatic improvement I can get.  I'm also entertaining thoughts of exploring higher VHF/UHF and beyond bands.  That might well require a second tower - or a way to temporarily put up antennas when I have some use for them. 



6 comments:

  1. dumb question. looks like the coax goes to a connector and then wire looped several times ,then zip tied, then to the antenna. why? asking for a friend...Keith.

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  2. It's a coaxial cable "Balun", and it part of the matching network between the 50 Ohm coax, and whatever the impedance of the Driven Element is. It looks identical to the ones on my M2 antennas.

    Our "Antenna Season" ends in October, if we're lucky. It didn't get above zero today, and it's -5* right now. Monday night/Tuesday we're expecting -15*, or colder.

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  3. Moved to a new home last year, too busy to put antennas up yet. Still need to figure out the grounding since the radio room is opposite side of the house from the incoming power ground rod. Add in concrete, landscaping and a sprinkler system, I may be going remote or switch to mobile only...

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    Replies
    1. My radio room is about as far from the power ground rod as it's possible to be and that's pretty easy to deal with. Well, easy in concept may be difficult in reality. Sink a few ground rods near the radio room, and bond them all together with something like heavy wire or the braid from some RG-8 coax or just buy some braid (ham dealers tend to carry it, but you'll see it at home stores sometimes).

      Sinking ground rods can be easy if your soil is sandy or rougher if the soil tends to have large boulders in it. I hired an electrician to sink a power ground where the original one was corroding away, and I sunk the ones in and around the concrete pad my tower is on. We have pretty sandy soil, but we're not immune to having good-sized rocks in it. Sometimes you get lucky.

      The operating position is less than 1/4 wave from ground at 10m but the lower the frequency the better. (1/4 wave at 28.0 MHz is 8' 4").

      Also, tie all the grounds together, making an effectively larger ground area. More ground is more better. The rigs are on a steel desk that's connected to both the house power ground and the outdoor ground rods.

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    2. Parts 1 and 2

      https://thesilicongraybeard.blogspot.com/2020/03/spring-cleaning-summer-preparations.html

      and

      https://thesilicongraybeard.blogspot.com/2020/03/spring-cleaning-summer-preparations_13.html

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  4. I used a big hammer drill and a ground rod driving adapter, and I drove my ground rods in quite easily, rocks and all.

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