Hamming Hijinks

Between being plain silly and the weather, my attempts to construct a multi-band end-fed wire antenna were nothing short of silly. And the ending was one of those “DUH!” moments, too.

I had built my new mobile mast  specifically to attach a 20-40-80m end-fed wire antenna to for use up in the Owhyees and other locales where I like to roam for photography and day drives. Intended to be used as a NVIS and inspired by comment exchangess with Denis Gagnon, VE6AGE, it would be deployed by tension or laying on bushes.

I go out and move the vehicles around so I’ve got a playground for this work. The sky is grey with black here and there, but I’m hoping to get enough time to work things out before any serious rain hits. A little sprinkling here and there won’t hurt me.

I hook up my tape measure and the end of the wire spool to the top of the mast. I back away from the vehicle, unrolling wire and watching the tape measure. When I get to 17 feet, I cut the wire for the 20 meter section. My plan is to very carefully trim it down, little by little, until I have 1:1 SWR or pretty close. I trim off the end of the wire and bend it around a small bungee cord. That I connect to the larger bungee cord that’s connected to a fixture on the house. With the freshly cut wire nicely tensioned, I move to the back of the vehicle.

There I hook up my trusty antenna analyzer. I set the frequency to 14.070 MHz and check the SWR. Pretty high, so I go out to the end and unhook the wire from the bungee. I trim it back, strip the new end, wrap the exposed wire wround the bungee cord, and hook it back up. Back to the vehicle I go, and check the SWR again. Good, it’s dropped.

Back and forth I go, back and forth, back and forth until finally I’m getting in to 1:1.4. Getting there! My next cut makes the SWR go back up, though! What the @#)$(&@#$&*(!! happened?!?!?!

There was no doubt about it. To get a lower SWR, I’d have to go to a higher frequency, which meant I’d cut the wire short. I’d been so careful to only cut a little at a time, except at first when I had such a high SWR. After that it’d been steadily dropping. The analyzer still read 14.070, so I hadn’t messed that up.

Curious about the length of the wire, I grabbed the tape measure and walked it out to the end of the wire. 13 feet 2 inches. WHAT?!?!! The calculated length was 16 feet 6.7 inches or so. I’m standing there staring at it, wondering how that happened.

I’m sure you see the error of my ways. It was about then that I realized what an idiot I’d been. If not, I’ll let you try to guess what happened…refer to the 4th paragraph from the top.

See it?

It was then that I looked down at my hand, over at the antenna mast, and started cussing myself out. The tape measure was still connected to the top of the mobile mast, along with the wire. I hadn’t been measuring an end-fed long wire, I’d been measuring a center-fed long wire and trimming one end of it. The tape measure, as most are, was metal, was connected to the top of the mast along with the wire, thus making the overall electrical length of the wire I was trying to trim much, much longer. Plus, I’d left the tape on the ground once I cut the wire at the start of the whole process.

Right about then it started to rain and I had to gather up everything and get my meter, tools, etc. under cover. I also called it quits for the day, as it looked like it was going to be quite a while before the rain stopped.

Which turned out to be a good thing.

I hate to waste wire. So I started thinking about a way to salvage that 13 feet, somehow. I could always use it to hook up something, sure, but it now had a ring lug soldered on one end.

I was sitting in the living room watching TV with my wife when it popped into mind what I could do with it. I could turn it into a 10m end-fed wire antenna. Actually, I could turn it into the first part of a 10-20-40-80 meter end-fed wire antenna, hopefully. I did some calculations and it turns out the 10m wire would be closer to 10 feet. Definitely salvageable. That became my plan, then, and I worked out the lengths for the four wire sections to make the 10-20-40-80m antenna. Satisfied, I put the new design away, planning to work on it the next day I had a dry evening.

I told my wife about all this as we were getting ready for bed, having a good chuckle at myself and happy with how I’d salvaged the situation. All definitely wasn’t lost yet.

I’d gone to bed and was laying there dozing when it hit me.

Suddenly, I was wide awake, wondering how I’d missed the obvious.

The whole point of this antenna was to have a single, convenient, easily portable end-fed wire antenna that would work well as a NVIS on HF. IF amateur radio satellites used it, IF I had helped other hams build fox hunting yagi antennae with it, IF I had just suggested a similar idea to another ham for his grounding radials for his portable field antenna, then WHY the heck hadn’t I thought of this earlier?

Remember that metal tape measure?

It’s marked with feet and inches. Why couldn’t I simply connect that to the mast, unreel the necessary length of tape measure, and have my antenna that way? Need a lower frequency? Let more tape out. A higher frequency? Wind up the necessary amount of tape.

Plus I can use the tape measure to measure things.

The only downside is that I can’t just deploy the whole thing, suspend the far end, and quickly change bands via jumpers.

The next evening, I hooked the end of the tape measure to the mast and unreeled 16 feet 7 inches of metal tape. Properly suspended by bungee cords, and more or less parallel to the ground, I hooked up the antenna analyzer and measured it on 14.070 MHz. A little fiddling around with the length of the tape and I eventually had a SWR of 1.3:1. Not bad, at all.

So, I unreeled out to 28 feet. After fiddling with the length, I wound up with 30 feet 2 inches for a nice 1.1:1 SWR on 7.0704. PSK31 on 40m anyone?

As you can see from the pictures I jammed my 100 foot steel long tape with a tie wrap. I plan to build a wedge I can jam in there. The neat thing is, I could still, with some effort, wind up tape without having to remove the jam. That allowed me to slowly zero in on the lowest possible SWR, provided I started long.

I’m off to the store this weekend to buy me a nice long tape to toss into the car and leave it there as my end-fed, completely adjustable, totally tune-able to any desired frequency antenna. As long as I don’t need more than 100 feet of radiator I’ll be fine. Once I have the new tape, I’m going to work out each PSK31 frequency along with a couple others of interest and create a lookup table. All I’ll have to do is park, attach tape measure to mast, look at the table, unreel to the desired length, insert jam, hang that end of the tape measure, and get on the air.

Nice. Compact. Portable. Fully adjustable. Pretty near an ideal wire antenna.

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4 Responses to “Hamming Hijinks”

  1. Pat KC6VVT Says:

    Part of the NVIS principle is that you need to know the MUF, or Maximum Usable Frequency, to make sure your signal reflects back down to Earth, instead of mostly radiating into space.
    Glad you found the measuring tape method, and I prefer the refill tape (cheaper), A large binder clip folds a small loop at the end at the resonant point chosen, and a couple of smaller ones attach the folded end to the main length.
    Stow by loosely folding the antenna tape in multifoot lengths to insert into an old folding chair bag that fits into my truck mounted tool box, as I hated the tedious crank on the tape reel.
    73 de Pat KC6VVT.

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    • Bill Says:

      Hello Pat!

      That’s a good point about the NVIS that I do need to keep in mind. I’m familiar, in theory anyway, with the MUF but I tend to forget about it. Thanks for that reminder!!
      I had been hopping back and forth between the tape measure as a unit and a refill tape. The refill also has the advantage of being lighter, at least than the one in my pictures. Possibly, also, of being easier to hang at the far end.
      Have you by any chance tried using this setup with the far end up high? If so, how high up do you see having to go to exit NVIS mode? I plan to experiment with this aspect as well “just ’cause”.

      73 de Bill, KC7JSD

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  2. Pat KC6VVT Says:

    Currently, I use my extension antenna mostly horizontal for NVIS. As I told Denis, I now leave my 10M whip on the mount, attaching the other antenna at the same point with a ring terminal. This gives me some additional vertical ground wave component to work nearby mobiles.
    For a year, I had a potato launcher to send a fish line up in a convenient tree for vertical operation of my tuned 1/4 wire on 80M and 40M for DX, but seldom needed that, as the whip or a tuned band element did well enough without the added length or hassle of launching it..
    BTW, i clamp the antenna tape fold with the binder clamp around a short length of PVC pipe, that has a rope pull loop to attach with a bungee cord to a convenient mailbox, fencepost, tree, etc.
    I also use my ICOM IC-7000 rig with an AH-4 Tuner at the antenna base. Although I have each band marked on the tape, different locations cause minor fluctuations in that tuning.

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    • Bill Says:

      I’ve been thinking about what you just said. You’re doing almost exactly what I did screwing up my original antenna trimmiing, but with the vertical component. I can visualize what you’re saying, but it’s got me curious…I would expect the extension to be shorter than if it were the only component there.
      I noticed, once I got the tape to the correct length, that if I moved it around side to side and somewhat vertically as well, it did change the SWR. In this case, though, it was only by .1 or .2 at most. But I can see it changing based on what’s around you. Here I have my house, tree, fence. In the Owyhees, nothing but sagebrush. It’ll be interesting to see just how much that changes things. Different type of dirt, too.
      I think I’ll steal that PVC hanger idea. Thanks for sharing that.

      Like

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