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Within the last several days I shared the little 9:1 unun that I made for myself - if you missed it you can check it out here. This evening (well, that is the evening I started writing this - who knows when I'll finish and publish it!) I used the little unun to put some wire in the air.
I had a spool of left over cable from extending my fire alarm system into our addition when we did that project, so I cut off a length of it for my random wire. There are actually a couple neat resources available for knowing what lengths of "random" wire are likely to work best, but I used the info available here and decided to cut my wire at about 36 feet, to use on 40 - 6 meters.
I actually soldered all the wires in the twisted shielded pair together at the ring terminal, so really the shield of the cable is probably doing most of the RF work. Anyway, after I cut it and put a connector on, I hooked one end to my fence out front, and connected the other end to my unun. Without connecting a counterpoise or ground I scanned from 0 - 30 Mhz with my Rig Expert AA-54 to make sure I was in the ballpark.
The scale of this graph isn't great, because it tops out at an swr of 5:1, but in the amateur bands, everything above that was at least under 12:1 or so. I figured that once it was in the air, it would probably still be in line with something my tuner could handle, so I started working on getting the wire up.
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Since this is a temporary antenna, I didn't want to get crazy with buying stuff to hang it up. I've usually got mason's line around because I end up using it for projects around the house. I needed something however, to get the end of the line over a tree. Thanks to my bad grammar, when I posted the statement on Twitter that I was looking for something to use,I made it sound like I wanted to throw my garage over a tree...thanks to VK5OI for catching that :-)
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Anyway, I ended up finding a little plastic bottle (my YL says it was from bouillon) so I filled it with gravel, tied one end of the string around it, and threw it like it was going out of style (and got it on the first try!)
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Those of you that read my first post on the topic may recall that my intention with this little 9:1 unun and random wire was to use the metal roof of our addition as that counterpoise. Rather than try to figure out a way to mount the unun, and then add a way to connect a jumper wire from the unun's ground side to the roof, I came up with something to kill both birds with one stone.
At the top of the metal roof, there is a lip that covers the roof-to-wall connection. I drilled a small hole in the edge of this (in a spot that any water running through the hole, would just land on the metal underneath, and run down the roof.) It was then simply a matter of sticking the counterpoise lug through the hole, and spinning the wing-nut on from the bottom (I used a star washer on the bottom to make sure I pierced the paint and got onto the bare metal.) This accomplished the job of holding the unun in place, AND making my connection to my giant counterpoise! When I take it down I can always caulk the hole if I really feel its necessary.
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I connected my antenna wire to the other terminal, and then looped the other end through an insulator. With those details done, I tossed the end off the roof to the back yard where the end of my mason's line was waiting patiently. Once I tied it off, I walked around to the other end of the line that was waiting for me on the other side of the tree, and hoisted the whole thing into the air! |
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I'm not too worried about wind, trees, etc. pulling on the wire, because mason's string is not strong stuff - at a moments protest it will just snap, letting the wire drop with no harm to the roof or house, so no worries there! In order to give it a little wiggle room however, so it wouldn't snap in a light breeze, I didn't tie the other end off - I just used a super high-tech counter-weighting arrangement:
Remember when Costco sold Scoop Away cat litter in buckets? That was great for two reasons - afterwards you had a useful bucket AND the buckets were a recyclable plastic. Now their litter comes in plastic bags that are much less recyclable. Boo on you Scoop away!
Anyway, in the bucket is half a brick to give it some weight. In a prior life I had drilled holes in the bottom of this particular bucket, so it won't hold water and get funky!
With the wire in the air, this was the new view out of the window at my temporary operating position:
When I first put the antenna analyzer on this however, things didn't look so hot - some of the bands were so out of wack that my little LDG YT-100 tuner wasn't going to have a hope of tuning it. I made a wild guess that because of the angle, with the metal roof directly under, I was getting some unexpected interaction between my radiating element and counterpoise. To address that, I went to another standby in the temporary antenna arsenal - bungee cord.
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This gave enough separation that the SWR curve across my targeted portion of the HF spectrum looked like something my tuner would handle! 40 meters was the worst at 8:1, but that's still tune-able. Because I only have about 3 feet of feed-line from here to the back of the rig, I'm not too concerned about feed-line loss :-)
So how does it work? It's hard to say from just a few contacts, but I managed to catch a couple of fellow WWFFers on 40 meters (both CW and Phone) and I hopped around all the bands between 40 and 6 to make sure it would tune up. What I can say for sure, is that it "works" and I will be able to be on the air more reliably from home from my new temporary shack (in the corner of a closet), while I finish up the basement shack project!
A Quick Update!
Less than 24 hours after publishing this post, I changed the antenna :-) I was in the back yard working this morning, and it dawned on my that I really underestimated the distance from my house to the trees in the back corner. After stepping it off, I decided that I could probably fit enough wire to get 80 meters into my list of "tune-able" bands. After dropping the antenna down, adding another 37 feet of wire for a total length of about 72 feet, I now have access to everything from 80 through 6 meters on this wire!
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