Antennas
The purpose of this page is to discuss different types of antennas, especially those that will be useful in the mission of the Sheriff's Posse.
Stealth Loop
After reading the article I Love My Loop, I started wondering how a loop antenna would work if it were installed on the inside of the fence around a suburban lot. A crude estimate of the wire needed for my lot was 288 feet, and when I realized that it was greater than a full wavelength at 80 meters, I decided to try it. I was looking for something cheap, easy to install, and efficient. The first two conditions were met, and the third remains to be proven. The bonus is that this antenna could be set up so it's not visible from outside the property, so a homeowners association couldn't bug a homeowner about it. After reading some of the antenna projects on the Western USA SATERN website, I decided to see what I could do. If it didn't work I could always take it apart and build something else. Here's the parts list for the project:
| Plastic clothesline | $4.94 x 2 |
| Clothesline separator | $2.39 x 8 |
| 500 feet #14 stranded wire | $45.38 |
| Unadilla W2AU 1:1 balun | $24.95 |
| Coleman 10-inch steel nail tent stakes | $2.99 x 2 |
| Total | $105.31 |
Okay, so I didn't realize it was over $100. That's still pretty cheap for an HF antenna, though. Here's a picture of all the parts (click on any of the pictures to bring up the full sized version):
The first three items came from Home Depot.
- The plastic clothesline is nonconductive and is meant to be in the sun. We have a strand of it that's been in the Arizona sunshine for several years with no ill effects. I got the idea from the excellent www.westsat.org website, where you can find many other antenna-building tips. I only used one roll of the clothesline.
- The Clothesline Separator is shaped like a tall, skinny letter "S" made out of sturdy plastic with a plastic pulley near the bottom and space below that for a strand of plastic clothesline. It's one of those items that's not made for ham radio but is an obvious choice for it. At my Home Depot, they were in a box near the rope and plastic chain area. They were all covered with dust, the bar code stickers were so old they were falling off, and I can't find them in Home Depot's product list, so they may not be in stock at your store. If you go to Unifire's website and put "2010-6019" into the search box, it will lead you to a page where you can buy them for $1.25 each. Home Depot had some nice plastic pulleys there too, but I liked the idea of being able to remove the antenna wire from the support without untying the rope.
- Another antenna-building website said you could buy a 500-foot roll of #16 wire in various colors from Home Depot for around $25. I didn't see those rolls in the wire area, but they had various colors of #14 wire. For some reason I've always liked to use green wire for dipoles and radials, so I picked that over red, white, and black.
The balun came from Ham Radio Outlet
- The balun was one of a choice of three at Ham Radio Outlet (I try to shop at my local radio store when I can, rather than shopping mail order). I chose the 1:1 balun rather than the 4:1 balun for no obvious reason. It is called a Unadilla W2AU 1:1 balun.
The tent stakes came from The Sports Authority
- I chose the Coleman tent stakes over the generic bucket full of plastic stakes at 49 cents each, just because the steel spikes looked sturdier. My back yard is full of rocks below the surface and I thought ths shorter plastic stakes would break and wouldn't go in deep enough. Also, the Coleman stakes have a sturdy plastic top with a hole just the right size for the clothesline to pass through. You can order them from the Coleman website.
So here's my idea. I tied a length of clothesline around the post that holds up the block wall. I hung the clothesline separator from the clothesline. Then I tied another length of clothesline to the bottom of the clothesline separator. I measured two feet out from the bottom of the post and drove a tent stake into the ground at right angles to the clothesline. Then I passed the clothesline through the hole in the tent stake and tied it as tightly as I could without pulling up the stake. Here's what it looks like:
Here's a side view of the setup. The reason for all this is to keep the wire from touching the block wall. Maybe there are more "elegant" ways to do that, but this is what came to mind first. I put the slot for the pulley side of the separator in a position where the antenna wire would have to fly up and inward to be removed from the separator. If there's a disadvantage to that, the clothesline is stretchy enough to be able to pull the loop around the post and flip the separator over. This shot is from the east end of the yard looking west.
Here's the feed point. The "Big Signal" W2AU Balun says in its instructions "Pass the antenna wires thru the eye hooiks then back on themselves - to securely fasten the antenna wires to the hooks. When connecting heavy wire, hold eye hooks with pliers to prevent eye hooks from turning, solder the balun's flexible leads (one at each eye hook) to the antenna wire nearest it. DO NOT SOLDER ANTENNA WIRE TO EYE HOOKS."
Here's how the balun is mounted. A single drywall screw with a large washer holds the clothesline separator. If you wanted, you could tie the clothesline to the balun, run it throuogh the pulley, and pull it up from ground level, then lower it down when you were through with it.
Here's how it looks from the ground. The copper wire is nice and shiny. It won't be for long, though.
Here's the support at the east end of the yard. I flipped the clothesline separator over here and on the west end. Since the wire goes up to the balun from here, it seemed that it would be easier for it to escape if I left the open end up.
Same setup at the west end of the yard.
From the west end looking east. The ground-mounted Hustler trap vertical is visible at the left, with its (green) radials on the ground.
This is the corner support at the west end of the yard. Because the wire is totally supported by pulleys, it's easy to grab the balun and move it from side to side if that's ever necessary.
All the supports were installed during the afternoon, and when it came time to start unrolling the wire it was already dark. Of course it's no fun installing an antenna unless you have some kind of adverse condition, so it was finished in the dark, and as a result I have no precise measurement of the antenna's length. I "stepped off" the approximate length by walking around the path of the antenna wire and counting three feet per step, which gave a figure of 288 feet. To my surprise and delight, when I came in from the dark to test the antenna, the ARRL Sweepstakes was occupying most of the phone bands and this gave me an excellent opportunity to test the antenna. So from my QTH in Glendale, Arizona (one mile from the west city limits of Phoenix), running 100 watts, here are the ARRL sections that I contacted using the loop antenna:
75 Meters
Eastern Pennsylvania, Eastern Washington, Georgia, Idaho, Indiana, Kansas, Illinois, Iowa, Maryland/DC, Michigan, Minnesota, Mississippi, Montana, Nebraska, New Hampshire, Northern Long Island, Oklahoma, South Dakota, Tennessee, Vermont, Western Washington
40 meters
Idaho, Kansas
15 Meters
Illinois, Kentucky, Ohio, Puerto Rico, Virginia, West Central Florida
On 75 meters I also contacted every state that borders Arizona (except Mexico). California was easy. I get the impression that this antenna is a real "barn-burner" on 15 meters. Everyone I called came back to me right away, and no one asked for a repeat of any of my information. On 75 meters it wasn't so easy, but maybe that was because there was a LOT of QRM there. Also, through "the kindness of strangers" I was able to exchange signal reports with Gavin, GM3MOU in the UK. He gave me a 35 report on 75 meters, which was quite a thrill. Not bad for an antenna just thrown up in the back yard.
Update
The antenna seemed to work well, but started causing a problem with my cable TV system. My TV remote control sends an RF signal down the coaxial cable from the TV to the "digital gateway," and from there the signal is relayed to a central control panel in the neighborhood that responds to the command and sends the desired channel change (or whatever) back to the TV. When I transmitted on 75 meters with the loop, the TV signal would become pixellated and freeze and the audio would be lost. If it was a long transmission, the entire signal would be lost for a few minutes. So I dropped the feed point down to a lower level. The TVI was gone but the SWR suffered. Here are pictures of the new setup:
The new feed point location. Yes, the patio roof needs repair.
The west end of the yard. The clothesline separator was previously tied to the post on the left, but to take up the slack it is now tied to the post on the right.
A closeup of the revised west corner setup. No tent peg was used for this one.
The full length of the yard with the lowered feed point. Here are the results of SWR measurements made with an MFJ-860 wattmeter:
|
Loop Antenna
SWR Measurement |
|||
|
Band
|
Freq
|
SWR
|
|
|
OLD
|
NEW
|
||
|
10 meters
|
29.700
|
1.3:1
|
1.9:1 |
|
29.500
|
1.3:1
|
1.9:1 | |
|
29.000
|
1.4:1
|
2.1:1 | |
|
28.500
|
1.5:1
|
2.2:1 | |
|
28.000
|
1.5:1
|
2.5:1 | |
|
12 meters
|
24.950
|
1.5:1
|
2.5:1 |
|
24.900
|
1.5:1
|
2.5:1 | |
|
15 meters
|
21.450
|
1.5:1
|
2.5:1 |
|
21.400
|
1.5:1
|
2.5:1 | |
|
21.300
|
1.5:1
|
2.5:1 | |
|
21.200
|
1.5:1
|
2.6:1 | |
|
21.100
|
1.5:1
|
2.6:1 | |
|
21.000
|
1.6:1
|
2.6:1 | |
|
17 meters
|
18.150
|
1.5:1
|
2.4:1 |
|
18.070
|
1.5:1
|
2.4:1 | |
|
20 meters
|
14.350
|
1.5:1
|
2.5:1 |
|
14.300
|
1.5:1
|
2.6:1 | |
|
14.200
|
1.5:1
|
2.6:1 | |
|
14.100
|
1.6:1
|
2.7:1 | |
|
14.000
|
1.6:1
|
2.8:1 | |
|
30 meters
|
10.150
|
1.8:1
|
2.9:1 |
|
10.100
|
1.8:1
|
2.9:1 | |
|
40 meters
|
7.300
|
1.5:1
|
2.6:1 |
|
7.200
|
1.5:1
|
2.8:1 | |
|
7.100
|
1.6:1
|
2.9:1 | |
|
7.000
|
1.7:1
|
2.9:1 | |
|
75-80 meters
|
4.000
|
1.5:1
|
2.4:1 |
|
3.900
|
1.2:1
|
1.9:1 | |
|
3.800
|
1.0:1
|
1.4:1 | |
|
3.700
|
1.2:1
|
1.8:1 | |
|
3.600
|
1.5:1
|
2.4:1 | |
|
3.500
|
1.7:1
|
2.8:1 | |