Vertical vs. Horizontal
WARNING: USE CAUTION WHEN WORKING WITH ANTENNAS. DISCONNECT ALL EQUIPMENT ATTACHED TO IT AND USE CAUTION AROUND ELECTRICAL LINES. NEVER WORK ON AN ANTENNA THAT IS NEAR ONE IN USE
Polarization:
There are two ways to polarize an antenna, Vertical and Horizontal. Horizontal being a beam or most dipoles and wire antennas, and Vertical being vertical antennas and some dipoles and wire antennas.
Confused yet? Let me explain that last statement. A vertically polarized antenna is any antenna that goes straight up in the air, and a horizontally polarized antenna is any antenna that is not totally vertical or at a right angle to the ground. Basically, a horizontally polarized antenna is parallel to the ground.
Although generally it is preferable to use the same polarization as the station you are talking to, that is not always possible. Some hams run into restrictions such as room and ordinances that say No Antennas. This may mean that you will have to erect a Flag Pole antenna.
Pros and Cons:
Vertical:
Pro: It takes up less space
Con: A vertical antenna is, by nature, a noisy antenna. Also it is omni directional making receiving weak stations difficult.
Horizontal:
Pro: More directional - makes receiving weak stations easier.
Con: Long lengths for dipole type antennas - heavy rotor and large turning space required for beams.
Tips:
Vertical antennas usually work best with a counter pose (ground plane). You can purchase kits for most vertical antennas or you can make one for much less money. To do this I recommend the following:
1. Get a length of multi conductor cable, such as telephone cable.
2. Strip the outside jacket and remove the wires.
3. Cut the wires for the length of the band that the antenna covers. The more the merrier. 243/frequency in mhz. You can solder to wires together if necessary to make one long enough.
4. Strip one end of each wire.
5. Take a piece of #12 or heavier copper wire long enough to go around the base of the antenna and strip it and form it into a ring.
6. Solder the lengths of wire from step 3 to the wire from step 5 alternating lengths. ex 160,80,40,20,15,10,160,80,40,20,15,10......
7. Attach this to the point of the antenna where the shield of the coax is connected.
8. Spread the wires as evenly as possible and cover with dirt or create a barrier with caution tape if using for portable use.
Typically when building antennas, the larger the diameter or the conductor, the better within limitations. Larger elements make radiation and receiving better BUT, the larger the diameter of the element the more wind load, and the greater the weight. Also, unless you already have the material, its more expensive.
Baluns:
The use of a balun somewhat controversial. Some say that one is not needed, the rf gets pushed back up the line anyway, while others swear by it.
I recently purchased an antenna analyzer and tried my antennas both ways. I found that I had a better match across a wider frequency range with my home made current balun in circuit than without it.
Here are pictures of my current balun and instructions for making:
The form is a 12 length of 4 PVC drain pipe purchased from Home Depot. The coil is 18-21 (in this case 20) of RG-8/u close wound. The resulting length of the coil was 4.
I used a 25 length of wire cut from a 50 length of cable. This gave me a factory installed connector on the end. I drilled 2 small holes for the red tie wraps and installed them to hold the wire while I wound the coil. You can start winding from either end. The next step was to anchor the other end of the cable in a similar fashion. I had marked the 20 length on the cable. When I reached in, i drilled the holes.
The next step was to drill a hole at the top and bottom of the coil for the large tie wraps. Insert one in the form at the bottom hole then add a second one to it and push it out the top one.
Keep the coil flat and close wound, DO NOT OVERLAP THE COILS . Then tighten the two large tie wraps. I suggest the one on the outside of the coil first then the inside. Clip the ends of the tie wraps. Follow this step 3 more times placing the large tie wraps at 90 degrees from the previous one.
Finish by covering with a layer of plastic tape.
CAUTION - DO NOT LET THE BALUN COIL COME IN CONTACT WITH METAL OR WIRE AS IT WILL CAUSE IT TO MALFUNCTION
Drill a hole in one end for mounting however and where ever you desire. I drilled 1 1/4 hole in one end and mounted it to the feed point of my beam. This allowed me to keep it away from the boom.
For my fanned dipole I drilled two holes 7/8 diameter across from each other and hung it on the form for the dipole. The mast I am using for it is 1 schedule 40 PVC conduit. If it is to hang against a metal mast, you can fashion a wooden or PVC hanger to mount it to, then attach the hanger to the mast.
CAUTION: some PVC is made with the use of lead. Using that type of PVC will yield unpredictable results. To test for lead transmit for a short while, then feel the coil (with the transmitter powered off.) If it is warmer than usual, it is either made with lead or has metal in it and should NOT be used.
Multiple Band Antenna Feed Point
Here is a neat feed point for a multiple band antenna feed point. First take a threaded 1-1/2 PVC Tee and 3 threaded caps, a 1/4 x 20 eye bolt, 2 1/4 x 20 bolts, nuts, washers, and a 2 aluminum split bolt 2 section.
Drill a hole in the top of the tee for an eye bolt, 1/4-20 x 1. Drill a hole in each side of the tee for the conductors of your coax to go through.
Now, drill a hole in one cap for the coax to go through. Feed the coax through the hole and strip back approximately 3 of insulation. Separate the shield and the center conductor by separating a small section of the shield at the point where the outer insulation begins, then working the center conductor through the shield. Next apply water proofing sealer and tape to the coax. Finish by placing a tie wrap around the water proof tape to act as a strain relief. Screw the cap with the coax on the bottom of the tee. Now pull the center conductor through one of the holes in the side of the tee and the shield through the other side.
Now, drill a 1/4 hole through the center of the 2 remaining caps. Place a 1/4-20 x 2 bolt through each hole and fasten with a flat washer, lock washer, and a nut. You can apply some lock tight if you wish. Screw the end caps into the tee.
Take s split bolt and place the upper part of it over the 1/4 x 20 bolt on one end cap. Place one of the coax conductors on the bottom section along with your antenna legs for one side of the dipole and tighten the split bolt. Repeat the process for the other side.
Hang it up and get on the air.
Contributed by: KA3PMW
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