Homebrew Travel Antenna

Size: px

Start display at page:

Download "Homebrew Travel Antenna"

Randolf Tucker
5 years ago
Views:

Homebrew Travel Antenna This is a low cost homebrew two band travel antenna for 20 and 40 meters. It is based on the B&W Travel Antenna concept with a telescoping whip and a loading coil.

1 Homebrew Travel Antenna This is a low cost homebrew two band travel antenna for 20 and 40 meters. It is based on the B&W Travel Antenna concept with a telescoping whip and a loading coil. A piece of 1/8 inch thick aluminum bar stock is formed into a window bracket which is fastened to the window sill with a C-clamp. The end of the bracket is bent down at a 45 degree angle to permit the antenna to lean out and away from the building. A short length of RG-174 coax cable with alligator clips on one end is the feed line. A 33 or a 16 foot length of wire with another alligator clip is used as the counterpoise. The telescoping whip, from Radio Shack, is six feet long when extended. The loading coil is wound on a 5 3/4 inch length of closet pole wood 1 1/4 inches in diameter. There are 46 turns of #18 stranded wire used on the coil. I placed taps at 14 turns and also 44 turns from the whip (top) end of the coil. On 20 meters, the coax feed line is clipped to the coil so that 14 turns are used for loading. For 40 meters, the clip is used at either 44 or the 46 turn tap. Above the loading coil. I glued in a 13 inch piece of 1/4 inch dowel rod to increase the radiator length to seven feet. To enable the telescoping whip to quickly plug into the loading coil assembly, I used fishing pole ferrules (from Bass Pro). These are the

2 metal parts that permit long fishing poles to be made in two or more sections for travel and slipped together when used. On the bottom of the loading coil, a 1/4 inch stud cut from a 2 inch bolt is tapped into the wood coil form. A wing nut is used to secure the coil to the aluminum window bracket. The second photograph shows the antenna clamped to a stool with the C-clamp. The feed line and counterpoise wires are clipped to the coil at the 20 meter tap and ground connections. The aluminum window bracket is 18 inches long with holes drilled on both the bent end and the straight end to permit the coil to be mounted either at a 45 degrees tilt angle or vertical. You may notice the round button object left of the C-clamp in the photo. This is a steel washer that has been super-glued to the aluminum bracket to permit a magnetic mount 2 meter whip to be placed on the bracket to extend it out of the window for improved 2 meter operation. If you do not have a window sill to fasten the C-clamp, then the window may be lowered down onto the bracket. If this option is used, I tie a length of nylon cord from the antenna to some stationary object in the room to reduce the chance of it falling to the ground. The coil tap positions were found experimentally. I used a sewing needle clipped to the coax cable "hot" alligator clip and pierced the coil wire insulation to make contact with the wire to test various tap locations. I moved the needle position one turn at a

time while measuring reflected power. Once the best tap position was found, the insulation was stripped and a solder lug or a wire was soldered to the coil turn.

3 time while measuring reflected power. Once the best tap position was found, the insulation was stripped and a solder lug or a wire was soldered to the coil turn. Results using this antenna are similar to a mobile antenna's performance. While never as good as full size dipole, it does work and QRP contacts can be made while traveling. Travel Antenna Details Here are some more detailed photos of the travel antenna coil assembly: The loading coil is wound on a 5 3/4 inch length of closet pole wood 1 1/4 inches in diameter. There are 46 turns of #18 stranded wire used on the coil. I placed taps at 14 turns and also 44 turns from the whip (top) end of the coil. On 20 meters, the coax feed line is clipped to the coil so that 14 turns are used for loading. For 40 meters, the clip is used at either 44 or the 46 turn tap. Photo 1 above shows the coil assembly with the whip connection on the left. There are a total of 46 turns of wire on the coil. Starting from the left: The 20 meter tap is at turn 14. There is a wire soldered to this tap and it is connected to a solder lug mounted on the right side of the coil. 40 meter tap #1 is at turn meter tap #2 is at turn 46 The screw for the ground connection goes into the wood and makes electrical contact with the 1/4 inch mounting bolt on the right end of the coil. The shield of the coax cable and the counterpoise wires connect to the ground connection.

4 The second photo above shows a schematic of the antenna.

The last photo shows a close-up of the bottom of the coil assembly. The 20 meter connection from turn 14 is at the top. 40 meter tap 1 (44 turns) is on the left.

5 The last photo shows a close-up of the bottom of the coil assembly. The 20 meter connection from turn 14 is at the top. 40 meter tap 1 (44 turns) is on the left. 40 meter tap 2 (46 turns) is to the right of 40 meter tap 1. The ground connection is to the right and has no wires connected to it. The screw for this solder lug goes into the wood and makes electrical contact with the 1/4 inch mounting bolt (with the wing nut).

3-Phase Motor Demo. R Hoadley 10 Oct 2009

3-Phase Motor Demo. R Hoadley 10 Oct 2009 3-Phase Motor Demo R Hoadley www.coolmagnetman.com 10 Oct 2009 1 Basic Layout 2 3 4 Each Electromagnet 5 Each Electromagnet The electromagnets I had were: About ¾ diameter core About 1-3/16 long About