Clothes line reel, end feed antenna, with built in L matcher

Keeping antenna wire from getting all tangled up in the field is a big problem. An inexpensive campers clothes line reel solves this problem by allowing you to deploy and rewind the wire on a spool. Here is a way to add an "L" matching network and resistive SWR bridge to the clothesline reel for to make complete end feed antenna package. The one described below is built for 40 meters and uses 51 feet of wire for the antenna. I use #28 stranded, Teflon insulated wire. There might be enough room on the spool to use more common # 24. 51 feet is a compromise length. 66 feet would be a 1/2 wave on 40 meters, but is getting a bit long to handle. 51 feet keep the end impedance reasonably high and makes the wire length a little easier to handle in the field.

No-name, $1.48 Wal-Mart camping clothesline reel with "L" matching network built on top of spool.

The tuning capacitor (a pollyvairicap), an RCA jack to connect to the rig with, and a resistive SWR bridge with LED indicator is built into a bottom of a 6 oz plastic drinking tumbler, which has been cut down to be about 1 1/2" tall. Once all the parts are mounted and wired up, the tumbler is glued to the top of the spool.

Spool removed from housing, showing matching coil wound on spool. #24 wire, 25 turns = 9.8 uH. Two holes need to be drilled in the top of the spool to access the wire leads of the coil. There is a slot in the spool which the clothesline rope normally attaches to, use this slot to feed the bottom end of the coil inside and up the middle to the top of the spool. Cover the coil with vinyl electrical tape to hold the wire in place.

Toroids on a stick.

In order to make the inductor variable, three FT37-43 ferrite toroids are hot glued to the end of a dowel. This makes a slug to slide into the hole in the middle of the spool and hence into the coil. A hole is drilled into the bottom piece of the clothesline reel shell for the dowel to stick out of. A rubber grommet of the proper size inserted in the hole will give enough friction to hold the position of the slug after adjustment.

Construction notes:

The reel comes with a little spinner knob on the spool. This will need to be cut off and the stump trimmed down so the tumbler will fit flat on the top of the spool. Once the tumbler is glued to the topof the spool, the tumbler becomes a large knob and is used to wind the antenna wire back onto the spool.

The plastic tumbler is a 6 oz "glass" found at Wal-Mart, two for 50 cents. The plastic is fairly brittle. A hack saw can be used to cut the bottom section off. A dremal cutting wheel can also be used, but use eye protection. The wheel melts the plastic more than it cuts it, so it would be easy for the cutting wheel to bind up and shatter. Also, little pieces of plastic tend to go flying as you cut.

The tuning cap:

Pollyvariable caps can be hard to find - if that's all your looking for. But their easy to find in a cheap radio. If you don't already have a cheap AM/FM portable radio you can rip one out of, you can buy one for about $5.00.

There are four variable caps in the tuning cap. Two are for the AM section and typically have a max. capacitance of 100 to 200 pfd, depending on if its the osc or ant section. The FM section uses capacitance in the 30-40 pfd range. You will have to identify which section is which, probably with a capacitance meter, or tracing the circuit in the radio. It should be easy enough to figure out which sections go to the AM part and which to the FM part.

Some tuning caps can be screw mounted, but mine was pcb mount only. So, I simply glued it to the bottom of the tumbler with some PVC glue. (the kind used to glue PVC pipe, the model glue sold to kids don't work for nothing). The tuning cap has a short shank on it. If your radio was directly tuned with a small knob attached to the cap, you might be able to recycle and use that. Or you can make a shaft extender by using a piece of 1/4" aluminum tubing. File a notch in the middle of one end so it fits over the notches on the side of the capacitor shank.

Once you wire up all the parts into the bottom of the tumbler, glue it to the top of the spool. Use Hot Glue the first time. This way, if you need to make any changes to the wiring after testing, it can be removed. Once your sure everything is working properly, then you can use the PVC glue to permanently glue the tumbler to the spool.

Counter poise:

Counter poises make end feed antennas a lot less "touchy" A 1/4 wave length of wire laid on the ground is ideal, though a shorter piece will usually do the trick too. A ground lug on mounted to the outside of the RCA jack would give a place to connect the counter poise too. I plan on simply soldering the wire to the RCA plug used on the end of the jumper wire coax between the reel and rig.

 

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