A Cheap Indoor Dipole for 80m-15m

Antenna PartsI finally got my hands on an HF transceiver last week.  It’s a gently used IC-735, with CW, SSB, AM, and FM on all bands 160-10 meters with the exception of 60 meters.  It has had the MARS modification done on it, so it will transmit on any frequency between 100 kHz to 30 MHz.  It has a max power output of 100 watts in CW, SSB, and FM modes, and 40 watts in AM.  A handy rig to have for a ham who’s just starting out.  It’s certainly not as spiffy as the brand new DSP rigs with huge LCD displays and power computers under the hood, but there are more than enough features to satisfy the beginning to intermediate operator.  Since I got the rig on the air on March 10th, I’ve had six contacts with my straight key, each in a different state, so I only need 44 more states to get WAS!

But I’m getting ahead of myself.  The fanciest, most expensive rig on the planet isn’t worth a hill of beans without an antenna to send and receive signals.  I’ve avoided HF for a long time because I assumed the antenna requirements would be too costly in terms of space and money.  I live in a townhouse with no attic, no basement, and a postage stamp yard, and putting up antennas outside is entirely out of the question.  There simply isn’t enough space to string up a full sized dipole indoors for most of the HF bands.  I had the inspiration, however, to try setting up an antenna for 20 meters, which is a popular HF band and should also resonate on 10 meters if designed carefully.

You can see the design here.  It’s a semi-square with a 12.6′ base leg and two 9.6′ legs at 90 degrees.  At my shack the base leg runs east to west, and the two shorter legs run north to south.  It hangs 7.25′ above ground level around the ceiling, suspended with no-damage .5 lb plastic hooks attached to the wall.  Obviously this isn’t a very ideal setup, but the results speak for themselves I think.  Sure, other setups will have less noise and a lower takeoff angle, but I’ve had signal reports of 579 and above from as far away as California.  With a tuner, I’ve been able to load it up on all bands between 80 and 18 MHz with full power and an SWR no higher than 1.3:1.  Your mileage may vary, and with indoor antennas a lot of things must be taken into account such as wiring inside the walls, what material the walls and exterior of your building are made of, how many floors are above and below you, and most importantly of all, especially in an apartment situation you must take the RF exposure into account for both yourself and your neighbors.  With all of these factors in mind, however, there’s no reason any ham with a room at least 12’x16′ can’t put up a modest antenna to at least get started on their WAS certificate.

The radiation pattern is pretty close to omni-directional, which is what I was shooting for in my setup.  This increases the noise level somewhat, but allows for contacting stations at all points of the compass, any time of day, without having to rotate the antenna.  In point of fact, however, because the antenna isn’t secured to anything permanently the feedpoint can be shifted left and right to adjacent hangers to provide some slight directivity in the direction of the leg that gets shortened in this process.  In this scenario, however, any gain this antenna might provide is pretty much lost, so I wouldn’t recommend trying this unless you want to experiment.

I used very inexpensive and easy to find materials to put the antenna together.  The antenna itself is made of #14 7-strand copper-clad steel available currently at 24 cents a foot.  I bought 100′ since the price drops to 19 cents per foot and you can never have too much antenna wire laying around.  The kit of 16 clear no-damage 1/2lb hooks cost $6 from the hardware store.  I also got a bag of ten 1/2″ PVC couplings to act as standoffs and supports where needed.  This bag cost $2.  For the feedline I used a standard 6′ RG 8/U coax line I bought from Radio Shack a while back for around $6.  I had to cut one of the ends off and strip it for the feedpoint itself, but the other end has an PL-239 on it conveniently.  Altogether I spent around $20 for the entire antenna, not counting tools I had laying around already.  If you don’t have any tools, at the very least you will need a wire cutter and stripper, and preferably a set of pliers, a drill and bits, and some electrical tape.

Lateral supportOnce you have all the parts, antenna construction is pretty simple.  I measured and marked spots every two to three feet and hung up the no-damage hooks.  I had a problem at first at the corners because I ran the wire directly through the hooks.  There was too much strain and after about 20 minutes the hooks came flying off the walls with the wire.  Not a safe situation so be careful of this.  I solved this issue by using one of the PVC couplers at each corner, and using a short bit of wire or string looped through the coupler and over a sturdier hook that actually screws into the wall.  This supports the wire away from the wall and relieves some of the strain on the hook.  I used a similar technique to hang the feedpoint and center of the dipole.  The coax goes up through the middle of the coupler and is split at the top.  The two antenna wires enter the coupler through holes drilled in the sides, then go up and over the top where they meet with the shield and center conductor of the coax.  Two more sets of holes provide tie points for a short bit of wire from which the hole assembly hangs.  This means the centerpoint can be moved back and forth between the different hooks as mentioned before, very easily.

Corner supportI haven’t contacted any juicy DX with this antenna yet, but considering how inexpensive it was, and that it only took me about two hours to put it up, I’m more than satisfied with the performance so far.  I’ve gotten great signal reports and have had no trouble making at least one or two contacts every night, without trying very hard.  I’m sure there are many improvements that could be made to this design, and I encourage everyone to experiment with it and share your results with me.  However, if you’re short on cash after dumping your allowance on a rig, this design should provide plenty of inspiration to anyone who thinks they can’t put up an antenna.

Antenna feedpoint