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The Balcony Boomer Antenna for 2 Meters
Add a reflector to your Balcony Buddy
Courtesy LD Blake, VE3VDC 3-07

See text for details

This antenna is an experimental combination of a 1/4 wave monopole and yagi style reflector.

The problems I was looking to solve are three fold...

  • First; using an omnidirectional antenna on an apartment building balcony results in a considerable amount of RF entering the building. This is a waste of signal as the building simply absorbs most of it. It also poses a health risk as RF exposure has been shown to cause problems for some people.

  • Second; I am surrounded on all sides by other hams and repeaters. If I used a strongly directional beam antenna I would surely lose contact with a couple on the back side of the building. Turning the beam their way is not an option since it would flood the building with even higher levels of RF than are present now.

  • Third; the balconies on this building aren't exactly antenna friendly. They are solid sheets of steel a meter tall with an angle iron hand rail about 20cms above that. The clearance between the handrail and the balcony above is a rather tight 140cms. Just barely enough room for a 2 meter half wave.

A lot of steel

I have tried half wave, jpole, loop, quad and other designs without much success. The biggest problem is that it's almost impossible to tune up an antenna with so much metal in it's near field. Second to that is the matter that all that metal is highly refelective, tending to send any signal originating from inside the balcony back into the building.

For some time I've solved the third problem by using a 1/4 wave monopole on my balcony railing. The first version was the Copper Ducky that has proven to be a very reliable performer. More recently I changed over to an aluminium rod design I call the Balcony Buddy which gives equivalent performance but is far easier to build.

The trusty monopole grounded to the railing seems to be the only one that will settle in and work decently. As a friend told me: "If it's in the way of your antenna, make it part of your antenna".

So highly directional beams are out because they would cut me off from local chatter. Omnis produce too much RF in the building. What to do?

Answer: a fixed position, somewhat directional antenna that will reduce RF in the building to safer levels without being so directional as to cut me off from local repeaters and hams.

So I started searching for antenna designs to fit my needs and finally ended up at a 2 element Yagi beam. The advantage of this design is that by changing the spacing between the driven element and the reflector we can also shape the radiation pattern somewhat. As the spacing increases the beam widens, closer spacing gives a narrower beam.

This is the radiation pattern for a 2 element Yagi antenna with a somewhat longer than usual element spacing...

2 element yagi

If we take the blue line as the balcony railing with the building being behind the beam (i.e. below it on the left image) we see a radiation pattern that, while not strongly directional will significantly reduce the RF levels in the building behind it. If we take the antenna's gain over a dipole into account a reduction of about 6db should be possible.

However; I'm not going to use a 2 meter yagi on this balcony. There just isn't enough clear space to tune it up and there's no way the landlord is going to let me hang it outside the balcony railing.

Still, it does suggest a rather interesting compromise: add a reflector to my existing 1/4 wave antenna. So I got busy and modelled my balcony and antenna.

This is the pattern for my monopole on the balcony, confirmed more or less by Field strength readings. It's not truly omnidirectional because of the influences of the balcony and building...

Monopole on balcony
Adding a reflector at .15 wavelength gave me this...
Monopole with reflector

The difference in patterns is surprising and this does seem to suggest that adding a reflector will accomplish my goals. Doing a little math this seems to be saying that I will reduce RF in the building by between 6 and 10 db over the omnidirectional antenna, depending on direction. As a bonus I will have about 6db of additional gain in my good direction.

This was encouraging, so, I decided it was worth a try.

Building the Reflector

Antennas and plumbing supplies seem to go hand in hand. The reflector is built using some common plumbing parts, a piece of aluminium tubing and a bunch of hose clamps.

Reflector parts

The parts are on the left. Included are 1/2" PVC "T" fittings, hose clamps, 1/2" PVC pipe, a length of 1/2" tempered aluminium tubing and plastic weather caps.

The first step is to cut the aluminium reflector. For 2 meters I chose 1.08 meters, which the modelling software indicated would give me the best front to back ratio or, in my case, the best reduction in RF entering the building.

The boom for the reflector is made of PVC plumbing pipe. This I cut long, because I wasn't sure of the spacing I'd end up with. After experimenting and trimming so there's not a big chunk sticking out over the balcony, it ended up 45cm long.

The second piece of PVC tubing was cut to 30cm to give me a way to clamp it to the balcony's vertical bar using hose clamps.

The "T" fittings have to be modified. You need a slip through fit for the PVC boom and for the aluminium reflector tube so your reflector assembly will be easily adjustable.

There are two steps... Modified T fitting

  • First use a rat tail file and cut out the internal ridges in the long section that prevent putting pipes too close. Don't remove the ridges from the short section. Test your work by trying to slide them over the PVC and Aluminium tubes to make sure you get all of the ridges out. You are looking for a snug fit that can be moved by hand.

  • Once you have a slip over fit, take a hacksaw and put a cut along the long side of the fitting. This will allow you to use hose clamps to tighten up against the tube inside the T fitting locking it into place, as shown on the right.

Now it's time to assemble the reflector...

First use some PVC solvent cement to put the modified T fittings on the ends of the plastic tubes, one on each. This stuff dries in seconds and doesn't let go, so make sure you get them installed all the way down the first time. My technique was to put the glue on the end of the tube and inside the T fitting's short side and then quickly pound the T fitting into place with my hand.

Boom Mount The reflector Now insert the aluminium tube into the T fitting on the longer PVC piece and slip it about half way in. Add a couple of small hose clamps, tightened only snug as you will want to be able to move this for adjustment.

Next insert the boom section into the T fitting on the other PVC tube and position it just in from the end. Add a couple of small hose clamps, again tightened firmly but not finally, so you can adjust it.

Place the plastic weather caps on the top of the reflector and the open end of the boom and you're all done.

The reflector

The finished product should look like the picture on the left. The active element is the aluminium tube reflector, the rest is just support structure. You should note that depending on the structure of your balcony, you may have to modify the mounting technique used here. The important thing is to be able to adjust it to find the best SWR and RF reductions.

It is now time to install everything and see what happens.

Installation and Tuning

The first step is to install the Balcony Buddy or a similar monopole onto your balcony, if you don't have it there already. You should make up a second vertical whip for your antenna. When you adjust it for the reflector it will have to be shortened a fair bit, so keep the original in case you want to go back to an omnidirectional antenna.

Now comes the reflector. Position the upright white PVC tube against the side of the railing, with the boom at the top, immediately under the antenna. Using hose clamps lock it into place making sure the back end of the boom piece can slide in and out for adjustment.

Finished installation The result should look like the picture on the right.

The first step in adjustment is to center the reflector on the monopole. Measure and mark the center of the reflector. Now measure from the top of the monopole's bracket to the floor of the balcony. Finally slide the reflector up or down until it's center is at the same height as the top of the monopole's bracket. (Note: this is a fairly critical adjustment.)

Now measure between the reflector and the antenna. They should be 30 centimetres apart, center to center. Slide the boom section in or out to get this distance, making sure the reflector and antenna are exactly parallel.

Now that you have your preliminary settings, it's time to run coax to your radio, fire it up and start adjusting the monopole's SWR. The goal is to have equal SWR readings on 144mhz and 148mhz so you want to take readings at opposite ends of the band and write them down.

If the antenna is too long you will have a better reading on 144 than 148 and you should trim a few millimetres off the top of the monopole. Do not cut the reflector!

Stay in the cycle of test-adjust, test-adjust until you get the lowest SWR you can, with both ends of the band being equal. I managed to get mine to read under 1.1:1 all the way across the 2 meter band.

The antenna is now ready for use!

If you are inclined to experiment more, you can try changing the spacing between the reflector and monopole and see what effect that has. You can also try moving the reflector up and down to gauge it's effects.

My reflector is currently at 30.3 centimetres and the monopole turned out to be 468 millimetres tall for best SWR. The final adjustments on your balcony may be quite different.

The Results

I haven't noticed any big differences in S-Meter readings from repeaters in my area. One repeater got stronger, another weaker, but most have stayed about the same. A couple of hams have commented they can hear me better and one even told me he could hear me now, after not hearing me at all. So I am guessing my transmitted signal is a bit better, perhaps with a more even pattern perpendicular to the balcony.

The big news came from Field Strength readings taken 1 meter inside my balcony window, just before installing the reflector and right after finishing the SWR adjustments. The before and after readings, both taken at 10 watts, are shown below...

nearly full scale much better

Is this a good antenna?

Signal reports have been good so far, the match is excellent and the neighbor's cat seems to have survived... So I'm calling it a success. 

Editor's note: This project uses mostly metrics.
Use this handy calculator to convert lengths, sizes, etc. 



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