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The Balcony Buddy 2 Meter Antenna
An easy VHF/UHF antenna solution for cube dwellers.
Courtsey LD Blake, VE3VDC


Basic Plan Putting a VHF or UHF antenna on a metal balcony is not a simple matter. There are many things that will limit what you do, especially if you are not on the top floor of the building. Beams are almost always too big or too cumbersome and their mounting structures often take over your whole balcony. Base type verticals are usually way too tall to fit. Magnetic mount antennas don't really have enough metal to stick to and may fall. So, unless you have permission to go beyond the balcony railing, you end up stuck with indoor antennas or using your HT on the balcony. The "Balcony Buddy" offers a very simple and flexible solution to the problem. It can be mounted to any vertical metal bar on your balcony or fire escape and, because it is so compact it will be almost invisible from the ground, making it a "near stealth" antenna.

For new hams this design also offers an extremely easy first antenna project. It is made entirely from commercially available bits and pieces that you can get at your local ham shop and hardware stores. The only tools you will need are a small screwdriver, an adjustable wrench, a pair of pliers, a measuring tape and a fine cut file. Tuning is simple; accomplished through adjusting the length of the radiator.

The antenna itself is a basic 1/4 wave monopole that uses the metal structure of the balcony as it's groundplane. Gain is unity (+6 DBi) but that is better than most indoor or rubber ducky antennas achieve, so you will almost certainly see some improvement in performance by getting your antenna outdoors; especially if you live in a "concrete cliff".

What You Need

Everything you need On the left you see a shot of everything you need to build a balcony buddy. In the picture are a mounting bracket, SM-1 mounting bolt, AS-1 adaptor, a length of 3/16" tempered aluminium rod and a run of RG-8X coax with PL-259 connectors installed. All these parts, except the aluminium rod, should be available at any ham or CB radio dealer.

Not pictured is a dollop of liquid silicone rubber (fish tank sealer recommended) needed to waterproof the bracket after assembly.

You can probably find the 3/16" aluminium rod in 3 and 6 foot lengths at your local hardware store. It can also be purchased in 12 foot lengths from metals suppliers for a couple of dollars each. Make sure you get tempered aluminium, the regular stuff is way too soft and might bend in the wind.

One type of bracket On the right we see a model RV-1, one of many possible mounting brackets you can use. These are readily available at most ham radio and CB radio dealers, even some truck stops carry them. Durham Radio shows a good selection in their online catalogue; everything from modified vice grips all the way to fancy dual mounts for making HF dipoles.

Your choices will depend on the structure of your balcony. To determine which mount is best for you it is wise to do a bit of measuring and reckoning in advance. A bracket that's too small to fit over your railing is no use to you at all. Also stay away from cheap stamped steel brackets, use cast aluminium whenever possible. The cheapies may look ok but many rust and some will bend in strong winds.

SM-1 mounting studs Next we see the SM-1 antenna mounting studs on the right. I've taken one apart to show you the components. The connector end shown in the foreground goes under your bracket and is where your coax connects. The plastic washer is an insulator that sits on top of the bracket and prevents the live center stud from shorting to the bracket. The lock washer and 3/8-24 nut sit on top of the insulator providing the mount point for the antenna.

Also note there are two types of SM-1 mounting bolts. The one in the foreground is brass and is generally strong enough for most VHF and UHF antennas. However the stainless steel "SM-1s" in the background is far less likely to react against the aluminium brackets, causing corrosion, and is recommended for anything more than short term use.

AS-1 whip adaptors Now we see the AS-1 whip adaptors, again on the right. They are threaded on one end with a 3/8-24 thread that fits into the SM-1 mounting stud. They are drilled right through with a 3/16" hole that is the perfect size for aluminium or brass rods. There are also 2 setscrews on the sides that make the antenna adjustable up and down about 15mm, for fine tuning. If you build more than one antenna you will find lots of uses for these handy adaptors.

The last part is the coax. I suggest RG-8x for balcony/apartment use. It's a relatively low loss cable that is more than suitable for short runs on VHF and UHF. It is a thin cable (1/4" diameter) like RG-58 but with 5 times the power handling and considerably less signal loss. It is also very flexible making it easy to route out an air conditioner box or through a small window opening. For runs up to about 12 metres it's every bit as good as the more expensive coaxes.

Building The Antenna

This is a very easy antenna to assemble. It shouldn't take more than about 5 minutes to assemble the bracket, SM-1 and AS-1. The weatherproofing steps will probably take longer than the actual assembly. The only tricky part is getting the right starting length for the aluminium radiator rod.

A 1/4 wave antenna needs to be a specific length to work. When building for an unknown environment --and the conditions on balconies vary rather a lot-- your best bet is to start off too long and then trim for lowest SWR. To get your starting point you can use the magic number formula of:


7500 / Center Frequency == Length (in centimetres)

Doing the math for you:

6 metres 7500 / 52 == 144.2 cm
2 metres 7500 / 146 == 51.3 cm
1.2 metres 7500 / 223 == 33.6 cm
70 centimetres 7500 / 440 == 17.1 cm

So before assembling the antenna you need to cut your aluminium whip to the length appropriate to the band you will be operating on. The cleanest way to cut tempered aluminium is with a file. A hacksaw just tears the metal and leaves a lot of burrs. Take the corner of your file and, using it like a hacksaw, cut the whip to length. Then clean up the cut, giving yourself a smooth radiused tip. The metal is rather soft so it shouldn't take very long.

Assembly order Now that you have your whip cut the next step is to assemble everything. An assembly order shot, showing an exploded view, is on the left.

The first step is to make sure everything is clean. You may have to polish the aluminium rod with a bit of steel wool to get any grease or varnish off. Wipe everything down with a dry cloth to make sure there's no greasy residue.

Second: apply a thin bead of liquid rubber to the shouldered side of the plastic washer, being careful not to get any into the hole itself, and then place the washer with the shoulder side down on top of the bracket.

Third: insert the bottom of the SM-1 through the bottom of the bracket. Don't apply the rubber here; you want a good electrical connection as the outer shell of the SM-1 makes the coax ground for you.

Fourth: Put the lock washer on the top of the plastic washer.

Fifth: Thread the 3/8-24 nut onto the top of the SM-1's center stud and tighten it with a wrench. You want this rather tight but be careful not to crack the plastic washer.

Sixth: Apply a bead of liquid rubber around the base of the nut and out onto the plastic washer. This is necessary to seal the small gaps created by the lock washer. You want to make sure water can't get into the hole where the SM-1's center pin comes through and short out the antenna.

Ready to install Seventh: Add the AS-1 adaptor to the top of the nut and tighten it securely by applying opposing pressure between wrenches on the nut and on the adaptor. Don't just reef on it with a single wrench; this will also spin the bottom nut and will probably break the plastic washer. Please note that on some mounts the AS-1 will not go all the way down because it hits the center pin of the SM-1 inside the nut, this won't matter so long as it is tight.

Finally: Insert the aluminium whip and snug up the setscrews in the side of the AS-1 adaptor.

The finished antenna should look like the photo on the right. Allow the rubber to cure overnight and you are ready to install the Balcony Buddy and tune it up.

Installation and Tuning

Now that you have your antenna ready to go, all that remains is to install it on your balcony and adjust it for the lowest SWR.

As mentioned above the antenna must be installed on a vertical bar of your balcony, as close to the top rail as you can get it. If it's at all possible get it onto the junction of a vertical bar and the top rail so that the bracket straddles the "T" junction. Note that mounting it too low will result in part of the active section of the antenna being very close to the balcony structure which will affect it's performance rather badly.

Before mounting it, you should take your file and scratch away a little bit of paint from the balcony where it will contact the bracket. This provides a solid ground for the antenna. After removing the paint apply a liberal bead of liquid rubber to the bare metal and immediately position the antenna.

Now tighten the bolts evenly making sure the bracket is as straight as possible.

Don't worry about the liquid rubber, the bolt pressure will force it out of the contact points, giving you a good weather seal between the bracket and balcony rail, to prevent the steel of the railing from rusting. (If you don't like using liquid rubber in this spot, try marine grease instead.)

Once the antenna is mounted, you can attach the coax to the bottom of the SM-1 connector. Tighten it "fingers tight", don't use pliers as this might damage the sleeve of the coax connector. You should wrap the connection with a double layer of electrical tape to make sure no water can get into the connector. There is a special tape called "coax seal" you can put in this spot but I don't favour it because it's almost impossible to get off, later.

Now you can route your coax into your apartment and hook up your SWR meter and radio. Take a few moments and tune around; you should hear any conversations and band activity right away. Hopefully coming in better than with your indoor or rubber ducky antenna. However, you should not try transmitting until you tune the antenna for best SWR.

The goal of tuning an antenna is to have an equal SWR on both ends of the band. In this condition you can be reasonably sure the antenna is resonant within the band and thus operating at optimal efficiency.

Always use your radio's minimum power setting when testing SWR!

As a starting point, test both ends of the band you've cut your whip for and write down the readings. On the first pass the readings will (hopefully) be quite bad, with the low end of the band reading slightly better than the high end. This will tell us the antenna is too long and you can go ahead with the next step.

If for some reason the high end is better than the low end, the whip is too short and you will have to cut a new one, longer than the first, and try again. However, given the way we calculated the starting length, this should not happen.

Please note that during the cycle of test and cut, you should always insert the aluminium rod all the way to the bottom of the AS-1 adaptor and tighten the setscrews only gently.

Tuning the Balcony Buddy is easy:

Take an SWR measurement at the low end of the band and write it down.

Take another measurement at the high end and write it down too.

If the low end reads better than the high end, the antenna is too long. You should trim about 5mm off the aluminium whip and go back to step 1.

If the high end reads better than the low, the antenna is too short, go on to the next step.

Once you get your first "too short" reading stop trimming the whip and move it up a little in the AS-1 adaptor and gently snug the setscrews.

If the ends of the band now read nearly equal, you are done.

If the antenna still reads too short, go to step 5.

Should you run into problems try making a choke with 5 turns of coax, 10cm in diameter, as close to the antenna as you can. This should help eliminate coax radiation effects that might detune the antenna somewhat. If this is the problem, you will likely have to re-tune the antenna afterward.

If all goes well, your Balcony Buddy should now be ready to use. You can clean up the end of the whip, tighten the setscrews and put a little bead of liquid rubber around the top of the AS-1 where the whip goes in, and you're all set to go.

To keep the aluminum whip looking shiney-new for a long time, shine it up gently with fine steel wool and give it a triple coat of car wax.

My Results

I built a 2 metre version of this antenna and used it for nearly 8 months on my 6th floor balcony with satisfactory results. I easily got the SWR under 1.2:1 across the entire 2 metre band. I talked all over the "Golden Horseshoe" (the west end of Lake Ontario), working repeaters 80 and 100km away with as little as 10 watts. A few at 50 and 60 kms only needed 5 watts for full quieting. I also was able to work simplex conversations at 50 and 75kms on 5 and 10 watts with no problems.

There are some limitations to this design. At 6 metres the whip can often be too long to fit under a balcony above. On my balcony this left only 5 cms of clearance and the SWR simply would not come down. I also don't think there's much application for this above 70cm. The way the SM-1 comes through a grounded bracket does introduce some capacity that will become more pronounced as frequency increases. I doubt you will get this setup to tune correctly on 900mhz.

Overall I'd say this is a pretty good compromise antenna that will serve you well on a balcony. The signal reports are nothing to brag about but it did a whole lot better than an indoor Jpole or the rubber ducky on my handy talkie.

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



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