Aruba Antenna Construct

During a short stay at the 'One Happy Island' Aruba, ran into a situation where the range of an automatic garage door opener was very limited, this to the aggravation of the owner who informed me that even with a new remote, it did not work properly.

A look at the remote indicated it's frequency to be 433.920. A VERY common low power frequency used by many simple remote control systems. The next step was to look at the remote receiver, this was a China made garage door opener type CAME VER 06 des.

What is interesting is that the specifications (see manual) say nothing about a remote control, nor the frequency used and no antenna is supplied!.
Checking the actual in the garage, revealed that an antenna was installed, it's length (if it was an end fed dipole) looked designed for 220 MHz and not the remote frequency of 433 MHz.

Upon opening the main unit to investigate how this antenna was connected, I was shocked to see it was connected using a piece of four core insulated cable.

It was clear that whoever installed this had no clue about working with radio frequencies and how to deal with them.

It was thus clear that there was room for improving the range of the remote transmitter to be able to open and close the garage door from a greater distance. The challenge to extend the radius of the remote was accepted and thus the next step was a new antenna to match the remote frequency.

I need it now

Did I mention I was there for a short stay. Finding an antenna for 433MHz should not be a problem, should it? It turns out that I could not find anyone who had one, from electronic shops to security companies on the island, no one had antennas close to the frequency needed. To order one from Europe or the USA would take too long, the only other option I had was to make one, because I could. And so the search for antennas became the search for antenna parts...

I chose to build a 1/4 wave antenna as I could determine 50 - 75 Ohms at want and at the time of determining what parts I needed I didn't know nor care about the impedance. The parts I needed...

• A square female BNC panel mount connector.
• A male BNC cable connector.
• Coax cable to connect antenna to receiver. (did know impedance when purchasing)
• Copper wire to construct the antenna elements.

Finding an actual 'RadioShack' on Aruba (as radio amateur and electronics fan) was very disappointing, they only sold overpriced household goods. TechShack Aruba is the place to go. I was told they used to be the official 'RadioShack' in the past. Not only do they have a very wide variety of audio visual equipment, but also a surprising large assortment of various sorts of electronic components. Not only did they have the 75 Ohm RG59, but also the BNC parts I had to have for this antenna.

A short roll of standard insulated copper wire, for normal house wiring, was obtained at a local hardware store. A mega bonus was when I got back from shopping for parts, the diameter of the insulated copper wire was exactly the thickness of the solid inner conductor of the RG59 coax. This meant I could use the same wire for the antenna and the ground plane elements and did not need to use the inner core of the RG59 coax. The stripped copper code of the household insulated wire also fitted very snugly into the BNC connector.

1/4 wave antenna dimensions

Using the 1/4 wave antenna calculator, got the measurements for the 5 antenna elements for the remote frequency of 433.920 MHz.

Measured off 5 times 6.8 inches (did not have a metric measuring device handy), added an inch or three and cut that from the 5 meter roll of electrical cable. Fastened one side to a conveniently available terrace chair leg and the other to a small hand drill. Pulled the cable taught and gave the drill a good 30+ windings. The result was a very straight taught piece of insulated copper wire, ideal for making antenna elements. Compensated for the fact that part of the main receiving element of the 1/4 wave antenna is in fact itself shielded, and cut the cable to size for each part of the antenna.

Antenna construction dilemma

All the components are created and now the actual assembly needs to take place. Spoiled as I am when at base, here in Aruba things can be and are different. The fact that I 'assumed' a soldering iron suitable for working on this antenna build would be available was short lived. After many frustrating attempts to locate a soldering solution that could only heat up the BNC connector a few degree, or destroy it and melt the insulation, I realized another alternative solution was needed. This is how the idea of a solderless 1/4 wave antenna was (hastily) born.

Antenna redesign, mechanics it is

The question that arose was: How to design and construct a 1/4 wave antenna with no welding or soldering options. Fastening and attaching different sections of the antenna would have to all be mechanically based. Nuts, bolts and bits and pieces.....
The ground plane elements could be bolted down with nuts and bolts, but the coax connection needed a two way fastening system and since the dimensions of all components fell well into the weak current electrical category, the good old house hold 'how to join two wires' came to the rescue. Of to the hardware store again for some more small vital bits. Thus soldering had to be replaced with:

• 4 small 2M nuts and bolts (to fix the 4 ground plane elements to the BNC panel mount. And an extra nut to secure the coax shielding.
• Electrical connector strip, with an inner diameter that matched to center pin of the BNC panel mount.
• Crimp terminal to attach the shielding of the coax to the antenna.

Antenna build

Installing the Aruba 1/4 wave antenna

Having assembled the solderless 1/4 wave antenna, it was now time to engineer the mounting. As the main garage door opener is located up against the asbestos corrugated garage roof panels, a wooden support beam was the easiest place to make a fixture. Now the idea was to get the antenna as high as possible up against the roof. Making use of common electrical piping fixtures, an antenna mount was quickly assembled.

Aruba antenna results

As luck would have it, the receiver as we know was 75 Ohm, a 1/4 wave with ground plane at 45 deg = 50 Ohm. A steeper angle will tend to increase the impedance. This worked out (sort of) fine for mounting it in a notch of a roof panel.

Did it work? Although far from a good antenna build and match to the receiver, yes it worked really well, extending the range of the remote transmitter by about 150 meters with a wet roof, and 200 meters with a dry roof. There was no option to mount the antenna outdoors.