Portable Radio Mast - Increase Walkie Talkie Range

A radio mast can provide better radio communication, especially if it is used with a repeater. Radio waves travel in straight lines. The earth's surface is curved. These two factors limit the distance communication can be achieved using walkie talkies on 'flat' ground.

There is a formula which gives the maximum theoretical distance radio waves can travel in 'line of site' to the horizon.

It is: Horizon (km) = 3.569 times the square root of the antenna's height (meters)

So, a person using a walkie talkie standing (1.82 meters) can communicate a maximum of 4.81 km's to the horizon on flat ground. Between walkie talkies the theoretical distance of communication is up to 9.62 km. If they were lower, for example sitting in kayaks with a (60 cm) antenna height, the maximum distance would be 5.52 km.

If one of the walkie talkies had a higher antenna height e.g. at 5 meters high, the distance could be longer. If this higher walkie talkie was to re-transmit the message, for example if it was attached to a simplex repeater, the total distance could be longer still. I say 'could be' as its is also effected by other factors - the power of the transmitter also comes into play as well as obstacles in the path of transmission.

This tutorial explains how to make a 5 meter repeater tower out of beverage cans. Using a simplex repeater, on flat land, it can theoretically increase the range between two walkie talkies from 9.62 km to 25 km. (An Increase of 160%).

1. First off remove the lid with either a can opener (fast but rough) or by filing off with a bastard file (slower but better finish)
2. Remove the bottom of the can with a craft knife and scissors, trim with the scissor to make it the finish neat
3. Tap the top of another can with is top removed
4. Wrap with packing tape or duct tape

1. Cut off the bottom of the can and insert in another can with its top removed
2. Add another can
3. Keep adding cans until the tube length is about 1 meter long unit.

Make more units. These will be attached together when the mast is assembled.

In an attempt to provide added strength to the mast (See Step 6 for revision in design), a spacer and support lines were added:

Cut a 2 cm thick piece of foam into a octagon shape. Glue corrugated cardboard to both sides. Some glues will eat into the foam, I found using a hot glue gun worked well. Cut a hole in the centre of the foam sandwich, so a length of tubing will fit snuggly through it. Cut a small 'V' into 4 of the edges of the foam sandwich. These will guide the strengthening lines . Add some loops of tape for the guy ropes to be attached.

In a similar way that some ventilation poles use strength cables, secure lines from the top to the bottom of the mast. I found picture hooks could be used along with a small windlass to tension the lines. These lines are designed to add tensional strength to the mast.

Disassemble back into units, ready for transportation 'into the field'.

Having made an antenna mast the next challenge was how to erect it.

Three guide lines would be used to support it, but how long do they need to be? And how far from the base to secure them into the ground? The answers came from revisiting Euclidean geometry which had also been useful in a previous project to mark a right triangle:

Euclidean Geometry

The guide lines attached to the mast will make triangular shapes to it, With the guide line being the longest side.

Euclidean geometry says the longest side of a right triangle squared equals the sum of the other two sides squared. (a squared + b squared = c squared theorem)

E.g .

• 3 x 3 = 9
• 4 x 4 = 16
• 5 x 5 = 25
• (9 + 16 = 25)

Applying this to the challenge of erecting the mast:

If a guide line is attached 4 units up the mast and made 5 units long, it will reach the ground 3 units away.¹ With this knowledge the guide line ground positions can be measured.

Measuring
Lay a length of line from where the guide line well be secured to the mast and bring it down to the base. This will be 4 units long.

• Fold this length of line in half and mark with a permanent marking pen. Fold again in half and mark with pen. The line has now been marked into 4 measuring units.
• Use these units to measure the guide line to be 5 units long.
• Attach the guide line to the mast.
• Measure 3 units from the base and secure the guide line into the ground.
• Do the same for a second guide line secured in the ground 120 degrees from the first. With two guy line already secured to the ground, raise the mast and secure the third.

It can be a mental challenge to realise your original plan needs to be changed and act (or 'Pivot') on this realisation. The spreader which was meant to add strength but it was doing the opposite. It caused the joined cans to buckle out of alignment, weakening the mast. The original length of the mast was to be 7 meters but this needed to be changed to 3.5 meters while doing the field tests due to the buckling. The spreader was reluctantly removed. Its removal will also make construction easier.

A 5.25 meter beverage can tower (weighing only 620 grms) was erected while on a camping trip. The plan was to send up a simplex repeater using a 'climbing bear' holding on to a 5 watt transceiver. However, not all beer cans are created equal and while the climbing bear was being sent up a 'minor malfunction' occurred with one of the French lager cans. So we 'pivoted' again by throwing a line over a tree branch and then sending up the climbing beer clutching the transceiver and simplex repeater. This worked well and communication with the transceiver was easily achieved using the .5 watt walkie talkie. The ideal place to use the repeater tower would be on open flat ground.

Here some more testing of .5 watt walkie talkies.

Here's how to make one water proof.

Another way to get extra height to extend range without constructing a repeater tower is to hoist the transceiver attached to the simplex repeater up a tree.

A dog ball thrower can help with this:

Drill a hole in the ball and screw in a self-taping screw.

Attach a line - builder line works well.

Lay out line in a zigzag on the ground.

Use the thrower to launch the line over a branch and back down to the ground.

Place the transceiver and repeater in a bag and attach to the line and hoist back up the tree.