AMX TXC16 Plus Specifications download pdf (Page 48)

SG-2000 MANUAL 41

The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA

11.1 Antenna Wire Size

Antennas are working their best when current in the antenna is high. A large wire will

radiate more efficiently than a small wire.

Stranded wires will also radiate better than solid wires. Because AC electrical voltages

are carried by the surface of a wire, stranded wire has more surface area and therefore

radiates more efficiently.

If you wanted to design a good half wavelength antenna for HF work, you would

select the largest wire possible because you know that at power levels of 150 watts and

up, the difference between number 14 wire and number 6 wire can be as much as 3 dB.

This means that just changing the wire size can double the effective radiated power

coming from an antenna.

If you want to get the effect of a higher power transmitter, just increase the size of

antenna wire. You can easily make a 150 watt radio perform like a 300 watt radio.

Another consideration with any antenna is the size and location of the counterpoise, the

electrical “mirror” of an antenna. In the case of a center-fed dipole, it is the "cold" end

of the dipole. On a vertical antenna, it is the ground system or the metal of a vehicle

which is acting as a mirror. The counterpoise must be larger than the antenna or the

system will not radiate effectively.

If you are ever working on an HF radio and you get RF “bites” when your hand touches

the equipment or your lips touch a metallic microphone, you likely have a situation

where the antenna is electrically "bigger" than the ground or counterpoise and so the

counterpoise is radiating.

The height of an antenna over ground or counterpoise varies by the kind of antenna

which is in use because this determines the take-off angle of the radiated signal. This is

not an issue with vertical antennas as much as with horizontally mounted antennas.

In a vertical antenna the ground, or counterpoise, is parallel to the surface of the earth.

Since the maximum radiation from vertical antennas is shaped something like a donut

with a pencil through it with the pencil representing the antenna, you can see how the

ground (which would slice the donut shaped RF pattern horizontally) would have little

effect on take-off angle.

When you turn the antenna (yes, and that donut and pencil) over on its side to

represent a horizontally mounted antenna, the donut becomes two half donuts lying on

the surface of the earth. The take off angle — which is the amount of energy going

toward the horizon — is lowered as the horizontal antenna moves up from ground

level. The angle approaches its minimum one wavelength or more above ground.

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AMX TXC16 Plus Specifications Page 48