Friday, November 16, 2012

The Vee Beam Antenna


The Vee Beam Antenna


If you're lucky enough to have the room, perhaps you may like to put up a multiband Vee Beam antenna for the HF bands.

The dimensions of this antenna were provided by Nick, VE3OWV... Each leg is 300 feet in length... I used galvanised

fencing wire with the ends spaced 170 feet apart... This is an unterminated Vee Beam which can be used as a

bidirectional antenna...



The layout of the antenna and a radiation pattern of an unterminated Vee Beam...





If each end is connected to earth through a 600 ohm non inductive resistor the antenna is called a terminated Vee Beam

and the front to back ratio approaches about 3 S points... Even so the gain is slightly less than the unterminated type...

For ease of construction, I sloped the antenna because of the height of the trees... The trees here are not very high so

the antenna runs from about 30 to 5 feet in height..



The tree in which the feedpoint is located and the 600 ohm (12 to 1) balun...





The direction in which the antenna runs must be carefully considered as it has a narrow beamwidth, especially on

the higher bands... If the ends are not terminated but left open, the SWR is higher across the HF bands and an

external tuner and tuned feeders may be needed to match it to the transmitter on all bands...

The feedpoint impedance is about 600 ohms, so I used a 600 to 50 ohm balun (12 to 1) at the feedpoint and ran

50 ohm coax to the radio...



Antenna wire support poles...





In my case the SWR on the 40 and 80 metre bands is very high and on the 30 metre band about 4 to 1...

On the 20, 17, 15, 12 and 10 metre bands the SWR of the antenna is about 2 to 1 or less and the inbuilt antenna

tuner of my transceiver (an Icom IC-7600) is able to match it to the radio..

Even though the SWR of the antenna on the lower bands is very high, the internal ATU of the IC-7600 is still able to match

it to the radio so operation on all HF bands is possible here... This may not be the case with some other radios though...

My other radio, a Yaesu FT-450 with an inbuilt ATU is not able to match the antenna on the three lower bands...



The antenna wire supported by a tree and one end of the antenna wire...





As the frequency of transmission is increased the effective length of the antenna is also increased giving better performance.

Construction of the antenna is straight forward... Of course the higher in the air you can get the wire the better...

If you have the room it would be well worth your while giving an antenna like this a go...


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