Receiver/transmitter with the feedline
is attached to one end and the other terminated through a resistor
(300- 600 Ohm) to ground. The value of the resistor should be
equal to the wave impedance of the transmission line that created
by the antenna wire and the ground under the wire. So, optimum
value of the resistor depends on the height the wire above the
ground and diameter of the wire. Beverage Antenna has SWR close
to 1.0:1.0 in a wide spectrum of the radio frequency band when
the optimum value resistor is used and the antenna fed through
line with impedance that is equal to the wave impedance of the
Beverage Antenna has practically
unidirectional radiation pattern (small back lobe of course is
present) with the main lobe directed to the resistor-terminated
end. The wide of the lobe depends on to ratio "used frequency:
antenna length."I believe that the paragraph gave enough
theoretical knowledge to build a Beverage Antenna.
Figure 2 shows Beverage Antenna that I have installed at my backyard. Length of
my Beverage antenna was equal to 20- meters. The length was fixed
by the length of the fence. Antenna wire was stapled to the fence.
I used to a 16- AWG (1.3- mm) wire in strong black plastic insulation.
The wire was bought at sale at Home Depot- 22 cent/meter. The
wire used to in electrical job. The antenna wire was placed at
height 1.8- meter above the ground. Height of the fence defines
it. Theoretical value of the wave impedance of my antenna was
close to 500- Ohm. It is allowed me use 450- Ohm terminated resistor
and transformer 1:9 to feed the antenna through coaxial cable
RG8X 50- Ohm. At my case the cable had length in 50 feet. At both
end sides the Beverage Antenna had RF and electrical grounding.
Below we discuss all parts of the Beverage Antenna.
Terminated resistor of the Beverage Antenna
I need termination resistor for my Beverage Antenna.
It should be 450- Ohm, non-inductive, 20...
50- Wtts Broadband termination resistor. Power of the resistor depends on output power of
used transmitter. The resistor may dissipate up to 50% of the
RF power going to the antenna. It is not a problem to buy such
resistor online through internet. However, the chipper one costs
$ 50.0 USD. I decided make the termination resistor by myself.
I bought a kit with 25 e.a. usual 4.7-kOm/2.5-Wtt
metal resistors for $ 5.0 on e-bay. Eleven such resistors switched
to bridge have resistance 440- Ohm. Figure 3 shows the home- brew termination resistor.
Coin in 25- cents is placed beside the termination resistor. Dissipative
power of the resistor should be 27.5- Wtts.
However my experiments show that the resistor could stand at least
50- Wtts for a short time.
So, the Beverage antenna may work with transmitter
with output power 100- Wtts with CW
and SSB mode.
Figure 2 Practical Design of Home- Brew Termination Resistor