Many years ago W1AW used to have a big (6 wavelengths per leg as I
recall) rhombic for 20 meters pointed west. It was mainly used for the
code practice and bulletin transmissions. When the new 90-foot tower
with stacked monoband Yagis was installed we ran some A/B antenna tests
on the air and asked people to send in signal reports.
We found that the rhombic was equal or better than the stacked
monobanders right on the boresight of the antenna but it had a narrower
radiation pattern. The Yagis covered the west coast better overall.
On the other hand, the rhombic was not as high (mounted on telephone
poles) and it could be used on other bands, although with lower gain.
By the way, the W1AW rhombic was unterminated as I recall. There really
is no need to terminate a rhombic unless you are concerned about
interference (on receive or transmit) in the rear direction.
Alan N1AL
On 9/13/19 4:21 PM, Fred Jensen wrote:
Mike: Rhombics can be operated either terminated or unterminated. If
unterminated, they are bi-directional with half the power in each
lobe. If terminated, the resistor absorbs half the power in the
reverse lobe. Either way, half your power goes the "wrong" way,
either behind your desired direction or heats a big resistor. They
have a very low radiation angle and a fairly narrow beamwidth which is
why they're flame throwers and very common in military and commercial
stations, particularly in the days of point-to-point radio circuits.
V-beams, sometimes called Half-Rhombics are sort of likewise only
broader azimuth patterns more suitable for maritime ship-shore
telegraphy circuits. For ham applications, Google W6AM
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
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