Some baseline rules for matching “random“ antenna lengths to specific frequencies
or frequency bands:
Tuner
L
L
F
e
e
d
e
r
Ant
●
If the antenna is fed via a balanced feeder (ladder, twin lead etc.) the value of the
relation L
Ant
/ L
Feeder
should be more than 2/1
●
The length L
Ant
+ L
Feeder
should be more than
λ
/2
●
The antenna system L
Ant
+ L
Feeder
need not be resonant. Some antennas that are less
than a quarter wavelength per side exhibit impedances that are very low. These very
low impedances can be difficult to match and some adjustments to lengths may be
necessary. Antennas are multiples of a half wave present very high impedances to the
tuner and may result in internal arcing of the tuner elements
●
If L
Ant
+ L
Feeder
is small in comparison to the wavelength (i.e. 160m Amateur Radio
band); the internal tuner elements are exposed to very high RF voltages. An antenna
i.e. 2 x 10 meters length could be matched at a wavelength of 160 meters, but the
output power of the transmitter must be reduced (see “Antenna Matching”)
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