To match or not to match - Impedance transformation
The matching network is often used when trying to match antennas with
complex feedpoint impedances.
Any wire, half a wavelength long on a given frequency, will have a
very high feedpoint impedance. You have to transform this to match
the 50 ohm's of your transceiver. It can be done in countless ways.
On this page i will give you some general ideas as how to accomplish this.
This 1:49 transformer is used with wires any multiple of 1/2 wavelength.
This is not a matching network, it's a wideband transformer and it has
some advantages compared to LC matching.
Normal LC networks are resonant on one freq. only, and will not work
anywhere else than the design freq. This transformer on the other hand
will work with resonant half-wave wires, and random lenght wires from
3.5 - 30Mhz.
Twist the wires for the first 2 turns tightly, this will give better performance.
The capacitor can be omitted, it will however give a better match on 10m.
Another way to do it is with the LC network. this has some advantages
compared to the transformer above. As the circuit is resonant, it has
some noise rejection outside the resonant freq. This can be a good
thing, but the disadvantage is that it will only work on 1 frequency.
The example here can be adjusted for different freq. with the use of
a trimming capacitor. This will have to be a transmitting type capable
of higher voltages than your normal trim cap.
Another example for 15m band.
Another good thing in your toolbox, is this transformer for use
with long-wire antennas. This is a 1:9 UNUN transforming from
UNbalanced to UNbalanced.
