one, transformer with a 1: 1 ratio serves like a choke. This transformer
balances the RF current in the antenna parts (for symmetrical
antenna) and suppresses the common-mode current on the outer braid
of the coaxial cable. Other transformers in addition to this job
provide transformation of antenna impedance to impedance of the
feeding coaxial cable.
should be guided when choosing the number of turns for primary
winding? With other things being equal, transformer with a single-turn
primary winding, compare to the double-turn primary winding counterpoint,
has about in four times higher lower frequency of the passband
together with the higher upper frequency of the passband.
for transformer used at 160 and 80 meter it is better to use double-turn
primary winding. For transformer used from 40 to 10 meter it is
better to use single-turn primary winding.
is the transformation ratio the more difficult is to obtain a
wide bandwidth since the leakage inductance of the windings is
increased. The leakage inductance could be compensated by switching
on a capacitor in bridge to the primary winding. The capacity
of the capacitor should be found at minimum SWR at higher working
frequency of the transformer.
The ready transformer could be tested. For the test the transformer
should be terminated to non- inductive resistor. Then SWR curve
should be taken at working range of the transformer.
73! de RU3ARJ