Just bought a 228 ATU. Front is immaculate, bottom and top have some scratches
but a paintjob will take care of that.
The SO239 sockets are well used so those are replaced with N-sockets in line
with all my other gear.
When the cover was off it showed that the toroid / switch has the plastic
melted on one side. Further inspection revealed that the capacitor connections
were swapped around: the TX is connected to the antenna side and the antenna is
connected to the TX side. This may have had an influence on not optimal tuning
practices but more likely it has been used with a badly macthed vertical
antenna and too much power.
I've been looking for an alternative configuration that will minimize / avoid
this problem of high losses in the main inductor.
What I have discovered sofar is that the greatest losses in a T-match appear
due to: (too) small variable capacitors combined with low frequencies and low
impedance.
I intend to use this ATU for coax-coax matching for "tuned" antennas in order
to get a 1:1 SWR across the band.
I am considering to use an 1:4 impedance transformation at the output using a
meaty toroid (T184-2) and have the tuner "see" a nominal 200 Ohm output towards
the antenna which gets "down transformed" to 50 Ohm for the coax.
Using the ARRL TLW software indicates this should at a minimum half the losses
in the main inductor while at the same time the capacitor values become well
within a range of far more practical values.
I know that there will be additional losses in the impedance transformation
toroid but that should dissipate without causing damage.
( Since I will be working with matched antenna's I do not expect any great
reactances or abnormal high impedances on the feeder. The impedance
transformation toroid "should" therefor run within a reasonable load area and
"should" not have extreem losses. )
Any feedback on the above proposed change will be greatly appreciated.
73, Marinus, ZL2ML
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