Earlier I invited on the list input in a proposed change to the TT
228 ATU.
I was considering placing an impedance transformer at the output
of the transmatch in an effort to lower the losses when matching
into a low Z.
Reading in the ARRL Antenna Compendium Vol 3 about the losses
and problem in a T-match when matching a 50 : 50 Ohm coax
connection has me made rethink placing this "un-un" transformer at
the output. The main problems are associated with reactances that
the antenna can present.
The objective is to prevent the melting of the plastic on the
toroid / switch. Since I intend to work purely into "matched"
antenna's extreem matching capabilties are not paramount.
I am targeting to match to a 1:1 SWR to prevent damage to the
transmitter. Secondly I like to obtain a larger bandwidth on 40, 30
and 20 meters with a minor interest in 80 meters.
Extensive simulation is leading me towards using a 1:9 transformer,
stepping up the 50 Ohm transmitter impedance to 450 Ohm and
then use a low pass L-network to match to 12.5 - 200 Ohm.
This setup has values for the capactior and inductor that are of
practical values. In a pinch I ca add on the back an extra connector
in which I can plug in extra capacitance (vitramon capacitors) for
matching on the "top" band. If inductance proves to be an issue then this can
added in line with the antenna.
I apprecieate feedback on this changed approach, many thanks in advance,
73, Marinus, ZL2ML
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