Sorry for delayed reply - been travelling, and going to be in Stcokholm quite a
lot in the next two months, so reading e mails intermittently.
The parallel tuned circuit tuner is very flexible: however, if the working Q is
too high, the ususal heating problems come in. Depending on how the antenna
impedance varies with frequency, it can have a lower bandwidth before retuning
than an L network: the opposite can also occur. Using a big link means a smaller
link tuning cap and more volts, so the vacuum variable could be used, but I
concur with the advice about a large air variable.
I use parallel tuned circuits with link coupling for 80 and 30 metres: 40m uses
a balun driving a balanced L as it gives wider bandwidth. I use a 500pF variable
on 30 with 680pF in shunt, and 1000pF variable on 80 with 1000pF in shunt. This
is for feeding an 80 m dipole at 60 feet, fed with open wire line. BTW, I mean
by 'open wire line', two 14AWG hard drawn copper wires separated 2.5 inches by
ceramic insulators every 3 feet.
73
Peter G3RZP
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