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Am 09.10.2018 um 19:20 schrieb DK7FC:
Hi Tom,
Why do you decide for a class-E at all? Do you see any actual
advantage
over a class D?
73, Stefan
Hi Stefan,
A very good question! Knowing you are a dedicated class D fan I have
to choose my words carefully ;-) ! - Well, I think class E would fit
my personal needs best:
- single ended circuit, that means no timing problems at square
wave drive with 50% duty cycle
- no fiddling with dead times or double frequency drive
- 28 V DC power supply is well sufficient for 180 W output
bringing about 18 kV rms to my antenna at a current of 0.6 A
(and that´s the voltage limit of the antenna)
- omission of all transformers between PA and the feeding point
of the antenna: matching is part of the output network and so is
the regular cable capacity
- fine tuning can be done in the shack
- perhaps even a little bit more efficiency than class D - but
that´s not so important
Meanwhile I found out that my nice commercial power supply (Ascom
Frako, 24/26.8/28.2 V, 20 A, short-circuit proof, "unkaputtbar")
has a control input at logic level for a DC softstart with a time
constant about 100 ms which won´t affect the long lasting signals
at vlf and avoids any key clicks. I´ll use this input for keying
thus omitting the problem with the first positive gate pulse.
Drive will be there all the time with constant phase and
asynchronous soft keying is done via the power supply.
73,
Tom, DK1IS
www.qrz.com/db/dk1is
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