Hi uwe es MF
I built a class E pa for 500 a few years ago and it worked
well and was reliable. The tuning at the frequency of interest is critical
but easy if you follow the correct procedure for tuning a class E pa. I also
built class D pa for 137 and used it for years without problems.
I now use Decca amplifiers which are Bridge Fet designs with
series resonant PA circuits, in my case matched to 50 ohms.
for 500 Khz make L 20uH and C 5nF these are the nearest
standard values available, adjust L for resonance.
If you copy the Decca circuit it will work extremely well and
run trouble free.
73 es gl de Mal/g3kev
Sent: Tuesday, May 29, 2012 10:24 PM
Subject: Re: LF: 475 kc Exiter
Sorry
Uwe, missed to answer in all the trouble...
I didn't know that a JUMA TX
is available for "500".
Well, the version for 137 kHz is fine but i think
60W is not really enough for a ordinary LF amateur antenna. But on MF, 60W may
be just right if one want to strictly stay below the limitation of 1W.
Do
you know how the PA is designed?
I'm just experimenting with a class D PA
for MF but am surprised about the "problems". I.e. i thought it is easier to
build. The output C of the FETs cause a heavy oscillation when the FET is OFF.
So actually i would prefer a class E which does not have this problem. A class E
would be really no problem, regarding the design. But i intend to use it for
various experiments, also with /p antennas, just for playing arround. Here, a
class E is not recommended at all since it needs a very accurate match to Z=R=50
Ohm. Otherwise the efficiency is decreasing dramatically, up to blowing up the
FET...
73, Stefan/DK7FC
Am 27.05.2012 09:39, schrieb Uwe Wensauer:
What do You think about the JUMA TX500 TransmitterI
In my eyes a small Rig with 60 Watt and built in Converter.
By the way, have a look at the filters in use – easy to built an
duplicate
Uwe, dk1kq
