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Tony
The G3YXM design some years back was reliable, two
versions one for 12v and the other for 100v. My 137 kcs TX is similar but with
several fail safe features added.
The set up in my case is a IC706 on 13.7 Mcs,
divider network down to 137 Kcs, driver tc4426 chip, 4 FET PA, matching
transformer to 50 ohms, LPF.
RF from TX fed via 50ohm cable to antenna some 100
yards away in a field, loading coil at base of antenna approx 0.5 mH
matched and resonated to 50 ohm feed.
Monitor SWR and DC current to PA at all times
during TX in case anything goes wrong.
Fortunately in my case the system is reliable and
stable. During stormy wx beware of SWR fluctuations and drawing excessive
current that might cause the PA FETS to expire, especially if using vy slow QRS
MODE
I normally work CW normal speed and seldom go
slower than QRS 3.
This is a class D pa
On 500 Kcs I use a different sort of TX, which is
class E single ended FET, which would also work on 137 Kcs with different values
for L and C.I built this TX in a few
hours and it has proved totally reliable after a number of years use,
designed for 50 ohms and fed to a 1/4 wave inv L antenna at 100 ft
high
There are plenty of designs about for class D and E
transmitters suitable for LF/MF on the web
De mal/g3kev
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----- Original Message -----
Sent: Tuesday, June 22, 2010 11:49
AM
Subject: LF: Re: 137 Revival
I fully intend to be QRV on 137 by the
winter.
On that note, can anyone recommend a reliable
foolproof transmitter that uses easily available components ?
Tony, EI8JK.
----- Original Message -----
Sent: Tuesday, June 22, 2010 8:26
AM
Subject: LF: 137 Revival
LF
How about a 137 kcs Revival, much more
interesting than 500, which is more like 160 metres.
CW, QRSCW, Invisible Ros etc
G3KEV
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