Hello Rob,
Instead of a SWR bridge i would recommend a voltage/current and a phase
meter. The voltage/current ratio should be 50:1, so you can easily
check for 50 Ohm. As i started with LF in 2003 i found that pdf from
Jim/M0BMU with a good description. The advantage of that tuning meter
is that you can see if the mismatch is caused by a reactive part (= not
in resonance) or due to an impedance that is not equal to 50 Ohm.
I'm not sure if the link is still working but i found the pdf in my old
LF folder and put it to
http://dl.dropbox.com/u/19882028/LF/LFtunemeter.pdf ...if you want to
take a look there...
73, Stefan/DK7FC
Am 15.05.2011 12:09, schrieb Rob, M0DTS:
Hi All..
I'm trying to put together my 137KHz transmitter after it has gathered
dust in the loft for a few years and will hopefully generate some
signals again soon..
I'm not so good with this LF so need a bit of help with an swr
bridge.. This will stop me blowing FET's this time i hope!
I've seen a couple of designs for an swr bridge and have tried out
G0MRF's one here which appears so simple
who could go wrong?!
I'm using a 3c90 core, a very small one (13mm) but i should be able to
get the same effect I'm sure, i just can't get any difference between
forward/reflect at all with 50R on the load port.. the only difference
i have in my build is the different core size.
I've tried increasing the bifiliar turns but just gave more coupling as
you would expect..
I guess I'm just very low on inductance by using the different core so
the q is too low and i don't 'see' the dip in reflected signal when
tuned?
Any ideas and a simple explanation of how it works would be useful..
Thanks
Rob
M0DTS
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