LF: LF SWR Bridge

["Rob, M0DTS" <rob@m0dts.co.uk>]

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