"L" Match for High power LF

Andre' Kesteloot akestelo@bellatlantic.net
Fri, 04 Dec 1998 23:46:27 -0500

vernall wrote:

> Rik Strobbe wrote:
> >
> > After blowing my actual 'balun' impedance transformer at the base of the
> > antenna (during a slow CW test with IK1ODO - I blame him for this with all
> > this dashes in his call, wouldn't have happened if his call was I5EEE ...
> > HI) I'm looking for an better toroid.
> > The Amidon FT140-43 are rather cheap, anyone who has any experience with
> > thiese on 136kHz. I wonder if they will be OK for a 500W 4/1 impedance
> > transformer (2/1 winding ratio) ?
> >
> > 73, Rik
> Why not try an "L match" ?   Presuming you already have a "loading coil"
> under your antenna, then the L match can be implemented by placing some
> capacitance across the coaxial cable that feeds the "cold" end of the
> loading coil.  The series inductance part of the L match is equivalent
> to a turn or so added to the loading coil, and slight retuning of the
> loading coil is all that is needed.  The capacitance values are likely
> to be in the range of 10 nF to 50 nF for 50 ohms to 5 ohms loop
> resistance.  Use polystyrene or polypropylene capacitors, voltage
> ratings to suit.
> An L match has handled up to 800 watts I have had available on 181 kHz.
> A further point is less chance of nonlinear currents being generated in
> an L match than a ferrite cored transformer (used after a low pass
> filter).  Blowing up a core suggests that saturation was an issue, and
> heating from harmonics may have been the failure mechanism?
> Bob ZL2CA