KB6NU's Ham Radio Blog

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Anyone know of a 30 W, EFHW tuner design?

Posted: 24 Oct 2017 12:00 PM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Bil, KD6JUI recently wrote to me asking about a design for a tuner capable
of handling 30 W, but, presumably, is not as big and heavy as a 100 W tuner:

I read online that you had been working with matching devices for end-fed,
half-wave (EFHW) antennas.

Maybe you could offer me some advice. Im looking for a manually operated
ant tuner to match end-fed half-wave wire vertical antennas. I understand
the impedance is as high as 2,000 to 4,000 ohms.

I operate from a kayak and am upping my power to 30 watts and want to build
a manual tuner (T-match??) to match my EFHW antennas (which are set up just
outside the kayak on the edges of islands). Right now, I use an EFHW
antenna cut for 20m and also use it on 17m and 30m.

I may very well have to design the thing myself using tapped toroids, but
am trying to find out if anyone else has a good design I could use.

Currently, I run 10w with a KX3, and the tuner is a circuit with three
separate toroids designed to match EFHW antennas for 40m, 30m and 20m (I
can switch them in or out of the circuit as needed) and a poly variable
cap. I dont think this tuner is capable of handling 30 W.

Thanks for any help and advice.

I replied:

All of our experiments with end-fed antennas were about building the best
9:1 unun that we could. If we needed an antenna tuner, we used commercial
tuners that we already had (i.e. the internal tuner in the KX3 or an LDG
antenna tuner for higher power). So, I’m afraid that I don’t know of any
designs such as the one you’re asking about.

I think that maybe what I I would do, if I were you, would be to scale up
the tuner that you’re already using. You should be able to calculate the
inductances of the toroids you’re currently using and recreate those using
bigger cores and larger gage wire. For a capacitor, I’d guess that you
could use a small air-dielectric capacitor.

If you’ll permit me to do a little blue-sky thinking here… It would
actually be interesting to do a little engineering here. Get a big antenna
tuner, hook it up to an end-fed and tune it, and then actually measure the
voltage on the capacitor. That should tell you what kind of capacitor
you’ll need.

You might even be able to simulate this somehow. Our club recently heard a
talk about using LT-Spice, and I’m thinking that if you modeled the antenna
as a 5000-ohm resistor, the simulation might yield some useful data.

I’m sorry that I don’t have a ready-made answer for you. I think what I’ll
do, though, is to blog about this and ask the guy who gave the talk if this
might be something that can be done with Spice. Maybe I’ll get some other
good comments about this problem as well.

So, Im blogging about this.

Does anyone know of a design that will handle 30 W and be light and
portable?
Does building the tuner with slightly beefier components make sense?
Does my idea of modeling the tuner and antenna make any sense?


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