I've been watching videos from Charlie Morris, ZL2CTM, recently - he's really doing a wonderful job. One of his projects is an End Fed Half Wave Antenna tuner with SWR meter.
My portable radios have built-in SWR meters and I figure it's better to tune for a minimum with the meter in the radio than one in the tuner - that also made the project simpler.
I didn't have the T68-6 toroid, just a smaller T20-6, in the junk box. I grabbed a 12 position switch from Jaycar and a 270pF polyvaricon (variable capacitor). Here's the very simple circuit.
Here's a close up.
In the back yard there is an end fed wire that rises up to the top of a 6m squid pole and then angles over to a pole on the roof of the garage. I guess it's about 12m of wire. A counterpoise runs along the ground under the back deck.
The box worked well for a project like this, it was easy to drill but strong enough to hold things like the switch without flexing.
The tuner worked well on 20m with a deep dip in SWR but a little more inductance (more turns) is needed for 40m.
Update
As mentioned, I'm working on a neater wiring system for the switched toroid. This is looking better:
ReplyDeleteHi Peter,
With an end-fed having a high impedance , and hence a high voltage , what level of RF power can you run with a polyvarcon varicap ?
I have a FT817 (5W max) which possibly should be OK ?
BTW , I really enjoy your website.
73/72 Frank . EI7KS in IO63XC ei7ks.frank@gmail.com
Hi Frank,
ReplyDeleteYes, the voltages can be a problem for polyvaricons. I've had them melt when running WSPR. I think 5W is about the limit for continuous carriers but 10W peak on SSB can work.
73
Peter