On Sun, 04 Sep 2005 15:21:01 -0400, Antonio Vernucci
wrote:

At my summer QTH, I cannot do more than using a "stealth" thin-wire
antenna.

For operation 40 through 10 meters, I had fairly good results using a
plain 30-ft wire and a tuner. But I do not like that solution because,
in my case, access to earth (water pipe) is not convenient.

So, I decided to switch to a symmetrical antenna that does not require
an earth connection. I have then mounted a square wire loop, about 15 ft
each side, fed with about 5 feet of 450-ohm ladder line. The antenna
impedance varies a lot across the desired frequency range, but it can be
easily matched by my tuner on all bands.

The antenna being symmetrical, and the tuner asymmetrical, it is
advisable to use a balun. Three solutions come to my mind:
1) using an off-the-shelf (e.g. MFJ, Vectronics, etc.) toroidal ferrite
balun at the tuner output. I do not like this solution because, on some
frequency bands, the antenna impedance gets very high, and I am not sure
on how the RF transformer behaves under those conditions

2) putting an RF choke at the tuner output. The choke could be built by
winding several turns of 450 ohm ladder line over a fat ferrite rod
(obtained by glueing several small rods to each other)

3) putting an RF choke at the tuner INPUT, by winding several turns of
the RG-58 cable connecting the transceiver to the tuner on a ferrite
rod. In this way the tuner body would be "hot", but this may not be a
real problem

Any comment on the pros and cons of the three approaches would be
welcome.

73

Tony, I0JX


Hi Tony,

I used the third method you mentioned for several years with good sucess.
I like that option because once the tuner is match the choke balun sees a
contant impedence and is not so likely to cause problems. However most
tuners use the opposite the Balun on the output. Except the new MFJ
balanced line tuner.

in any event let us know what you come up with
73 Dave KC1DI




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