Feeding a wire loop antenna
 

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:
=20
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

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




--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Thanks Dave,

I agree that the third solution should work well. But I will not be able =
to test it until I will be back there, and this will not be before =
several months from now.

I have verified that my Daiwa tuner has plastic tuning knobs and that =
both variable capacitors also have a plastic tuning axis, so the =
proximity of my hand should yield a limited error on the tuning point.

73

Tony, I0JX

"KC1DI" ha scritto nel messaggio =
news:op.swlf240ncdad2j@elbc-crz2m9noal...
On Sun, 04 Sep 2005 15:21:01 -0400, Antonio Vernucci =
=20
wrote:
=20
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 =20
plain 30-ft wire and a tuner. But I do not like that solution =
because, =20
in my case, access to earth (water pipe) is not convenient.

So, I decided to switch to a symmetrical antenna that does not =
require =20
an earth connection. I have then mounted a square wire loop, about =
15 ft =20
each side, fed with about 5 feet of 450-ohm ladder line. The antenna =
=20
impedance varies a lot across the desired frequency range, but it =
can be =20
easily matched by my tuner on all bands.

The antenna being symmetrical, and the tuner asymmetrical, it is =20
advisable to use a balun. Three solutions come to my mind:
1) using an off-the-shelf (e.g. MFJ, Vectronics, etc.) toroidal =
ferrite =20
balun at the tuner output. I do not like this solution because, on =
some =20
frequency bands, the antenna impedance gets very high, and I am not =
sure =20
on how the RF transformer behaves under those conditions

2) putting an RF choke at the tuner output. The choke could be built =
by =20
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 =20
the RG-58 cable connecting the transceiver to the tuner on a ferrite =
=20
rod. In this way the tuner body would be "hot", but this may not be =
a =20
real problem

Any comment on the pros and cons of the three approaches would be =20
welcome.

73

Tony, I0JX

=20
Hi Tony,
=20
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 =20
contant impedence and is not so likely to cause problems. However =
most =20
tuners use the opposite the Balun on the output. Except the new MFJ =20
balanced line tuner.
=20
in any event let us know what you come up with
73 Dave KC1DI
=20
=20
=20
=20
--=20
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

On Sun, 04 Sep 2005 19:21:01 GMT, "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

Dear Tony,

In my opinion, none of the ideas are all that great. However, you
surely have noticed that everybody and his brother are doing #1
without even worrying about it. Oh sure, you get the occasional thread
here which takes up all three methods to one degree or another. But
the vast majority of people using balanced feeders do not have Johnson
Matchbox tuners, and they buy tuners with the 4:1 in place, connect it
up and it works, after a fashion.

So long as you are running barefoot it's not a problem - nothing gets
burned up and you are not losing enough power percentage-wise to ever
see a noticeable effect on anything.

Now, to the bigger issue. Do you have a particular reason for
formatting your post so that I have to use the horizontal scroll bar
to read it. That's terribly inconvenient. No offense, but it's the
first time I have seen anything like that.

Cheers!