[AMRadio] Loop antenna feed question


George KB2Z Thermionic_Emission at earthlink.net
Sun Dec 4 18:20:53 EST 2005


Getting up a bit higher would probably improve things.
To get on the air I've used setups worse than I care to talk about.
Anything works better than nothing.
Right now I'm using a dipole thats about 54' each side, fed with a pair of 80'
RG-59 coax cables to a 4:1 balun in the basement, with 3' of RG-58 to a tuner.
Ladder line is useless in my situation.
Its hanging off 30' of chain link fence top rail, swagged together, 
run vertical, and bolted to a 4x4 post.
The 5100-b loads up anywhere from 80 to 10 meters. I have been told 
it can't work. Go figger.
Good luck, George KB2Z





At 05:43 PM 12/4/05, you wrote:

>John,
>
>    I to am a novice at this stuff. I'm having trouble
>visualizing your antenna. You said,
>
> >"the fence - of about
> > 450 feet diameter, and nearly (but not quite)
> > square."
>
>Could you clarify this to me?
>
>   I too have a horizontal loop. Mine is about 15' off
>the ground, and has about 240' of wire (roughly 4 X
>60'). I feed it with 450 ohm ladder line to the
>ground. My antenna is resonant at about 3.9 Mhz, and
>the impedance at SWR minimum (1.5:1) is about 80 ohms.
>I measure this right on the ground between the ladder
>line and my DPDT knife switch (I ground it out when
>not in use). I  then use a 1:1 current balun, and
>RG-8X coax to the shack.
>
>    My first try was to convert from 450 to 300 ohm tv
>twin lead at the hole in the wall, and go straight to
>a Johnson 275 matchbox with 300 ohm twin lead. This
>was dismal since the Johnson matchbox doesn't seem to
>have a wide tuning range to feed 80 ohms balanced. It
>did work unbalanced however, but poorly. So I switched
>to coax after a 1:1 balun for the run inside. If I do
>it again, and intend to feed this antenna at
>resonance, 75 ohm coax straight all the way might be
>an option.
>
>    This loop loads up like a SOB, and absolutely NO RF
>in the shack. The problem though is that my signal
>reports are usually poor (often) to great (once in a
>while). It seems that for this to work efficiently as
>a low horizontal loop (high angle radiator) for short
>skip, I need  good soil conductivity, or counterpoise.
>
>Stations beyond 500 miles can hardly copy me, and yet
>I can sometimes be full scale at 150 to 200 miles out
>early in the evening.
>
>Regards,
>Jim
>WD5JKO
>
>--- John Lawson <jpl15 at panix.com> wrote:
>
> >
> >
> >    Well - my Valiant is putting out stable rated
> > power on all bands - this
> > morning I'll suss out where the audio is
> > disappearing to - should be ready
> > for Air then...  now to turn to the Radiator.
> >
> >
> >     I'm still in the 'steep' part of the EasyNEC
> > learning curve - and I've
> > gone through the several ARRL antenna books - so I'm
> > properly confused.
> >
> >   I have a loop of 14ga hard copper wire around the
> > rear of my propery,
> > attached (with insulators spaced at abt 8' apart) to
> > the fence - of about
> > 450 feet diameter, and nearly (but not quite)
> > square. It is about 5' above
> > the ground, except for one leg which is attached to
> > the house, where it is
> > about 7'.  I am feeding it with 450-ohm ladder-line.
> > My Question to the
> > Antenna Gurus is this:  At the feed-point, should I
> > maintain the
> > ladder-line spacing where it joins the loop ends, or
> > should there be an
> > angle, ie. should the loop ends be wider than the
> > feedline pitch - and if
> > so, what should the included angle of the feedline
> > 'transistion' be...?
> >
> >    I've approached this from two or three analytical
> > directions, and of
> > course have different (and somewhat exclusive)
> > "answers"....  so I'm
> > Learning, which is a good thing.
> >
> >
> >     Cheers
> >
> > John  KB6SCO
> >
> >
> >
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