[AMRadio] Valiant and Loop progress


ltaft at charter.net ltaft at charter.net
Mon Dec 5 23:44:55 EST 2005


Brett,

Put the 80 and 40 dipoles together, ie common feed point, and let the ends of the 80 dipole hang down at the ends.  Hang the 40 dipole from the 80 wires using a bit of nylon rope for the first tests.  You can make a permanent setup with insulators to support the 40 after the initial tests to get the lengths correct.  Make a choke in the feedline at the top by wraping 8 turns or so of the coax around a 6 inch diameter plastic jug.  Trim the length the 80 first then the 40 and you can get the SWR low enough for use without a tuner. It won't tune to 1:1 so settle for less than 2:1. I have a 80/40/20 web of dipoles fed with coax on top of a 35 foot tower that works good.

73, Larry  K2LT

> 
> From: Brett gazdzinski <Brett.gazdzinski at mci.com>
> Date: 2005/12/06 Tue AM 01:13:10 WET
> To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
> Subject: RE: [AMRadio] Valiant and Loop progress
> 
> While on the subject of antennas, I wonder if anyone knows of a way
> to do what I want to do.
> I had a resonant 80 meter dipole above the house, the length was only 
> about 90 feet, so I had loading coils about 3/4 of the way out from the
> center.
> That worked ok for years, but the coax went bad at the feed point, and 
> while the antenna seemed to work ok, I had a bit of RF in the house, since 
> it was lengthwise over the entire house.
> 
> I have a resonant 40 meter dipole that runs at right angles to the house, 
> and most of it is over the back yard, no RF in the house.
> 
> I likely have about 90 feet there also, if I stay out of the trees.
> 
> I would like to have one antenna that is resonant on 80 and 40 meters 
> without an antenna tuner, that fits in the 90 foot space.
> 
> A trap dipole would be nice, but I have never found anything that holds up
> to
> AM at any but the lowest power levels.
> 
> I normally run about 300 watts carrier on 40 and 600 watts carrier on 80.
> 
> I made the mistake of trying one of those B+W all band folded dipoles, the
> lowest
> swr I could get about 4 to 1, maybe because of the close trees.
> They are also only good for low power on AM.
> 
> The next experiment was as much wire as I could fit above the house, about
> 42 
> feet each side, fed with open wire line for about 10 feet, then to coax.
> The first test showed the swr way off, so I put the antenna tuner on, and it
> 
> started arcing. I added another 10 feet of coax and everything seemed to
> work ok, 
> but a lot of RF in the shack, and I bet I loose power in the coax with a
> high swr.
> 
> I don't want to have to fool with an antenna tuner when changing bands, and
> would rather not use one at all.
> 
> The best bet would be some sort of antenna where the 40 meter dipole is, but
> I cant think of anything that would do what I want it to do.
> 
> The property is in the shape of a pizza slice, the point being my back yard.
> half way up the sides I have a medium size oak tree, and a 36 foot mast on
> the other side
> that is against the garage.
> Close to the tip of the slice, I have a real nice cedar tree that is like a
> mast,
> a very good antenna support.
> Out front, away from the crust is another medium size oak.
> The 40 meter dipole runs from that to the cedar, and is up about 40 feet.
>  
> Anyone got any ideas, other than ordering a pizza?
> 
> Brett
> N2DTS
> 
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