Subj: Re: TopBand: 160/80M beverage lengths, transmitting antennas
To: <topband@contesting.com>
Date: 09/10/96
To: jend@midway.uchicago.edu
CC: topband@frontier.net
Hi Jerry,
I rely less on the computer and more on real measurements, so my results may
disagree with models.
In a message dated 96-09-10 13:40:53 EDT, you write:
>I am looking for data on lengths of beverage antennas. I wonder what is
>a good length to use ??
In several tests here, both in Ohio and here in Georgia, current tapered to
somewhere between 75% and 50% of the initial value in 500 ft of distance
along a Beverage wire eight feet high on 2 MHz. That means very little gain
in directivity or signal to noise could occur by adding wire beyond that
point.
It's a very simple test to make, and very conclusive.
I can run between 500 and 1000+ ft. in almost
>any direction.
>Is it better to use bare or insulated wire, any particular guage,
>copperweld, stranded ??
The wire makes very little difference, since most of the losses are in the
ground below the antenna. I'd avoid wire with high resistance, any copper or
copper weld wire of # 16 or larger should be great.
>in several areas. I also have lots of 75 Ohm cable TV hardline, any
>ideas on connectors for the ends, and what about matching to 50 Ohm ??
Nothing to offer on connectors, except make sure the cable is properly
installed. The ground connection should be as good as possible, especially at
the feedpoint end. I use small choke baluns (ferrite sleeves) spaced every
hundred feet or so near the antenna end of the feedline to prevent the
feedline from carrying unwanted noise and signals to the area of the antenna.
Impedance matching between the antenna and the feeder helps increase the
signal level, and that helps the antennas signal override any signal leakage
into the feedline caused by poor current balance.
>My next question is what would be a good transmitting antenna ? Top
>loaded vertical, with/without elevated radials ??
I made some FS measurements here on 80 meters with a full size 1/4 wl
vertical .
The highest reading came from 60 surface radials, so all other systems are
dB down from that system, or percent of the 60 radial surface system.
>8 foot high counterpoise system.
4 wires 37 percent -4.3 dB, 8 wires 58 percent -2.38 dB, 16 wires 86 percent
-.63 dB, 60 wires 96 percent -.18 dB
>ground mounted radials
4 wires 28 percent -5.5 dB, 8 wires 53 percent -2.73, 16 wires 74 percent
-1.3 dB, 60 wires (used as reference) 100 percent 0 dB.
These measurements tracked with tests made later at a broadcast station. It
used 6 elevated radials (at about 30 ft) and they gained almost 5 dB going to
120 radials.
Models disagree with these measurements, so you decide. Just be aware model
verification is pretty light in this area.
Top loaded verticals have higher radiation resistance, and less ground loss
than a base loaded vertical for a given height. The improvement in efficiency
can be nearly four fold with top loading over the same height base loaded
short vertical. With a 1/8 wl radiator you will probably see less change, but
the change should still be very noticeable.
73 Tom
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