Date: Thu, 11 Dec 2014 19:48:30 -0500
From: Roger <roger@rogerhalstead.com>
To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: [TowerTalk] Antenna Gain and Reality
Doubling the number of antennas theoretically doubles the gain which is
an additional 3 db for each doubling although it's unlikely due to
losses in feeding and matching that this will be achieved. Losses in the
coax m
As most of us have both budget and land constraints that limit us to the
number, size, and height of our antenna(s) It's unlikely we can depend
on equaling the performance in the advertised figures. Often for 40,
75, and 160, a simple wire antenna, or vertical will out perform all but
the largest and/or sophisticated antenna or array.
I've had extremely good luck with sloping, center fed, half wave
dipoles. compared to some stations running Yagi antennas at reasonable
heights. Many times the first word in the response to my call, is
"Wow". Yes, I do run QRO, but the best sounding signal out of the
tetrode amp is at, or around the legal limit so there is little
incentive for pushing beyond the legal limit and those tubes are expensive.
--
73
Roger (K8RI)
## Feeding two..or three identical monoband yagis is a piece of cake..and NO
losses. Just use
a step down L network. 50 ohms in and 25 ohms out for 2 yagis. And 50 ohms
in and 16.67 ohms out for
3 yagis. The L network consist of a shunt mess of paralleled NPO 5 kv HEC
caps, from input
side to chassis...followed by the series coil. The coil consist of a few turns
of either .375 inch OD
or .5 inch OD cu tubing, and silver plated.
## The 25 ohm output side is of course strapped to 2 output connectors for
the 2 yagi case. The 2 yagis,
each 50 ohms....and equal length 50 ohm coax to the L network. 50 / 2 = 25
ohms. 50 /3 = 16.67 ohms.
## You wont blow it up with serious QRO either. Its also very broadbanded,
and easily covers the entire
40m band. Ditto with the higher bands. That’s tested by installing 50 ohm
resistors on the outputs....then
sweeping the input with your favourite analyzer.
## I find it hard to believe that a single vertical, dipole, or sloping dipole
will hold a candle to a 2 or 3el yagi
on 40 or 80m. Even a shorty 40 at 70 feet will clean out a half wave sloper,
with the top of the sloper at 100 feet.
You are not even in the same ballpark..even with the yagi and sloper pointed in
the same direction. I would
take a rotary dipole over a half wave sloper any day. A 2 or 3 el yagi is just
icing on the cake.
Jim VE7RF
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