[Sorry if this dupes to the reflector-email issues here]
Subject: Feeding a Lazy H - Properly
With all due respect Tom - when center fed, you do not use a twist.
When top or bottom fed, you do use a twist.
A little discussion on phase and feeding:
One reason the Lazy H is such a great antenna is because it has a null
straight up and another one straight down. The up one eliminates a lot
of noise and the bottom one provides very good insensitivity to height
above ground. To achieve this condition, assuming the wires are 1/2
wave apart, the wires must be fed in phase.
Bottom fed case (also top fed): A signal coming straight down hits the
top wire and 180 degrees later it hits the bottom wire. If we connect
the two wires with 180 degree phase line (straight connection with OWL
and Vf approx 1.0) and no twist, then the top signal is delayed 180
degrees by the phasing line when it arrives at the bottom -- at the same
time as the free space signal arrives; and if connected without a twist
then the signals add. If you introduce a twist, you introduce another
180 degrees of shift and the signal from straight up is cancelled. The
wires are fed in phase... drive at the bottom arrives at the top 180
degrees later via the connecting line, and the 180 phase lag is taken
out with a single twist.
Center Fed: We now have equal lengths to each element. With no twist,
the elements are fed in phase. The "connecting line" BTW can be a line
from each element to the ground or to anywhere, of any length, as long
as they are the same length... or if one is 180 degrees longer than the
other.... add a twist to get them back into phase.
Coax can be used for both the phasing line and the feed line, but for
the phasing line it's too long a discussion for an email and requires
good baluns at the right places to keep shield radiation from messing
things up. It works - I've done it, but I don't recommend coax for the
phasing line unless you know what to do and do it with some precision.
It does allow for a multi-band antenna however with some outstanding
properties. For simple coax feed by the time you get to the shack, come
from the bottom of the antenna with OWL to a few feet off the ground and
run the OWL horizontally above ground such that the entire length from
the antenna to the end is at least 1/2 wavelength. Short the end of the
owl and tie it to a ground stake for static discharge. Move along the
OWL with an antenna analyzer until you find the 50 ohm point and put a
high quality current balun there - then run from there to the shack with
coax. This works great, particularly for EDZ sized Lazy-Hs which have
high feed point impedances - it keeps all the potential loss from high
SWR on the low-loss OWL.
The other simple coax-fed case it to just put up two dipoles - one a 1/2
wave above the other (hang the bottom one off the top one). Feed them
each with a balun and coax. Tie the two coaxes together wherever it's
handy - you have a Lazy-H. Make sure the balun polarities are correct
and the feedlines the same length - or if the upper line is electrically
180 degrees longer, invert the balun to get the wires back in phase.
73
Hal, N4GG
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Tom Osborne
Sent: Wednesday, October 15, 2008 1:05 AM
To: Towertalk
Subject: Re: [TowerTalk] Feeding a Lazy H
Hi Michael
Most of the time if you want to feed it like this, you hook a piece of
twinlead from one antenna to the other. You put 1 twist in the line for
phasing. Then hook the feeder to the center of this line. 73
Tom W7WHY
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