Fig - Free and Open Source Software

Pamcia WinurN6B1S
PO Rod)7
Mrnlo Pari. CA 94026
The Care and Feeding of a Curved
Linear Array Antenna System
For low cost, very low maintenance,
yet acceptable performance, try this antenna system
for use in high-frequency amateur radio operations.
T
his article documents the performance
characteristics of a 39-elemenr curved
linear array (C LA) antenna. The system is
fully tunable for all amateur bands, costs less
than many other anten nas (in fact, many hams
already have one, if they only realized it), and
presents several unique advantages, which
we shall discuss later.
Design Constderenons
The primary motive in designing this antenna
system was aesthetic acceptability. Not
necessarily mine, I hasten to add. To put it
more dearly, I wanted to be able to do amateur
radio without getting thrown out of the
mobile home park I'm currently living in.
O ne high ly desirable solution had , unfortunately,
been eliminated by the removal of a
large pine tree a couple of years before. Said
conifer would have provided excellent camouflage
for a multiband vertical.
An indoor lcngwire was tried briefly. but
had a disturbing tendency of creating large
amounts of rf inside a metal box (the mobile
home). This solution was. therefore , quickly
d iscarded.
Being newly upgraded and eager to get on
the low bands after five years on VHF, I was
desperate for an answer. Considerable d iscussion
ensued among my ham frie nds about
the project. much of it speculative at best.
G iven that I had a massive amou nt of alu-
Photo A. 1h, Curved Linear Array antl'nna ,
shown installed at thr QmofN6BIS.
30 731orRadioAmateuf$ . April,l986
minum at my immediate disposal. several
friends suggested that I load up the mobile
home itself. I quickly realized, though, thai
none of them had offered 10 be inside the
house when this was attempted .
" . .. a rabbit living in a
metal cage on the porch
showed no ill effects
from my DXlng."
Finally. I threw the problem over to Bob
Tarone WA6ZBX, who was willing to find
the right solution for the situation. Hence his
creation of the CLA, or "awntenna.'
SpecifICations
The system we finally implemented is. essentially,
a fat longwire. It consists of a 9 by
4O-foot sheet ofcorrugated alumi num-in the
common vernacular, a porch awn ing (see
Photo A) .
The term "39-element curved linear array"
is a straightforward description of the
antenna; there are 39 ridges in the aluminum
sheet. each of them is curved (arched). and
they are arrayed linearly with respect to eac h
other. (There are also five smaller pieces of
aluminum hold ing the thing up. but we try to
ignore them.)
The awntenna is fed by a length of fourconductor
copper wire (courtesy of Pacific
Telephone) from an MFJ 901 tuner and a
Heath I04 A HF transce iver. (See Photo B.)
Maximum PEP output from the Heath is 100
Watts; I have no panicular desire to feed
more rf than that into the awning .
The height above average terrain (HAAT)
is about 9-1 12 feet . it is slightly higher on
the side nearest the house. slightly lower
away from it, creating a slope of approxi-
mately 5 degrees. The lengthwise dimension
o f the system is oriented almost precisely
east-west.
The antenna is not in electrical contact with
the house, so far as we can tell. A few short
screws attach it 10 the wood paneling on the
side of the house; evidently, they do not go
through to metal. Two Lbrackers which had.
secured the awning to the rain gutter were
removed during original implementation of
the system.
The five uprights are oot electrically isolated
from the antenna. but are insulated (via
mylar boones and plastic bolts) from the cement
into which they are bolted.
The awning also does not come in contact
with the porch below it. This was proven
conclusively in ea rly tests, when a rabbit liv-
Photo B. Bob Taron, WA6ZBX hoolu up rh ,
fred line for the aKlI" nna.