             BALCONY ANTENNA MOUNT by Harry Lythall SM0VPO

Many amateurs are very restricted with the space they have available for
HF antennas. I have documented a short antenna for the HF bands but here
is a simple method of mounting it,  and a method of further reducing the
physical length. I used to use an old CB (27MHz) half-wave antenna which
had a broken matching coil. This I used as a 1/4-wave antenna for 14MHz,
after removing the matching coil.     Today I find that CB antennas have
increased in price, so I found a cheap replacement that can be fitted to
the balcony of appartment dwellers.

ANT-MONT.GIF

THE ANTENNA
Above is the side view of a bracket, which can be 'thrown' together in a
couple of hours and gives surprisingly results.   I use six sections for
the antenna, each of which is 1 meter long. Each section fits inside the
previous section by exactly 10 cm.  The last section is adjusted so that
total length of the antenna is 5.35 meters. This resonates at 14.175MHz.
I used the following aluminium tubes:-

section 1 : 31 mm Dia. Wall thickness = 2.0 mm. (bottom section)
section 2 : 25 mm Dia. Wall thickness = 2.0 mm.
section 3 : 20 mm Dia. Wall thickness = 1.5 mm.
section 4 : 15 mm Dia. Wall thickness = 1.5 mm.
section 5 : 10 mm Dia. Wall thickness = 1.5 mm.
section 6 : 6 mm Dia. Wall thickness = 1.0 mm. (top section)

This is shown as item (1) in ANT-MONT.GIF.

THE BRACKET (6) & (2)
The bracket screws to a handrail of my balcony.  In my present situation
I have a 7 meter wide terras with a horisontal handrail, but there are 4
vertical steel pipes supporting the handrail.  The bracket is screwed to
one of these vertical supports (4).

The bracket is formed using 3-4 mm thick aluminium plate (6) with a 50mm
hole in the center of the top & bottom end. Bend the plate in two places
to prevent the plate becoming weakened. The two ends are each sandwiched
in between two nylon blocks (2).    Use a chopping board stolen from the
kitchen, if you can get away with it. Otherwise, the chopping boards are
available from (for example):

IKEA         (Sweden)
WOOLWORTHS   (UK)
SAFEWAY      (USA)

Drill THREE of the nylon blocks in the center, to fit the 31mm tube (1).
The fourth block (bottom) should be drilled with a 5mm hole. This allows
water to run out. The bracket is bolted to the balcony handrail using 35
mm exhaust (muffler) clamps (3).

THE COIL (7) & (8)
This is used to make the antenna resonate at lower frequencies.  I wound
all my coils using 4mm aluminium wire. Copper hydraulic brake pipe works
as well.    The coil is 10mm Dia (the same as a tin of DelMonte pineaple
chunks)!!. The coil pitch is 1cm per turn.  I used two pieces of plastic
conduit (7) to support the coil.

The coil uses about 1 meter of wire/pipe for every three turns.  Flatten
one end and drill a hole in it for conecting it to the antenna pole (1).
If you use aluminium wire then shorter pieces can be joined with a brass
insert from a car cable connector. Copper tube can easily be soldered.

FEEDING THE ANTENNA (5) & (9)
Feed the antenna with 50ohm coaxial cable braid connected to the bracket
(5) and the center conductor connected to an aligator clip.   Select the
band using the aligator clip (9):-

0 turns = 14 MHz (20 meter band) (VSWR - almost 1:1)
2 turns = 10 MHz (30 meter band) (VSWR - almost 1:1)
6 turns = 7 MHz (40 meter band) (VSWR - about 1.1:1)
51 turns = 3.8 MHz (80 meter band) (VSWR - about 1.4:1)
53 turns = 3.7 MHz (80 meter band) (VSWR - about 1.4:1)
55 turns = 3.6 MHz (80 meter band) (VSWR - about 1.4:1)
57 turns = 3.5 MHz (80 meter band) (VSWR - about 1.4:1)

OTHER INFORMATION
The mounting is very rubust, yet the wind resistance is rather low. Both
my antennas have stood up to gale force winds; they hardly wobble!!  You
do not have to use 5.35 meter of for item (1) if you want to work on any
other bands such as 18 MHz. If you intend to use more than 10 watts then
make sure you have 1 cm or more of insulation between the aluminium pole
(1) and the bracket (6).

Files:    BALC-ANT.TXT
          BALC-ANT.GIF

Have fun with QRP de Harry Lythall - SM0VPO @ SM0VPO.SL0ZS.SOLNA.AB.SWE.EU
                     Ron Lythall   - G0TLA @ GB7NND.#23.GBR.EU
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These files are available for automatic download from two different PMS on
the packet network.  All files are compressed into a single ZIP file.  You
may request them as follows:


Packet command:   SP 7PSERV @ G0TLA.GB7NND.#23.GBR.EU
Message title :   QRP/BALC-ANT/BALC-ANT.ZIP @ (insert your BBS address)
Message title :   /EX (or Ctrl+Z)

                ------------- or -------------

Packet command:   SP 7PSERV @ SM0VPO.SL0ZS.SOLNA.AB.SWE.EU
Message title :   QRP/BALC-ANT/BALC-ANT.ZIP @ (insert your BBS address)
Message title :   /EX (or Ctrl+Z)
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Files are also available via the INTERNET at the following addresses:

http://user.tninet.se/~acz732k/
http://hem2.passagen.se/sm0vpo
