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2 Meter Slim Jim Antenna
Using 300 Ohm Twinlead
This design is based on
the standard Slim Jim
antenna
This 2 Meter 300 Ohm Slim Jim antenna is constructed from regular
300 ohm twinlead.
(The same type used for TV antenna
installations.)
It is very easy to build and does not take days to
construct.
The measurements above are not extremly critical but may
have to be lengthened or shortened for your particular operating
frequency.
You simply take a piece of 300 ohm twinlead about one
inch longer than in the picture above, trim both of the ends down to bare
wires, twist and solder
both ends. Tape to prevent moisture from
seeping inside twinlead if used outdoors.
Your final
length for the total antenna length will be about 58
inches.
Then on one side of the twinlead, measure up about 19
inches from the bottom of the antenna.
Cut out a complete section of
the wire (ONE SIDE ONLY) of about 1 inch at the 19 inch point.
This
creates an air gap and also technically creates some capacitance at this
point.
Assembly of the antenna is complete except for attachment of
coax and final SWR adjustment. Once you get the hang of it, you can make
this antenna extremly fast. Makes a great emergency antenna for attic
installation out of the
weather!
NOTE: Some builders use a 1 : 1 air choke made from
about 6 coils of coax at the base of the antenna with one end attached to
the antenna feed points and the other end is equipped with a Pl259/barrel
connector. This is your choice. See the "Ugly Balun" project for
ideas. The rule here is to keep the coils of coax touching each other
except the outside ones. Using a PVC core to wind the coil on is the basis
of the "Ugly Balun" style.
SRW ADJUSTMENT
and FINAL INSTALLATION
Now create some sort of temporary support (non-conductive) with
the antenna hanging straight down OR lay it out on the ground, table, work
bench, etc so you can attach the coax (50 ohm small type like RG58) to the
feed points, center conductor to longest side, shield to the other. There
is a very good reason to use small coax at the antenna.....your fingers
will let you know why if you have large hands! Those tiny wires inside the
twinlead are very difficult to work with using large coax like
RG8.
The usual connection points will be around 4 inches Plus or
Minus from the bottom of the antenna, however due to various construction
methods, brand and type of 300 ohm twinlead used, these points may change,
so have bare wire on both sides of the 4 inch point as far as needed to
allow for adjusting SWR.
Attach the coax in a temporary fashion,
center conductor of coax to longest side, shield to the other, by twisting
each end tightly onto the bare conductors of the 300 ohm twinlead. One
piece of electrical tape wrapped on one side will keep them from
shorting.
Now get the antenna up and away from surrounding
metal objects at least 20 or more inches and as high as possible for SWR
adjustment. Your permanent location is the
best.
Note: Coax should hang
straight down from bottom of antenna during tuning and final
assembly.
USE LOWEST AMOUNT OF POWER POSSIBLE WHEN ADJUSTING
SWR!
Move both
coax connection points equally up or down for best (lowest)
SWR.
After lowest SWR is obtained, (you may not be able to
achieve a 1:1 so just trim for lowest SWR), solder coax to antenna, with
center conductor to longest
side and shield to the other, seal end of coax from
weather and let it hang down from bottom of antenna.
This Slim Jim
antenna can be used inside by supporting from string, nylon cord, etc from
a high point in the room or used outside by hanging or supported from a
suitable length of PVC pipe, (see standard Slim Jim
design) wood or other
NON-CONDUCTIVE MATERIAL.
Again, keep it away from conductive
objects a minimum of 20 inches from the bottom, sides and top. If long
runs of coax are needed to connect to your rig, then it is suggested that
a short length of RG58 type coax be used AT THE ANTENNA connections, then
add a barrel type connector and convert the coax to lower loss type such
as Rg 8 going to your rig.
Trying to use the large type coax at the antenna is very
difficult due to sizes of wire and limited space between conductors of
twinlead.
This is not a high power antenna. Stock 2 meter radio
output is recommended.
Always use the lowest power needed for each
contact. No amps!
SEE
SLIM JIM PLANS ELSEWHERE ON THE
SITE
CONVERT A J
POLE TO A SLIM JIM ANTENNA
ALSO SEE THE
COPPER TUBING VERSION
Have Fun! 73
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