2 Meter Slim Jim Antenna Using 300 Ohm
This design is based on the
This 2 Meter 300 Ohm Slim Jim antenna is constructed
from regular 300 ohm twinlead.
(The same type used for TV antenna
It is very easy to build and does not take days to
The measurements above are not extremly critical but may
have to be lengthened or shortened for your particular operating
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.
length for the total antenna length will be about 58
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.
creates an air gap and also technically creates some capacitance at this
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
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.
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
USE LOWEST AMOUNT OF POWER POSSIBLE WHEN ADJUSTING
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, withcenter conductor to longest
sideand 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
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
This is not a high power antenna. Stock 2 meter radio
output is recommended.
Always use the lowest power needed for each
SEE SLIM JIM PLANS ELSEWHERE ON THE
CONVERT A J POLE TO A SLIM JIM
SEE THE COPPER TUBING VERSION
Have Fun! 73
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