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Tune Around! Topics For
Technicians! |
6 Meter
Homemade J-Pole
Antenna The 6
meter repeater we use in my neck of the woods has a receive frequency of
53.110Mhz and a transmit frequency of 52.110Mhz. This antenna that I built
according to these dimensions seems to be performing quite well. I have
gotten several compliments as to how my transmissions sound and I seem to
be able to hear quite well on it also. MATERIALS Copper Tube and fittings dimensions
are given as inside diameter (plumbing
dimensions) 20 foot length -- 1 inch diameter Type L Copper Tube (Hard Drawn) 4 feet -- 3/8 inch diameter Type L Copper Tube (Hard Drawn) 1----1 inch copper Tee 1----1 inch copper 90 degree elbow 1----1 inch to 3/8 inch copper reducing coupling 2----1 inch copper pipe caps 1----3/8 inch copper pipe cap 2----1-1/2 inch stainless steel hose clamps 4----3 inch stainless hose clamps 1----3/4 inch x 5 inch (sch 40) PVC pipe 10—3/16
inch x 8 inch black nylon zip ties 60/40 solder and flux plumbers sanding cloth fitting brushes of the appropriate sizes (Optional but will make your life easier) BernzOmatic propane torch BernzOmatic micro torch good
copper pipe cutting tool INSTRUCTIONS: Refer to drawings and photos
below I'll start out by saying that it is understood that you are proficient in accurately measuring and in soft soldering techniques. If this is
not the case, you may want to talk someone into helping you with this
project as it can get quite frustrating for someone not experienced with
the previously mentioned skills. It is imperative that the ends of the pipe to be soldered as well as the inside of the fittings are cleaned by sanding or brushing (fittings) until they shine like a new penny. Also, the pipe ends as well as inside of fittings should be coated
with paste flux just prior to
soldering. It can't be stated
enough; check and double check your measurements before you cut and
solder. Uh-O's are easier fixed before the antenna pieces are cut and
soldered than after it is
assembled. The 3/8
inch copper tube section measurement at top of J pole is not
critical. I started out with a piece of roughly 4 feet of copper pipe and
added the reducer and then joined the 1 inch tube to the reducer and 3/8
inch section of pipe, being careful that I ended up with the overall
measurement of 161.04 inches from the top of my 3/8 inch pipe cap at the
end of my 3/8 inch pipe, down to the top of the “bull” on my 1 inch tee
attached to the other end of my 1 inch pipe. Notice the measurements are not “center to center” but are metal to metal measurements. Refer to drawing below. In other
words, for example, the SPACING DIMENSION given as 5.04 inches-- is the
dimension from the inside wall of the longer 1 inch pipe to the inside
wall of the shorter 1 inch pipe. When you
have finished soldering the short length of 1 inch pipe to the 90
degree elbow and it is attached to the tee and long length of 1 inch
pipe you will need a stiffener between the 1 inch pipes. This can be
accomplished by using a piece of 3/4 inch PVC pipe (see drawing below).
Measure and cut a piece of PVC pipe and cut slits back 3/8 inch from both
ends so a nylon tie can pass thru the slits and go around the 1 inch pipe
and be tightened up so as to provide a stiffener, so the elements will not
sway and move relative to one another in a high
wind. After the
antenna is assembled and soldered, you will need to fasten the coaxial
lead from the radio to the antenna. I used (2) 1-1/2 inch hose
clamps. Strip
about 8 inches of the outer jacket from the coax—being careful not to
damage the shield. separate the shield and the insulated center conductor
so each lead can be soldered to a hose clamp. This is where a micro torch
comes in handy. I have a BernzOmatic torch and it is worth it's weight in
gold. Outside with the wind blowing, an electric soldering pen simply will
not cut the mustard! I placed a
little flux on the hose clamp and placed the center coax wire on the hose
clamp and used the micro torch to heat up the connection until it was
ready for the solder. I fed wire solder onto the wire and hose clamp until
a sufficient amount had built up on the wire and clamp junction to insure
a good connection. After the
first clamp had cooled, I proceeded to solder the coax shield wire to the
second hose clamp in the same manner as I had done the first hose
clamp. After the
second hose clamp had cooled, I measured where the FEED POINT dimension
was located and used sand cloth to clean the area so my hose clamps would
make a good electrical connection. After sanding, I re-marked the FEED
POINT dimension on the pipes and attached and tightened the hose clamps at
the marks. I then formed a coil of 5 turns with an approximately 5 inch diameter to form a coaxial balun that is necessary when using 50 ohm coax to keep RF energy from backing up down your feedline. Use nylon ties to tighten up the coil loops and to attach it to the antenna as per the picture drawing. You may
have to play with the hose clamp positions up or down slightly to get the
best SWR readings. Me, I got
lucky. I placed them the first time and with my handy antenna tuner, which
is part of my radio setup, I got a perfect match the first
time. Use the
(4) 3 inch hose clamps to attach the bottom leg of the antenna to a mast
of some sort---and don't forget to ground the antenna. It may save
you major headaches down the road.
By
what my ham buddies are reporting to me, the antenna seems to be performing
quite well.
Using
5 watts, my transmit is loud and crystal clear and my reception seems to
be pretty darn good.
I am
using an Icom-7000 transceiver along with an IT-100 tuner by LDG
Electronics.
My project was the result of info
gleaned from various sources posted on the
internet. Question? Email Tony apye1849 AT
yahoo.com (don't forget to remove the AT and add @ with no spaces!) Editor note...It is not required that the measurements used in this article be cut to the hundredths of an inch. The tuning tap points (coax attachment points) at the base of the antenna can be adjusted up or down for best swr. The J-pole antenna is very forgiving with the construction as long as the overall measurements are close. If you don't have the skills with copper tubing construction, seek help from a ham radio friend. Sometimes they require a cool drink, cup of coffee or a visit to McDonalds in return! Some work cheaper than that! GRIN! 73
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