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Having recently taken an interest in
amateur radio , and being a experimenter and tinkerer , I had to
build my own antenna .
The simplest , cheapest and easiest to tune has to be the
vertical dipole . ATM I'm very much into 2 meter and 70cm so this
is
what I was aiming to cover building my dipole .
The very first thing I did was source a pole , in this case it
was a 8 meter collapsible squid pole made from fiberglass . The
last two
pieces were to thin and whippy so were removed , leaving me with
a still flexible 6 meter pole . So the first consideration was
weight ,
the antenna simply had to weigh next to nothing . The next
consideration was sourcing parts for the build , and for this I
took a trip to
my local Bunning's , to see what was available for DIY antenna
building . Now at first I had watched a lot of YouTube video and
read
a lot of DIY antenna build guides . So having a slight idea of
what direction to go in I was of to Bunning's .
1. PVC pipe , cheap dial calipers say 22mm OD , Bunning's sells
it in 1 meter lengths ( you just need one length )
2. 90 degree elbow to fit
3. T connector to fit
4. 10mm aluminum tube ( Bunning's sells it in 3 meter lengths ?
or 1 meter lengths / 3 meters is cheaper if memory serves )
5. I used 22mm wood dowel inside the T piece for the elements
6. You will need assorted self tapping screws
How to build it .
I start by fitting the wood dowel
inside the T piece , a good interference fit is what I strive
for . When the dowel fits well I use a saw to cut it of flush
with the PVC fitting . Once I have both ends done , I then drill
a 10mm hole as central and as straight as I can through the
dowel for my 10mm
aluminum tube .
The tube was cut to 24inches ( 610mm ) the first time I
did this , just to be on the safe side and not make the radials
to short . As it turned out this was a little
on the long side . I would suggest 20inches ( 510mm ) to start .
I press the tube into the dowel a few mm past the dowel face on
the inside , this might be
between 15mm and 20mm leaving you with just over 19inches (
490mm ) of radiating element .
Once the PVC T piece has the dowel and aluminum tube fitted , I
drill a small hole through the PVC - Dowel and aluminum tube ,
and
screw in a self tapping screw long enough to go through both
sides of the aluminum tube . The screws serve two purposes ,
they hold
everything together as well as allowing us to connect the coax .
That's it , that's the hard part done . All we do now is fit a
short length of PVC pipe to give us a arm to hold out the antenna
, we fit the 90deg
elbow and another length of PVC pipe , which can be mounted to a
pole , and in my case its almost perfect as it slips over the
squid pole
and becomes a interference fit , holding it firmly in place with
no need for further hardware .
Tuning the Dipole
You will need a SWR meter for this
part .
I start by checking SWR @ 144.050mhz ( low ) and 147.950mhz (
high ) to see what I get .
Apparently the rule for tuning is :
High SWR on high freq = Antenna is to long
High SWR on low freq = Antenna is to short
Using a pipe cutter , I trim both elements ( 1/4inch at a time )
until I get close to equal SWR or the lower frequency is almost
1 to 1 .
Its important to clean the ends of the antenna where you are
trimming as rough ends can affect the SWR reading .
With this antenna I was 1.04 ( low ) and 1.34 ( high ) when I
decided to clean ( de-bur ) the ends . After re checking
the SWR it was 1.03 to 1 to 1.04 to 1 across the 2 meter band .
( 17 1/4 inches or 438mm )
On 70cm ( 430mhz to 450mhz ) its about 1.8? to 1
And I'm using 10 meters of RG58U to connect the antenna to my
radios , as well I have used RG174 with good results .
( Maximum power might be 5watts of transmit power )
This is my 3rd Bunning's Dipole , and they are amazingly light
weight , and can be used on 70cm .
( I call it the Bunning's dipole as the parts come from
Bunning's )
If you're into hand held transmitters , then a simple dipole
like this one can seriously increase your range for
both receiving and transmitting , and it simply kills any rubber
ducky or small to medium whip .
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