The Dipole
ref:
PKW
ref: ITA
ref: Wolf.
This antenna is the basic. It is simple to make and cost can be nearly nothing.
Most antennas are based on a dipole, Yagi's use a dipole antenna as the radiating element, vertical half wave antennas are "end-fed" dipole antenna.
And so can mobile antennas be brought back to this principle.
A dipole antenna : developed by Heindrich Rudolph Hertz around 1886 is
an antenna with a center-fed driven element for transmitting or receiving radio frequency energy.
These antennas are the simplest practical antennas from a theoretical point of
view.
ref: wikipedia
The antenna consist out of one electrical guiding wire with a length corresponding to the frequencies.
Often this wire is made out of copper, but any electrical guiding material will be oke.
The 50 ohm feed point is in the middle of the antenna.
At that point the wire is separated and connected to a coax cable.
At the ends of the dipole there are insulators to make sure the antenna
The Dipole can be found in many different shapes, it maybe erected horizontal (it is called then a Horizontal dipool)
(as in the second picture above.)
Or could be erected vertical (iow Vertical Dipool), as in the third picture above.
Another common shape is in an up side down V shape (it is called then in Inverted V antenna)
as in the first picture above.
Finally you could find it in an angle of 45 degrees (called a sloping dipool).
With the variate of each shape the patterns of the antenna changes and there for personal preferences may vary.
WHICH LENGTH ?
The first symbol is lambda, it is the sign for wavelengths.
The formula then is 299,8 divided by the F which is frequency in Mhz ) will give us the wavelength of the frequency.
Example: channel 52 (27,555) 299,8
27,555
10,88 meters
This is approximately 11 meter (thats why everybody speaks about the 11 meter band.)
WHAT DO WE NEED ?
A dipole is a halve wave antenna, the length of the dipool for 26,285mhz (my design frequencie) would there for be : 5,70M.
So we need :
2 pieces of 2,85 m copper wire.
Two end insulators and one center piece.
Coax cable to connect the antenna to the transceiver.
center piece
Electrical guiding
material
Rope
The "professional" insulators can be bought on any ham market or ebay etc.,
you could get the through me (cost 15 euro together. mail 19SD348@planet.nl ).
But, u do not really need them.
You can make it from wood or plastic see the chapter "SKYPPER" for another idea.
A search on google might give u a hand a swell.
MAKING THE ANTENNA WORK !
All you need to do is connect the individual wires (2,85m) to the center
insulator, and connect the end insulators to the other end of the wire.
Connect the coax cable to the center insulator.
Then connect the rope to the other side of the end-insulators and pull the antenna in the air.
Now you need to check the SWR with your SWR meter.
Keep in mind that SWR varies due to - height
- ground capabilities
- nearby structures
Make always sure u make the antenna a little longer then designed. .
When the SWR is the best, lower in frequencie your antenna is too long.
when the SWR is the best, higher in frequencie your antenna is too short.
Start extending/cutting the length on EACH side !
On the eznec file u can see that the gain is 0,0 dB.
This is correct a dipole doesn't have any gain compared to a dipole.
This antenna is a reference antenna to others when gain is expressed in dBD !.
SWR MEASUREMENTS:
Below u can see how the MINIVNA antenna analyzer responded to the antenna:
The best resonant frequencie was : 26,270 mhz
The Bandwidth ( 2:1 points) of the antenna is: about 1,5 mhz !
Results:
On 02 oktober 2008 (sunspot minimum) stations from
Italy,Spain,Balearic island,Sardinia,Cyprus, Macedonia, Bulgaria,
Corsica, Ireland were worked in a morning with only 15 watts, on 27mhz.
Now that is loads of fun with only little money spent !.
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