A PKW wire DIPOLE
A dipole made by 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, And vertical half wave antennas GPA / antron 99 are actually “end-fed” dipole antenna.
And so can mobile antennas be brought back to this principle. The radiating part is one leg of the dipole and the car is the other half.
In short a well known antenna and all antenna theory basics starts with the dipole.
Actually, it is used as THE REFERENCE antenna for things like gain !
A dipole antenna : developed by Heindrich Rudolph Hertz around 1886 is an antenna consisting out of a center-fed driven element with an halve wave electrical length. This antenna is proberly the simplest practical antennas from a theoretical and practical point of view.
The antenna consist out of one electrical guiding wire with a length corresponding to halve the wave of the frequency.
Often this wire is made out of copper, but any electrical guiding material will be ok.
The impedance in the middle of that antenna is roughly 70 ohm’s, but can vary with polarisation and height above ground from say 20 to 100 Ohms.
At that center point of the antenne, the wire is separated and connected to a coax cable.
At the ends of the dipole there are insulators to make sure the antenna isnt in contact with anything else.
The Dipole can be found in many different shapes,
It maybe erected horizontal (it is called then a Horizontal dipole)
Or could be erected vertical (iow Vertical Dipole),
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.
A commenly heard misunderstand is that as an inverted V, the polarisation is vertical.
IT IS NOT ! The antenna still has a horizontal polarisation !
( evan wkikipedia had that wrong lol).
Finally you could find it in an slooping angle of 45 degrees (called a sloping dipole).
If so, and you use a metal supporting mast …you actually get some additonal gain and it will be a bit focused..
With the variation 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 (that’s why everybody speaks about the 11 meter band.)
WHAT DO WE NEED ?
A dipole is a halve wave antenna, the length of the dipole for 26,285mhz (my design frequency) 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.
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The “professional” insulators can be bought on any ham market or ebay etc.,
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. (It is wise to start with a bit longer element lengt…say 2,9m (in my example) )
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 frequency your antenna is too long.
when the SWR is the best, higher in frequency your antenna is too short.
It thus possible the antenna wont be 1;1 ! Just search for the lowest “dip” that is what you want.
Start extending/cutting the length on EACH side OR simply fold back the ware this will work aswell.
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 frequency was : 26,270 mhz
The Bandwidth ( 2:1 points) of the antenna is: about 1,5 mhz !
Results:
On 02 October 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 a little money spent !