THE HALF WAVE VERTICAL

Probarbly the best know antenna on ouwer 11 meterband !  
Everyone has used this type in the past or will use it somewhere!

Although the half wave vertical comes along with various names the PRINCIPLE is all the same.
The only (electrical) difference, is how the 50 ohms from the coax cable is brought over to the antenna and visa versa.
The reason why this antenna type is so popular are probably the following:

• The length is "only" about 5,50 meters
• This antenna does not require any radials
• Easy to erect!

To construct this antenna most use black markings on the aluminum to judge the length and give the user a satisfying S.W.R.
But there are also those who use other technichs to controle the S.W.R. in such away that it becomes possible to change the SWR from the bottum of the antenna.

The theory behind this antenna is quite simple, its as the name says a half wavelenght long tube or wire with its feeding point at the end.
With that comes a high impedance, we overcome that problem by putting in a transfer device to put that impedance back to around 50 ohms. This always includes sometype of a coil. It can be a small one made on a print for or a strong solid one. Be carefull with those "print" coil types, they can not handle high power.

HOW HIGH SHOULD I PLACE THE 1/2 Vertical ?

The following diagrams are constructed over good ground.
In the first diagram we see that the take-off angle is quite low (A-16 degrees) while the antenna is only a half meter above the ground!
In the second diagram (B) where the antenna is situated 6 meters above the ground, we see that the take-off angle is in the order of 35 degrees but still at 16 degrees its only several dB's down to the lower one. This means for Real long disctance DX the lower antenna will be better of most of the time. In the summermonths with the sproadic E openings the antenna situation B will be better most of the time.
When we come to a height of 15 meters we reach the same thing the angles C and D are almost the same as angle A and B .
When the antenna is put as high as 25 meter above the ground the lowest angle is around 5 degrees (G) and there are several side-lobs higher (F/E)

                    

                   


Conclusion:
A vertical (halfwave) almost sitting at the ground IS capable of working DX! ( better then any horizontal antenna at that height! )
But placing a halfwave vertical much higher is not always favourble.
For this height reason, DX-expeditions sometime favour vertical antennas!

RADIAL KIT:
Although there are those who sell an additional radial kit there is almost no difference when you add these radials to the antenna
This antenna-type does not require one.

GAIN
Another issue is the gain, since it's electrical length is only a half wave. You can look to it as a Dipool (only end fed),
Now you'll probably realize that the antenna does not have the  gain many manufacturers would like you to think it has, measured the right way.
The gain of the antenna is 2,14 dBI in freespace. 
There is NO WAY you can produce 10dBI or more from these kind of antennas. I've anyone can produce this there wold be no use for a 5 or 6 elements yagi !

Finnally it is of no influence how pritty the antenna is with fiberglass/without..there are those with lightbolds on top etc etc..don't care about that. The basic counts...

A very intresting link:  THE IMAX 2000 EXPOSED
                                                                                                                                                                                                                                
 BACK