OnLine CustomFastJS calculators
Copyright pc1l 2008

MHz center frequency fC

mm radiator diameter d

factor V °

 


Radiator Length

mm
 
(300/f).500.V
 

Advised Total Length

mm
  (300/f).1000.V  

Tube Length

mm
  (300/f).250.V  

'Schlankheitsgrad' S °

    (300/f)/d  
ChassisPart Height
mm
  (300/f).(145/3)  
Advised Tube Diameter D
mm
     
Diameter Dmin
mm
  D=d.3  
Diameter Dmax
mm
  D=d.4  


Click on the Picture

Click on the Picture

This script calculates the values concerning VHF UHF and SHF SperrTopf Antennas .. Based on the Karl Rothammel and ARRL Antenna Fundamentals :-)

1 - Type the desired center frequency fC in MHz.

2 - Type the desired radiator outer diameter d in mm. You have to know that d : D is between 1 : 3 and 1 : 4. D is the inner diameter of the tube. It is possible to calculate from radiator to tube or from tube to radiator : click here and scroll to VHF UHF SHF spertop.

3 - Type the factor V, if you do not know it, click the input, now the value 0.94 disappears, and then click the Calculate Button.

4 - ( A ) Now, the calculation delivers the so called 'Schlankheitsgrad' ( and already the ChassisPart Height too ). Now you will find easily the V factor, use the diagram above. Click on it.
     ( B ) Type ( the found value, input factor V ) and click the Calculate Button again.

For example : fC = 1280 MHz, d = 6 mm, factor V = 0.94 => you find the correct values. The Advised Total Length is the required length of the inner conductor to attach easily the antenna to a mast.

5 - The Reset System button clears the outputs and sets defaults again.