OnLine CustomFastJS calculators
Copyright pc1l 2008

MHz center frequency fC

mm radiator diameter d

factor V °


Radiator Length


Advised Total Length


Tube Length


'Schlankheitsgrad' S °

ChassisPart Height
Advised Tube Diameter D
Diameter Dmin
Diameter Dmax

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.