Antenna Calculators

The best part about Amateur Radio is assembling your own antennas from scratch. It's cheaper, and likely works better than a commercial equivalent for the same band. If Mother Nature decides to damage your antenna, (and she will... just give it time...), then repairs / rebuilding is just as cheap as the first time.

How long should it be? Figure it out below:

Wavelength Calculator

 MHz
feet; inches; meters.




Ohm's Law

Enter any two values and hit your TAB key:
  Volts
  Amps
  Ohms
  Watts




Jpole Calculator (1/2 Wave)

NOTE: For better 70cm performance, attach center conductor to the "Long section." Shield attaches to the short section.

Enter The Center Frequency

 MHz

Long section dimension is: feet,    inches,     meters.
Short section dimension is: feet,    inches,    meters.
Feed point dimension is: feet,    inches,    meters.
Spacing dimension is: feet,    inches,    meters.

Inside (spacing) dimensions are metal to metal measurements, NOT center to center.
The caculations are based on 1/2" diameter copper pipe.

A choke very close to the feedpoint (within 3-4 inches) is highly recommended to prevent RF from heading down the feedline into your rig. For the 2-Meter band, four turns of coax at 5in diameter should suffice.





Dipole / Inverted "V" Calculator

The dipole / inverted vee antenna is one of the most effective
wire antennas you can use.

Enter The Values For The Dipole / Inverted Vee Antenna Calculation
Enter Freq with three decimal places ie: 3.900, 7.263, 14.300, 145.390, etc...
Full Wave = 984 / Half Wave = 468 / Quarter Wave = 234


 MHz

Percent smaller for the Inverted Vee

Your dipole's total length is: feet,   inches,   meters.
Each leg of the dipole is: feet,   inches,   meters.


Your Inverted Vee's total length is: feet,   inches,   meters.
Each leg of the Inverted Vee is: feet,   inches,   meters.




3 element yagi

 MHz

A. Director:
B. Driven on a side:
C. Reflector:
D. Spacing:
E. Total length of driven:




Helical Antenna Calculator

Enter values and click on calculate.

Wavelength: M
Or
Frequency: MHz
Number of Turns:
Space between coils: wavelength
Results:
Antenna Gain: dBi
Impedance: Ohms
Diameter: cm
Space between coils: cm
Length of wire: cm
Half Power Beam Width: degrees
Beam Width First Nulls: degrees
Apperature: m2




Cubical Quad Antenna JavaScript Calculator for CB and Amateur Radio Communications


JavaScript PROGRAM by N6ACH Ron vanVarden
thanks to Scott McClements for the round off problem and to Roger KC5LCA for stream-lining the interface

Enter the center frequency: MHz 
All directors are optional
Elements
Element -
Total Length
Wire -
One Side
 Spreader -
Half Length
Spreader - 
Total Length
 Element -
Spacing
  INCHES / CM INCHES / CM  INCHES / CM  INCHES / CM INCHES / CM 
Reflector  
Driven 
Director 1
Director 2
Director 3
Director 4
Director 5
Total Boom Length > FEET= INCHES= CM=

How to mount and feed.

Horizontal or vertical polarization of an cubical QUAD-Antenna is determined by placement of the feed point (feed gap on the driven element) - Parasitic elements need to be mounted in the same orientation as the driven element. If tuning gap is present on the parasitic elements, doesn't the placement of this gap effect the polarization. Feed line is made out of standard coaxial cable (RG8/RG58) 50ohm unbalanced, to attach this feed line to the balanced drive element (Quad loop) without proper matching is not advisable, instead use an 1:1 balun

Gain vs Spacing

The gain of an antenna with parasitic elements varies with the spacing and tuning of the elements, and thus for any given spacing there is a tuning condition that will give maximum gain this spacing. The maximum front to back ratio seldom, if ever occurs at the same condition that gives maximum forward gain. The impedance of the driven element also varies with the tuning and spacing, and thus the antenna system must be tuned to its final condition before the match between the coax and the antenna can be completed. However, the tuning and matching may interlock to some extent, and it is usually necessary to run through the adjustments several times to insure that the best possible tuning has been obtained.