Horizontal Indoor Antenna #2 ... VE3KL

Input Area 1

Used to Calculate Antenna Width
See diagram below

Frequency [MHz]
( 3.5 to 54 MHz )
Select Units

Maximum Antenna Width [Less Than]
Minimum Antenna Width [Greater Than]

Input Area 2

Input the Antenna Width (In Selected Units)
Keep width between Max and Min limits given above
Antenna Width

Frequency [MHz]
Coil Inductance [uH]
Length of Wire 1
Length of Wires 2,3
Length of Wires 4,5
Gain [dBi]

Antenna Description...3.5 to 54 MHz

The antenna shown above is a horizontal dipole that is bent on each end to allow its mounting in a confined space. The antenna is further shortened by the use of two loading coils that are separated by 0.1 wavelengths. The antenna is constructed from five wires.

Wire 1 is separated into 1a and 1b to denote that it is center fed. Wires #2 and #3 are of equal length as are wires #4 and #5.

This antenna is balanced (symmetrical) which means that a current Balun or choke will inject equal currents into each half with no current injected onto the outside of the coaxial cable. Hence it is a very good antenna for use indoors as RF current will not travel down into the radio shack.

The design algorithm is most accurate between 3.5 and 30 MHz where only a small amount of trimming is necessary to set its best operation to the frequency of interest. For the six metre band, the antenna will resonate approximately 4% lower than the predicted value. This can be corrected by trimming wires 4 and 5 or by slightly reducing the inductance of the coils.

What the Calculator Does

The calculator computes the SWR, Gain, Coil Inductance and Length of all wires used in the antenna.
Input Area 1 is used to specify the Frequency [MHz] and desired units {Metres, Feet or wavelengths]. The Coil Inductance is the required value at the operating frequency

How to Use the Calculator

First, input the centre frequency and units (Metres, Feet or Wavelengths) for calculation in the box named Input Area 1. Then press Calculate.

The calculator then computes the Maximum and Minimum antenna allowable width of the antenna. If you have a large room it is recommended that you use the Indoor #1 calculator, on this site, that does not use loading coils.

Then select the width of your antenna and press Get Output. Check that the length of Wires 2,3 are suitable for your room width.