|Harmonically Related Antenna
International Broadcast Bands
These two pages describe the assembly and parts measurement of a 1/4 wavelength, end fed receiving
antenna for all the International Broadcast bands. This very same technology has been applied to dipoles
tuned for the Amateur radio (ham) bands.
Wire length dimensions are listed in the chart below. For those SWLers without adequate real estate for
the lowest bands, those elements may be omitted from the design. If you skip the 120 meter wire, you will
still receive 41 meters, but instead of on the antenna's 3rd harmonic it will be on its 5th and 7th due to the
overlap in effective coverage of each wire and their close "multiple relationships."
It should be noted that the transformer is hung from the antenna insulator close to the junction of
the elements and the ground wires are heavy gage copper or flat copper braid. If a tower is
utilized or even a metal mast, the ground should already exist at the attachment point of the
support rope. Antenna height above ground is a matter of the installation's facility, convenience,
and experimentation. At the beta site location, minor difference was noted in overall signal
strength between 12 feet and 45 feet elevation, with a little gain noticed at the highest position,
on the higher bands. The differences on the 49, 41, 31, and 25 meter bands, 12 to 25 feet above
ground seemed to be the point of diminishing returns.
A Note on Antenna Design
If you want to design your own multi-element 1/4 wavelength-resonant antenna for specific center
frequencies other than shown above, you may find the following guidelines helpful:
1. Divide the desired frequency in MHz into 234 for the element length in feet.
If you want to know the answer in inches, multiply the result by 12.
2. Quarter wave antennas will work well on the ODD multiples of the fundamental resonant frequency
(see chart above), up to a point. Depending on several other factors, the 7th, 9th, or 11th harmonic is
probably as far as this principle should be taken.