I've heard that in the early spark-gap wireless telegraphy era people would use kites with a wire acting as antennas and if the receiving side had a wire length that was an even division or multiple of the wire length on the transmitting side, the two antennas would be tuned to each other - if transmitter sparked, the receiver would also produce sparks. I suppose this was similar to how Lecher line works, where it is possible to obtain a standing wave with multiple peaks and nodes (higher order harmonics) when the wire length is a multiple of the wavelength of the RF signal propagating in the wire. I haven't found any information on this subject and I'm wondering if anyone ever tried anything similar to this in the receiving antennas. Thanks


2 Answers 2


A dipole is resonant on every frequency where it is an odd multiple of (slightly less than) $\lambda/2$. So normally we talk of half-wave dipoles, but 1.5-wave, 2.5 wave, and 3.5-wave dipoles are similarly resonant. They all have a feedpoint impedance of about (72+0j) ohms in free space.

For monopoles, being half a dipole, the resonances occur at (slightly less than) odd multiples of $\lambda/4$.

Their radiation pattern is not identical, however. Whereas a half-wave dipole has two broad lobes, as the dipole gets longer it acquires more, narrower lobes.

This effect of multiple resonances is sometimes used to an advantage in constructing multi-band antennas. For example, a dipole that is resonant on 40 meters (about 7 MHz) also works on 15 meters (about 21 MHz).

But when operation in only one band is required, it's not common to use more than the first resonance. There's no particular advantage to making the antenna longer, and it's cheaper and mechanically easier to construct a smaller antenna.


Yes, in the early spark days, the fundamental frequency of the transmitter was largely determined by the self-resonance of the antenna system. Any sort of spark generator naturally generates RF energy at many frequencies, but those close the self-resonance of the antenna would be more likely to be effectively radiated.

Receiving antenna self-resonance isn't as important.


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