Rogues Gallery

The ‘halo’ is a VHF FM aerial, and in my opinion it is an abomination. The idea is that it is omni-directional (it receives from all directions), and that it is horizontally polarised. It’s a folded dipole, bent into a near circle, and as such it’s a severe design compromise, like a brick is a serious design compromise if you set out to build a helicopter. It’s the only aerial I know of that has a negative gain figure – in other words it’s got less gain than a dipole. Actually, I think it’s got less gain than an isotropic source. Is that possible? It sounds like perpetual motion in reverse. Anyway, the halo is pointless because all VHF FM transmissions are either mixed or vertical polarity, so a vertical halfwave dipole works better and is considerably more elegant.

Just to square the circle of absurdity, this particular halo has been mounted for vertical polarity! Since the response of a halo looks (in theory) like a doughnut, presumably this one will be a doughnut on its side.

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