Toroidal Antenna?

[Jdo300]

Hello,

This is kind of an odd-ball question. Is there a such thing as a toroidal antenna? If one were to take a toroidal core (non-metal) and wind some wire on it to pickup/transmit at a certain frequency, what would it do? My initial guess is that if it is to be a transmitter, that whatever emf it produces would be stuck inside the core. Is that true? If it were to be an antenna, would it be excited by outside radio waves or would only an internal signal source be able to excite it?

Thanks,
Jason O

[berkeman]

Yeah, a toroid would probably make a lousy antenna. For transmit, the flux mainly stays within the toroid shape as you say. For reception, if the windings are evenly spaced around the full toroid, then the fields cancel out and you get very little receive signal. If you only wiond half of the toroid, however, you can get some pickup. Winding a solenoid on a ferrite rod is a common antenna configuration, for example.

[ozerob]

This is a response to a post so old I am not sure you need the info...
Toriodal antennea are not (originally) wound on a ferrite toroid. Ferrite = UNUN = different
These things are very directional, peak at 6 to 10 db forward gain,
and as I made it, short rods of stainless steel arranged about three
quarter inch thick by 3/8 inch circles. If I take down my antenna I
will photo it for you. I can suck up signal from the local airport, this old peice of crap even works well at 70 cm. And can pass 120 watts at swr 1:3
OR - I guess this might be what used to be called a 'beam directional helical core emitter"
so - the notion of a toriodal emitter array is NOT the same as a 'antenna', toioidial works very differently as a transmitting element, I am on a different track from you

Thank you for posting an item that caught my interest. Should you feel a need to respond email ozerob@mts.net _ respond any way - I'm retired and nothing much is happening on 20 M these days - 73 -