Re: Ferrite rod antenna and RF amp for Valve radios
I've designed a realtively sophisiticated ferrtite antenna with a balanced topology such that, in theory, it should only respond to the H field. Even with this arrangement I don't get a perfect null inside a room. It may be that you have a mashed-up field in the places where you're experimenting, or the E field pick-up is quite strong. Can you try a portable transistor radio to see if that responds as you'd expect?
The other thing you could try is to add an emitter-follower to the output of your amp, add a series 47 or 75 ohms from the output and feed the radio through a metre or so of coax, so giving a bit of isolation.
John
|