3 - 30 MHz Choke

[VK6ZFG]

Colin

Of course one might ask why you have a lot of RF around the shack in the first place..

Is it proximity to the radiator/s ?
Coupling from the radiator/s to the feedline (assuming coax) and whether there are BALUN/s in use at the far end ?
Lack of an effective RF earthing system in the shack ?

And the big one - are you planning to install one of these chokes at EACH end of the relevant transmission feeder ?

It's all very well stopping it coming down the feeder but sometimes making sure the feeder is perpendicular to the radiator to minimise coupling is enough if a BALUN is in use.

Have you tried one (or more) of the simple clip-on RF ferrite devices where the coax enters the shack AND at the back of the gear ?

I think I saw a mention somewhere in one of your postings about an end-fed half wave antenna (see, someone does read them !), well that needs to be fed against an effective virtual earth to not have feedline radiation. That virtual earth needs to be a REAL earth - and not a flimsy excuse for one - for the antenna to be efficient at its purpose, let alone not have the feeder radiate.

Of course, again, I might not be remembering antenna and transmission line theory correctly...

Doug

PS Your graph has no textual references as to what you were measuring. If it is common mode rejection then 45dB at 5.xxx MHz is ok, otherwise a 45dB signal loss input to output (S21) makes for a very efficient dummy load to dump power into...

Hi All
 
The end fed ground independent antennas are misleading as they do actually require something for them to work against.  This is because all electrical circuits require two conductors for them to work.  While the coax feeder is provided with two connection points the end fed dipole is only has one connection and needs a second one for it for the feed to it to work against.
 
If an earth, or alternative, is not provided for the end fed antenna to work against it will find one by resorting to using the coax for this function.  This provides the illusion of it being ground independent.
 
Igor
VK6ZFG