Building an EFHW (End Fed Half Wave) Antenna Coupler

Started by swxx, August 30, 2017, 10:54:20 pm

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August 31, 2017, 02:46:45 pm #2 Last Edit: August 31, 2017, 02:51:22 pm by cockpitbob
Quote from: caulktel on August 31, 2017, 12:56:57 pm

This is the one I build, I must have about 8 or 9 by now. They work great for QRP.

This is my favorite EFHW coupler.  No variable capacitor.  Switching between bands that your wire is resonant on is nothing, and you can make the coupler water-tight and hang it outside in the rain.

The down side is the transformer needs to have more inductance (larger core and/or more turns).  That limits its upper frequency with all the extra parasitics.  With the variable capacitor you have a parallel resonant L-C circuit that, at resonance, has a very high impedance.  This is why you see them with smaller low inductance cores, or no cores (like in swxx's post).  With no variable cap making it a resonant tank circuit, all you have is the 2*Pi*f*L impedance of the transformer's inductance.

I still haven't figured out how the guy at managed to make a 200W coupler that covers 80M - 10M.
The best I've been able to do is 100W and 40M - 10M(and 10 is getting a bit sketchy).  But if I buy my next antenna, this will be it.

Either way, wasn't it wonderful of the founders of ham radio to make most of the bands harmonically related!


Just as an aside on the interesting point about the founders of amateur radio. As far as I know, initially, ALL were radio amateurs, including Marconi. Initially, ALL frequencies above 3MHz belonged to radio amateurs, without any license whatsoever. One can draw an analogy with driving vehicles. At first there were NO licenses and no rules. But later, the GOVERNMENT stepped in when it was found that Short Waves were NOT useless as had been thought.

They had been considered pretty useless as skip zone wasn't understood, it was not known that there was an ionosphere reflecting HF signals! So in tests, after 30 miles or so the signal disappeared and thus above 3MHz was considered useless. Then when hams in Europe and America started making contact, still largely unregulated, aha, then these air waves had value, and amateurs were now RESTRICTED to certain bands: 160, 80, 40, 20, 10 and perhaps also 15. AND those bands were wider than now! I think 20m was 14 to 14.5 or certainly 14.4 MHz.

So it may have not been amateurs but governments who conceded these bands, or decided upon them? Perhaps with or without amateur input?

A very important things that has always NEEDED TO BE DONE and now more than ever and yet NO IARU SOCIETY ANYWHERE is doing it: as acknowledgement of the role of amateur radio and radio amateurs in all communications development from the outset, the ORIGINAL amateur radio bands (even if smaller as we have now) at 160, 80, 40, 20, 15 and 10 meters should be given IN PERPETUITY to the amateur radio service.

Only this will protect encroachment upon it by the money-men and their regime poodles (governamints).


QuoteI still haven't figured out how the guy at managed to make a 200W coupler that covers 80M - 10M.

Testing it right now, and filming a video... Not sure if I'll have it done by Monday, probably next Monday...