[NCC] EFHW? Any experience?

Mon Sep 16 11:12:41 EDT 2019

Hello Anthony, Bob, et al., 

End fed half wavelength antennas will radiate, but their performance will essentially always be inferior to a center fed half wavelength antenna.  There are two main reasons for this.  

In order to radiate EM waves, there must be a complete circuit in which current flows where part of that circuit is a radiating structure (antenna).  This is easy to picture in a center fed half wavelength antenna, where any current flowing into one conductor of the feedpoint flows out of the other conductor, thereby making a complete circuit.  When you feed a half wavelength antenna at the end, the radiating structure has only one conductor.  You cannot make a complete circuit with only one conductor.  Any current flowing into the end fed half wavelength antenna must return to the source by some means via some other conductor (often called the couinterpoise).  The return current conductor will be the outside of the feedline, the matching network, the station, the ground, and any other conductor in the vicinity.  The return current conductor will not be controlled nor will it have a consistent impedance.  If you block the return current by adding sufficient choke inductance to the outside of the feedline, you will simultaneously block the ability of the half wavelength antenna to radiate.  

Second, the feedpoint impedance of an end fed half wavelength antenna is very high.  The matching network must be designed carefully because the high voltage needed to match such a high impedance is likely to saturate a ferrite transformer core and cause high losses.  Choking the counterpoise further increases the feedpoint impedance, exacerbating the matching difficulty and losses.  A non-ferromagnetic transformer core mitigates the saturation, but can be unwieldly.  

I hope this helps everyone understand some of the engineering aspects of an end fed half wavelength antenna.  

73, 

Jim, W8WTS

-----Original Message-----
From: NCC [mailto:ncc-bounces at contesting.com] On Behalf Of Anthony Luscre
Sent: Sunday, September 15, 2019 2:57 PM
To: Robert Hayes <kw8n at aol.com>
Cc: North Coast Contesters <ncc at contesting.com>; MRRC Mailing List <mrrc at contesting.com>
Subject: Re: [NCC] EFHW? Any experience?

I have used one for the last 3 years as part of my portable FD setup.
I used the 132 feet MFJ-1982HP EndFed 1/2 Wave 800W 80M-10M Wire Antenna.
It was up about 25 ft in surrounding trees. It worked well on 80, 40 & 20M.
I had no problems with RF getting back into the radio, but as usual, I was only running 5 watts.

On Sun, Sep 15, 2019 at 2:10 PM Robert Hayes via NCC <ncc at contesting.com>
wrote:

> Has anyone tried any of the End-Fed Half Wave antennas?
> I have been a current feed kind of a guy, but this could handy for a 
> simple quick temporary all band antenna when travelling.  (And 
> recognizing the patterns on the higher frequencies will not be broadside to the wire).
> 73 Bob KW8N
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