[Elecraft] EFHW

[K9MA]

I think what this thread is about is effective, very lightweight 
antennas for backpacking, SOTA, bicycle touring, etc.  These are 
antennas that, not including the support, weigh just a few ounces. 
Whether they could be made to work better with hundreds of long radials 
is completely irrelevant.

Without question, the EFHW minimizes resistive losses due to the high 
feedpoint impedance, and eliminates the need for a feedline. If you 
model a typical antenna of this sort, say a 66 foot wire with a single 
38 foot support, and move the feedpoint around, you will find very 
little difference in the far field.  End fed is within a fraction of a 
dB of center fed, and requires no feedline.  Even 38 feet of RG-174 
would weigh much more than a simple EFHW tuner, and the coax loss would 
be about 1 dB on 20.  Now, one could make some ladder line with some 
number 26 wire and spacers, but imagine trying to get that untangled 
every time you put up the antenna.  (Another consideration:  These 
antennas should be quick and easy to put up.)

As I said, if anyone knows how to make a better, lighter antenna, let me 
know!

An aside:  There are two major loss components when feeding any antenna 
near ground.  One is due to the resistance which appears in series with 
the feedpoint. (I'll call this the feedpoint loss.)  The extreme example 
is a short vertical fed against ground, where the effective resistance 
of the connection to ground is large compared to the feedpoint 
resistance.  Raising the feedpoint resistance will reduce this loss, the 
other extreme being the EFHW.  The other source of loss is the 
interaction of the electromagnetic field of the antenna with the ground 
within some fraction of a wavelength from the antenna.  Even a vertical 
EFHW, with very low feedpoint loss, needs lots of long radials to 
minimize this loss.  Ideally, you want to minimize both sources of 
loss.  If a big radial system isn't feasible, it still helps to minimize 
the feedpoint loss.

73,

Scott  K9MA

-- 
Scott  K9MA

k9ma at sdellington.us