Posted by
Don Wilhelm-3 on
Mar 26, 2005; 10:52pm
URL: http://elecraft.85.s1.nabble.com/eflwa-tp376233p376235.html
RC (and all),
Actally the real term 'Long wire antenna' was reserved in the past for a
wire that was greater than one wavelength - they are in the class of
'Traveling Wave Antennas' (Vee beams and rhombics are also in this same
class), and they are fed at the end (using whatever means necessary to
properly match the antenna).
OK, enough for semantics, for your real question, any wire fed at a current
loop (an odd 1/4 wavelength multiple - counting from the far end of the
antenna) will exhibit a relatively low impedance with respect to ground,
making it easier to feed with today's tuners.
The antenna you propose is simply a dipole with one half of it near the
ground, so it should feed easily with a 40 to 75 ohm impedance range, BUT
the proximity effect of the nearby ground will be quite different on the
antenna wire and what you have termed a 'counterpoise'. The proper
electrical length is what really matters, and the length calculated from
antenna formulas will likely not work properly because of the effects of
earth below it, so your plans for an easy to feed antenna that does not
produce 'RF in the shack' may not be so easily achieved.
I am fully in LB Cebik's corner in saying that we should stamp out the word
'counterpoise' from our typical ham usage. That thing that we often call a
'counterpoise' is really a part of the antenna system - and the entire
system must be analyzed, not just the part that we intend to be the
radiator. For example raised radials on a vertical antenna (ungrounded) can
and will change the resonance point of the antenna system if their length is
changed, because they are a part of the antenna system, and they DO radiate.
If pairs of radials are arranged in physical and electrical opposition to
each other, the radiation will cancel, but I digress - what you have
proposed is not a counterpoise, it is a functioning and radiating part of
the antenna system.
RANT OFF ------
73,
Don W3FPR
> -----Original Message-----
>
> Now unless I misunderstand an EFLWA (end fed long wire antenna ) can
> be used as long as it is a 1/4 wave length of the lowest operating
> frequency and has a counter poise? 80m would be 66' as would be the
> counter poise. the K1 w/KAT1 should have no problem tuning this or a KX1
> on 40/30/20m.
> 72/71 de "rc" kc5wa
>
>
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