[TowerTalk] Conclusion, G5RV vs. Dipole

[n7ws@azstarnet.com]

At 11:20 AM 10/16/00 -0600, n4kg@juno.com wrote:
>
>Unless I am mistaken, there is a HUGE misunderstanding
>of how the G5RV antenna works.

And how!  

>
>The ONLY way it could act as a Top Loaded Vertical is for
>the currents in each side of the balanced transmission line
>to be EQUAL and flowing in the SAME direction.  If that were
>the case, they could be tied together or replaced by a single
>wire and attached to the two sides of the horizontal wires at
>the top.  I do NOT believe that is the case.

Actually, that is *exactly* what Varney proposed in his original 1958 RSGB
Bulletin article.

>
>IF the feed is indeed as a split balanced dipole of various 
>electrical lengths, then the ladderline is acting as a balanced
>transmission line with EQUAL but OPPOSITE currents in
>each side and it does NOT radiate.  
>
>As a balanced dipole, it acts as:
>
>3/8 wave (short ) dipole on 80M
>3/4 wave (long) dipole on 40M
>2 Half Wave dipoles in phase on 30M (Voltage Node feed)
>3 Half Wave Long Wire on 20M (current Node at feed)
>(almost) 2 Full wave LW's in phase on 17M  (near voltage node)
>9/4 wave LW on 15M (neither current nor voltage node at feed)
>5/2 wave LW on 12M (current node at feed)
>Two 2WL LW in phase on 10M (voltage node at feed)
>
>BTW, as originally designed, the ladderline was meant as
>an impedance transformer that provided a reasonable SWR
>on SOME bands (but NOT ALL) without the need for a tuner.

No, the "stub" as Varney called it, was meant as a 1/2 wavelength feeder on
14 MC/s (the notation of the day).  Varney alternatively proposed an
open-wire feeder from the antenna to the a.t.u. As a matter of fact, he
actually recommended this for the bands other than 20 meters. 

He also (mistakenly in my view) believed that on the bands other than 20
meters, part of the antenna was "folded" into the open-wire "stub."

It continues to amaze me that hams practically worship the idea of an
"all-band" antenna, where "all-band" means that by hook or crook, a "match"
can be achieved at the input to the transmission line.  At the same time,
they will tout the "gain" achieved by some number of half-waves, while
totally ignoring the fact that the "gain" achieved is often in the wrong
direction.

I just don't get it.

Wes Stewart, chief operator at N7WS

ps.  With shameless immodesty, I direct you to:
http://www.azstarnet.com/~n7ws/ladder.htm
for some more of my thoughts on related material.


>
>de  Tom  N4KG



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