OT:G5RV thoughts

[n7ws]

I realize that this is off-topic but allow me a few
thoughts about the ongoing G5RV discussion.

I have placed Varney's original paper here:

www.k6mhe.com/n7ws/G5RV.PDF

Reading this will reveal the following:

1. Varney *did* intend to operate the antenna on
multiple bands, although 20-meters was the design
center frequency.

2. A version with an all open-wire feeder *is* still a
so-called G5RV.  Varney even specifies that a version
*without* the coax is better on some bands.  

3. The only thing "magical" about the antenna is the
choice of radiator length.

4. On 20-meters, the open-wire section of the coax-fed
version *is not* a "matching section" but an impedance
repeating section.

5. Varney repeats an often made error when he states
that some part or another of the antenna resides in
the open-wire line, i.e is "folded into the feeder."
If this were true we wouldn't need acreage for
operation on 160-meters.

Wes  N7WS




       
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[N2EY]

In a message dated 5/19/07 11:02:07 AM Eastern Daylight Time, [hidden email]
writes:


> www.k6mhe.com/n7ws/G5RV.PDF


This is the 1958 article, which states that the antenna was designed in late
1945-early 1946, but does not refer to any earlier article.
>
> Reading this will reveal the following:
>
> 1. Varney *did* intend to operate the antenna on
> multiple bands, although 20-meters was the design
> center frequency.
>

Yup. The antenna was specifically developed for the limited space he had in
North Buckinghamshire, and he wanted coverage of 160, 80, 40, 20 and 10 meters.
15 was not a ham band then, and for 160 he tied the feeders together and fed
it against ground as a toploaded vertical.

> 2. A version with an all open-wire feeder *is* still a
> so-called G5RV.  Varney even specifies that a version
> *without* the coax is better on some bands.  
>

Yup. He specifies in the diagram that the feeder should preferably be a
multiple of a quarter wave at 20 meters.

> 3. The only thing "magical" about the antenna is the
> choice of radiator length.
>

I disagree! The choice of feeder length plus radiator length makes it easier
to match , in either version.

> 4. On 20-meters, the open-wire section of the coax-fed
> version *is not* a "matching section" but an impedance
> repeating section.
>

Agreed. On 20, the antenna is essentially 3 half waves long, which means a
feed impedance of 100 ohms or so, nonreactive, depending on antenna height. The
34 foot openline feeder just repeats that 100 ohms nonreactive to the other
end.

> 5. Varney repeats an often made error when he states
> that some part or another of the antenna resides in
> the open-wire line, i.e is "folded into the feeder."

I wouldn't call it a mistake, but it can be a very confusing image.

What is meant is this: In the case of a resonant dipole, where the antenna
wire itself is a resonant length, the feedpoint is nonreactive;  that is, the
feed impedance is a pure resistance at the resonant frequency. If a feedline of
the same impedance is connected, it will operate without standing waves, and
can be of any length without affecting the match or impedances.

But with a dipole that is not resonant, such as the G5RV on 80 meters, the
feedpoint is reactive - the impedance there has both resistive and reactive
components. If a feedline is connected, it will operate with standing waves. And
there will be points on the feedline where the impedance is a pure resistance.
If, at that point, the feeder is connected to a second piece of the correct
impedance, the second piece will operate without standing waves.

IOW, if the length of the antenna and feedline are chosen correctly, the
entire *system* will be resonant, and the impedance at the shack-end of the line
will be easy to match.

Of course in practice there are lots of compromises because the bands aren't
in perfect harmonic relatiionships (the center frequency of 40 meters isn't
exactly twice the center frequency of 80), there are end effects and ground
effects, etc.

> If this were true we wouldn't need acreage for
> operation on 160-meters.
>

Not exactly. A double-sized G5RV could be made - 204 foot flat top and 68
foot feeder, and the same principles applied.

---

The thing I find fascinating, at this point, is that while there are many
references to the antenna having been developed in 1946, nobody has yet found an
article describing it before 1958. Perhaps it was just passed around by
word-of-mouth until G5RV got around to writing it up in 1958?

73 de Jim, N2EY


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