[Elecraft] G5RV saga

[Christian GONDARD]

Another point of view :

I am using a 2x20 m doublet and a 300 ohms ladder line for 3 years, and I am
very glad with it, especially for its "all bands capability".

I am following with interest the discussion about the advantage/disavantage
to use a balun with this kind of antenna, which is rolling on the reflector
for some days.

Generally speaking, I think that they are no general rules on this subject,
because the impedance appearing at the end of the feed line near the
transmitter can vary in large proportions, and a balun can have very strange
behaviour/performances, depending on the bands, the length of the feed line,
the length of the doublet, the height over the ground and its quality
(resistivity). In most cases, losses in the feed line (parallel line or
coax) can be "moderate", i.e some dB and just "noticeable"; it is perheaps
not so moderate on the high part of the spectrum (21, 24, 28 MHZ), and here
a parallel line can have a strong advantage over the coax.

I want to emphasize on another side of the story, which can have, on my
point of view, a much stronger effect on the "effeciency" of the antenna : I
want to speak of the radiation pattern of such antennas, especially in the
vertical plane.

It is easy to show (many softwares compute that very easely) that this
pattern is characterized by "lobes" which send and receive HF waves in
specific directions. This is true in the horizontal plane, and that will
give some directivity to select some specific area of interest to establish
a radio contact. This is also true on the vertical plane, and that will give
the way radio waves will hit and be reflected by the ionosphere.This
interaction directly impacts on the capability to reach long distances.
Generally speaking, if you are interested in DX ing, you need low or very
low angle of radiation, that means radiation lobes in the vertical plane
very close to the horizon.

The position of the main lobe is depending on 2 main factors :
* the length of the doublet : the more the length, the higher the lobe (not
good)
* the ratio between the wave length and the height of the doublet over the
ground : under a ratio of 1/4, the main lobe is vertical (you warm the
clouds) : not good for DX, very good for short distance QSO.

And here, we are not speaking of "some dB" of losses in transmission lines;
the difference between a low lobe and a high lobe can easely reach 10 to 20
dB !!!

If you consider the situation of a "very small pistol" (or a "pebble
launcher" : french expression : any english equivalent ? !!), the antenna
will be less that 10 m (30 feet) high and 2x15 or 2x20 m long. That means
that the antenna will have a good behaviour on 40 and 30 m bands; if it is
2x20 m long it will work also well on 80 m (but main lobe will be high,
because the antenna is too low); on 20 m main lobe will be near 30 degree;
on high bands main lobe can be at 45 degree : really not good for DX ing
!!!

By the way, this is (was) my situation; I worked many DX (QRP and QRO), but
I am very patient by nature, so I spend 99% of my time to listen ; listen
and listen ..... : one day or another I am always able to achieve QSO with
rare DX stations : I need 10 days to log VP6DI, the last day of the
expedition ....

I am now using 2 kind of doublets, because I think that a single one can not
efficiently cover all the bands between 80 and 10 m.
Doublet n�1 is a 2 x 20 m doublet at 10 m high for 80 to 30 m
Doublet n�2 is a 2 x 8 m doublet at 10 m high for 20 to 10 m

The 2 antennas are spaced by 20 m and are at right angle; the separate
transmission lines are 300 ohms parralel lines (without balun) about 20 m
long. After some months of use and many A/B comparisons, I found a large
difference, especially on high bands (15 to 10 m),  at the advantage of
doublet n�2 for long distances DX : 1 to 3 S points = 6 to 18 dB ...., with
a correlated disadvantage for short skip stations ("you can not have the
butter and the money for the butter" : another french expression). Doublet 2
is also efficient on 30 m DX but it is not so clear.

I hope that this page can help in the discussion, despite my "rough" english
...

Best regards to everybody

73

Chris / F6FTB ex FB8XV / K2 #644 (waiting for the KPA100 ....)