Topband: WD-1A 2-way Beverage

[RA6LBS]

Hi Dave!

Вы писали 22 ноября 2008 г., 23:19:36:

> Is anyone here using WD-!A wire for a bi-directional Beverage having
> success? I notice that mine performs very good in the forward 
> direction, but has severely reduced gain in the reverse direction.  I 
> would like to hear if others are experiencing this reduced gain in 
> reverse direction. I did not notice this with my old 2 
> wire  bi-directional Beverages (which I replaced with the WD-!A wire).

> I am not sure I am setting up correctly. MY measured SWR is good 
> (less than 1.5) in both directions through 10 mHz.  Any thoughts will 
> be appreciated. I am closely following the ON4UN Antenna Book design 
> and am in agreement with Tom, OH2BEN' who is using the same design.

The WD-1A, as all his brothers all around the world, have some
attenuation at our frequencies of interest (1-7 mhz) when serving
as a transmition line. And that`s the mode in reverse direction in a
bi-directional Beverage antenna. This attenuation is responsible for different
signal levels from "forward" and "back" direction of reception.
The transmission line impedance of WD-1A is around 170 ohms by the way
in Russia, Finland, Germany, UK and Iam pretty sure in US too.

The  value  of  attenuation  in  a  transmition  line mode depends on
the insulation material used by manufacture but seems to
be near the same around the world and equals around 6 db per 300 feet
at 1,8 mhz.

Signals from the back direction will be around 9 db down from the
forward direction at 600 feet. And RF signals from Back direction of
reception is not "injected" at feed point, so direct multiplication of
attenuation by length does not play here.

And this prevents us to use WD1A in a  bi-directional Beverage longer then
about 600 feets. While there are some reports of success while
using it at a greater lengths. It depends on a noise floor of
particular QTH by the way.

The  WD-1A and similar CAN be used while at a modest lengths. Up to 200 meters =
600 feets from my experience and direct A/B test with classic
Beverage antennas. The  reverse  direction  will  be  greatly
attenuated while extending the line over.

YMMV of course.


The wire is great for its strength , simplicity of installation and
should be regarded as a good starting point for us - small pistols -
who cant make it longer or for some other reasons.

One should remember also the vertical pattern difference at say 6000
and 1200 feet length of Beverage antenna.

And they are still quite usable in a staggered and broadside arrays of
course.

The number of transformer turns using BN202-73 is 2/(2+2), 2/5 and (2+2)/5
for WD1A feed with 50 ohm coax while antenna at 6-8 feets.

When feed with 75 ohm line the numbers are 3/(3+3) 3/7 (or 8)  and
(3+3)7 (or 8).
  

-- 
Andrey
RA6LBS/AB2ZB                          mailto:ra6lbs at volgodonsk.ru
                                 
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