MODIFICATIONS of the Spiderbeam (Version 1)
-----------------------------------------------------------------
Note: These modifications apply
only for version 1, today version 2 is delivered.
Two different types of modifications were performed
on
this antenna,
which already has very remarkable data:
1. Nicer look (mecanical):
Flat construction instead of bonded
fiberglass tubings, as well as using nearly
invisible guy lines. This also helps
to reduce detuning, caused by rain.
(The original tubes are used, just modify the length
of the guy lines).
2. Electrical:
With the target to reduce the SWR
on 10 m band, having sufficient bandwidth.
The modifications improve the antenne on all bands.
Pictures showing the new design:
- Picture 1: Modified
antenna with operator
- Picture 2: Modified
antenna
- Picture 3: Feeding
and supporting wires
Mechanical:
Guy lines.
Chapter 3.3 (construction guide) start with the 4
upwards
guy lines.
Turn buckles were added in the 4 upwards
guy lines to set the exact length
to hold the tubes in a flat horizontal position.
The turn buckles connect to the vertical mast with a
40
cm kevlar rope in a loop.
The 4 horizontal guy lines
were replaced by 1mm Monofil line (this is the same line
as fishing line, just somewhat heavier and UV-protected type),
bringing 2 important
advantages:
- The rain water is absorbed by the kevlar which
becomes
slightly conductive. This produces
a detuning of the nearby elements. Monofil
line remains unchanged by water, and
detuning is eliminated.
- Furthermore, Monofil line is nearly invisible and
improves
the look of the antenna.
The knots in these ropes are replaced by snap
hooks (carabin hooks).
- Close the open ends of the fiberglass tubes to prevent accumulation
of water.
The 4 downwards guy lines
are also replaced by 1mm Monofil line.
This helps to improve further the look of the antenna.
Also here the lines are
connected by snap hooks, which make the disassembling
of the antenna much faster.
Electrical:
The lowest SWR on 10m without modification was 1.5 and
here
are the values
which I measured on the original beam.
Then, I measured the balun, terminated by a
non-inductive
50 Ohm resistor.
The result was: Above 25 Mhz, the SWR began to
increase,
reaching 1.5 on 10 m.
This was corrected by adding a capacitor of 30 pf in
parallel to the output.
To obtain the required space to install the capacitor,
the housing may not be
filled with Epoxy in the segment of the output screws.
Also the separator next to these
screws is left out. Here the capacitor may be fitted.
See picture on page 19, construcion guide.
(Use Silver Mica capacitor 30 pf or 33 pf 500 V, or air
trimmer capacitor).
Make sure to seal the ends of the coax with Epoxy to prevent humidity inside the coax.
Applying this modification, the SWR of the balun remains at 1.0 up to 40 Mhz.
Now, the SWR of the antenna already improves.
But in order to reach a value lower then 1.1, and to
remain
below 1.5 over
a segment of 500 Khz on 10 m, the elements have to be
further optimized.
The new data was received by optimizing wit the NEC
program (4NEC2).
Here follows the new construction data:
(The additional length for the junction wire/monofil
is included)
Band
Reflector
Director1 Director2
------- ------------
------------
------------
20m
1049cm
988cm
15m
699cm
655cm
10m
524cm
490cm 485cm
Page 12
WIRE LENGTH of the elements
Band
Reflector
Director1 Director2
--------
------------
------------ -----------
20m
222cm
234.cm
15m
253cm
295cm
10m
315cm
319cm 435cm
Page 13
Length of the MONOFIL line
Band
Reflector
Director1 Director2
--------
-------------
------------ ------------
20m
510cm
485cm
15m
275cm
315cm
10m
216cm
183cm 409cm
Page 15
Distance of elements on boom (measured from the center
of antenna)
Note:
Page 14, 4.2. Final assembly.
The cable-ties an the ends of the spreaders: Mount the
cable-ties at a
distance of 4.95 m instaed of 5 m, when using above
construction
data.
The dimension of the feeding dipoles remains
unchanged,
however the
following has to be observed:
The feed point is 60cm above the center plate,
as
described
on page 20.
Keep a distance of 12 cm between the 15m and the 20 m
dipole.
Tie slightly together the two hose pieces upwards from
the balun to obtain the
required wire distance.
The 10 m dipole runs parallel to the 15m dipole at a
distance of 11 cm.
Do NOT fold back the ends of the dipoles as
suggested
on page 21, as the wire
may brake this way. I suggest to fold the free ends
back
by forming a radius of
about 1cm. Adjustment is done by bending the ends
closer
to the wire ore by opening
the ends wider without the danger of wire break.
The result of the full optimization is the low SWR
on
the 10m Band, and further
improvement of F/B ratio and bandwidth on the other
bands
without loss of gain.
The measured data of the modified real antenne
confirms
the expected result.
Here is the measured data,
measured with an antenna hight of 10m above ground.
The first QSO with the modified antenne on 20m with
Alfred,GI6FHD
gave a report
of S9 in foreward direction, and S1 in backward
direction.
After a CQ call on 15m a pile-up from Japan began,
which
allowed to contact
11 JA-Stations within a few minutes.
The rig on my end was the small TS-50 (max. 100 W PEP)
running on the car battery.
What more do we want ?
Finally, I have the following
suggestion:
At the junctions between the
elements
and the Monofil line, a 4 cm polyamide hose
is filled with Epoxy.
For me, this is a very time
consuming
and complicated job.
Instead, I use Silicone Sealant
in tubes, as you find it in DOY Shops.
This is easy to work with and
hardens
sufficiently in 24 h.
It is weatherproof and
UV-resistant.
I am interested in obtainig your feedback after the
construction
of this antenna. Thank you.
- My E-Mail address : see here
With my best 73s - and good DXing
Felix, HB9ABX
Many thanks to Dave HB9KT, Hansjörg HB3YDA, and
Max HB9BKS for the active participation in these extensive
antenna tests.