Saturday, February 25, 2012



Technical informations
The principle of this antenna is very simple: a normal 3 element Yagi with Director and Reflector in a V-shape.
The resulting antenna can be built using wire elements strung on a supporting cross.
The creator of this antenna system is Dick Bird G4ZU, in the ARRL Antenna Compendium Vol.3 he published this antenna project to single-band 10 meters and named it  “Bird-Yagi”.                                                      
The concept behind this antenna was developped by Cornelius Paul "Con", DF4SA. He has done a lot of work and development to a multi-band version he called "SPIDERBEAM".

Antenna parts

The antenna is constructed with a 7+ meter Vertical rod, 4 Horizontal rods at 2.75 meters each on a cross system all attached with simple copper-wire.

Antenna requirements summary
This antenna is perfect for Dx'peditions as it is:
1. Light (only 2,7 kg including a 8 meter fibreglass pole)
2. Easy to errect (no bolts or screws/5mins max)
3. No impedance adaptor or balun required.
4. Max power capability of 2kw.
5. Tough and durable (professional fisherman type fibreglass rods used)
6. Easily transportable (folds down to 1 meter)
When installing beam antennas it is better to get them errected as high as possible, because an antenna with less gain errected as high as possible will produce a better signal than one of a higher gain errected at a lower height.
It´s low weight makes it much easier to put the skypper-beam higher up and choose better locations.
Use it while travelling, activate a nearby mountain, island, castle or lighthouse, put it on the roof for a contest weekend, this antenna goes everywere you need high gain and very good performance!

Antenna Performance
forward gain is about 5dBd (7,2dBi) in free space (= 12dBi in 8m height above ground) and stays nearly constant over the whole band.
F/B ratio is about 25dB or better
SWR stays below 1:1
BANDWITH: 26,5 to 28,5 down swr 2:1

On-the-air test´s confirm these results.
These are the simulations in NEC2 with the software “Antenna Optimizer”.
Like you can see, the pattern diagram is very selective, with noteable front-to-back performance around 27db . The vertical diagram pattern with the antenna at 8 meters height, presents the elevation peak at 18° with 12,14 dbi and 5,14dbi at 5°.

Free Space

Antenna 8 meters above ground

Vertical polarization
This is the next development of the Skypper beam: "the vertical polarization"!
It's very easy... it´s necessary to use only one 2 arms (and not 4) of the central cross, junted of the vertical pole with a isolant rubber.
Off course the gain are more low of the horizontal polarization, but the vertical radiation patterns are very interesting.

                                           Avertical polarization:  4 meters above ground

Comparsion with other antennas

This is the comparsion with other antennas ( Dipole, Vertical, X-Beam, Hex Beam, Moxon, 2&3 element yagis,1-2&3 element Quads).  All these antennas have something they are good at and this type of comparsion does not necessarily show the best features of each. For example, the X-Beam can have a low F/B ratio at high gain which I like as a contester;  the hex beam construction lends itself to multi-banding; the Yagi is good for interlacing, the vertical has good radiation at low angles, some are easier to match impedance,  etc, etc. More informations on:
They are the parameter charteristic of this antennas, developed with AO software...
All modeling done in "Free Space", 27.6 MHz, Resonant (reactance=0), Al 6063-T832 tubing, dBi gain units, 20 segments/half-wavelength = ~21" / segment.
AO varies the dimensions of the antenna to best achieve the tradeoff specified, which were Gain 40%, F/B 40%, and Rx=0 20%; this results in an optimization that may be different from other comparisons.

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