Qubical Quad 7 el 50 MHz (en)

To build the antenna, I used technical information and calculator from http://n6ach.com website.

Be careful: you should use the frequency of resonance 52.120 MHz, because this will be the best to work in the most useful range (50,0 – 50,5; SWR: 1,1 – 1,2). This is not a mistake. I built the first testing version of 6el QUAD 50MHz two years earlier and then I used the 50.150 frequency to do the calculation. It turned out that parameters that the antenna has now, it had on 2MHz lower height and, unfortunately, I didn’t cope with tuning it up, even during trials like changing of the height, adjustment, distance, etc..

After making these experiments, I built 7el antenna, made of suitable, long lasting materials (pictures below).

Basic materials:

1. Graduated boom, square profile 35x35mm (3m) + 30x30mm (2×1,7m), lengths approximated, one element is put into another, protected with screw from displacement, lenghts of particular elements should be matched so there is no need to drill simultaneously in two elements of boom in place of installation of pipes to rods.

2. 12mm pipes each 30cm long (14 pieces) for insulating rods, perpendicular to the boom, holes should be drilled precisely at right angle.

3. Fiberglass insulating rods 10mm thick and 1m long, grinded (drill, sand-paper) to slip them easy into pipes, protected with screws from displacement.

4. 50mm thick pipe mast with boom nailed with ready-made holder from market (a little bit above the rotor).

5. Sailing strings used as bindings to suspend antenna, because of its weight and span.

6. 1,5mm2 wire to make the antenna (squares), band clips for binding the wire ( in place of binding the wire there should be drilled holes with band clips in them to protect from displacement).

7. Gang box to protect the connections with concentric cable, I used electrical tape to bind the concentric cable (there is possibility that band clips will do some damage to the concentric cable).

8. Mast – in my case, antenna was installed on 10m height – military telescopic mast with stay anchors.

The antenna is powered directly as it is shown in the pictures and it didn’t require tuning up, it achived 1,1 – 1,2 SWR in range of 50,0 – 50,5. Maybe there will be another chance to do precise measurements and save them as graphs. After local trials, it seems that parameters of the antenna shouldn’t diverge those factory ones. The only one material problem is to get the insulating rods, other materials are available without any problems. According to making of the antenna, you need a little bit of patience, space and, particulary, precision.

The antenna is powered by about 40m of H1000 cable and connected with 5m of H155 cable. As it is shown in the pictures, the antenna is installed directly on solid rotor YAESU G-1000 so it doesn’t cause unnecessary stresses of rotor elements during strong winds.

Generally, the antenna works faultlessly in spite of 2009 disadvantagous propagation for Poland in comparison with other European countries. I coped with connections with 8R1DB, D44TD, etc. and I recieved very good raports from European stations, usually above S9.

73, Greg SP5LGN

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