Vertical Vacation Antenna for 80, 40 and 20 Meter-Band, by Herbert OE3BMB
This antenna is a full size λ/4 for 20m and 40m band, and a shortened λ/4 for the 80m band.
Generally on the 40m band the SWR is under 1,6. In 80m and 20m band at the resonant frequency the SWR is about 1,1. I aligned for 3,700 kHz and for the CW-range I insert a 10 cm piece wire between feed and coil.
What do you need?
1 piece aluminium metal sheet, approx. 8 x 8cm, minimal 1 mm thickness
50 cm stranded wire 2,5 mm² for bypass
at least 10 pieces of round plugs, male and female (for wire Ø up to 2.5 mm²)...
Example for the "round plugs"
Construction instructions - PL-Socket for feeder
Ground Plan for PL-Socket
Mark first the aluminium sheet with a line in the centre. Saw in here the sheet from both sides approx. 2 cm. Drill 20 mm of the edge in the centre a 15 mm Ø hole as it is shown on the sketch. Make four small holes near the edge at the hole side*), where the four male round-connector sockets have to be soldered (remove insulation). The heads of the cases are to show outwards. See illustration. Now fix the PL-socked (the antenna connector must be on the same side as the radial-connectors), by drilling the holes and fasten it with blind rivets or small screws. (Proceeding in reverse, the soldering of the insulation of the PL-socket becomes too hot). Solder to an approx. 3 cm copper wire (no stranded wire) a male round plug. SolderThis to the PL socket center. Now bend the aluminium piece at the cuts.(see picture).
PL-Socket for Feeder
*)The diameter of the holes should have just the size, that the round plugs (without insulation) could e inserted.
Construction instructions - Coil
Now the coil must be winded. Stick on the plastic tube double-sided tape along 2 strips (better 3). Wind there - completely closely - 2.5 mm ² strand wire to 33 turns (at a coil of 53mm Ø) or 36 turns (at a coil of 50 mm Ø). I made 2 turns more, which I unreeled (if necessary) at the alignment. At both sides should be left approx. 20 cm. Strip the wire at the ends. Afterwards prepare a 9 m (antenna) and a 50 cm (bypass) piece of 2.5 mm ² strand wire.( strip the wires at both ends.
Earth Peg with PL-Socket
Fix the piece with the PL-socked by means of a hose clamp to the earth peg. The thread must show downwards. Drive out the telescope mast and put it down. Fasten the coil approx. 25 to 30 cm from the l end with a tape to the mast. Then connect the antenna wire with the bypass line provisionally by means of block clamps, alligator clips, or something similar. Lead he antenna wire to the top, and fix it with tape severaltimes to the mast. Screw in the pivot peg, insert the antenna mast. Attach the antenna to the bypass wire and attach it provisionally to the PL-connector. Connect also two radial with approx. 18 m and one with approx. 9 m and spread them out on the soil.
An additional SWR Analyzer is of advantage, but it will work with a measuring bridge (SWR meter) as well. In order to avoid troubles, align with lowest power.
First determine the point of resonance on 40 m band. If it is to low, shorten the antenna about 10 cm. If it is too high, length it with 10 cm at the top. I achieved a SWR on the entire 40 m band of 1,5. (the impedance was 35 Ω). (You can replace one long radial with a 9 m radial, but only for the 40 m band)
Attach the transceiver, ground it, and go!
With inserted pipe
To work more comfortable and for a better radiation I inserted an approx. 1.5 m long pipe between earth peg and mast (see photo). The pipe serves as a transport case for the telescope mast. Being able to change impedance and thus the SWR you may raise one or more radials on the ends. A tuner is recommended. Result: On 80 m the antenna obtains usually better results as a mostly too low positioned dipole in the vacation or fielday QTH. On 40 m and 20 m it is equal the usual groundplane antennas. There is still room for improvements, and I am grateful for relevant suggestions.
all components together
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