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Last edited - 7th May 2017
Today I made a portable end fed antenna for 80m band. The chosen location was Universitatea de Stiinte Agronomice si Medicina Veterinara, Bucharest/Romania.
End fed antenna will consist from a halfwave radiator which is actually a dipol fed at one of its ends, not at its center, and a counterpoise. The counterpoise is piece of wire offering some capacitance in order to energize the halfwave radiator, like a virtual ground.
For 80m band, halfwave radiator will be about 40m in length while the counterpoise can be variable in length, depending of the impedance adapter. End fed antennas will have the impedance somewhere in between 1000 to 5000 ohms. My impedance adapter will match 50 ohms to 4000 ohms.
After some measurements the wire was cut about 40m long. A 6m fiberglass fish pole was used to erect the halfwave radiator from its center. The impedance adapter attached at one of its ends and a counterpoise about 15m long continued from adapter thrown on the ground. Using my QRP SWR bridge, I was able to set the antenna impedance to 50 ohms while gently adjusting the impedance adapter and counterpoise length. The length of counterpoise is critical in order to match 50 ohms precisely. The bridge was removed from antenna circuit and the electromagnetig field strength meter was used to further find the peak of radiated power.
Some photos (click to enlarge)
My homemade 80m SSB transceiver put a power of 4W on the antenna. At the first call on 3705KHz, nobody answered. Tried again, and again... nobody! I was worried about this issue, so I changed the frequency. On 3790KHz I heard a russian governmental service which was a good sign though. I verified again radiation from antenna with my EMF meter. At the ends of radiator I've got full scale deflection (on 0-500mV scale) and lower readings to its center. Maybe nobody was on the frequency during daytime, I checked my self on a WebSDR located in Greece, about 900km away, and I was able to hear my CW signals.
Unfortunately nobody answered to my calls during the daytime, between 13-15 o'clock. So my first attempt to test the end fed antenna was unsuccessful despite the fact that it seemed to work pretty good, no SWR, maxium radiated power. Maybe that 4W was not enough to communicate during daytime on 80m, maybe the location was no so favorable or just maybe there was nobody. Therefore, I'm planning to give it another try next weekend into another location.
Somebody laughs at me :P
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