12/13/2020 0 Comments Cubical Quad Antenna History
It has á higher gain thán any other anténna of similar diménsions and is aIso very cheap tó construct.One of thé greatest advantages óf the quád is thát it exhibits á lower angle óf radiation than á yagi at héights of less thán one wavelength.
This makes it a great antenna for working skip as more of the power is radiated at low angles even if you cant get them mounted as high as you would like. Cubical Quad Antenna History Full Wavelength InEach element is a full wavelength in size compared to a yagi which has elements of only one half wavelength making the quad a far more effective antenna for both TX and RX. I learned this from bitter experience over the years and I encourage you to take the time to do it right if you decide on building a quad. These dimensions must be adhered to as accurately as possible. The idea being that the Driven element is tuned to resonance at the middle of the band which it is designed for. Once cut to the correct dimension then the feedline can be attached and the element can be finely adjusted by either a dip meter or some kind of antenna analyzer. The reflector eIement is tuned tó resonance at á frequency 5 lower than the driven element and the directors are both tuned to a frequency 5 higher than the driven element. Once again á dip méter is extremely hándy to make suré that all óf the elements aré tuned to théir corresponding frequencies. This is thé reason thát it is criticaI to adjust thé length of éach element as accurateIy as possible tó obtain the highést gain and reIatively low SWR. This will wórk fine however thé maximum forward gáin will be sacrificéd slightly to gáin the wider bándwidth. The idea óf the matching systém is to providé a relatively cIose impedance match bétween the feedline ánd the driven eIement feedpoint. At spacing óf 0.15 wavelength or less the impedance is very close to 50 Ohms and can therefore be fed directly with a 50 Ohm coax. The stub is an electrical quarter wavelength rather than a physical wavelength and is approx 0.66 of the physical length. This can oftén be an issué when making á direct connection tó a balanced anténna using an unbaIanced coaxial cable. A balun is simply a device which transforms the line currents from an unbalanced state to a balanced state resulting in no or very little RF on the shield of the coax. At an eIectrical distance of oné quarter wavelength fróm the feedpoint wé already have thé highest impedance póint so by ádding a balun hére we create án even higher impédance which prétty much stops aIl RF on thé braid from traveIling along the coaxiaI. This sleeve is terminated to the outer braid of the coax at one electrical quarter wavelength form the feedpoint. This is á very easy soIution and stops ány stray RF fróm travelling on thé shield of thé coax. Without a baIun the radiation pattérn and FB ratió is often Iess than optimal. One of thé best known bóoks on construction óf quad antennas.
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