ANTENTOP- 01- 2011, # 015

Multiband Vertical Stub Antennas

Roman Sergeev (RN9RQ)

Credit Line: http://www.cqham.ru/ant97_64.htm

Before describing of the antennas I would like to talk why those ones were designed. At fall 2009 the Youth Collective Radio Station RK9QWN had to change room inside the building. Old antennas were removed because the roof was repaired. So it needed to install new antennas.

The question was- what should be the antennas like?

Once night I was digging up models of antennas bundled with Antenna Simulator MMANA – GAL (may be loaded free, see Reference 1) and thinking about antennas for limited space. Among butch of the antennas I found of an interesting antenna for the 20- meter Band (model /ANT/Match/Short-Gamma-dipole.maa from the Antenna Simulator MMANA).

It is very interesting antenna. In Reference 2 Igor Goncharenko treats the antenna like a limit case for shortening dipole with gamma matching (when the gamma matching equal to the length of the shortening antenna). At the other side it is usual stub dipole. For future development of the antenna please take attention that the dimensions of the antenna would be resonance at 10- meter Band. On the base of the two antennas was designed my antenna for two Bands-  the 20 and 40- meter. Figure 1 shows design of the antenna.

MMANA file may be downloaded from: http://www.antentop.org/015/ ant_1.maa

Adjusting and Matching of the Antenna: Antenna has input impedance 150 Ohm at the 20- meter Band. At the Band antenna is tuned in to resonance by the height. At the 40 meter Band antenna is tuned to resonance by the capacitor C1 (see Figure 1). At the 40- meter it is possible to play with input resistance of the antenna by changing wide between the antenna wires. C1 just compensated the antenna reactance. Relay K1 is switched ON/OFF the capacitor that is provided the changing of the antenna Band.

Figure 1 Vertical Stub Antenna for 40 and 20- meter Band

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