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ANTENTOP- 01- 2011, # 015

Multiband Vertical Stub Antennas

Disadvantage of the antenna (Figure 1) is not smart design. It is needed at least two spacer to build the antenna. So it was created antenna without any spacer. Figure 2 shows the design of the antenna. Parameters of the antenna (Figure 2) are almost equal to the antenna shown on Figure 1. Disadvantage of the antenna (Figure 2) is that the base distance is almost twice more longer with antenna from Figure 1.

MMANA file may be downloaded from: ant_2.maa

At the 40- meter Band the antenna has some disadvantages. First is the narrow bandwidth. As usual the bandwidth is not more then 60- kHz at SWR 2.0:1. Satisfactory SWR may be reached only at one portion (CW or SSB) of the 40- meter Band. But the disadvantage is common for all types of the shortening antennas. The problem may be solved if it would be used additional relay to switch two matching capacitors- one for CW portion and another one for SSB portion of the 40- meter Band.  Next disadvantage (that is also common for shortening antennas) is less gain with lambda/4 vertical antenna. However the gain of the antenna would be only less in 2- dB compare to lambda/4 vertical antenna.

So what is about a multiband antenna that is in the header? There is still spoken only about two Bands antenna. Figure 3 corrects the situation.

MMANA file may be downloaded from: ant_3.maa

The antenna works at 15 and 10- meter as Open Sleeve” antenna. Such design already was done by me and written off in Reference 3. It is possible to add wires for WARC as it was made for 15 and 10- meter Bands. Additional wires between gamma match and antenna wire (it is only for 40- meter Band) provide screening this antenna parts one against another. It allows decrease distance between the parts. So there is needed smaller spacer. By me was used  spacer in 450- mm length.

Adjusting and Matching of the Antenna: For tuning the antenna it should be used a SWR- Bridge or usual SWR- Meter.

At the 20- meter Band the antenna is tuned in to resonance by the height. At the 40 meter Band antenna is tuned by several steps.







Figure 2 Vertical Stub Antenna for 40 and 20- meter Band without Upper Spacer



At first antenna is tuned by the capacitor C1 (see Figure 3). Then antenna is tuned fine by changing width. Then antenna again is tuned by C1 and tuned fine by changing width.  It is needed several step to have the antenna tuned. After the antenna is tuned to 20 and 40- meter Band the 15 and 10 meter Band should be adjusted. It should be made just changing length of the proper to the band wire.

Antennas shown on Figure 1, Figure 2 and Figure 3 were simulated in MMANA in case to be installed those ones close to the ground (or equivalent of the ground- metal or concrete roof). For the installation several (the more the better) non- resonance counterpoises (4- 6 meter length) may be used with the antenna.




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Last Updated:

February 15, 2018 21:27