By Serge V. Satyr, RW3XA (ex: UA3XBY),

Obninsk, Russia

rw3xa@qsl.net

Translated by RW3XW

Credit Line:

http://www.feerc.obninsk.org/rw3xa/ant/gpxa_en.htm

Made in Russia

As a rule, we need taking some steps to make any antenna to be resonant on several amateur bands. The body of the aerial needs some special constructive elements to tune it into a resonance within different amateur bands. These elements can be concentrated (LC, L, C, for example, Cushcraft R7000 (http://www.cushcraft.com/amateur/r7000.htm) or distributed (loops, lines, for example, GAP-Titan (http://www.gapantenna.com/titan.html ). I.e. the antenna is broken up into several parts in between which there are those adjusting elements providing a resonance of the aerial. The more such elements, the more difficulties with their optimum adjustment, and reliability of a design as a whole leaves much to be desired because it is cut by insulators.

Certainly, because the aerial is a multiresonant one, it is enough to change the band in the transceiver - simple and convenient, but not so good if your neighbour HAM is on the air too - rustles and clicks from the signals is usual business even if he drives the different band. The multiband vertical can be made upon the other constructive principals: the radiating part of the antenna through a switchable matching network to the feed line. In the other word, input impedance of a random wire is of a complex value, so the matching network transforms input impedance of it into feed line impedance.

Naturally, for the reason of an accurate matching on each amateur band it is necessary to separate matching networks. In fact the common multiband matching is not the best choice - it is very difficult to achieve accurate matching (in fact for different bands matching circuits may be different) and to provide necessarily good quality, accordingly, will be more losses than for the separate network. As for the similar designs it is of a rare issue (for example QST (http://www.arrl.org/htdig/?q=Modest+45+Foot+DX+Vertical&cmd=Search!), Titanex (http://titanex.de/frames/gp.html) though they have some advantages before the other verticals. For example:

  1. Mechanical durability of the vibrator because of absence of insulators.

  2. An opportunity and convenience of the optimum adjustment of VSWR at the antenna-feeder point (i.e. network adjustment).

  3. Simplicity of installation due to lightweight aluminum tubing (except for capacitor loading above in my case).

  4. Greater selectivity due to the switching network of the antenna, better suppression of unwanted signals and harmonics of course.

  May be it sounds crazy, but this antenna realization is my former idea of using any random wire as HF multiband, of course except for the telescopic aerial of a household radio receiver 1 meter long, though I had similar experience nearly 20 years ago - RLT (short distance field test) on 3.5MHz... So, this time I'd like to share these results with those who may be interested in. Of course it's not a panacea and the full-size one band antenna would be the best choice, but in a series of multiband aerials, in my opinion, the given design obviously is worth considering of, especially for those who does not have enough space to set up something extraordinary, but DX chasing would be of desire.

Naturally, "random length" means reasonable length at which theoretical efficiency on the lowest frequency (1.8MHz) would be of at least ten percents, so the total length should be at least 10 meters long. Further, by means of separate LC matching network for every HF band, the aerial will be matching 50-Ohm active load, then the 50-Ohm coax feed line can be of any length. So the block diagram is just like this: the mast itself - the switched matching networks - the coax feed line. This vertical antenna is without traps, loops and similar mechanically unreliable elements. In simple words it's just telescoped aluminum tubing. And for some electric lengthening there're four wires top-hat folded capacitive loading at the top of the mast is used.

http://www.antentop.org/

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