High gain bets Beams

Once I heard Don Wallace W6AM and a neighbor comparing antennas on 20 meters. Don was running one of his rhombics aimed toward Europe.  His neighbor said he was running a 5 element mono-band yagi at 150 feet.  Anyway while I was listening they compared the two antennas getting comparative signal reports from many European stations.  Don's rhombic was almost always at least 20dB stronger than his neighbor who was running the 5 element yagi at 150 feet.

I understand that theory (EZNEC) does not always predict this result, but what happens on-the-air is what separates the big guns from the little pistols. A Rhombic will truly open and close the band.

A Rhombic Antenna = The highest development of a long-wire antenna.

Each antenna a K0UO was built for 40 meters and above, with over 600 to 700 foot per-leg and +1200' end to end, 6 to 7 Acres each on 80 to 100 foot wood poles. My four antennas each cover an area equal to five football fields. The Front to Back is like a brick wall, maybe +40dB or more. That makes them 4 to 6 Wave-Lengths long on each of the four sides, or 16 to 24 wave-lengths total for 40 meters, these may be the largest 40 meter Rhombic antennas in current amateur use. K3LR may have more gain with beams using 4 over 4 over 4 on 40 meters, but he needs to rotate.

Dick  AD4U from eham.net

At the W8IJ antenna page, he makes some interesting points in his modeling of the large rhombic antenna. Note: He is not overly excited about its merits or gain per area of antenna space used. He states, "Most of the rhombic's performance limitations come from the high levels of spurious lobes and the poor efficiency (50%), especially over normal soil.  The rhombic has one of the poorest gain-per-acre rankings of any high gain HF antenna array."

However I now use a Re-entrant system which is 90% efficient by re-phasing the power back in the antenna, instead of heating up termination resistors.

It can be truthfully be said, that "a Rhombic antenna occupies more space per db of gain than any other antenna" The Rhombic is a very high-gain antenna however it requires a lot of acres, and the efficiency when terminated is only about 50%. An alternate impedance-termination system, which was only used for a few large broadcast stations where input powers were above 50 kw, is called the re-entrant line termination. Clyde Haehnlen SK, developed the specifications for the Voice of America antenna system at the Bethany, OH Relay Station. That re-entrant Rhombic was 90% efficient by re-phasing the power instead of heating up termination resistors, in this system, the Rhombic is terminated in a transmission line, which in turn is coupled back to the input through the proper voltage-matching and phasing networks. Thus, the energy in the dissipation line is fed back to the antenna, so that considerably less than 50 percent of the energy is wasted. The old VOA Bethany site in Ohio had efficiency up to over 90%. This feeds-backs the wasted RF energy "In-Phase", back into the feeder end of the antenna. For any variation from the stubs frequency, the stub must be returned.  

I am now the only station using re-entrant line termination equipment, which is re-phasing the power instead of heating up termination resistors.

Clyde provided me with design information for re-phasing a few years ago before his passing.

A rhombic antenna does have the distinct advantage of working over very wide frequency ranges with flat SWR and high gain, something a basic mono-band yagi can never do. The rhombic is also a simple antenna, requiring only four supports (three supports for the Vee beam, and one support for inverted Vee derivatives).

Some of those points can be very positive for day-to-day use of the antenna in amateur radio service, remember amateurs are not point-to-point shortwave broadcasters, military or wire services, Amateurs just want to make QSOs! Also most amateur radio operators don't have tens of thousands of dollars to spend on tall towers and stacked mono-band beams, or the ability to climb and maintain such structures. Rhombic antennas were the ultimate antenna design back in the Golden Age of Wireless. However, building one required a large tract of land and a number of tall telephone poles, because they have dimensions several times the wavelength. To most amateurs the positive thing is there are no large mono-band antennas to maintain, or rotators to fix, and rhombics allows for instantaneous direction and band switching. They normally can be installed at very low cost, if you have trees to hang them from, all that is needed is a lot of wire and time!  Also the key concept with traveling-wave antennas is that there are no standing waves, which means that the current and voltage levels are the same everywhere along the antenna conductors. So the rhombic antenna does have the very distinct advantage of working over very wide frequency ranges with flat SWR and high gain. 

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