[TowerTalk] Beverage Termination video

[VE6WZ_Steve]

Jim,

Great explanation!

steve ve6wz

> The Beverage is a "traveling wave" antenna so in the "ultimate" case it would be infinitely long, and the power gradually radiates from the wire (and is absorbed in the ground under the wire).  The angle of maximum radiation, relative to the wire, is related to the propagation speed along the wire (which in turn is related to the height and soil properties).   The reason rhombics work well is that you have two wires at just the right angle, so the forward lobes reinforce.
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> The idea of the termination resistor is that if your wave hasn't attenuated (or radiated) much by the time it gets to the far end, you don't want it reflecting and travelling back, creating radiation in the opposite direction.  If you've already radiated most of the power, then the reflection doesn't contribute much to "backwards" radiation. For instance, if you have radiated 90% of the power by the time you get to the end of the wire, the 10% that reflects back from a mis-termination isn't going to be much of a contribution to a back lobe.
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> One way to examine it in a model would be to look at the power dissipated in the load resistor - you can get the segment current, and you know the resistance, so you know the power from I^2R.
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> There is a report online out there (I'll see if I can find it again) that has extensive measurements on traveling wave antennas (from the 30s or 40s) with different terminations, etc.
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> They were hot stuff before curtain arrays for broadcast became popular. All those HF TTY links, etc. were done with rhombics.  They're cheap and fast to install - telephone poles and wire, so they were popular for commercial point to point links.
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> And W6AM was famous for his field of rhombics on the Palos Verdes Peninsula in the Los Angeles area.