Home |
Search |
Today's Posts |
#12
|
|||
|
|||
OK, let's discuss dipoles vs length
Jeff Liebermann wrote:
On Sat, 11 Oct 2014 11:47:22 -0500, John S wrote: Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. Sounds about right except that it doesn't include any losses introduced by the necessary matching network and real ground losses at HF frequencies. Expanding my table to include radiation efficiency: There is no feed because it is the ANTENNA that is being analyzed, not an antenna SYSTEM. And while I don't know if the simulation included it, NEC can include the ground losses for the ANTENNA. http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain Radiation wl dBi Efficiency 0.050 4.75 99.09% 0.125 4.85 99.66% 0.250 5.19 99.93% 0.500 6.96 99.97% 0.625 8.01 99.93% In other words, there's nothing inherent in the length of the radiator that would affect radiation efficiency. If there is a drop in radiation efficiency, then it's mostly due to ground losses, material losses I2R, and matching losses). Ground and I^2R losses of the antenna are shown by NEC. Matching losses are NOT part of the antenna. I invite discussion in any case. NEC: Power Efficiency vs. Radiation Efficiency L. B. Cebik, W4RNL http://www.antennex.com/w4rnl/col0504/amod75.html Lots of examples of how "efficiency" calculations work, and how various common antenna configurations affect the results. (I need to re-read the article as there's plenty about this which I don't understand very well). Test cases 5 and 6 are short monopoles, which should have something to do with short dipoles. From the bottom of the page: "Unlike the vertical monopole, the horizontal dipole shows much more regular changes of radiation efficiency with changes of soil type, ranging from 80.01% over very good soil to 65.93% over very poor soil." Yep, and once the issue of size versus efficieny is put to rest, it would not be a bad idea to look at the real effects of ground, both in terms of height in wavelengths and soil quality. -- Jim Pennino |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Real Oil Drillers Discuss MC 252 | Shortwave | |||
Discuss about books | Shortwave | |||
OT , You may need to discuss this . | CB | |||
Anyone care to discuss... | CB | |||
Art Bell to discuss BPL on C-to-C AM TONIGHT (??) 3/20/04 | Policy |