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Amateur Radio

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  • $\begingroup$ This has nothing to do with infinite baluns. We are talking about loop antennas which are electrically small - only 1 percent of the wavelength (or so). Infinite baluns need to be of a size of the same magnitude as the wavelength... (1/4$\lambda$ or more) $\endgroup$ Commented Dec 23, 2014 at 14:26
  • $\begingroup$ @jcoppens Aren't they similar in that they each solve the problem of common-mode currents by making them an intentional part of the antenna? In an infinite balun, the idea is to make it long enough that the common-mode currents diminish to some negligible level. In a shielded loop antenna, the idea is to take them to a zero-voltage point, at which the feedline can exit. $\endgroup$ Commented Dec 23, 2014 at 21:06
  • $\begingroup$ @jcoppens antenna-theory.com on infinite baluns says: "This balun can be used whenever a separated ground region is available to merge the coaxial cable outside shield with one region of the antenna. Care must be taken when exiting the coaxial cable from the structure, so that the lead of the coaxial cable to the radio (transmitter/receiver) does not detune or negatively affect the antenna." Sounds very similar to what's described here, no? $\endgroup$ Commented Dec 24, 2014 at 14:53
  • $\begingroup$ books.google.com.ar/… means that the infinite balun has to act in the region where it blocks the current. A shield in an electrically small antenna evidently does NOT act as a choke. It is too small for that. $\endgroup$ Commented Dec 24, 2014 at 20:07
  • $\begingroup$ And, look at the reference you gave, @Phil. The article itself says "This balun works wonderfully. It has no bandwidth problems and is a very clever design. In addition, since the spiral antenna is a good radiator, the currents die off quickly as the spiral winds away from the center." This means that the antenna has to be large compared to the wavelength. In this thread, we're speaking about low percentages. $\endgroup$ Commented Dec 24, 2014 at 20:42