On Mon, Mar 31, 2025 at 03:20 PM, Joe WB9SBD wrote:
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
When I started in ham radio, 46 years ago, indeed almost nobody used baluns with dipole antennas. Nowadays instead it's very common to use them, and there are at least two good reasons for this change!
One reason is interference between radio equipment and other stuff in the home. Computers, switching power supplies, TVs, even refrigerators and lamps. When no balun is used, the feedline is part of the antenna, so the antenna extends into the shack and the home's electrical wiring, severely worsening the interference situation. With a balun that's working ideally, the feedline does not radiate, and does not receive signals, so is not part of the antenna. That moves the actual antenna out of the home, away from the switching power supplies and other stuff, reducing the interference both ways. Back before the 1980s this wasn't such a big factor, because there were no switching power supplies, no computers, no LED lamps, no CFL lamps with electronic ballasts, no LAN, and so on. TVI was the only point of concern, and sometimes handled by establishing time schedules for ham operation and for TV viewing. But today it's an important factor, because there are so many interference-causing and interference-sensitive things that it's not acceptable to turn them all off by a schedule.
The other reason is how hams assess the condition and usability of their antennas. In the "good old times", the test was whether the transmitter could be loaded up into that antenna, without arcing, and how many contacts it produced. The antenna would be cut by trial and error to such a length that it worked well enough with that one specific feedline, in its fixed position. At most a ham might measure the SWR, but many didn't even have an SWR meter. Today instead, with instruments like the nanoVNA, hams have become scientists, trying to understand exactly what's going on, and will discover things like the antenna being resonant outside the band and operating on one the sides of the resonance dip, or that moving around the coax cable will change the SWR, or that adding even a little piece of coax will drastically change the impedance, shifting the resonant frequency. So they prefer to use baluns, to reduce the sensitivity of the antenna's parameters to feedline conditions, in order to be able to at least begin to understand what's happening with their antennas, and to achieve a setup that works more like theory tells.
I began using baluns in 1989, when I got into packet radio, and needed to run a computer at the same time as a radio, and interconnect the two, hopefully without causing feedback loops.
About that 172MHz dipole, I would expect it to measure differently according to its position relative to the nanoVNA and other stuff, to be sensitive to feedline length, etc. The usual stuff. If a balun is added, I would suggest a current balun, since we don't know how the antenna will be oriented, what will be close to it, but we do know that we want the lowest possible common-mode current on the feedline.
