I have worked digital LF (136kHz) for so long I am only now, during the virus lock down, returning to talking to real people and putting up HF aerials
I have put up a 20m half wave dipole and it seemed to work ok, but on 50 Watts it would kill my Kenwood TS-590S computer access software on my lap top near the transceiver. My AIM4170 showed resonance at the same point as a below 1.4 to 1 SWR minimum, and the rig's SWR meter showed under 1.5, too. It became annoying so I built an RF current meter that uses a clamp on ferrite as part of the transformer. It was a kit by the late G4HUP that I have had knocking around unbuilt for years.
http://huprf.com/huprf/rf-current-meter/ It has two ranges, 0 to 100mA range, and o to 1 Amp range. I calibrated it and on the 100mA range it takes over 5W to go FSD. I was concerned to find it banging in to the end stop when I transmitted a 50W CW carrier into the antenna, meaning well over 5W was on the screen of the co-ax feeder near the rig.
I am using a commercial 1 to 1 balun at the centre of the dipole, rated 1.5kW over a range of 1.8 to 30 MHz. It is in a sealed plastic pipe and I have never been 100% about it as the originator's web site never said, nor showed what was inside it... (EDIT) I managed to get inside it without destroying it, I have questions and photos, no ferrite beads or toroids, but they are for a different thread, and later).
So I made my own 14 metre dedicated common mode choke, winding 11 turns of RG-58 co-ax on to an FT240-52 toroid, as per the details on the late G3TXQ's web site at
http://www.karinya.net/g3txq/chokes/I replaced the commercial "balun" (and it this point express frustration that newbies like myself have to try and decipher if even commercial manufacturers mean a balun or a choke in their blurb, they seem to be used at random for different or the same things), with my home brew one. It's in the same place directly between the dipole's legs, and fed with the same RG-58 of about 50 feet in length direct to my TS-590S antenna socket.
This choke improved current on the co-ax shield to only about 2/3 deflection on the 100mA scale, so well under 5W on a 50W carrier. For some reason I decided to utilise the good advice someone on this forum gave me, to put the hanger ropes on pulleys, and to try shifting the dipole along, horizontally. One end is getting into the edge of woodland, the other leg is near (within 15 feet) of my lattice work 40 foot wind up mast. I am glad I did have this idea as it was immediately apparent even movements of 15 feet, horizontally, made a big difference. Further towards to the edge of the woods made things very quickly worse. So did bring one leg nearer the steel mast. I experimented further and found a "sweet spot" where no RF current meter deflection occurred at all.
So what do I make of all this? Are objects UN balancing the operation of the dipole so one leg is "working harder" than the other?
My questions are, is this due to the dipole being near trees and / or the steel mast? Should I worry? I think I must if it also puts a lot of RF on the feedline braid.
Finally, and in some ways mainly, I am still far from clear as to whether a half wave simple dipole should have just a simple choke (a toroid of type X wound with Y turns of co-ax, the feeder co-ax to one end of the single winding, the legs of the dipole to the other end)? Or do I need instead, or as WELL, a true BALUN, in my mind a toroid with more than one winding, it's main purpose being mating an un-balanced coaxial feedline to what is a hopefully balanced half wave dipole antenna?
Thanks for reading! Any advice very welcome, thank you.