Any dipole antenna design that requires ferrite toroids is wasting transmitter power due to the mismatch between the rf cable and the antenna elements. The usual situation is the cable has a characteristic impedance of 50 ohms; the antenna should have an impedance of 50 ohms for optimum rf power transfer. For a simple dipole that is good for a single frequency. When you transmit at other than that design frequency, rf power is reflected back to the transmitter and has to be absorbed in the power output stage. That action causes the transmitter to run hotter and tends to decrease the operating life. You also get less energy transmitted for less communications range. Works the same for reception: the antenna sends less signal down the cable to the receiver. The ferrite toroids absorb the reflected energy due to mismatch to keep the transmitter happy, but the net result is less rf power transmitted and less signal reception. On the positive side: copper tape and toroids are relatively cheap. A better antenna design would use baluuns. These are a type of rf transformer that provides optimum impedance matching over the entire operating band. Problems are you need more real estate at the antenna to mount it and the price goes up. Pays your money and takes your choice.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ------------------------------------------------------------------------------------------ I ordered my first antenna kit from RST way back when I was building N56ML, and that antenna worked fabulously. When I bought N891JF over two years ago, it had serious antenna issues, and I thought I'd need to build another one, so I ordered another kit from RST, but then corrected the issue and forgot about it. About 18 months later I got the antenna kit in the mail. It'd been so long that I'd completely forgotten ordering it, and STILL didn't think I'd ordered it...I thought it was sent to me by accident. So I emailed Jim Weir and told him of his "mistake", and that I'd be needing one for my next plane anyway, and would send him a check, or I'd be happy to forward it to whomever it was originally intended, and I'd order another one. He said I had indeed ordered it, and he'd discovered the oversight and sent it on, despite the 18 month lag! I had a good laugh over that, but it made me wonder if I was losing my mind! I chalked it up to my uber-stressful job and moved on, however. I'd send you the kit but gave mine to Paul Visk a few months ago. I'm sure toroids and copper tape can be bought at Digkey or Newark, and copper foil from AS&S or Wicks, but an email or phone call to Jim might produce a kit in the mail, although you've probably tried that. Merry Christmas, y'all... Mark Langford ML at N56ML.com http://www.n56ml.com
