[TenTec] Not TT - Wire antenna question.

[ac5e at comcast.net]

Chuckle: Well, Rick, I cooked the balun in an MFJ 989 a dozen years ago, running a few hundred watts on 75 from a Hercules I. It stank something terrible. 

I also cooked the roller inductor running 100 watts from my Paragon to a wire antenna on 17 Meters. I tired of stinking tuners rather quickly so I changed to Ten Tec 238's and have had no further trouble. But I haven't tried to feed a comparatively low impedance antenna with twinlead again either. 

I generally agree with you, Rick, especially trimming the loop to resonance on 40 and then opening the loop opposite the feedpoint for 80/75. That will provide predictable feedpoint impedances on all the harmonically related bands from 80 up and very nice and predictable results. 

I also concur that if you are going to use twinlead by all means use a balanced antenna tuner. 

However, it's not always possible or convenient to use anything except a random length loop and the tuner one already has. Most of the random length loops I have tried (on bands where more than a half wavelength of wire was up) had feedpoint impedances in the 10-250 ohm range with minor excursions both up and down. Leading to a 5:1 max SWR at the feedpoint and correspondingly less for at transmitter end of the transmission line. And reasonably low coax losses as long as the length of line is kept fairly short. 

For such situations a choke placed VERY close to the feedpoint will cool the coax shield down to the point a ferrite balun will finish the job quite well. For "all bands" use two, one of 6-8 turns on a 100 mm form to be active on 20 and up, the other of 12-15 turns for the lower bands, oriented at right angles with as little space between them as possible. 

Or use the smaller choke and back it closely with a ferrite balun. Any of those combinations cool things down in a hurry. 

That said, my standard practice, down here in the semi-tropics, is to go straight from the feedpoint balun to a ground mounted lightning arrestor with a ferrite balun on the shack side of the arrestor. But I get between 100 and 120 lightning days a year and that's probably overkill in the higher latitudes. 

The one thing not to do is to run any appreciable length of coax between a ferrite balun and the antenna. A friend tried that - against my warning - and his smoke detector pretty warned them quickly enough to save his house. If your transmission line shield is close to a quarter wave most remote mounted ferrite baluns will get very hot, very quickly. Not good. 

And I suppose I had best say that's my two pice. At least on that subject. 

73  Pete Allen  AC5E