[Elecraft] KPA500 High Reflected Power Fault

[Monty Shultes]

Having hammed from college dorms to homes on acre lots (no rhombics in my past), I have settled on either an off-center fed 80 meter wire or an open-wire center fed 80 meter wire as the best compromise for an all-band antenna.  My LDG-1000 tunes the latter just fine.

I use a home-made humongous balun just outside the house to "match" the open-wire line to 52-ohm coax.  The balun was sold as a kit by a since-forgotten QST advertiser.  The core is 4 inches and the wire teflon-insulated #12, I believe.  It's mounted in an aluminum box.  It handles 600 watts very nicely with no effects attributable to power levels.  I tune the antenna with 25 watts, and that setting remains good with higher powers.  I have used all bands 160-10 meters, although 160 really doesn't work well.  I now also have a roof-mounted hexagonal beam for 20-10 meters.

Before QRO, I used an MFJ-949 with internal balun to "match" the antenna to a previously-owned 756 ProII.  The K3 tuner "matches" it FB with its internal tuner.

Actually, I had a friend with rhombics on two MARS frequencies provided by USAF so he could conduct phone patches to floating ice islands north of mainland Canada and Thule, Greenland.  Another story.

Monty K2DLJ


> If a tuner gets you to a good match at low power where there is a balun
> involved, but you run into problems at high power, I would first suspect
> that the balun is getting saturated. Using a balun between an antenna and
> the tuner many times is not a good thing to do. Using a balanced line tuner
> is really the best thing to do. Changing the length of feedline from antenna
> to balun does change the impedance that the balun or tuner has to deal with.
> And that chance can help at a specific frequency that has problems. 
> 
> Using a single antenna on multiple bands is very attractive. Unfortunately
> it is sometimes not an easy thing to do efficiently. In most cases antennas
> are always a tradeoff. There are so many constraints we deal with. Lot sizes
> deed restrictions, supports available, how much we can spend. You want a
> great antenna system and unlimited budget? I'm sure someone can sell you the
> land needed, someone can clear it, someone can put up multiple support
> structures and good antennas for the bands of interest. 
> 
> Most often what we wind up with is a compromise in one way or another. In
> many cases that compromise, with careful study and understanding, can result
> in a quite respectable antenna. The other trade off to consider is the time
> spent in getting the best antenna versus getting on the air a lot with a
> variety of antennas (or maybe just one). 
> 
> I must confess that I probably spend more time brooding over what could be a
> better antenna than getting on the air and making contacts with the fairly
> decent antennas that I do have here. 
> 
> 73 - Mike WA8BXN 
> 
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