[Elecraft] KPA500 High Reflected Power Fault

Gary Gregory garyvk4fd at gmail.com
Mon May 16 07:19:45 EDT 2011


Oh, and I forgot...the 'Fault' which was the original subject matter before
it morphed into the current postings lay not in the tuner or the amplifier,
but rather another 'item' used in the system...I believe he has it all fixed
and is busily working  DX...:-)

73's
Gary

On 16 May 2011 21:16, Gary Gregory <garyvk4fd at gmail.com> wrote:

> Using a Balun after the tuner with 50 Ohm coax between is NOT the best way.
> Sure you can make it work, but the resultant SWR may not be the
> best. Inconsistencies will/may occur...YMMV
>
> Too many papers on this subject have been written over the years to quote
> here on this very subject and I suspect that the authors are correct in
> their assessment.
>
> A 40M double extended Zepp (170' flat top) with open wire feedline direct
> to a tuner has served me well. Interesting lobe on 20M though, but great on
> 40M..:-)
>
>
> 73's
> Gary
>
>
> On 16 May 2011 21:05, Monty Shultes <montys at mindspring.com> wrote:
>
>> 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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>
>
>
> --
>
> VK4FD - Motorhome Mobile
> Elecraft Equipment
> K3 #679, KPA-500 #018
> Living the dream!!!
>
>


-- 

VK4FD - Motorhome Mobile
Elecraft Equipment
K3 #679, KPA-500 #018
Living the dream!!!


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