[Elecraft] NOT the feedline

[Ted Edwards W3TB]

I am following this with great interest.
Like Alan G0GNX, I also use an OCF, RG-8X out to the current balun in this
case, 300 ohm to the antenna.  K3, KPA-500 and KAT-500.

If I am running stations in a contest on 40m and also 80m CW, It "appears"
that my VSWR rises after a half hour and then the KAT-500 starts to try to
spontaneously retune.  Doesn't happen on 20m and up.  This past weekend in
CQ WPX, I reduced drive so that output was about 300 watts and it all
became tame.

I had thought that it was a heating of the RG-8X; then I changed my mind to
the current balun from Radiowavz that is rated for 1.5 KW.  I think it is
the balun just getting hot out there.  I had used a W2AU 4:1 balun with my
OCF, which is a voltage balun but I didn't know about that -- for upwards
of 40 years and with the Elecraft equipment for about 4 years since I got
the amp/tuner.  I just switched to a current balun last year with one that
I bought at Dayton.

I would have expected more problem with the voltage balun than with the
current balun.  I could change back to the W2AU if needed.

Interesting stuff, so I am reading along.  And my thanks to all of you.

On Mon, Jun 1, 2020 at 4:42 PM Fred Jensen <k6dgw at foothill.net> wrote:

> Nearly same experience Bob:  Sloping V, 135 ft legs, from top of 80 ft
> tower fed with homemade 600 ohm open wire using a DX Engineering 4:1
> "balun" [a strange, usually misunderstood piece of electronic apparatus
> often used for the wrong reasons] rated at 10 KW.  It warmed up
> noticeably at 1.2 KW RTTY use.  It helps to remember that one can
> saturate a ferrite core [especially when very hot] which creates a
> racket reminiscent of a non-synchronous spark gap TX.
>
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> On 6/1/2020 1:48 PM, Bob McGraw K4TAX wrote:
> > Based on my experience, balun power ratings are for MATCHED
> > conditions. It is rare that hams use a balun in a matched condition.
> >    Thus a 1:1 balun should see 50 ohms on the input and 50 ohms on the
> > output, while a 4:1 balun should see 200 ohms on the output and 50
> > ohms on the input.   In the case of a resonant folded dipole, a 4:1
> > balun is typically operating in a nearly matched condition. All others
> > combinations are unknown and random.
> >
> > I run about 500 watts on all bands.  My baluns are rated at 5KW! It
> > takes 3 or 4 big hunkin' pieces of ferrite to attain this power
> > level.   My 6 meter balun is a 1/2 wavelength electrically of RG-213.
> > No ferrite!
> >
> > Buy or build a balun of your choice.  Using an IR temperature gun,
> > measure the ambient temperature of the core.  Run about 1/2 rated
> > power carrier for 30 to 60 seconds.  Measure the temperature again.
> > If it is warm to hot, this is RF producing heat.   And likely
> > continuing will produce core failure.   This is not a good balun for
> > your application.
> >
> > One of my baluns work between the output of my KAT500 and the balanced
> > feed line connected to the center of a 256 ft wire.  That antenna
> > works 160M - 6M with zero issues.   Now, I do run a hybrid balun being
> > a 4:1 Guanella balun as a transformer, and it is fed with a 1:1 balun
> > for common mode rejection.
> >
> > Most single core, i.e. 2 or 3 cores stacked with 2 to 4 windings are
> > not at all a proper balun design   A Guanella balun will have 2 cores
> > with 2 windings and then another 2 separate cores with another 2
> > windings.  These are then wired to produce a 4:1 balun with good
> > common mode rejection.    Most "factory" 4:1 baluns are poorly
> > designed and built junk.
> >
> > See https://www.dj0ip.de/balun-stuff/ for further references.
> >
> > 73
> >
> > Bob, K4TAX
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to w3tb.ted at gmail.com



-- 
73 de Ted Edwards, W3TB and GØPWW

and thinking about operating CW:
"Do today what others won't,
so you can do tomorrow what others can't."