[Elecraft] NOT the feedline

Mon Jun 1 18:17:33 EDT 2020

One of my antennas is a commercial "G5RV" fed with 33' of 450 ohm ladder 
line, terminated in a PL-259 pair, with coax from there to the shack.  
Apparently this combination results in very high RF voltage at the 
PL-259, and it arcs over at 1000 W (not from an Elecraft amp!).  This 
combo goes wild when I attempt high power on 80M, although it is stable 
at 100 W.  Just another thing to watch out for!

73 - George, W3HBM

On 6/1/2020 5:59 PM, Ted Edwards W3TB wrote:
> [This message came from an external source. If suspicious, report to abuse at ilstu.edu<mailto:abuse at ilstu.edu>]
>
> 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
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>
> --
> 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."
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