[Elecraft] NOT the feedline

Mon Jun 1 18:31:55 EDT 2020

Even with a 1:1 SWR, 1000 W is pretty close to the 500 V peak rating for a UHF connector. Type N connectors are rated at 1500 V peak.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Jun 1, 2020, at 3:17 PM, George Kidder <gkidder at ilstu.edu> wrote:
> 
> 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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