[Elecraft] NOT the feedline

[Dave Cole]

Is it possible that Common mode is getting into the amp, and forcing a 
fault?

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 6/1/20 2:40 PM, Fred Jensen 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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