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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