Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0EP, May 24, 2019.
Because the "tuner" allows more power to be delivered to the antenna.
And I bet he has something else to sell that will "cure" it.
Why are you using a tuner?
Such an antenna should not be used where it's not already resonant, which is generally the fundamental and all harmonics of that frequency.
AND into the ferrite core - MOAR (sic) HEATING
I think you missed my point. It could be the ferrite in the actual end fed transformer heating up or it could be the ferrite in the common mode choke heating up. Either could heat up as the core saturates and cause the SWR to change with key down time. But yes, I agree the symptoms are consistent with core saturation.
Let me get this straight, because I'm interested in this technology, but you're saying that the common mode choke plays THIS big a part in this system that the common mode choke CAN heat up to the Curie point and impart this observation on the SWR meter with ONLY 100 Watts:
It slowly creeps up and then jumps pretty high.
That's got to be one WHALE of an amount of common mode current ...
Probably not, but saturated cores sitting on the coax feeder could create some pretty strange results once they saturate. But yeah, it's probably the ferrite in the feed point transformer though the test I described above is simple enough to perform and then you rule out one hunk of ferrite sitting in the antenna system. Divide and conquer...
The problem with the EFHW-8010 is likely to be one or more of the following - it is certainly NOT static that is causing the SWR change:
1. The matching transformer shown is a relatively low-power version. If the user ran close to 100 watts average power through it for an extended period, as with RTTY or FT8, it COULD heat up and progressively reach the Curie point within the toroidal core, causing the SWR to rise slowly at first and then skyrocket. If this happens and the operator is not aware of the core heating/SWR change, the core can be heated to the point that it will never fully recover, though there may be no visible damage to the case or even to the core(s) within the case. Once the core is damaged, it will then tolerate MUCH less power before beginning to heat.
2. The antenna was purchased USED and a previous owner ran the matching transformer right over the "Curie Cliff" and then sold it as "nearly new".
3. The antenna was strung too close to the ground (say, 4-6 feet or less) and 100W of average power was run through it on 80M. The transformer is less efficient and heats more quickly as it approaches zero feet above ground level, and this effect is enhanced at longer wavelengths.
The fix is to:
1. Re-string the antenna away from nearby objects and up at least 15 feet
2. Likely replace just the matching transformer with an 8010-2K, which tolerates MUCH more AVERAGE power. Transfomers are sold separately from the wiring - buy just what you need to save cost.
3. Stay within the following POWER limits when transmitting for extended periods and WATCH THE SWR IF PUSHING PAST THESE LIMITS or with a LOWER HEIGHT ABOVE GROUND LEVEL:
RTTY, JT-65, FT8: 80M/275W, 40M/325W, 30M/450W, 20-10M/500W
SSB PEP: 80-10M/1KW
These suggestions are based on actual experience, including installation and use of many of these antennas in many locations, and damage to a lower-power EFHW transformer from heating and disassebly and inspection of the matching transformer after the event.
Regarding the CMC overheating ad causing the problem: Not going to happen unless the internal core literally burns through the coax. As one poster above stated: "That would be one MEAN common mode current!"
The suggestion to discuss this with Danny Horvat at MyAntennas is a good one.
Brian - K6BRN
Ii wonder if the OP still has his antennas connected together per one of his other posts? That would toss most speculation out the window, wouldn't it?
Hmmm. Checked his posts. He's driving this antenna with an amp. Sooooo.... too much power?
Any other posts that are interesting?