The balun (1:1 current choke here) is a red herring. If you follow this thread all the way back, you'll see that the previous antenna was not balun fed, and it used a length of 75 ohm cable and stubs to match. And in this case the balun is made by InnovAntennas, specifically for this antenna (also of their design in the UK). If changing any one or two components had made a significant difference I would have noted it.
First was the antenna change. When that failed to show a marked difference then I replaced the feedline. Again, no change whatsoever. It's behaving the same today as it has since I first got on 6m with high power. So either the amp has an issue or it's something incredibly esoteric that will take a miracle to find and fix. I have tried going through an antenna switch and switching via the KPA-1500. No difference. All coax connectors are genuine Amphenol 83-SP1 and assembled correctly. New LMR-400 coax, purchased last year and stored inside over the winter, and new(ish) RG-213 patch cable inside the house. I don't ever reuse connectors or outdoor coax. Everything I'm seeing is pointing to the fault being inside the KPA-1500 at this point. - pjd -----Original Message----- From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On Behalf Of Adrian Sent: Monday, June 1, 2020 10:13 AM To: Alan - G4GNX <g4...@g4gnx.com>; Elecraft Reflector <elecraft@mailman.qth.net> Subject: Re: [Elecraft] NOT the feedline If you use a decent combination balun such as ; https://www.balundesigns.com/model-4116-4-1-hybrid-balun-1-5-54mhz-3kw/ if you have any metal structure in range of the field, or https://www.balundesigns.com/model-4115ocf-4-1-for-ocf-dipoles-1-5-54-mhz-5k w/ for a total current 4:1 balun. These are very robust at high power, and no other feedpoint RF common mode choke is required. I ran a K3 , amp and ocf dipole like this, with above balun earlier this decade with great success, had top 4a4a dxpedition total band vk points with this one antenna. Also the windom and ocf are different animals. The true windom uses the vertical section of its feedline as part of the antenna, such that any ocf dipole with a feedpoint common mode choke cannot be referred to as a 'windom' Adrian Fewster On 1/6/20 11:45 pm, Alan - G4GNX wrote: > I have a similar issue with ferrite 'balun' heating, although mostly > tested on 40 metres. I'm using an OSCFD (Windom) which has a main 4:1 > balun at the feed point, but also has a sleeve 'balun' consisting of 8 > ferrites wrapped in a plastic sleeve, about 3 feet from the feed > point. If I run the K3S at 100W, via the KPA500 in standby, then > through the KAT500 tuner, I see no problems. > > On increasing the power to 200W by using the KPA500 in Operate and > about 10W drive from the K3S, during a SSB 'over' the temperature of > the KPA500 rises and after a few minutes, the SWR readings on the > KPA500 and KAT500 start to rise. One of the Elecraft guys actually > very kindly went through my fault log and came to the conclusion that > the fault is with the antenna/feeder and I agree with him. What is > strange is that if I leave a solid carrier running at 200W, I can't > easily reproduce the issue and I wonder if its something being > affected by peak excursions with SSB? > > When things do start to go wrong, I can usually perform a manual tune > with the KAT500 and the fault will then not (mostly) be apparent. > > Anyway, I'm in the process of replacing the entire feeder with > Westflex 103 and much bigger ferrites. I will also replace the main > balun which is a 400W device for a 1KW device, as I think that running > the UK max of 400W may be pushing the spec of a 400W balun. Also, the > balun itself or connections to it may be faulty. > > The point now is that I have discovered some damage to the outer > covering of the sleeve 'balun' which may be the result of ferrites > overheating or may be the cause of movement of the ferrites thus > causing instability. Either way, heftier devices seem to be the order > of the day. > > Although the KPA500 temperature rise is somewhat expected, I feel it's > a bit higher over a short period than I would like and may be due to > reflected power. > > 73, > > Alan. G4GNX > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to li...@w2irt.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
