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 <[email protected]> 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 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] -- 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." ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
