Posted by
Rick WA6NHC-2 on
Feb 25, 2018; 3:53am
URL: http://elecraft.85.s1.nabble.com/KPA500-Faulting-on-high-SWR-on-power-rise-tp7638486p7638556.html
In my case, the 4:1 was shown as correct by comparing to a 1:1 (for me). I was able to find more usable bands with the 4:1 (meaning closer matches).
If the dipole is single band only, using a 75 ohm feed (choke at the transition from feed to antenna) is best. A resonant dipole is closer to 72 ohms, ignoring local conditions, one of which is elevation above ground. Inverted vee systems are lower impedance so 50 ohm is the proper choice (again, single band only).
For this example of multiband use AND open wire feed (for dramatically lower feed loss at high SWR) which alters the impedance of the system and the length of the feed matters; one can use an analyzer to find which transformer works best or simply try both.
The 4:1 presents a bit more device loss compared to a 1:1, but if it also provides near resonance on more bands, so that loss is negligible.
With open line (75-600 ohm typical) you don’t match the line with the balun, you match what the SYSTEM presents, antenna and feed.
Rick WA6NHC
Smell Czech correction happen
> On Feb 24, 2018, at 7:30 PM, Bob McGraw K4TAX <
[hidden email]> wrote:
>
> I question the 4:1 balun being the correct nor best choice. Typical of that antenna the feed Z of the radiator is more likely 25 to 35 ohms. The 4:1 balun is presenting something like 10 ohms to the tuner. Worst case for high current and hi loss in the tuner causing heating. A 1:1 balun would seem more likely correct.
>
> Many seem to "think" a 4:1 balun is correct when using open wire or a balanced line to "match the line".
>
> Bob, K4TAX
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