Balun change?

[sv2bwm]

I have the Ten-Tec 229B tuner and I use the internal balun 4:1 for feeding open wire 450 ohm in a 80m all-band doublet antenna (20+20m).

If I bypass the antenna tuner, the antenna tunes around 21MHz/15m for a 1:1 VSWR and around 3,6MHz/80m for a higher than >>3:1 VSWR.

So question is, do you think I should change the internal balun to a 9:1 (50x9=450) ??? :confused:

Thanks in advance...

[sv2bwm]

Anyone????

[G3TXQ]

The doublet and 450 Ohm line will present a very wide range of impedances to the tuner on the different bands.

I just modelled the antenna and guessed the feeder might be 35ft long. I got low impedances on 15m (70 Ohms) and 80m, and very high impedances on some other bands - as much as 3.5 KOhms on 30m and 20m. So there's nothing that says a 9:1 impedance transformation would be better than a 4:1.

Don't be misled into thinking that because it's 450 Ohm line that will be the impedance at the tuner - it wont. You dont use 450 Ohm open wire because the antenna feedpoint impedance is 450 Ohms; you use it because it can handle the very high VSWRs this antenna presents without causing high losses.

73,
Steve

[sv2bwm]

Thanks, Steve. I got the meaning now....