[TenTec] 160 meters, ten ted 238 tuner, part two

[Steve Hunt]

Rick,

I was talking about the CM impedance rather than the Differential-Mode 
impedance. If you switch in parallel with each other the two 1:1 chokes 
which form the 4:1 Guanella balun, you have a 1:1 with only half the CM 
impedance of a single choke. It seems a shame to throw away that 
hard-earned CM impedance :)

73,
Steve G3TXQ


On 31/10/2013 22:21, Rick - DJ0IP / NJ0IP wrote:
> Yes Steve, you are correct.
>
> You have two windings (transmission lines) with the 4:1 Guanella.
> Usually the bifilar windings are about 100 Ohms.
> Their inputs are in parallel and their outputs are in series.
> This gives us 50 Ohms on the input and 200 Ohms on the output.
> But if we re-wire the outputs to also be in parallel, then the two 100 Ohm
> transmissions lines in parallel give us 50 Ohms on both ends.
>
> Unfortunately the reverse does not always work.
> Most 1:1 Guanella baluns simply run a coax cable around a single toroid so
> you don't have the two transmission lines to play with.
> But, if you build your own 1:1 Balun using two 100 Ohm bifilar transmission
> lines rather than coax, THEN you have the possibility to switch it to a 4:1
> or 1:1.
>
> Having a switchable balun is a big help when you are trying to cover the
> entire HF spectrum with a single antenna and you only have a marginal
> antenna tuner, like the built-in tuners in transceivers.  This can come in
> handy when traveling light on portable expeditions.
>
> 73
> Rick, DJ0IP
>
>
>