>
> The 1/2 wave xfrmr is
> simple to do for monoband setups, but becomes more complex for triband
>
situations, which is what most guys have.
Alternating-impedance series-section transformers like the "Twelfth Wave"
transformer can be pretty broad.
http://www.tuc.nrao.edu/~demerson/twelfth/twelfth.htm
And an interesting thing is documented here:
http://ourworld.compuserve.com/homepages/demerson/12thfdbk.htm
it says this:
"For example, from WD8KBW, in transforming from impedance Z1 to impedance
Z2, an arrangement could be:
... Z1 (any length), Z2 (La), Z1(Lb), Z2(Lb), Z1(La), Z2 (any length) ...
If Z1 is 50 ohms and Z2 is 75 ohms, then the electrical length La is 0.0392
wavelengths, and Lb is 0.10385 wavelengths."
I've actually built a couple of these and I use one basically from 5MHz
through 21MHz.
I use a single-section twelfth wave transformer on either end of my RG-6/U
run to my 20m/17m Moxon to match 50 ohms on either end . I cut it for
15.9MHz, and it's plenty broad to cover the two bands with acceptable SWR.
Honestly, I think if you used a twelfth wave transformer cut for 15m on
either end of your 75 ohm run to a tribander, it would transform the
impedance "well enough," and certainly, the two step version would work
great. The biggest problem there is all those connectors to install.
73
Dan
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|