[Elecraft] Semi OT: ratios of unun windings

[John Grebenkemper, KI6WX]

Mike;
You need to compute the inductance of each winding, and from this compute
the inductive reactance at your operating frequency.  As a rule of thumb,
the reactance should be 10 times greater than the operating impedance of
that winding.  If you are using it for receiving only, you can go below this
somewhat, but if you go too low, the effectiveness of the UNUN will be
reduced and its loss will increase.
-John
 KI6WX


> Good evening, all.  I'm in the process of beginning to experiment with a
> wanna-be Beverage, and had a question about winding an unun for
> it.  Through the ARRL Handbook & Amidon's literature, I've calculated the
> number of primary & secondary turns needed for the chosen core.  BTW, the
> antenna is for LF, receive only.
>
> I've come up with a ratio of 18:54 turns (50 ohms:500 ohms).  Is it
> permissible to reduce this to 9:28, or even 3:9?  As in, I assume the
magic
> isn't in the exact number of turns, but rather the ratio between primary &
> secondary windings.  Although 1:3 would be the next step, I get the
feeling
> that this would not allow for adequate coupling between the
> windings.  Working the formulas backwards, the 3:9 actually turns out to
be
> a 50 ohm:450 ohm match, which is still adequate for my testing (since the
> impedance of the antenna at LF is only an estimation anyway, and is only
> for receiving).
>
> Does all this make sense?
>
> 73,
>
> Mike Boice, KW1ND
> Nampa, Idaho
>