[Elecraft] OT Tuner ranges

[Bob McGraw K4TAX]

I've had several to ask in general,  "so what or when is the correct 
application for a  4:1 balun?"   The folded dipole is an excellent 
application and case for a 4:1 balun.  The uniform folded dipole feed 
impedance at resonance is ~300 ohms.  When erected less than 1/2 
wavelength above earth the impedance drops to near 200 ohms, depending 
on height.   Thus the 4:1 transformer action in the balun bring the load 
to near 50 ohms.    Even it the feed Z of the folded dipole is 300 ohms, 
and height above ground supports this, the SWR seen at the radio is only 
1.6:1.

These thing we call baluns should have two functions to perform: (a) 
unbalanced to balanced conversion, and (b) some degree of Common Mode 
Rejection.    Both are equally important, although most commercial 
designs fail to address item (b).

Again I agree with Don's comment earlier, the concept of using a 4:1 
balun to "match the feedline Z" is purely fictitious information.  The 
feed line, depending on length vs. frequency being some numerical factor 
of a wavelength, has some transformer action.  Thus the feed Z of the 
antenna and the feed line in combination, will present some value of Z 
expressed as R +j.   It has little to do with the actual feed line 
characteristic impedance.

If one believes the 4:1 balun matches the feed line which happens to be 
600 ohms, and the feed line is correctly terminated into its 600 ohm 
characteristic impedance, the feed Z at the balun is 150 ohms, 
presenting a 3:1 SWR.

There is an excellent presentation on impedance matching coming up at 
the Huntsville Hamfest in August.

73

Bob, K4TAX





On 5/24/2018 12:06 PM, Ignacy wrote:
> There are reports online that 1:1 has lower losses. My experience is that
> with lower-range tuners 1:1 does not cover some frequencies but 4:1 does.
>
> Ignacy, NO9E.
>
>
>
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