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.
--
Sent from: http://elecraft.365791.n2.nabble.com/
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
