[Elecraft] 9:1 Balun AND "random antennas"

[Richard Fjeld]

Jim,

If you don't object, I'd like to save this and forward to people as 
arguments develop on these subjects.

  I wish you had touched on '4:1 baluns'.  Except for this group, so 
many people I talk to think a balun should be 4:1, even in their 
tuners.  I think it is DX Engineering that addresses this well.

Dick, n0ce


On 1/31/2017 12:50 PM, Jim Brown wrote:
> All of this discussion becomes badly confusing by failing to describe 
> these circuit elements by their real name. The word "balun" is a 
> bastard -- it is widely used to describe nearly a dozen things that 
> are VERY different from each other.
>
> W4TV got it right by adding the correct description, and this post 
> starts to get at it, but adds another bastard word, unun.
>
> Two-windings that are coupled by a magnetic field are a TRANSFORMER.  
> If the two windings have a terminal in common, they are an 
> AUTO-TRANSFORMER. A coil of coax is a common mode choke (and not a 
> good one). A section of transmission line wound around a ferrite core 
> is a COMMON MODE CHOKE, and if well designed (choice of ferrite 
> material, number of turns) can be a very good one.
>
> Transformers and auto-transformers transform impedance by virtue of 
> their turns ratio. Arrays of common mode chokes can also be used to 
> match circuits of different impedances.
>
> Last I looked, there was no description of the Elecraft "balun" 
> telling us what it is. Perhaps Eric or Wayne could add that to the 
> catalog listing for it.
>
> Another point. SWR is NOT an indicator of how well an antenna works. 
> High SWR DOES increase loss in a feedline, but that matters only with 
> long feedlines and small diameter coax. That does NOT matter for 
> typical portable (or even mobile) operation, where feedlines are much 
> too short for loss to matter.
>
> A high value of SWR as seen by a transmitter DOES limit that power 
> that the transmitter can put into the antenna. That's where the 
> antenna tuner comes in -- it transforms the impedance at the 
> transmitter end of the feedline (or the end of a wire plugged into the 
> coax connector combined with the counterpoise connected to the 
> chassis) to the 50 ohm resistive impedance that the transmitter wants 
> to drive.
>
> If we make RF current flow in a wire, it will radiate. How well it 
> radiates depends, of course, on its orientation. A wire laying on the 
> ground doesn't radiate very well. :)  A wire without a counterpoise 
> will use whatever it sees as a signal return. If that return happens 
> to be the earth, the earth, which is essentially a big resistor, will 
> burn much of the transmitter power. The "good" lengths of wire Wayne 
> and those spreadsheets list are simply lengths that are likely to 
> present an impedance within range of most antenna tuners for the bands 
> that the operator is likely to use.
>
> 73, Jim K9YC
>