[Elecraft] BL2 Balun Question

[Ron D'Eau Claire]

Terry, to answer your question, that ground connection simply ensures the
balun pcb and the outer shield of the coax cable feeding the balun remain at
a low RF potential, even if you feed a fairly high impedance load. 

You are correct to connect them to the A and B terminals. Either wire to
either terminal is fine. The "balun" isolates the wires from  the coaxial
line. IF the balun and rig are close to each other, I'd not use the balun
for short end fed wire / counterpoise wire setups.

Note that the RF currents flowing inside a coaxial transmission line *are*
balanced if the line is terminated in a balanced load. The balance is
determined by the load, not the transmission line. 

Since RF flows on the surface of the conductors, there are actually three
(3) conductors in a coaxial transmission line: 1) The center conductor, 2)
The inside surface of the shield and 3) The outside surface of the shield. 

A properly installed coaxial line will prevent coupling between the inside
and outside of the shield. If, for example, one connects a coaxial line to a
dipole by unbrading a length of shield, twisting it and soldering it to one
side of the dipole the inner and outer surfaces of the coaxial shield are
now connected in parallel. RF currents now flow down the outside of the
shield in parallel with that side of the dipole. In some situations, this is
of little concern but if one wants the advantage of the inherent shielding
provided by coax, it is important to decouple the outer surface of the
shield from the inside surface.  

The "balun" can provide this function by suppressing RF currents flowing out
of the end of the coax that would otherwise flow down the outside of the
shield. Grounding the pcb keeps it at a low RF voltage even when feeding a
high impedance load, if the ground is effective at the frequency in use. 

73, Ron AC7AC


On 6/8/2017 11:47 AM, Terry Brown wrote:
> I have the BL2 Balun and use it for balanced lines to Coax.  Occasionally,
> when I am using a wire and counterpoise to the BNC binding posts, I try to
> match a shorter wire for 80 meters than what I really should due to lack
of
> space in RV sites.  I believe I am connecting the Balun correctly; hooking
> the long wire to A and the counterpoise to B on the Balun inputs.  I can
get
> a shorter wire to tune that way.
>
>   
>
> My question is:  what is the purpose of the GND connection on the Balun?
> Does it need to be grounded when in use?  Looking at the circuit diagram
in
> the manual, I don't think the counterpoise should be attached to the
ground
> connection?
>
>   
>
> I'd be interested in how others hook up their BL2 Baluns.
>
>   
>
> Thanks and 73's,
>
>   
>
> Terry de N7TB
>
> _