[Elecraft] BL2 Balun Question

[Bob McGraw K4TAX]

Your operation is similar to one I encounter when operating from our RV.

A balun has several primary and in may cases mutiple functions. Some, 
all or none may be contained in the specific balun design:

(a) operation between a balanced and an unbalanced circuit. Hence BalUn 
meaning balanced to unbalanced.  This is typical where the coaxial 
unbalanced output of a transceiver is connected to a balanced load such 
as a balanced antenna which is fed with balanced line.

(b) a balun can offer impedance transformation characteristics such as 
found with a 4:1 or 6:1 or other transformation ratios. In the case of a 
4:1 balun it transforms a 200 ohm balanced load to a 50 ohm unbalanced 
source.   Optimum results attained here would with a folded dipole 
design offering some 200 to 300 ohm load being transformed into a 50 to 
75 ohm source.

(c) Correctly designed a balun should offer some degree of common mode 
current rejection.  Thus the reduction of common mode currents induced 
into the feed line thus flowing back into the station equipment.

In your case the use of the balun between the transceiver to the 
balanced feed line is correct.  Then the "ground" terminal should be 
connected to the transceiver reference ground point.  Ideally a driven 
ground, although in a RV perhaps just the metal framework of the 
vehicle.   As to using a wire, yes connect the random length of wire to 
terminal A and If you use a counterpoise, be it elevated on on the 
ground as in a radial field, then it can connect to terminal B.  In this 
case the counterpoise should be connected to "ground".  The application 
of the balun in this configuration is then simply to prove some 
impedance transformation as in a 4:1 balun and to control common mode 
current.   That is provided the balun is correctly designed for such.

In the case of the BL2 balun, it is switchable between a 4:1 ratio and a 
1:1 ratio.  Your specific application will likely require the use of 
either at one time or another depending on your antenna configuration.

My personal reference for this discussion and balun designs in detail 
can be found at the DJ0IP website. http://www.dj0ip.de/balun-stuff/
<http://www.dj0ip.de/balun-stuff/>


73

Bob, K4TAX


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
>
> _