[Elecraft] Baluns - give me a kit!

[Ron D'Eau Claire]

Sure, the KAT1 or KAT2
> auto antenna tuners will probably match any antenna I string up, but
> wouldn't it be better to at least get close to the 50-ohm impedance that
> the K1/K2 want to see? Maybe I'm missing something here, but...
> 73 de Jerry/k6iii


No.

The purpose of the balun is NOT to achieve a match to your antenna in most
cases. That is exactly what  the KAT1 or KAT2 accomplish.

The ONLY purpose for the balun is to convert between a balanced and an
unbalanced circuit.  An "unbalanced" circuit, like the output of your K2 or
K1 or your headphone jack on the front, has a single "hot" line using the
ground as the return part of the circuit (sure, your phones have two "hot"
lines, but that's because you have two earpieces. Each one is fed by an
unbalanced output).

Some circuits are "balanced" instead. They move the signal along with two
"hot" lines. Neither line is "grounded". The signal in each line is 180
degrees out of phase with the other line. It has certain advantages in
transmitting power, avoiding noise, maintaining high-efficiency, etc.
Indeed, a good part of the audio path moving along the circuit boards of the
K2 uses a balanced circuit just to avoid picking up digital noise from the
surrounding circuits.

In an antenna feedline, a "balanced" feeder is great for providing very low
losses at high SWR's. No one has accomplished that with coax yet - at least
at anything like the low price of a balanced feedline. But to work as a
feedline that does not radiate or pick up noise, the currents in the
balanced line must be 180 degrees out of phase and equal in amplitude. In an
antenna system, a "balun" (for balanced to unbalanced) can do that for you.

That's the only reason to use a balun in an antenna system.

4:1 baluns became popular when it was needed to convert from a 75 ohm coax
(used to be very popular - almost as much as a 50 ohm line is today) to 300
ohm balanced line. Those baluns combine the function of a balun with an
impedance transformation as well. That is the ONE case where a "balun" is
used to achieve an impedance match along with converting the circuit from
balanced to unbalanced.

One last point is that baluns are bi-directional. The balun can convert
either way - balanced to unbalanced or unbalanced to balanced.

Ron AC7AC
K2 # 1289