[Towertalk] rcs8v as U/L/B stack switch

[k6ll@despammed.com]

Any sp3t switch, shorting or
non-shorting can be
used for Upper/lower/both
switching of monoband antennas.

It's a little hard to draw, so
let's see if a word description
is enough. Position 1 is upper,
position 2 is both, position 3
is lower. The transmitter connects
to the switch wiper.

For a non-shorting switch:

Connect 1/4 wave of 50 ohm coax
to position 2. At the free end,
install a coax tee.

Install coax tees directly on
position 1 and position 3.

Connect 1/4 wave of 75 ohm coax
from the position 1 tee to the
position 2 tee.

Install another 1/4 wave of 75
ohm coax from the position 3 tee
to the position 2 tee.

Connect upper antenna to position
1 tee and lower antenna to position
3 tee.

Theory: When "upper" is selected,
position 2 is open. This open is transformed to a short by the
1/4 wave of 50 ohm coax. That short
is transformed to an open at position
1 by the 1/4 wave of 75 ohm coax.
Therefore, no power goes to the lower antenna.
-----------------

For a non-shorting switch:

Connect a tee directly to position 2.

Connect a 1/4 wave of 50 ohm coax
to position 1. Install a tee on the
free end.

Install a 1/4 wave of 50 ohm coax
to position 3. Install a tee on the
free end.

Connect 1/4 wave of 75 ohm coax from
the position 1 tee to the position 2
tee.

Connect 1/4 wave of 75 ohm coax from
the position 3 tee to the position
2 tee.

Connect the upper antenna to the
position 1 tee.

Connect the lower antenna to the
position 3 tee.

Theory: When "upper" is selected,
the shorting switch shorts position
2. This short is transformed to an
open by the 1/4 wave of 75 ohm coax
between 1 and 2, so only the upper
antenna is connected.

I think K2TR or W6SAI came up with
this scheme, at least for the
non-shorting version. I saw the
shorting version in use at K6NA.


Dave Hachadorian, K6LL