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T-Bias interface


T-Bias interface

I had a comment a few weeks ago asking for more details about the T-Bias device used to send DC over the active RF coax to my 43′ vertical antenna.

This is used to switch the matching network such that:

0 volts = 60 – 6 meter operation
+12 volts = 80 meter operation
-12 volts = 160 meter operation

I based the design on the one from Phil, AD5X, on his website:

Here is my design:

T-Bias schematic

The photo shows that I used the parallel capacitors to get the 0.03 uf feedthrough capacitance.  The RF choke is a Radio Shack 100 uh standard choke.

T-Bias (Shack End)

Here you can see how I kept the 12 volt input from the wall wart isolated from the chassis, allowing me to use the switch to flip polarity as needed. I mounted the connector on a piece of fiberglass circuit board (no copper).  Then I riveted the fiberglass to the chassis.

12 volt isolated connector


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