Another option for "front end" sequencing control involves the use of a
microcontroller to time R=>T and the the reverse switching events. For the
past two years, I've been using an Arduino Nano-based controller to manage
amplifier switching as well as a PIN diode T/R switch to silently control RF
switching of a Drake C line. To date, RF ingress has not been an issue.
The Nano's I/O is completely optically isolated with the use of external
photo transistors and photo-relays. The photo-relays are used to drive
heftier devices like vacuum relays, PIN diodes, and Zener bias switching.
The board has an integrated RF sample port such that switching events cannot
occur in the presence of RF. Where RF needs to be sampled away from board,
an external RF sampling board is used. In both sampling versions, RF is
sensed down to less than 50 mW of power. The board samples up to 4 inputs
(including RF presence) and switches a maximum of 8 output channels.
To the point of this message topic, the same board also emulates the KD9SV
"Front End Saver." On my QRZ.com page, I have written the C++ code to start
basic control of the FES. Need more devices switched or need to
conveniently change delay times? Just activate another port by modifying
the software. Or, change switch times in 1 ms increments with a simple
software edit.
The board includes two optional relay coil accelerator circuits, and
includes W8ZR's idea of using a small muRata DC-DC converter, bootstrapped
to the +12V supply to generate +24V to power common vacuum relays. More
board info is available in the 2014 ARRL Handbook or on my QRZ.com page.
One only populates the parts on the board of interest. For example, if
relay coil acceleration is not of interest, the parts are omitted and does
not affect the rest of the board's operation. I still have a few bare
boards remaining. PM if there's an interest.
Paul, W9AC
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