Ever since my previous adventures into TV antenna Frankenswitches, I've been looking for a simpler/cheaper way to accomplish something similar. A design for an antenna autoswitch that others could perhaps build/use for their own MythTV / SageTV setups.

DisEQc satellite multi-switches are widely and cheaply available. This past weekend, I picked up a simple 4-way DisEQc-2.0 switch for CDN$8 from Active Surplus.

Now, designing/incorporating a full DisEQc protocol front end for one of these would be optimal, but also complex and potentially expensive. So I'm thinking of something much simpler.

The disassembled DisEQc switch is shown below, and a larger version is here.

It appears to use pin diodes for the switching, with fairly straight and simple signal paths through those devices. One pin diode per input (four in total), plus two extras near the middle where they connect to the downfeed. Those two extras have me a little puzzled, but I think they're there just to provide additional isolation between the two pairs of inputs (left and right).

Each of the primary four pin diodes has a cascaded pair of transistors driving the bias, to switch it on or off. These four pairs of transistors are wired directly to GPIO pins on the unlabelled PIC controller chip on the board.

There is one extra pair of transistors, whose function I have not determined -- but that probably has something to do with powering the PIC. EDIT: they're for sending response packets from the PIC back to the receiver.

My plan, is to remove the PIC from the circuit board, and replace it with four TTL signals from the parallel (printer) port of my MythTV PVR box (or perhaps connect it through another one of those USB / GPIO gizmos).

Plus a ground wire, and a +12V supply line for the multiswitch, rather than trying to wire the +12V into the downfeed coax as is normally done with DisEQc.

Comments, suggestions, and wisdom would also be appreciated.
I'm a software/firmware geek, not an RF engineer!

Cheers