closed circuit AREDN mesh network

Don't know how often this idea could be used, but say you have unused pre-existing 75 ohm coax already strung in the house (and running cat5 to do DtD isn't practical), and you don't want to clutter up over-the-air spectrum tying a pair of nodes together via wifi.  Use the 75 ohm coax for the 2.4GHz connection.  Yes, the nodes are 50 ohm impedance, but we'd want to attenuate the signals out of the nodes anyway, using passive impedance transformation circuits.  That' coupled with the losses of a long length of RG59 or RG6 (better choice anyway, usually better shielding) should attenuate the transmitters to not blow the doors off the receivers.  As mentioned, simple attenuators can also do the impedance transformation.  A pi network of resistors would do it.  A 180 ohm resistor on the 75 ohm side to ground, a 68 ohm resistor on the 50 ohm side to ground, and a 100 ohm resistor between the 75 and the 50 ohm sides.  One of these circuits should attenuate around 9dB, and we'd use a pair, one at each node where the 75 ohm coax ends.  Getting the funny wifi connectors can be done by taking apart those plastic antennas that came with the nodes (I'm thinking of the kind that came with WRT54G's).  Remove the dipole antenna part inside, leaving a coax pigtail on the funny connector, and build the attenuator circuit on the pigtail with an F connector at the 75 ohm input/output side.    

This picture shows the adaptor cable without the attenuator.