John Young says:
Back in 2007, you posted a link to the West Chester Guerilla Drive-In, where we project 16MM movies at secret locations from the sidecar of my 1977 BMW motorcycle:
The kit-built AM transmitter in the photo you posted is the MacGuffin, a secret AM transmitter in a waterproof case hidden somewhere in the area, and broadcasting around the clock. In order to find out where movies are going to be shown, you have to find the broadcast, tune in, and discover the secret access code.
This year, the audio for the AM broadcast includes a freshly-recorded cover of "Brazil", which you will probably remember as the soundtrack for the Ministry of Information in Terry Gilliam's awesome 1985 movie.
You can see the MacGuffin and hear the first bit of the secret message on the Guerilla Drive-In website.