Updated picture of the KMDT feeds, which has now been expanded...
The picture shows the two Radio Shack PRO-433 and four PRO-2055 scanners that I'm using as receivers. The 433s were obtained new, and the 2055s second-hand from eBay. They are not the highest quality radios out there, but they do a good enough job and are more economical than the dedicated R121 airband receivers that I considered using. The scanners are fed from an AV-5 base station antenna purchased from Aircraft Spruce, and mounted using Radio Shack hardware. The signal enters the basement, and passes through a PAR VHF-FM notch filter to prevent the receivers being overloaded by nearby broadcast stations. It is then boosted by a WRP-125 airband preamplifier, before being routed across the room to a closet containing the rest of the hardware. A Stridsberg MCA208M active multicoupler is used to split the signal to feed the scanners, with the unused outputs being fitted with 50-Ohm terminators. The audio outputs from the scanners are connected to a pair of Delta-44 four-input audio cards via the breakout boxes located on top of the scanner stacks. The cards are installed in an off-lease Compaq Evo PC which I obtained from Tiger Direct at the bargain price of $150. The PC is running CentOS Linux, and runs six instances of DarkIce to stream the audio to LiveATC. Processor loading is currently around 20%, so the system will happily be able to add the other two scanners I intend to install in the coming weeks. Power for the scanners come from a single power supply via a homemade distribution block, avoiding the problems associated with so many "wall-wart" transformers!
