I now have the two NYC Heli feeds up and running. The two feeds run off of one machine (Mac Mini G4) and a Behringer USB soundcard. As the receiver site is remote (at a friend's business), I had to build the system as compact and self-contained as possible. My goal was shoebox-sized for two feeds together, and while I couldn't make it that small it's still fairly compact. I bought a 40mm ammo can on eBay and proceeded to build the system into that box. The plan was to have it entirely contained within, including a UPS, and just jacks on the outside of the box for the connections. I owned no equipment before starting on this except the handheld scanner, and bought everything on eBay, PartsExpress, RadioShack, ScannerMaster and BestBuy.
Here's what the equipment is:
PC: Mac Mini G4 1.25Ghz / OS 10.5, no integral audio-in
Sound: Behringer UF202 external sound card
Power: ?? 420w UPS on sale for $24 at BestBuy
12v 3A universal power supply feeding both scanners and cooling fan
Jim Airband bandpass filter installed
Case: 40mm Ammo Box
Pass-through connectors from PartsExpress (BNC, RJ45, IEC Power)
3" 12v cooling fan from RadioShack
1/4 Wave Magnetic NMO Mount Airband antenna from ScannerMaster
Plenty of BNC cables, couplers, audio cables, etc. I did find a nice item at RadioShack that helps the dual channel feed... "Aircraft Adapter 1/8" Stereo Jack to 2 1/8" Mono Plugs Model: 42-2495"... it combines 2 Mono 1/8" male plugs into one stereo 1/8" female jack. That, plus a 1/8" stereo to dual RCA cable gets the audio into the USB input device.
The ammo box was quite a pain to cut holes in with the Dremel. I went through about 12 cutting blades. I didn't have the perfect tools for it, but it worked out in the end. I also reused some old Molex connectors to provide a power disconnect for the lid which holds the cooling fan.
My initial plan was to have the box connect via WiFi at the location, but the particular Mac Mini I ended up with didn't have built in WiFi (or audio input, which I assumed it had). A USB WiFi dongle proved unreliable in testing, so Ethernet it was. In any case, here's the build.