I don't have many answers for lots of Chris' technical questions up top, but since this stickied thread will probably draw a fair share of folks seeking how-do-I-do-this type answers, here's how we have done things so far. We've run 16 races on this equipment, give or take, and it's still somewhat a work in progress, but I'd say it's 95% stable at this point and this is what I've learned.
Handhelds: we run mainly Motorola GP68's. We started with SP10's and SP50's that I was able to pick up cheaply on eBay back in '10. Added the GP68's as the SP's died out. The nice thing about the 68's is that they are fully-programmable by the user, so you don't need Motorola's proprietary secret handshake software. That flexibility is also the downside, as any user can accidentally re-program the radio so that it doesn't work anymore if you don't have the keyboard locked. I think that Troy thinks that there is something funky with the mic circuit on the GP68 versus the other Motorola non-GMRS/FRS radios, but I'll let him discuss that if/as he sees fit.
That said, if I could find something else that would work with my existing Motorola-based equipment and that worked better, I'd use that instead. I really like the SP50's but they are getting hard to find, and I don't have the equipment to program them anyway.
Car Radio: After a lot of back-and-forth using the SP50's in the car and getting anywhere from somewhat poor to somewhat good results, we switched to a Motorola mobile radio last year and it has done a lot of good things for stabilizing the quality of comms with the driver. We just run a magnetic-mount NMO antenna (of which I need to have the cable length modified, apparently). The plus side of the mobile radio is that it has stronger transmission signal than the handhelds and runs on car power, so you don't have to worry about finding a battery eliminator; of course, if the car is 100% dead, so is the radio, but you'll be coming back in on the hook in that case anyway so the radio is sort of irrelevant at that point. But it sends out a strong signal which means we can usually get driver transmissions nearly everywhere the car is on track. Cons are that the radio is not user-programmable and as far as we've been able to sort out, using it requires a somewhat pricey car harness that routes to the 16-pin connector on the back, and it really really works better if you're using good helmet kits. Speaking of which:
Helmet Kits: we started out using the cheapest helmet kits we could find, and our comms sounded like it. We now are shooting for high-quality mics in every driver helmet and it really makes a big difference. Maybe a bigger difference than transitioning from the handheld in the car to the mobile radio in the car. We are using a NASCAR-style harness, so the drivers can get away with using earbud-style headphones, but I use dedicated mono headphones in a DIY earmold (using a DIY earplug kit from Cabela's) and I like those a lot better. I still tape them into my ears with electrical tape, even when under a balaclava.
Frequencies: we are on UHF 450-470MHz somewhere, depending on how we have the mobile radio programmed. We try to monitor all of our programmed radio channels when we are at the track on Friday so that we have minimal interference, but that's been pretty hit-or-miss because most of the other teams aren't broadcasting much on Friday compared with Saturday and Sunday. So we have to be kind of flexible on what channel we are running on during the race.
Aside: sometime in the last 2 years, I tried to get licensed by the FCC to use specific frequencies the way that the big race teams do (Cup, Indy, etc.) and it was an unmitigated disaster. I work with forms, rules, government bureaucracy and bureaucrats, and the application of rules to forms all day long in my day job, and it was a nightmare trying to get licensed, to the point where I literally abandoned my efforts (and $200 filing fee) because it was so impossible to decipher. If somebody knows how to navigate this maze successfully, I would love to talk with you about subscribing to your newsletter.
Headsets for non-drivers: I picked up some used Nextel Cup officials' headsets for our crew to use when talking to the drivers. I think they're pretty effective, but I don't find them very comfortable, but they are useful when at a louder track.
Push-to-talk button: we have ours on the steering wheel at 9:00, and I prefer it there. You always have your left hand on the wheel, so that makes it easy to find. I've driven in cars that have it velcroed to the wheel in some other position, or near the gearshift lever (but not on the gearshift), or on the gearshift lever, and all those other places are just less convenient. If you make your drivers look down to find a PTT button, they are not looking at where they are driving, and we should minimize that.
Notes on Good Comms: Both driver and crew need to remember that the radios work better if you press the transmit button, wait a second, and then begin speaking. Speak slowly, speak loudly (but don't yell), don't mumble, and keep your questions or announcements short and to the point. It really does work best if you end every transmission with "over" if you have said anything more than "roger." It isn't the worst idea to repeat important transmissions back to the sender: "Pit in two laps, copy". But really, the biggest enemy of clear comms is just not pressing the transmit button before you start to speak (side note: when driving, pay attention that you aren't hamfisting the transmit button while driving, the crew doesn't want or need to hear road noises over the radio). If you want to hear effective comms, I recommend scanning the aviation bands, those guys have it down cold in a life-or-death business. Our comms don't have to be that good, but it can't hurt to try.
And a couple of semi-random tips that we've learned mostly the hard way:
If you run a battery eliminator, you may also need to run some sort of noise filter to keep alternator whine out of your radio circuit.
If you have the ability to do so, put a coiled cord headphone extension between the car harness and your helmets. When your drivers exit the car without remembering to unplug their helmets first, the extra length will keep them from falling on their butts, and the cord will take the brunt of the damage, rather than your car harness.
Mount your helmet mics so that they exit from the driver's side of the helmet and plug in on the driver's side of the car, rather than on the side of the helmet that is toward the middle of the car. This makes it a lot easier for your teammates to help plug in your helmet kit (earbuds to kit and kit to car harness) when you forget to do that.
Wherever you mount your in-car radio, make it easy for the driver to change the volume. It is annoying to have a too-loud radio in your ear and not be able to do anything about it.
Finally, in my experience, the drivers want and need to hear from the crew less than you think they do. If they need information (like lap times), they will ask for it. I am of the Kimi school on this : let them concentrate on their job, they know what they are doing. Good radio comms are an invaluable tool, but they become valueless if they become distracting to the driver.
Cheers.
Pat Mulry, TARP Racing #67
Mandatory disclaimer: all opinions expressed are mine alone & not those of 24HOL, its mgmt, sponsors, etc.