my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » drive in radio sound

Author Topic: drive in radio sound Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 05-23-2003 01:02 AM                        I have recently obtained a L P B am radio system for my collection, comprising of 1 T8 coupler,TX2 transmitters, T7A control unit. Could any one please help with circuits and setup details for the system, thank you Stan Gunn.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 05-23-2003 01:16 AM                     Not familiar with that brand, but proper impedance matching of the antenna (whatever you use) and tuning out the VSWR is probably the most critical issue.  |  IP: Logged Ken Layton Phenomenal Film Handler Posts: 1452 From: Olympia, Wash. USA Registered: Sep 1999 posted 05-23-2003 02:16 AM                     LPB is what we have for an AM transmitter (carrier current) at the Skyline drive-in. Here is contact info for the manufacturer: LPB Communications 960 Brook Road, Unit 5 Conshohocken, Pa. 19428 Phone: (610) 825-4100 or 877-LPB-COMM Fax: (610) 825-4047 URL: www.lpbinc.com Email: info@lpbinc.com or sales@lpbinc.com  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 05-23-2003 05:17 AM                        Thanks Ken I have made contact with them, cuold you please advise me how the antenae is set up as I as Yet have no experiance with this type of system. best regards.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 05-23-2003 07:54 AM                        When I worked at the Grandview Drive-In (1967-1970), I built a "home brew" AM transmitter that we coupled to the existing underground speaker wiring ("carrier current"). As Paul mentioned, it's especially important to tune the output stage to minimize VSWR (on a tube output, adjust for minimum plate current). It's also very important to choose a frequency that has minimum interference from other stations. Back then, we used the old unused USA civil defense "Conelrad" frequency of 640 khz, but sometimes had late night interference from an AM station in Cuba that sometimes came in to Western New York when propagation (or propaganda ) conditions were just right. AFAIK, we had one of the first drive-in radio systems in New York state. [ 05-23-2003, 12:42 PM: Message edited by: John Pytlak ]  |  IP: Logged Ken Layton Phenomenal Film Handler Posts: 1452 From: Olympia, Wash. USA Registered: Sep 1999 posted 05-23-2003 10:50 AM                     Ours is a "carrier current" system which means it has a coupler box instead of an antenna. The coupler box (mounted near the transmitter) feeds the radio signal into the existing underground speaker cable which basicly makes the speaker cable the antenna. This setup replys on the underground speaker cable being in excellent condition with no breaks, shorts, or leaks to ground. It was installed two years before I started working at the drive-in and I never did have a manual for it.  |  IP: Logged Barry Floyd Phenomenal Film Handler Posts: 1079 From: Lebanon, Tennessee, USA Registered: Mar 2000 posted 05-23-2003 12:06 PM                        I think I've got one of those systems. Mine says LPB "Cinefi" on one cube and something about a "coupler" on the other. I doubt I'll use it, as I have no idea how to hook it up.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 05-23-2003 12:48 PM                        Barry, if you get a chance, email me a picture of your transmitter. The Cinefi system was popular with Pacific Theatres' "United Drive-Ins" group, that had a majority of the Seattle/Tacoma area drive-ins up here in Washington. Some of that equipment found its way to other drive-ins as United closed various properties. Most of the stuff is totally obsolete. The early transmitters used analog tuning with vernier dials... not something that would work well with today's digital radios. The later models were phase locked, but you can't find parts or documentation for any of that stuff any more. If one dies on you (and I had a couple do that), you can pretty much forget about getting it repaired... unless you just get lucky and find a bad part by accident. If you really want to back up your sound (which should be FM) with an AM transmitter, LPB and Radio Systems both put out good models that aren't all that expensive. If you're using Smart's processor, theres a mono-sum output for an AM transmitter (or a speaker system). It would probably be a good idea to get a low-end modern AM limiter. The FCC imposed a rather stiff pre-emphasis curve on AM some years back. Your sound would probably be a bit muddy and dull without the limiter, other problems with AM notwithstanding. Inovonics makes some of the better low-priced models. Look for mention of NRSC compliance if you go this way. John: mentioning Conelrad really dates you! I was glad to see them drop the old EBS system in favor of EANS. We used to hold our breath when dropping the station's carrier (twice) for those old tests. It wasn't unheard of for the transmitters to blow fuses (or other sundry parts) when kicking them off and on like that... and of course, Murphy's Law held that it was far more likely for this to happen if your transmitter was remote controlled and at the other end of town from your studio! (Paul's too young to remember any of this!)  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 05-24-2003 12:29 AM                        Jack Your luck is in ,I have both of the cinefi systems you mentioned, also manuals for both systems. Could be a good addition to the manuals site. Ken do you still use speakers on the system, or is it the same as the cinefi, haveing to take all the line transformers out of circuit.  |  IP: Logged Ken Layton Phenomenal Film Handler Posts: 1452 From: Olympia, Wash. USA Registered: Sep 1999 posted 05-24-2003 12:41 AM                     Yes, speakers are still in use at the same time as the radio xmitter. The transformers in the junction boxes are still used as normal.  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 05-24-2003 12:54 AM                        Thanks Ken All is comeing clear, I had worked out all the interface wireing,it was just the output that had me tossed, the CINEFI does away with speakers on the posts, a short curly cord connecting to the car ant.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 05-24-2003 02:52 AM                        quote: from Stan: Your luck is in ,I have both of the cinefi systems you mentioned, also manuals for both systems. Could be a good addition to the manuals site. Great idea, Stan. Brad would be the one to talk to about that. I wouldn't bother with the vernier-dial version though, unless someone asks for it. With the digital radios out there nowadays, that transmitter just isn't stable enough to be really useful. The digital one might be worth keeping up though. Seems I recall that one running 10-20 watts or so, and it sounded pretty good.  |  IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.