LPB (AM and FM) I used an AM LPB at the radio station I worked at.

Decade (FM) I've heard this one on the air too.

Radio Systems (Phase II series transmitters, I think)

Catel

Marble "Skycaster" units ...only heard about them.

If you can tell me anything on these or other units, let me know please.

Thanks,
Chris

 

It's called the model FM-100 Super Pro FM Stereo transmitter kit ($249.95) and has a companion transmitting antenna called the model TM-100 True Match FM Antenna Kit ($39.95).

I built one in about 8 hours and it's a real professional unit with stereo line level inputs and a mike input for paging! It seems to be very stable and has good limiting free from distorion or frequency drift. The transmitting frequency is the range of standard FM broadcast band 88-108 mhz and you can program the frequency by going into test mode and holding the up/down buttons till you see the freq you want on the digital display. It has eeprom memory to hold frequency without need of battery backup. With the TM-100 antenna it covers the drivein field quite nicely.

It's worth a try if you like building things (or known a tech who could assemble it for you).

There's some used broadcast gear at Harris' site: http://www.broadcast.harris.com/used-eq/

I guess if you were going to have the Cadillac of drive-ins w/FM sound, you'd have a good old analog Orban Optimod! Probably for most ears, a less expensive consumer expander/compressor/limiter in a standalone or multi-effects rack box from a guitars-n-drums music store would work OK. Set it for least compression on a passage w/what you'd consider "normal" level, & let it just crush the screaming trailers down. Those trailers are so compressed already in production, it should hardly be noticed.

------------------
William Hooper
Junk drawer: http://www.geocities.com/hollywood/theater/3622
Theatre Empire: http://members.xoom.com/saenger.1
 

I've not built the FM 100 kit but I built one of Ramsey's lower end units for outdoor film show use with my 16mm projectors. I found it very easy to build and the instructions were very easy to follow. I'm sure the pro unit is more involved but I assume that the instructions that come with that kit will be equally understandable. Also, if my memory serves me correctly, you can buy the Ramsey Fm 100 Super Pro in either kit form or factory built.
 

I'm using a compressor on my home cinema, and it does a great job balancing the volume between those screaming trailers and quiet dialog.
 

Hey, isn't this like the "virtual stereo" way back when, what was it called?
 

I use it at our church on occassions to broadcast the worship services from the santuary down to the other end of the building to the nursury workers, and I've used it several times with my mobile DJ system.

When we open our drive-in, I'd prefer to use a rack mount model similar to the Decade, or the Skymaster.

I've got an AM transmitter too, but haven't quite yet figured how to hook it up. It's two big bulky "cubes" (about 8" x 8" x 6")that mount on the wall. (I believe it says "LPB Cinematronics" on the name plate)

Drive-In patrons are different type of folks from what I've been able to see. They don't really care about 7 channel surround sound - SDDS, DTS or THX approved systems. Most of the drive-in patrons are there to "experience the drive-in" - not to experience the sound systems. Today's remaining drive-ins are very limited with their abilities to deliver the soundtrack to the customer, something that you "indoor guys" will never have to worry about.

Although keep in mind... drive-in theatres were the "FIRST" to feature "Stadium Parking"

 

LPB is located in Canoga Park, Calif. Here's their phone number: (818) 340-4590

Is your LPB white? Either you have 2 transmitters or you have a transmitter and a coupler (Carrier Current). The carrier current setup superimposes the AM radio signal on the existing field speaker wires for its antenna. This system assumes your field wiring to be in excellent condition (no shorts, breaks, or leaks to ground) otherwise you'd blow the transmitter.

You can rack mount the Ramsey FM-100, just buy a 2U high "rack mount shelf" which is the same thing people do to rack mount their CD players for intermission music.

The Ramsey FM-100 is MUCH better than any of their low-end transmitters. You've got to see all the stuff that goes inside it.

In the USA, doesn't the FCC Regulations Part 15 still limit the power and distance of transmissions in the FM and AM broadcast bands? Radiating about 3/4 mile is likely to get some complaints from people having interference on their radios, or upset with their young kids listening to "bad language" movies from the nearby drive-in.

Way back in the late 1960's, when I worked at the Grandview Drive-In, a neighboring conservative church group got on our case when we played the R and soft-X movies in the off season, and teenagers would park next to the lot when they were turned away at the boxoffice.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
 

The Ramsey kit meets Part 15 requirements for low power FM. The export version of it is equipped with a 5 watt "booster" module installed (you could transmit across town with that one).

The FM-100 puts out about 50 MILLIWATTS (if I remember right, I don't have the manual in front of me). Surrounding terrain, antenna height, antenna placement, and having a metal fence around the theater all affect the distance the signal will travel and reception quality. If the transmitted signal is TOO strong, you can always find a way to reduce it. Remember there are alot of driveins with no neighbors near them.

At the Skyline drive in here in Shelton, we have an old LPB AM mono transmitter with a carrier current coupler into the field speaker wires. To the right of the theater is a couple of 100 acre farms and to the left of the theater is a used car dealer and a gas station. The theater is built on a hillside with a WOODEN fence around most of the property (except for a chain link fence along the back). Carrier Current isn't suppossed to transmit far, but I think being on a hillside must make our system like an "antenna farm" because I can hear our radio signal a mile down the road at the Indian casino before it fades out to nothing.

With that much range, you'd probably need the whole gate/expander/compressor/limiter bit. The expander would pull up suiet sounds you'd need, & the gate would keep out Whatever else is down there.

Boxes like that used are usually all over pawn shops & rock-n-roll music stores, & with even less compression than most radio stations use I'll bet it would make a big difference in ease of listening to movies on a car radio.

Or find an old CBS Volumax & plug it in for the classic pumping & slamming early top 40 radio sound, if you have a sense of humor & no conscience or mercy. Everything will sound like an action movie trailer, & the folks in the cars will grow exhausted & homicidal.

Of course today almost all remaining drive-ins use FM. There are several models to choose from made locally. The problem is with an unlicenced 50 milliwatt transmitter you are at the mercy of a new licence.

Say you choose 91.1 FM and do all your slides and signage for that frequency, then a new licenced station opens up within 75 miles on the same frequency and before you know it on some nights you hear Slim Dusty instead of Mel Gibson!

You can of course buy a 10 watt unit and blow anything else away, but that brings another set of problems - you affect others who have paid big $ for their licence. The key is to use a low power unit and choose a frequency that is in use already, but a long distance away. Your low power unit will be OK if the station is 150 - 200 miles away and they will not licence another station on the same frequency in the same state - applies to Australia anyway.

I think I'll go down to the garage and seek out my original blue Cine-Fi hire radio. I wonder how many ramps still have Cine-Fi clips hanging on them???

David
 

Boy a CBS Volumax!! Now there's a relic...probably the first successful solid state broadcast audio processor. Actually I have one in my collection of junque. Actually if you just needed mono sound, it would do the trick for non-discerning drive-in patrons. You may need some transformers to adapt it since it's balanced in and out. Two would do stereo
 

Bill, the radio station I worked at has an old volumax on AM and an Optimod 8100A on the FM. Memories......

Has anyone heard of Broadcast Warehouse? They make a rack mount 100 mW FCC legal (part 15 reg.) transmitter for FM. About $300-400. Comet antenna for around $100.

I keep hearing about a Skycaster unit. Anyone have info on this?

I might go with an AM and FM config. (for redundancy-one blows up the other's similcasting) AM still looking...FM Decade?

Still have plenty of time to look and shop.
--Chris
 

I believe Steve ______? (I forget his last name) at the Swan Drive-In in Blueridge, Georgia uses one of these at his theatre. Worked very well when I was down there in September. Give him a call or email him.

If someone's using one of these, what do they do? Send L&R, & leave Center unused?

 

anyone else heard that one?

anyway, regarding FM Drive-in transmitters, I f you are unlicensed in the U.S. your maximum output power is limited to around 100 microvolts at 10 feet(I think, It's been a while.) Regarding compression, it wouldn't hurt. The main reason why commercial broadcasters use it is to prevent overmodulation, or for FM, carrier deviation over 75 KHz. The reciever will detect such an occurance as clipping of the audio signal. Overmodulation also is against the FCC's rules. IMHO if you put a harmonic free signal into the air with proper compression, you should be able to use as much power as you want.

Josh

This post is several years old but for those who have the desire to try and build their own drive-in fm transmitter here are some very cheap (and Australia) kits that can help. Halve the prices to get $US
http://www.ozspy.com.au/kits/kits.htm (this one is illegal in Australia methinks as it puts out 200 microwatts)
http://members.ozemail.com.au/~auselec/commun.htm
http://ieee.uow.edu.au/~daniel/projects/radio_link/ (super cheap)

Slightly more expensive but currently on special in the US is
http://www.mp3playerstore.com/buy_it_now__/link-it.htm

cheers Peter

The radio broadcast industry has to agree on a single standard (which they have not done). And "next generation" music discs like DVD-A and SACD have to become commonplace (also hasn't happened). Until those foundation level advancements happen, 5.1 surround car stereos will remain a very small niche market item. Only after those developments happen will one be able to digitally transmit an AC-3 bitstream to car stereos in the drive-in.
 

Run the Dolby Cat69t taht is 50% modulated and set the gain stages for the transmitter to that and you will not have to worry about overmodulation

Since the transmitter will be recieving Lt and Rt they will transmit the centre and surround channels in a standard matrix mode which some car units now decode

Sony has a consumer unit now out on the market - MDR-DS5100 Wireless Surround Headphones. It will take any encoded L/R outputs, as well as a 5.1 input; it then outputs a L/R signal that has been processed to create the Virtual Surround that Dave is talking about. Obstensibly its purpose is to broadcast the processed signal to its complimentary headset receiver, but the output is easily be sent to any line level input such as the FM stereo transmitter. The resultant processed signal creates a psychoacoustical soundfield that simulates 5.1 surround sound in any 2 channel playback system, be it the headset or a standard stereo car receiver. In the headset it sounds quite impressive, but I have heard this same system used in some TV sets and computer 2 channel playback system and even though it requires a person sit equidistant between the two speakers in the close-field "sweet spot," a car environement puts the occupants close enough to the sweet spot that surround effects will still be perceived.

And you are totally right Dave, what a great marketing tool it would be to be able to claim that you are the first Drive-in in the world to have Dolby Virtual 5.1 Surround Sound! Throw this up on the screen using the Dolby Surround logo snipe and it will be the talk of the town. It should even get a few free newspaper stories written about it.

Frank

PS, In NYC, the Sony unit is available at J&R Music World.
 

Also, commercial broadcasters transmit horizontally while the Ramsey antenna punches out vertically. If you use it on low power your interference to TVs and other broadcasters should be minimal. And the "capture ratio effect" will allow the licensed broadcaster to win out in any conflict. Unless of course your nextdoor neighbor is trying to bring in a distant signal from 75 miles near the horizon then you could be considered "interference".

Bill BuncH
Misawa, Japan