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Posted by Stan Gunn (Member # 554) on 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.
 

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Posted by Paul G. Thompson (Member # 655) on 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.
 

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Posted by Ken Layton (Member # 133) on 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
 

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Posted by Stan Gunn (Member # 554) on 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.
 

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Posted by John Pytlak (Member # 331) on 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 ]
 

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Posted by Ken Layton (Member # 133) on 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.
 

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Posted by Barry Floyd (Member # 385) on 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.
 

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Posted by Jack Ondracek (Member # 1466) on 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!)
 

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Posted by Stan Gunn (Member # 554) on 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.
 

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Posted by Ken Layton (Member # 133) on 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.
 

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Posted by Stan Gunn (Member # 554) on 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.
 

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Posted by Jack Ondracek (Member # 1466) on 05-24-2003, 02:52 AM:
 

quote:

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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.

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