Carrier Current Radio. What is it?

Perhaps oversimply, Carrier Current allows the introduction of an AM radio signal into a buildings electrical system to allow a station to 'broadcast'. This can be a simple and relatively inexpensive means to start a radio station on campus. Special equipment is used to connect an AM transmitter into the electrical system for broadcasting. This will REQUIRE the services of a campus electrician and should NOT be attempted by a student.

We will not try to sell you on Carrier Current technology on this page, rather pass along some tips from LPB, Inc., one of only two companies that we are aware of that sell Carrier Current equipment. The other is Radio Systems. Keep in mind that the documents do have a bias towards LPB equipment. CBI presents these documents because we feel the technical and legal aspects are valid and could be an aid to stations. Note that some of the documents may have incorrect pricing or contact information (LPB’s current phone is 610-825-4100). CBI can be of assistance in many ways, including putting you in touch with the author of many of the documents!

In addition to the tips below, you will find that many members of the CBI list and CBI have experience with Carrier Current systems and can be of assistance. You may also find some local engineers who can help you with your Carrier Current system(s). Contact CBI or your local Society of Broadcast Engineers to see if a local engineer can assist you.

The first document is a discussion of the theory beind Carrier Current. A good general document mixed with legal history and theory.

One of the most important aspects of the purchase, installation and Maintenance of a carrier current system is to understand the design theory and approach. The Carrier Current Design document is not only of use to those who plan to implement Carrier Current, but also to those who want to do maintenance to a system. It is important that someone who maintains a system be aware of the considerations that may have lead to the design of the system or for them to recommend upgrades. It is not possible to stress enough the importance of documenting your work. Any Carrier Current system design should be detailed in several places on and off campus.

Those who own a Carrier Current system AND use it with success will tell you, that you can't run this system with out maintenance! It simply can't be done. All broadcast stations pay an engineer to maintain. The good news is that Carrier Current Maintenance CAN be done locally and often with qualified on site help, sometimes by students. This tech document describes the maintenance needs of most stations! Too intimadated to do this yourself? Having problems discovering where this 'secret equipment' is located? You are not alone. If the above tech sheet doesn't help, . We can help you locate a local engineer OR someone else who can help.

Sometimes, when all else fails to deliver a strong signal, Neutral loading will save the day!. While the LPB document found here describes how to wire for this, CBI STRONGLY suggests that this and any other maintenance be done under the supervision of qualified personnel. Sometimes, for existing systems, this simply means showing the drawing to a campus electrician. Sometimes, this means contracting a local engineer, but this is not normally the case.

Campus AM Antennas. Another option for campus radio is the use of an AM antenna system. If ever there was a confused issue, this is it. The problems stem from a misunderstanding of the rules and the FCC’s failure to make them more clear on their side.

There are two different rules for AM antennas on a campus. One (Part 15.219) allows for a campus antenna system with 100mW (1/10th of a Watt) of power, in a specific design. This system has no limitations in terms of coverage and can be used on or off a campus, and even by commercial entities. The other rule (Part 15.221b) makes a specific rule for the campus of “an educational institution” and references the field strength rules of Part 15.209 to create the perimeter limitations. These rules are NOT the same. You cannot apply them to each other.

The linked technical note will help you to understand the distinction of each of these systems. Please do not be fooled into thinking that the Part 15.221b rules allow you unlimited power on campus. They do not, because the power must drop off at the perimeter. Since the physics of AM don’t allow you to make the signal powerful all over the campus and dead at the perimeter, there will be system compromises. Please read the note and ask for help before designing or buying such a system. There are options.

One option to consider is that the Part 15.219 rules do not limit the number of systems you can employ. The author of that technical note is in the midst of deploying no less than 6 systems in the areas around his College to spread the station signal, legally, into the greater community. Stay tuned for updates…

-CBI