Casper, Wyoming’s Carrier Current Community Station
AM Stereo 1670 is a Carrier Current AM radio broadcast station which uses the neutral power grid line to transmit a low level AM radio signal to nearby AM radio receivers. Although this might sound extremely limited in range, the neutral power grid line could cover an entire community or several city blocks. Any typical power socket in a home or business that is also on this same neutral power grid line will be capable of receiving the transmitted signal since these power outlets are connected with one wire to the neutral power grid line to complete the power circuit.
This type of radio service is regulated by the Federal Communications Commission (FCC) in the United States. The section of the FCC Rules that contains these regulations are located in Title 47, Part 15 of the Federal Code. Specific information regarding the Part 15 rules can be found in a public release PDF document and can be accessed by following THIS LINK. The specific sub-part within the document is Pt. 15.221.
During the late 60’s and well into the mid 90’s, Carrier Current AM broadcasting was very common with colleges and universities where students had the opportunity to learn everything involved with radio broadcasting. Although rarely found operating in communities during those years, there were and continue to exist Part 15 low power stations.
Some low power community stations operate under the Part 15.209 rule which allows for an unlicensed radio transmitter in the AM broadcast band using a short antenna and very low transmit power of 100 miliwatts (.01 watt). The antenna, feedline and ground lead if any is used cannot exceed 3 meters in length (aprox 9.6 feet). With a good ground system and no obstructions near the antenna, this flea power signal can extend well beyond 1 and 1/2 miles, with some reports of coverage as much as 3 miles with good conditions!
However even with this range, the signal can experience interference easily and often only receivable in very sensitive radios often found in vehicles and portables in open areas. It is difficult to receive these weak transmitted signals on a typical table top radio inside a home, especially a mobile home where the outer walls are metal, creating a shield preventing good reception. One way to avoid this problem is for the listener to attach an external AM radio antenna such as a “loop” antenna or outside “long-wire” antenna. However the outside long-wire antenna is not always possible due to space limitations, neighbor-friendly issues or hazards.
Carrier Current broadcasting, operated under Part 15.221, is very different from the Part 15.209 specifications. In Part 15.209, the transmitted signal is emitted from an “Intentional” radiator, meaning that the signal is emitted by a conductor such as a rod or wire less than 9.6 feet in length placed into open space, and with a maximum power permitted of 100 miliwatts (.01 watt).
In Part 15.221, the transmitted signal is “Injected” into the electrical utility service wires on the power grid. This forms a “wired” wireless radio transmitting system. Since the power wires have a very low impedance (1 ohm or less), far more transmitting power is needed to effectively send the signal through the power lines. 100 miliwatts would not drive the power lines enough to pick up the signal on a radio a few rooms away. Power levels up to 50 watts are permitted and most Carrier Current stations can provide effective coverage with as little as 10 watts and even 5 watts.
With this method, the radio signal is sent right into any AM radio receiver that is either plugged into a wall outlet, or a portable radio within 200 feet of the power lines. Although the power grid system consists of transformers mounted at various points and will block the transmitted signal by internal shielding, this is overcome by “Injecting” the signal into the power grid neutral wire, which does not pass through the transformers. The neutral wire can be the same neutral wire that is extending for several blocks to several miles delivering the transmitted signal right into the listener’s AM radio.
AM Stereo 1670 KROCKS ZeroPointRadio operates under Part 15.221 into the Casper Wyoming power grid system, injecting the AM 1670 signal onto the neutral power grid line at a nominal power output of 15 watts and a maximum of 50 watts. AM Stereo 1670 KROCKS ZeroPointRadio uses two LPB AM 25 transmitters with the CCUFF C-QUAM and ASMAX C-QUAM exciters and two LBP TCU-30 power line coupling units. One serves as full time operation while the other serves as a standby backup.
In Part 2 of About AM Stereo 1670 KROCKS ZeroPointRadio, we will examine more closely the transmitter systems and power line coupling units as well as go over some basics and history of Carrier Current broadcasting.