iAMradio Uses
i. AM. radio

Low Power AM Broadcasting for Educational Institutions
Carrier Current & "Free Radiate" unlicensed equipment

Free Radiate Systems
Carrier Current Broadcasting
Low Power AM Transmitter - TR-6000

CP-15 Carrier Current Coupler - "Phase II"
AT Series - Fiberglass 20ft. "Free Radiate" Antenna

"Free Radiate" Systems

In 1990, the FCC amended the unlicensed low-power AM regulations to allow the use of an antenna to provide AM radio coverage on the campus of an educational institution. This provides many broadcasters with an exciting new opportunity to cover a large acreage from a single transmitter installation.

The new federal rules now allow the use of an AM vertical antenna on many educational campuses*. To help you benefit from these new regulations, Radio Systems, Inc. has developed an efficient, easy to install and operate, complete AM transmission package. The system includes a proprietary AM antenna, antenna tuning unit, transmitter, all hardware, cable and connectors, and complete installation instructions. Contact Radio Systems for regulations and pricing to see if a vertical antenna system is right for your station.

FCC Rules - Original Text

free radiate

Complete AM Antenna Package / Free Radiate System $4,845.00

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Carrier Current Broadcasting

carrier current"Carrier Current” is the original form of low-power UNLICENSED broadcasting that utilizes the standard electrical wiring of a building as a broadcast antenna by purposely “coupling” AM radio signals into the power lines. Once very popular on college campuses, it has today mostly been replaced by Internel radio stations. But for colleges, Universities, High-Schools, Camps and other institutions that still want to be “ON-the-Air” with a signal receivable on a normal AM radios - Carrier Current represents the only unlicensed option to operate a "real radio station" on the standard AM band.

This technology was first commercialized by Dick Crompton, founder of Low-Power Broadcasting Company in the 1970’s and 80’s and today, in his tradition, Radio Systems remains the only available commertial source for Carrier Current equipment and expertise.

Radio Systems is the nation's primary provider of carrier current transmitters, AC line couplers, and accessories for college and institutional on-campus AM radio stations. Carrier current is the legal, fast and inexpensive route to start a radio station for your organization.


TR-6000 Transmitter

Brochure PDF

A solid state, variable power, 10 watt digitally-synthesized AM transmitter with internal audio limiter and detector circuitry.

Radio Systems' TR-6000 represents a leap forward to the new Millenium in low-power AM RF design. The successor to the industry-standard TR-20, the TR-6000 features numerous improvements in both audio quality, efficiency and technical specifications. This solid state, 10 watt design is based on class D amplification, so the transmitter runs cool to the touch, even at full power. And, output efficiency is quadrupled, up to 80%, over its predecessor. New features abound, as well, including remote control capability, a front panel power and audio VU meters, headphone monitor, and efficient, flat-pack design that can be easily rack-mounted.

There are even multiple TXCO oscillator and external synchronization options.

TR-6000 10 WATT AM Transmitter $2,995.00

Maximum Modulation
Output Circuitry Monitoring
AM radio is always fighting high back-ground noise levels, so maximum audio modulation is important for the best possible signal to noise ratio. The TR-6000 has an internal 100% peak modulation limiter which automatically controls the transmitter gain to stop over-modulation distortion. The limiter has a full 40 dB gain reduction range. Limiting action is controlled by input gain level setting. The TR-6000 is a totally solid state unit and benefits from the extended frequency response and stability of transistors through the final output stage. Extremely dependable and long life operation is achieved by utilizing Class D circuitry. This allows the TR-6000 to be used in facilities where the only available power sources are batteries or solar power. The result is a highly efficient, cool-running unit. The TR-6000 output can be monitored through its built-in audio detector circuit. These components effectively comprise a miniature radio whose audio output is provided on a phone jack on the side of the transmitter. Headphones can be utilized for on-site monitoring, or the signal can be wired to remote amplifier. Because the detector monitors the signal envelope at the final output of the transmitter, performance of the entire audio chain can be evaluated.

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R.F. Power Output

Adjustable to 10 watts

Type of Emission

Amplitude Modulation (A3)

Frequency Range

500 kHz to 1.7 MHz

Frequency Stability

± 20 Hz (-20° to +50° C)

Carrier Shift

2% maximum

Harmonic Attenuation

35 dB or better


-55 dB below 100% modulation

Audio Input (for 100% modulation)

-50 dBm minimum

Frequency Response

20 Hz to 15 kHz ±1.0 dB maximum

Audio Distortion

Less than 2% @90% modulation

Modulation Monitoring

LED Power Meter, Built-in envelope detector

Modulation Limiting

Built-in 100% peak modulation limiter, 40 dB gain reduction

Power Consumption

48 watts at 24 vdc


w-15" h-6" d-2"


4 lbs.


1 year - parts and labor

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"Phase II" CP-15 Coupler

Brochure PDF

An antenna matching unit design specifically for loop antennas with built-in reactance compensation.

Radio Systems' CP-15 Coupler is a unique antenna matching device with sophisticated, specialized circuitry for low power AM broadcasting. Existing electrical wiring is frequently used as an antenna for low power systems. This wiring, not intended for energy at RF- frequencies, present a hostile environment for radio equipment. The CP-15 Coupler has been designed to efficiently transfer RS energy into these antenna systems and protect the transmitter unit.

A specially developed, two stage system is employed for impedance compensation. Two broad band transformers are combined to provide a total of 15 impedance settings. A decade capacitor switching system is also incorporated to provide reactance correction and cancel any antenna grid reflection of radio energy.

The proper combination of impedance and reactance settings are determined throughout the internal bridge circuit. The meter allows the "nulling" of reflected power and maximization of transmitter to antenna energy transfer. In the match mode, 90% of the transmitter power is automatically "dummy loaded" to protect the transmitter circuitry. The three output circuits provided are fuse protected by high voltage, high pass capacitors.

CP-15 Coupler $495.00

Direct SWR Readings

Improved Matching
The "Phase II" coupler has a bridge and meter circuit which can be used to directly read the standing wave ratio of the carrier signal. Transmitter to antenna match can be quantitatively evaluated and a direct ratio calculated. The CP-15 two stage coupler, with integral reactance and impedance compensation, provides an exact match into a wide variety of antenna systems. This efficient energy transfer insures maximum signal strength and radio coverage while protecting the transmitter from damage due to high VSWR conditions.


Power Input 20 watts RMS maximum

Input Impedance

50 ohms unbalanced

Output Impedance

1 to 50 ohm in 15 ranges with built-in capacitance decades

Matching Circuit

Two stages: multifilar wound ferrite transformers


VSWR bridge, forward and reflected readings

AC Line Connection

500V maximum, line to line and ground


W-9" H-9" D-3"


5½ lbs.


1 year - parts and labor
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AT Series AM Broadcast Band Fiberglass Antenna

Brochure PDF

Radio Systems’ “AT” Series of vertical “whip-style” AM Broadcast Antennas are specifically designed for efficient radiation in an easy to install short fiberglass vertical profile.

The antenna is constructed of rugged fiberglass and anodized aluminum for durable long term wear and use.

The adjustable antenna tip and center loading coil assure maximum radiation and low reflect power at the full range of frequencies.

Ordering Guide
Model AT-53 530 kHz to 640 kHz
Model AT-65 650 kHz to 730 kHz
Model AT-74 740 kHz to 900 kHz
Model AT-91 910 kHz to 1060 kHz
Model AT-107 1070 kHz to 1220 kHz
Model AT-123 1230 kHz to 1390 kHz
Model AT-140 1400 kHz to 1620 kHz
Model AT-162 1620 kHz to 1730 kHz

AT Series Fiberglass Antenna $995.00

All antennas are physically similar.
Model AT-162 specifications shown below.

Base Pipe: 10 ft. length, 1.050” O.D., .82” I.D. Aluminum Type 6063-1832 with No. 215-Ri Gold Anodized Finish (.8mil arodic coating stnd. etch.)
Loading Coil Form: Natural Paper Phenolic XX Grade Coil Form. 22’ length,
1.625” 0.0. 1.250” I.D.
Winding: 17” of #18 Copper Enameled Wire Close Wound. (612 Micro henry)
Sleeve Insert - Top: 1.625” length, 1.250” O.D., j.o1u’ I.D. Tapered. Type 606l-T6 aluminum with clear anodized finish (Mil-A-8625C).
Grooved for “0” ring.
Sleeve Insert - Bottom: 3.250” length, 1.250” O.D., 1.054” I.D. Tapered. Type 606l-T6 aluminum with clear anodized finish (Mil-A-8625C). Not grooved.
Covering: White Vinyl Shrink Tubing 30 mil.
Caps: White A.B.S. Cemented in place.
Tip Base Pipe: 71” length, 1.050” O.D., .824” 1.0. Aluminum Type 6063-1832 with No. 215 RI Gold Anodized Finish (.8 Mil arodic coating stand. etch.)
Tank Fitting and Locking Nut: Chrome Plated Brass.
Ferrule: Nickel Plated Brass.
Tip: 49” length, .500’’ O.D., .022” wall, adjustable stainless steel tubing, Type 316 Heat 150907.
Tip Bali Acrylic: .625” Diameter
Fasteners: 6 only .375” length, -20 Allan Head Set Screws Holo-krome.
Temperature: -40 Degree Centigrade to 85 Degree Centigrade

SP Series Splitters
RF transformer type, low loss splitters, available in 2 to 8 output configurations.

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