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Radio
Broadcast Technical Consulting and Sales |
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Working in the field AM Transmitters |
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Here is Mark making AM
field intensity measurements in, of all places, a boat. The photo was
taken on Lake Bemidji while conducting a field intensity study on KBUN AM
Radio. The exact location was determined by a Global Positioning System
receiver. (summer 2002) Click on the photo to see a larger version of the image.
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A typical test setup for diagnosing and aligning an AM transmitter. On the lower left is an IFR
A7550 Spectrum Analyzer. Data from the analyzer is captured by a notebook computer, which is on top of the stack of equipment on the right. To the left of the computer
is a variable RF sample attenuator with multiple outputs. They feed a Tektronix 2213A 60 MHz Dual Trace oscilloscope on the lower right and a Delta Electronics SM-1 Splatter
Monitor above the oscilloscope. Above that is a Potomac Instruments AG-51 Audio Oscillator and Potomac Instruments AA-51 Harmonic and IM distortion analyzer.
The trick is to adjust the transmitter so that the harmonic and intermodulation distortion are at a minimum while the "Q" quadrature modulation of the AM carrier are at a minimum. This is true of monaural and AM stereo transmitters. We installed more than 40 Motorola, BE, and Delta AM Stereo Systems. Clean modulation on an AM transmitter is more difficult to obtain than on an FM. In AM, the transmitter must be as linear as possible to produce the best sound. Detuning a water tower re-radiator.
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A typical display on the IFR A7550 Spectrum Analyzer. |
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Questions?
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page last edited 06/19/2007
