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RF test antennas and selective filters for the broadcast engineer
fm broadcast stations are required by the FCC to make periodic signal
integrity measurements, some of which are designed by the National Radio
The instrument of choice is the spectrum
analyzer coupled to a suitable antenna. While approximate AM readings
are sometimes obtained with "whip" antennas,
the severe impedance mismatch and lack of calibration yield imprecise
results. Harmonic measurements require that a known antenna factor be
employed to convert spectrum analyzer input voltage to field intensity
units. The industry standard LP-3 provides
Another key tool is the AM notch filter, which is often necessary to eliminate errors when measuring harmonics with a spectrum analyzer. Frequently, internal non-linearities create artificially high harmonic or spurious indications when the fundamental carrier is unsuppressed.
By "notching" the primary frequency, reliable accuracy is ensured. Our low-loss port on the am notch filter allows measurement forays well below -80 dBc at +- 75 kHz, which are required when conducting NRSC tests on stations with power levels of 5 kw and above. See Breaking the 80 dB barrier.
Chris Scott & Associates is a small design and consulting firm specializing in radio broadcast. A partial listing of clients and customers is available.
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