RM-3500 AUTOMATIC MODULATION METER

The Automatic Modulation Meter RM3500 has been designed to simplify the task of measuring amplitude and frequency modulation on signals in the range 1.5MHz to 1.2GHz. By eliminating the need to tune a local oscillator and make level adjustments the RM3500 speeds up measurements and reduces and reduces errors.

AM and FM measurements can be made at full accuracy over the frequency range 1.5MHz to 1.2GHz and with reduced accuracy and sensitivity to 2GHz. On FM, five range are provided with full-scale readings of 1KHz, 3KH, 10KHz, 30KHz, and 100KHz deviation. Peak positive, peak negative or mean deviation can be displayed. On AM five range five full scale readings of 1%, 3%, 10%, 30%, and 100%. Peak, through or mean of percentage modulation can be displayed.

For ease of measurement, three bandpass filters with nominal upper cut-off frequencies of 60KHz, 15KHz and 3.5KHz, a CCITT psophometric filter or a 750us de-emphasis network can be selected to filter the recovered modulation.

The different range and functions are selected by front panel push buttons with LED's providing positive indication of function.

Specification
RF INPUT
Frequency Range	1.5MHz to 2.8MHz, 3.2MHz to 1.2GHz with a useful response, with reduced sensitivity, to at least 2GHz.
Tuning	Automatic tuning selects the largest available signal. Correct operation requires spurious signals to be >10dB below the wanted signal.
Acquisition Time	Typically less than 100ms to locate and lock to the carrier signal. Setting time for the demodulation and AF circuits is additional and is typically 1 second.
Lock and Level Indicator	A LED indicates that the instrument is locked to an input signal and that the level is within range.
Input Impedance	50 ohms nominal.
Input Level	The unit will lock and measure modulation for input carrier levels in the range 2mV to 1V. Full specification for noise, accuracy etc. only applies over the input range 10mV to 1V.
Maximum Safe Input Level	0.5W continuous.
Local Oscillator Feed-out	Typically < -60dBm.

FM MEASUREMENT
FM Ranges	Five range with full scale deviations of 1KHz, 3KHz, 10KHz, 30KHz and 100KHz.
Accuracy	2% of full scale. See Audio filter specification for additional error due to AF response. Residual FM is additional.
Residual FM	< 20Hz at 100MHz, < 100Hz at 500MHz, <200Hz at 1000MHz.
Distortion:	<1% at 50KHz deviation with a 1KHz tone.
FM Measurement Modes	Peak + Ve, Peak - Ve and Mean deviation.

AM MEASUREMENT
AM Ranges	Five ranges with full scale indications of 1%, 3%, 10%, 30% and 100%
Accuracy	2% of full scale. See Audio filter specification for additional error due to audio response. Residual AM is additional.
Residual AM	Less than 0.5% with a 15kHz bandwidth selected
Distortion	<1% for 50% AM with a 1kHz tone.
AM Measurement Modes	Peak, Through and Mean of peak and Through.

AUDIO FILTERS
60KHz Bandpass Filter	25Hz-60KHz 1dB, typically 12Hz -72KHz 3dB with HF roll off at 80dB / decade.
15KHz Bandpass Filter	25Hz, 15KHz 1dB, typically 12Hz -19.5KHz 3dB with HF roll off at 60dB / decade.
3.5KHz Bandpass Filter	25Hz, 3.5KHz 1dB, typically 12Hz - 4.0KHz 3dB with HF roll off at 100dB / decade.
CCITT filter	Complies with CCITT Volume VP 53.
De-emphasis network	750us de-emphasis, 3dB bandwidth typically 12Hz to 212Hz. HF roll off 20dB / decade.

AF OUTPUT
Demodulated AF Output	Front Panel BNC.
AF Output Level	0dBm corresponding to full scale deflection.
AF Output Impedance	600 ohms

IF OUTPUT
IF Output	Front Panel BNC.
IF Output Level	Typically 100mV
DISPLAY	Type Moving coil meter with 0-3, 0-10 and 20dB scale with % and KHz notation.
Overload	The meter is fully protected.

POWER REQUIREMENTS
Mains	240V or 120V selectable, 117V + -10%
Frequency	48-60Hz
Power	Approx 6VA
Fuse	Rear panel 100mA