Frequency range 1.5MHz to 1.2GHz
Useful indications to 2GHz
AM and FM measurement over full range
LEO indication of lock, level low and high
Analogue display
CCITT VP53 Psophometric Filer
De-emphasis network
Very low noise
Optional RF level measurements.

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.



Frequency Range


1.5MHz to 2.8MHz, 3.2MHz to 1.2GHz with a useful response,

with reduced sensitivity, to at least 2GHz.



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.
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FM Ranges  Five range with full scale deviations of 1KHz, 3KHz, 10KHz, 30KHz and 100KHz.



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.
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AM Ranges Five ranges with full scale indications of 1%, 3%, 10%, 30% and 100%



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.

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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.
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Demodulated AF Output Front Panel BNC.
AF Output Level 0dBm corresponding to full scale deflection.
AF Output Impedance 600 ohms
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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.
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Mains 240V or 120V selectable, 117V + -10%
Frequency 48-60Hz
Power Approx 6VA
Fuse Rear panel 100mA


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