The Spectrotek SFM Contact Device

 

Complete technical details and setup information for the SFM are available in the Instruction Manual.

The Spectrotek Frequency Modulator (SFM) is a compact circuit board designed for producing output voltages that are suitable for use as a contact device for research use. During operation, the SFM requires a sine wave input signal from a computer sound system, a cell phone, or an audio signal generator.

The SFM was designed at the suggestion of Ken Uzzell as a replacement for Ken's popular but now discontinued PFA-2 and PFA-7 contact devices. If you would like to visit Ken's archived web site with details about his PFA units, it is available here at:  Ken's Archived Web Pages.

The modulation signal source for the SFM may be the audio output signal from a cell phone, MP3 player, a computer sound system, or any stand-alone frequency generator capable of generating either a sine wave, triangle wave or square wave signal.

The SFM has an on-board 3.1 MHz carrier oscillator module which may be turned on or off by the operator as desired. The carrier oscillator may be easily replaced with a different frequency oscillator module.

SPECIFICATIONS:

Power Requirements:

• A single supply voltage of +19 to +24 volts DC at a maximum current of 0.2 amperes maximum is required. The optimum supply voltage is +19.

Input Impedance:

400 Ohms, AC coupled, overvoltage protected to 20 volts.

Input Signal Level:

• 0.1 to 10.0 volts peak-to-peak with a frequency range of 1,000 Hz to 50,000 Hz with a sine wave input signal, or,
• 2.0 volts to 10.0 volts peak to peak with a frequency range of 0.1 Hz to 200,000 Hz.
• The optimum audio voltage is from 2.0 to 5.0 volts peak to peak.

RF Carrier Frequency:

• 1.0 to 5.0 MHz. The SFM is shipped with a 3.10 MHz oscillator, but customer selected frequencies may be specified at the time of order.
• The carrier frequency of the SFM may be changed by plugging in a different frequency oscillator module.

Output:

• Output voltage16 volts peak to peak, switch selectable for a positive or negative waveform or bipolar AC
• Output current user adjustable from approximately 1.2 to 5.3 mA into a 1500 ohm load.
• The output signal is switch selectable for audio square wave only, or audio square wave plus 3.1 MHz carrier wave.
• Over the specified input frequency and input voltage range, the output waveform is a square wave with a duty cycle of 50%, +/- 3% or less.
• The rise time of the output signal measured at the OUTPUT of the SFM is 25 ns +/- 5 ns.

Electrode Lead Length:

• For direct connection to the SFM – two single wire leads, each no more than 75 cm long.
• For coax cable connection – 50 or 75 ohm coaxial cable, the length of the cable not to exceed 6 meters from the output of the SFM to the current limiting rheostat. From the current limiting rheostat at the end of the coaxial cable to the electrodes, a pair of single wire leads each no more than 75 cm long may be used.