McVCO SPECIFICATIONS

These specifications, where they are not inherent to the design,
are "typical" of the instrument performance. They are an attempt
to fairly characterize the instrument inspite of limited testing
capacity. Comment from users is welcome and revisions to the
specifications will be made where they are in error.


			PREAMPLIFIER

Input Type		Differential, with Zin=10K Ohm for f<30Hz.
			Isolation of the seismometer coil and
			its cable leads from ground must be
			greater than 5M Ohms measured with the cable
			disconnected from the instrument. Isolation
			less than this can unbalance the preamp.
			Connections for S and T resistors provided.			

Gain Adjustment		42dB in eight switch selected settings
			6dB apart. Usually starting at 42dB
			with a maximum setting of 84dB

Gain accuracy		Better than 3% across all ranges

Frequency Response	Low pass, 4 pole, 30Hz Butterworth 
			filter (-24dB/octave above 30Hz).
			Preamp is direct coupled but DC per-
			formance is affected by offset control.
			No offset control interference for
			signals with periods less than 300 s.

Output noise level	Vn(out) = 3 mvrms at maximum gain setting
			decreasing proportionally with gain. 
			Equivalent to 20 mvpp at the ADC input
			or 0.4% of ADC span for +/- 8 ADC counts

Sensitivity		2.6 uvrms at the input with maximum gain
			produces 35 mvrms at the ADC (100 mvpp)
			with 3 mvrms noise for SNR = 21.3dB
			(SNR = 10 Log (Vs^2/Vn^2) for rms voltages)

Second Channel Preamp	User defined


			MODULATOR

Output Range		+/- 125Hz from center frequency, absolutely
			limited because the instataneous frequency
			is calculated from the A to D conversion
			which exactly spans this range.

Deviation Sensitivity	(Output Range)/(ADC Span) = (250 Hz)/(5 V)
			Other sensitivities are emulated by scaling
			gain in the preamp.

Analog to Digital	12 bit successive approximation ADC sampling
Conversion		at 660 sps for single channel operation and
			330 sps for two channels

Frequency Resolution	The sinewave generator minimum frequency
			change is 250Hz/4096 which fully resolves
			the 12 bit ADC


			AUDIO CARRIER OUTPUT

Center Frequencies	Any of the following center frequencies are
			switch selectable for both channels.
				680, 1020, 1360, 1700
			       2040, 2380, 2720, 3060

Center Frequency	The sinewave generator output is crystal
Stability		derived so the main factor in off center
			operation is preamplifier output offset.
			This offset is actively regulated by
			the microcontroller so that the output
			frequency is within +/- 2Hz of center
			frequency after auto-zero on reset and
			adjusts to within 1Hz long term.

Output Type		Transformer coupled with DC blocking cap.
			Secondary floats and has a reflected dif-
			feriential output impedence of 600 Ohms.

Output Amplifier	Output amplifier is a summing inverter
			with provision for second channel carrier
			and the import of an external carrier.

Output Level		0 to 4 vpp into 600 Ohms (5.2 dBm max).

Noise + Distortion	Better than 45dB down relative to the
			carrier at full power into 600 Ohms.
			Better than 47dB down relative to the
			carrier at 1 vpp into 10K Ohms.


			POWER AND EVIRONMENTAL

Supply Voltage Range	11 to 20 VDC. Can withstand the unloaded
			output of a 12V, 30W solar panel indef-
			initely (approximately 20V shunt regulated
			by power input TVS).
			Internal power switch assures microcon-
			troller reset, ON at 11V, OFF at 10V.
			Reverse polarity protection diode.

Power Consumption	Single Channel, 220 mW at 12 VDC (18mA)
			Two Channel, 300 mW at 12 VDC (25mA)

Protection		All inputs and outputs protected by 15V
			transient voltage suppressors (TVS) ex-
			cept the power input TVS which is rated
			at 20V.

Operating Temperature	Units with commercial grade parts have
Range			have tested successfully to -40 deg. C.
			Potentially destructive high temperature
			tests have not been conducted. The sug-
			gested range is -30 to +70 deg. C.

Board Size		L=7.7", W=3.9", H=1.0" (max)