MEMO is a part of the INTERBALL 2 wave consortium.
The instrument consists of two sets of magnetic sensors, including ULF/ELF (0.1 Hz - 1.0 kHz) triaxial search-coil magnetometer and three separate HF (40 kHz - 2 MHz) search-coil magnetic antennas, as well as a processing unit. Interfaced with other wave experiments (POLRAD, NVK-ONCH, IESP), it is mainly designed to transmit waveforms of two to five electromagnetic field components, in the frequency range 5 Hz - 250 kHz, over short time intervals.

In the ULF/ELF range, the three orthogonal magnetic sensor consist of a 8 metal core around which 8.104 of wire are wound. The three magnetic components measured are aligned along the X,Y and Z axis of the satellite. They are denoted Bx, By, Bz.

In order to avoid mutual induction, the three HF magnetic antennas are located at different places on the same boom. The minimum and maximum distances are 42 and 90 cm respectively. They consist of ferrite cores around which approximately 102 of wire are wound. The three magnetic components measured are aligned along the 1, 2 and 3 axis.

For the two sets of sensors, flux feedback systems enables the adjustment of the bandwidth to the desired specifications. Preamplifiers are used to increase the measured signals to a level where they can be analyzed on-board.

MEMO uses the HF electric sensors of POLRAD. The three signals issued from the differential preamplifiers of the electric signals E1, E2, E3 are transmitted to POLRAD where they can be attenuated by 4 step attenuators (0, -20 dB, -40 dB, -60 dB). A connection allows to send them to MEMO. During the time interval where the POLRAD relaxation sounder is ON, one of this signals, sent to MEMO in a 4 kHz bandwidth, is used to perform high resolution measurement of the electron density.

The power supplies of the low frequencies electric sensors and magnetic sensors are within IESP and NVK-ONCH respectively, which means that the sensors are switched ON or OFF at the same time as those two experiments. The signals issued from the preamplifiers of the magnetic sensors are sent to NVK-ONCH . The signals issued from the differential amplifiers of the electric sensors are sent to IESP. The electric signals are entered into a multiplex which selects two channels: Ey and Ex or Ez. By telecommand, the Ey channel may be fed by one electric or one magnetic signal measured on-board the sub-satellite, then transmitted to the main satellite through the STO telemetry system operated at 400 MHz.

The signals associated with the two electric channels plus the signals associated with the three ULF/ELF magnetic channels are passed into the extremely low frequency pass-band filters (5 Hz-1000 Hz). In parallel, the signals associated with the same two electric channels plus the signals associated with the three VLF magnetic channels are passed into low frequency pass-band filters (1-20kHz). The five outputs are sent both to MEMO and, after amplification, to step frequency analysers (SFA's). The SFA's allow to place pass-band filters of 800 Hz bandwidth anywhere in the range 1-20 kHz, by steps of 500 Hz. Under request, the filtered signals may be memorized by MEMO.

Logical connections allow exchanges of commands, technological parameters and status between all wave experiments. They are used for common modes of operation (in flight calibrations, recording of POLRAD or NVK-ONCH data within MEMO, triggering of data collection, etc.).

The first processing of MEMO consists in a filtering of the HF data. In order to have a correct signal/noise ratio in the frequency domain of interest one can pass the HF signals: in wide frequency band (WB) filters (40-240 kHz), low frequency band (LB) filters (40-120), or narrow frequency pass-band (NB) filters (120-240 kHz). The decision is taken by telecommands.

All signals entered into MEMO are amplified by 3 step amplifiers before being digitized with 8 bits words : 12, 24, 36 dB for the HF signals, 6, +6 and 18 dB for the VLF and ELF signals. There is an exception for the SFA signals which have a two step amplifier : -9, +6 dB.

According to the operation modes, controlled by the microprocessor (here a NSC 800), several digitised waveforms are sent to each of the two memory systems: a small memory system MEDOR (512 height bits words) and a (relatively) large direct memory access system DMA (786000 height bits words).

Two (exceptionally four) digitized waveforms are systematically sent to the MEDOR system. A fix number of samples (generally 256, exceptionally 128) of each waveform are recorded at the rate of taking off of a MEMO format by the connected telemetry system (respectively 0.2 s and 0.4 s for the STO system working at 40 kbits/s or 20 kbits/s, 0.5 s for the SSNI system). MEMO cannot be connected to two different telemetry systems at the same time. According to the time interval between two collects of 256 or 128 samples, the MEDOR data are low resolution data.

Two to five digitized waveforms are sent to the DMA system. N samples of each waveform (with N varying from 128 to 171000) are either periodically recorded (with time periods of 0.2 to 64s) or recorded after a POLRAD flag or a NVK-ONCH flag has been received. The DMA data are essentially high resolution data. However in some MEMO modes, the DMA system is used to produce low resolution data. In that case, the time intervals between two collects of 256 or 128 samples are given values of the order of values imposed with MEDOR by the telemetry systems.

All MEMO data are formatted by the NSC 800 microprocessor. The MEDOR data are systematically sent to the telemetry system. A test on the amplitude levels is performed on the DMA data before they are transmitted to the telemetry systems.