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AgTEM towed TEM electronics

AgTEM towed TEM electronics is only available at the discretion of our electronics provider and is specifically designed for Wallaby and Wallaroo.

 AgTEM towed TEM electronics is designed for continuous acquisition while walking, including compact walked in-loop survey, and vehicle dashboard use.

AgTEM towed TEM electronics can efficiently regulate output voltages from 3.5 to 18V for efficient small loop operation, and provides flexible loop connectivity. In a mobile system, to keep battery weight low, ability to transmit at very low voltages, exactly at desired current, by adjustment of voltage is advantageous. Additionally, this prevents drift of voltage as does occur if the battery powers the transmitter loop directly.

AgTEM electronics is split into a transmitter, a receiver, a dashmount or pivot mount touchscreen/computer, and optional large external batteries used for extended high power operation. The other power option is small batteries that can be carried on-board commercial aircraft as hand luggage. These fit into the transmitter and can operate the whole system for about one hour. In standard configuration, the transmitter and receiver are connected by a synchronization cable and power cable and the GNSS receiver can be one within the computer, or can be one with full view of the sky, on top of a vehicle cabin. AgTEM-electronics are designed to be backpackable with strain and rain protected connectors and ability to continue operating in rain (i.e IP53 or NEMA 3). The receiver electronics and computer are in IP67 rated enclosures with similarly rated connectors. Flexible loop connectors facilitate rapid whole of system testing using shorted loop turns and quick loop interchanges.

Electronics and firmware in this product is made by our electronics provider but packaging is conducted by Groundwater Imaging Pty Ltd to tailor to towed TEM requirements. Warranty and service are provided by Groundwater Imaging Pty Ltd

AgTEM-electronics operate at 200Hz, 100Hz or 25Hz, or lower, full waveform frequency, which is equivalent to stacking frequencies of 400Hz, 200Hz or 50Hz as quoted by a competitor. These frequencies are for countries with 50Hz power. For 60hz power countries the frequencies are 240Hz, 120Hz and 30Hz, or lower. Realize that high frequency is good for reducing only random noise by stacking but low frequency is essential for imaging deeply in all but resistive terrain, and for some forms of movement noise removal involving stripping of movement noise as a post-stacking offset detected beyond useable decays. In conductive environments, lower frequencies are essential for deeper imaging, as forward modelling can prove in advance of survey.

AgTEM electronics continuously update display of data as coloured posted point maps and as decay curves with an all-important reference curve for gradual fine comparison of change during survey.

AgTEM receiver A/D conterters are 24bit Sigma/Delta type for low noise operation and are coupled with overload protection and signal amplification of 1x, 10x or 100x. The system is protected for operation under power lines. Pre-amplifiers positioned on receiver loops further add amplification, low-pass filtering, damping, impedance matching and reduction of systemic noise pickup in connection leads.

AgTEM-electronics operate from <1Amp (for test loops such as shown below) up to 45 Amps (practically about 40Amps). Ramp time is kept manageable using 200 Volt avalanch voltage to give ramps typically on Wallaby of 6 to 9 uS into single turn 6 x 6m loops. Higher avalanch voltage would add to late time waveform decay, electrocution danger, cost and weight while lower avalanch voltage would increase ramp times.

AgTEM-receiver is fully sealed with a pressure equalization vent and cross-case heat conduction coupled with internal fan-forced circulation. Best quality A/D conversion and preamplification requires considerable power so the entire case is made of ribbed, heat-conducting aluminium such that operation in excess of 40 degrees celcius ambient temperature is feasible. If this case is used within the transmitter loop it must be rigidly fixed but it is fine at more than 1m outside of it. The receiver must not be fully packed into an additional box that prevents escape of heat if used in hot conditions.

AgTEM-transmitter is air cooled via an elaborate system designed to keep metal content, problematic when in or near transmitter loops, to a minimum. In an internal chamber, air circulation is fan forced and heat generating components and heat absorbers are fixed to heat sinks that sink heat through a 'firewall' to a fan-forced ventilated tunnel connected through the battery compartment which is open to the atmosphere via the rain protected cable entry port and another rain protected vent. Connections are all made by openning the transmitter lid, passing cables through the rain protected vents, making connnection, then closing the lid, a solution that protects from both rain and mechanical strain.

AgTEM input power can be supplied either by: 

- 2 x 7AmpHr 12.8V LiFePO4 batteries commonly used in security systems, 20 of which can be carried in hand luggage on commercial aircraft,

- 25.8V (nominally 24V) 54AmpHr to 120AmpHr LiFePO4 batteries suitable for continuous operation for a full 12 hour day (at up to full power with the 120AmpHr option), or

- 2 x any 12V (or 12.8V) batteries of opportunity as can be sourced at remote localities.

AgTEM receiver allows for connection of up to three receiver loops via either 3 component or single component cables attached to 3 connectors with rotated component pins so that three component cables can be used interchangeably with single component cables and diagnostic testing of components can occur simply by swapping connectors. 

 For further interim details please see the AgTEM, Wallaby and Wallaroo pages or contact us because many details and features not listed are under development and/or subject to negotiation. For instance, features of dual transmitter operation and multiplexed dual transmitter loop outputs and continuous current adjustement are pending completion as of November 2024. In the photos, see all the hardware is capable of these options but firmware still is not ready. Linear time gate storage, for improved noise post processing, and operation at up to 625 kHz sampling frequency (in just one or two receiver channels simultaneously due to data storage limitations) have been partially tested and can be negotiated with our electronics provider for commercial release.

Prohibited fixed loop and airborne use: Similarly, we refer negotiation to our electronics provider for provision of GNSS time pulse synchronization for continuous survey with the fully disconnected AgTEM backpack receiver, operable while walking, and a static transmitter (eg. Monex 200Amp transmitter). In this form large fixed hand laid transmitter loops may be used with roving AgTEM backpacked receivers and walked receiver loops such as the large, but very light, collapsable Wallaroo Z-component receiver loops, situated in front of the operator, balanced suspended across operator shoulders, by a pair of smaller orthogonal X and Y component loops behind the operator. Airborne, and semi-airborne use of AgTEM electronics is prohibited due to agreement with our electronics provider. Further, there are patent restrictions that prohibit airborne use of the Wallaby structure with its internal overlapping receiver loop.


Links & Documents

  • AgTEM
    • Airborne EM Compared With Land Based And Waterborne Systems