TM-7 SAM Receiver

The TM-7 is Gap Geophysics’ receiver system for ground and airborne magnetic data logging. This advanced modern system is used in all GapGeo’s magnetics, SAM and SAMSON surveys, as well as environmental and explosive ordnance detection by GapEOD.

Starting with the TM-2, which dates back to the mid 1970s, and the TM-3 (1986), which was one of the first digital logging magnetometers, and then the TM-6 which was designed for the fast sampling requirements for the SAM technique, the TM-7 is the latest evolution developed by our in-house geophysical and engineering specialists. It represents GapGeo’s solution for maintaining the best cutting-edge proprietary receiver system for our clients as possible.


The TM-7 incorporates a fast sampling, highly accurate counter, which interfaces with commercially available magnetic field sensors. Importantly, the quantisation noise of the counter is an order of magnitude lower than that of available magnetometer sensors, enabling us to achieve very high signal to noise ratios through stacking, and so enabling the success of the SAMSON technique.

It has GPS navigation (using an internal L1 receiver or external DGPS), which directs the field crew as they walk (or fly) the system down the line. Data is logged to a flash card, and synchronised to GPS time, at micro-second accuracy.

The user interface is conveniently via a hand held, touch screen device. The software constantly logs timing and position information, and so the TM-7 can be used for either moving or stationary logging. It can be used with up to four sensors, for when extra local precision is desired (such as with explosive ordnance detection). The system can also log any serial data stream (two channels in the standard model).

The counter technology, and the achievable high sampling rates, enables a variety of filtering options to eliminate sources of noise and interference.

Many years of efficient, successful surveys have demonstrated it to be a robust complete solution for our clients’ exploration needs.

TM-7 SAM Receiver


With four fix sampling rates, but also available is an alternative sampling mode where any speed between 1 to 4800 is selectable, with a wide range of filter options. Thereby, the system can be tailored to deal with specific interference problems.

Mag data range: 20, 000 – 100,000 nT (limited by the sensor)

Technical Specifications

Number of Cs Vapour Sensors1 – 4
Sampling RatesUp to 9600
RMS Noise0.02 nT
Counter absolute error0.043 nT @ 50000 nT = 0.9ppm
Larmor measurement range350 – 131000 nT (equivalent)
Minimum detectable signal50 mV p-p
Mag data range3000 – 110000 nT
User InterfaceRugged Handheld running WM5/6
Data storage mediaCompact Flash card (Type II)
Real-time clockSynchronised to GPS PPS
Data time-stamp precision1 microsecond
Power supplyLi Batteries