**4. Indoor Comparison Experiment**

To further compare the performance of the IF3602 LNA in the receiver, we experimented with the simulation using a small-loop TEM device in the laboratory. Figure 13 shows the schematic diagram of the comparison test. The devices are shown in Figure 14, and the parameters of the device are as follows:


**Figure 13.** Schematic diagram of laboratory simulation comparison test.

To keep the circuit filter from interfering with data observation, a low-noise LT1028 amplifier board with an amplification factor of 10 was used as the pre-stage, and the same post-stage circuit as the IF3602 low-noise circuit was added, which was adjusted to have the same frequency band and similar gain as the IF3602 amplifier. Both groups of experiments were taken 128 times superposition average to avoid the influence of the amount of superposition on the quality of the received data. The results are shown in Figure 15.

**Figure 14.** The laboratory simulation comparison test and TEM devices.

**Figure 15.** Comparison of the data observed by the receiving device in the laboratory.

According to the results, the IF3602 amplifier receiver has a smoother signal and higher data quality than the LT1028 amplifier receiver after taking a double logarithm. The effective data length of the IF3602 amplifier raw data is 800 μs, which is about 2.6 times longer than the LT1028 amplifier receiver.

The relationship between TEM detecting depth and detecting time is described using formula *h* = 2*t*/*σμ*0, *σ* is the electrical conductivity of the geological body and *μ*0 is the vacuum magnetic permeability. Since the location of the experiment remains unchanged, the electrical conductivity values of the two geological bodies are the same, and the vacuum magnetic permeability is a fixed value, so the performance of the system is only determined by the effective length of the data. The receiver with the IF3602 amplifier increases the TEM theoretical maximum detection depth to about 1.6 times that of the original system, according to the result and the TEM detecting depth formula. In addition, because of the smoother performance of the IF3602 receiver observed data under 128 times of superposition, it is suggested that the number of superpositions can be reduced to have the same SNR as the LT1028 amplifier receiver while still accessing the higher detection efficiency.
