The input (top left) is terminated with a 51 Ω. A first limiter with 2 x 1N4148 clamps the signal to a maximum of approx. 1.4 Vpp. A very first Amplifier built with a BC849C amplifies by a factor of 10. Then, a second limiter follows.

As we now may have generated some harmonics, a lowpass filter shall attenuate those, in order to have a more or less "pure" sinewave. As the output impedance of the amplifier is approx. 500 Ω, this lowpass also has an impedance of 500 Ω.

Now three LT6551 (Quad Video Amplifier) take over. They generate 12 outputs, from which one is used to feed a AD8307 (Low Cost, DC to 500 MHz, 92 dB Logarithmic Amplifier) to monitor the level of the signal.

If this level falls below -10 dBm, or, if the inside temperature rises above approx. 85 °C, a beeper is activated to alarm he user.




Inside the case of the FuMu.

Output is limited to approx. 1299 mVpp. Horizontal scale is input level [mVpp].

The device is equipped with an Envico® Interface. It can be powered entirely by an envico basestation. In case the output level is too small, or the internal temperature is too high, an alarm is generated (not only acoustically) and then recorded by the Grafana database system.

All envico sensors are equipped with a male DSUB-9 connector with the following pinout :

Pin	Signal
1	+ 5 V
2	DATA (not used here)
3	GND
4	GND
5	CLOCK (not used here)
6	GPIO (used to e.g. reset an integrator)
7	+ 9 V (for power-hungry sensors)
8	+ 9 V (for power-hungry sensors)
9	Alarm (pull-up resistor on base-station)

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