PeakTech 4125 Function Generator
The operating manual supplied on CD clearly relates to an older version of the device (Figure 1). The front panel of the newer version in fact has a USB connector for an external hard drive. On the other hand the manual still shows the connector on the rear panel, which looks completely different. The reference inputs and outputs are labeled ‘20 MHz’ but customarily these are 10 MHz. It’s a shame that the manufacturer does not (yet) offer a newer version of the user manual.
Irritation begins at switch-on: the noise of the fan is loud and intrusive, arising not from any defect but more probably from excessive rotational speed, providing abundant ventilation at the price of peace and quiet. For around 35€455 / £420 / $540 one might expect something different.
Operation, as on all such devices, uses soft-keys surrounding the LCD together with a rotary encoder switch and a keypad. BNC connectors are used for the signal inputs and outputs. The description that follows mentions the means of performing individual functions only when they are particularly good or terrible solutions.
Sinewave signals can be adjusted up to a frequency of 25 MHz, which accounts for an acceptable 20 % of the sampling frequency. There’s an informative discussion on sample rates and ratios at . This provides sufficient reserve for the use of a simple output filter. The maximum amplitude amounts to 20 Vpp up to 10 MHz and 10 Vpp above this. The offset possible is ±10 V. All specifications relate to Hi-Z (= high impedance, unterminated) outputs.
Squarewave signals are limited to 5 MHz and additionally to a duty cycle of 50%. The maximum frequency is too low to clock modern microcontrollers or digital circuitry for test purposes.
Pulses are also limited to 5 MHz. Unlike the duty cycle, the <10 ns rise and fall times indicated are not adjustable. Ramp signals can be generated up to 1 MHz. There is no Sync-Output for triggering oscilloscopes externally if you alter the amplitude and offset. The handbook mentions this function but I was unable to find it. The PeakTech product does indeed provide two channels but they do not have the same characteristics. You can use all types of modulation and the frequency sweep facility on Channel 1 only. In reality this is not a serious restriction. Differential outputs for audio or rapid digital signals are certainly possible but are somewhat complex to set up. You can copy the characteristics of one channel over to the other but you cannot link them. For instance, as soon as you change the frequency, you have to transfer this across. With modulation the maximum internal modulation frequency amounts to 20 kHz, which makes it suitable for the audio range. Reference frequency: the reference output (10 MHz in fact) provides a trapezium-shaped signal of 1.6 Vpp into 50 Ω.