There are many ways to generate a low frequency sine wave for testing a VLF SAQ receiver. One could build a DDS generator or use a readily available audio function generator. I needed to design a simple sine wave audio generator and I came across a Texas Instruments document “Design of op amp sine wave oscillators” . The buffered phase shift seemed quite interesting and it didn’t use small tungsten lamps. In the schematic below the output signal is at node number 6.
Op amp used in the simulation is TL071 and with the component values shown in the schematic the generated sine wave has a frequency of 17.5 kHz. A dual power supply is used (+9V and -9V).
In the picture below the generated sine wave is shown: it seems quite clean but when testing the real circuit things may be slightly different.