We usually think of RTL-SDR as a cheap alternative to “real” radio, but this amazing project led by [Rodrigo Freire] indicates that the two classes of devices should not be mutually exclusive. After nearly 6 months of work, he developed and documented a method for integrate the RTL-SDR Blog V3 receiver directly into the Yaesu FT-991 transceiver.
Professional hacking results are possible from the fact that the FT-991 already had a USB startup capability. In particular, it had an internal USB hub that allowed multiple internal devices to appear on the computer as something like a composite device.
Unfortunately, the internal USB hub only supported two devices, so the first business order for [Rodrigo] replaced the original integrated circuit of the USB2512BI hub with a USB2514BI that offered four ports. After the swap was over, he managed to attach the RTL-SDR device exactly to the pins of the new chip.
Of course, that was only half the battle. It had a well-integrated RTL-SDR from the outside, but to be useful, the SDR will need to turn on the radio signal. To do it, [Rodrigo] designs a custom board that downloads the IF signal from the radio, powers it to an amplifier, and ultimately transmits it to the SDR. The board uses built-in switches, controlled by GPIO ports of RTL-SDR Blog V3, to activate the tap and preamp.
In the video after the break you can see [Rodrigo] demonstrates its modified FT-991. This isn’t really the first time someone has eavesdropped on Yaesu with a software-defined radio, although this is certainly the cleanest installation we have ever seen.