Geekcreit offers a nice signal generator board for appr. 30 euros with microchip ADF4351. Frequency range 35 MHz - 4.4 GHz (!)
Highlights
With OLED display
Host computer USB & serial port
Integrated key operation
Good man-machine interface
Many improvements on the phase noise, phase spurious and loop filter
Module has 35 MHz - 4.4 GHz frequency output, point frequency, sweep, frequency hopping and other basic functions
Dimensions: 88mm * 67mm
Power supply: 5V-15V (DC 5.1MM); 5V (USB)
Bandwidth: ADF4351: 35MHz - 4.4GHz; ADF4350: 137MHz - 4.4GHz
Module step: 100KHz(min)
Frequency error: ± 1KHz
Output: OUTA OUTB two way
Module phase noise: better than -100dBc @ 10KHz (noise is different with different band phase)
Module output power: 7dBm (MAX)
Module interface: The external communication port of the STM32 USB can be configured to USB or analog serial port (in default)
Module program download mode: SW module, three-wire system (GND SWCLK SWDIO)
https://www.banggood.com/Geekcreit-Signal-Generator-Module-35M-4_4GHz-RF-Signal-Source-Frequency-Synthesizer-ADF4351-Development-Board-p-1416998.html?rmmds=mywishlist&cur_warehouse=CN
Off-topic:
Visit to the city of Gent, Belgium, July 31st, 2019