This small NOVATE SKY65135 board is sold on Ebay for about 17 EUR. It is indicated to be able to output 1W at 2.4GHz and is powered by 5VDC, and could be suitable as an SDR transmitter output, which can be used to transmit to Qatar Oscar 100 QO-100
Powered by 5VDC, a green LED lights up. The EN pin must also be set to 5V potential. The red LED lights up. At maximum power, the board consumes less than 800 mA at 5V and does not heat up much. I do not have the impression that a heatsink is not necessary (To be seen in the long run) Here is my measurement campaign carried out on 2400 MHz. The input signal used is a CW tune generated by Adalm-Pluto (with SDR Console).
I let you discover the datasheet of the SKY65135