My very simple experimental set up for the 2,4 GHz uplink as follows;
Using a "Low-jitter GPS-locked precision frequency reference 400 Hz to 810 MHz output mini version." module from http://www.leobodnar.com set to 800,020 MHz.
Output level at 800 MHz is about +8 dBm, frequency tripler with BFR91A and a Mini Circuits MMIC ERA 4 as driver. Measuring +12 dBm outut from ERA4. As "Power Amplifier" I am actually using a Mini Circuits Low Noise High IP3 Pre-Amp with +21 dBm P1dB. (Mini Circuits PSA-545+)
Feeder cable loss 0,8 dB so remaining power to antenna is about +20 dBm.
Antenna used is a WiFi 23,5 dBi "grill antenna" with linear polarisation.
This set up works quite well on CW with 100% copy. I also tried to reduce the power to +10 dBm inserting a 10 dB pad in between PA and antenna. Much weaker signals of course but still 100% copy on CW.
With this simple antenna I guess the minimum power for CW would be apx +5...6 dBm.
Here in Sweden maximum allowed power output is 100 mW (+20 dBm) pep to the antenna system. No ierp limits.
This sound clip is recorded via Web-SDR in SSB bandwidth with TX Power +20 dBm and the 23,5 dBi antenna.