QO-100 NB -Power Amplifiers
QO-100 NB - Power Amplifiers
Due to higher loss of driving level for the internal PA of the AMSAT-Transverter PA, I decided to go with the 20W PowerAmp by SG-Labs. After some measurements and combining information from AMSAT I decided to buy the newly available Version 3 of SG-Labs PA. After 2,5 weeks I received the PA from SG Labs without any issue. Communication with Hristiyan, LZ5HP was quick and easy. I ordered the PA with 3 three additional feedthrough capacitors to have the possibility to measure via directional couplers - Input Power - Forward Power - Reflected Power as relative DC voltages up to 5V. These 3 channels, will be measured later with my homebrew microcontroller project. PTT issue After mechanical work for the capacitors I connected the PA to my AMSAT-Transverter. From professional power supply, I saw a steady current of 0,5A, which was the Quiesant Current of PA. Ok, PTT doesn´t work as expected… The idle voltage level of AMSAT transverter is 3.3V and PTT active 0V. Adding a series diode e.g. 1N4148 in direction PA solved the problem! In addition the PA has a RF Vox and I reduced the decay time to minimum level (internal VOX HOLD TIME potentiometer).
NB - PA (20W - class AB, SG-LAB V3 PA)
Measurement Output Power vs. Supply Voltage (interesting)
I was really impressed about the functional and controllable power range (even with attenuation). The first picture shows the PA output power from driving level of AMSAT-DL QO-100 Transverter using 2% Driving Power of ICOM IC-9700. From investigation of AMSAT UpConverter, overdrive of TX mixer starts with 4% of Driving Power from IC-9700, see 2nd picture below. Communication via Satellite was possible down to 25dBm of transmit power, this is equal 0,3W power level.
SG-Labs 20W PA (pictures)
Up: Internal view of PA - Driver is NXP MMG30271B - PA is AMPLEON BLP9G0722-20 Left: Closed setup, ready for operation. Used some thermal grease from Thermal Grizzly Kryonaut. Heatsink in my case is 160x100x40 and is oversized, but was available from Flex1500 (something around 0.7K/W). After 1h of SSB operation maybe up to normal temperature of 37°C.
Here you can see my live measurement setup. Using directional coupler with 40dB attenuation + 20dB additional attenuation and using ADALM Pluto device for carrier measurement.