SBB5089 + SZP2026 2.4GHz 2W amplifier.

[G4EWJ]

I've seen a few people on QO-100 using these, so I got one to try.

The devices are designed to work on 5v, but the psu is providing 6.2v. The absolute maximum rating of the SBB5089 is 5.5v (the SZP2026 is 7.0v). I'd been using it for a while before noticing this, so it's obviously not immediately terminal.

The switching device is the MP1584 - the same as in the modules used in the BATC MK1/2 MiniTiouners. R1 and R2 set the output voltage according to the formula (R1 + R2) / R2 * 0.8v. (100 + 15) / 15 * 0.8 = 6.1v, so the chip is doing what it's told. Maybe the designer thought it was R1 / R2 * 0.8v, which would give 5.3v.

Putting a 470k ON TOP OFF R1 (marked 104, = 100k) brings the voltage down to 5.2v. Don't remove R1. That would make the voltage rather high.

To enable external bias control, I de-soldered R7, rotated it 90 degrees clockwise and re-soldered only the top pad near the R7 legend. This biases the amplifier off and needs 5v on the unsoldered end of R7 to turn it on.

I also changed R9 to 10k, to stop LD1 dazzling the ISS.

Performance wise, I found that that the output saturated at 1300mW with a carrier. On DATV, it was giving 300mW without degrading the -40dB shoulders of my source. My source degrades after that, so I couldn't take it further.

The Pluto on power 0 also drove it to 300mW. I'm not sure what the Pluto shoulders are like as the power setting goes up.

The Aliexpress page has a good magnifier to see the component numbers. https://www.aliexpress.com/item/1005006174150056.html

Brian