06:58 <_whitenotifier-3> [scopehal-apps] azonenberg pushed 2 commits to master [+6/-4/±0] https://git.io/fj8lj

06:58 <_whitenotifier-3> [scopehal-apps] azonenberg 0e5e5db - Moved fgtest/curvetrace to examples directory

06:58 <_whitenotifier-3> [scopehal-apps] azonenberg e9705ca - Initial version of freqresp example

07:00 <azonenberg> https://github.com/azonenberg/scopehal-apps/blob/master/examples/freqresp/main.cpp?ts=4 simple test of frequency response

07:01 <azonenberg> using the wavesurfer function generator to generate the signal then the waverunner to measure power before and after the DUT

07:02 <azonenberg> This approach eliminates the need to have a calibrated output level on the function generator (so you could for example use a cheap SDR as the signal source, which is what i plan to do for a 50 MHz - 2 GHz sweep tomorrow)

07:03 <azonenberg> you dont even need to know the scope's frequency response, it's entirely ratiometric and measures S21 directly

07:03 <azonenberg> all it relies on is the two scope channels being matched

07:06 <azonenberg> https://www.antikernel.net/temp/freqresp.png

07:06 <azonenberg> lain: ^

07:07 <azonenberg> Flat within measurement error (the spikes are i think one scope LSB high lol), if i averaged longer it would probably look nicer

07:07 <azonenberg> but for a quick and dirty test this is enough, i'll fine-tune once we have the faster signal source up

07:14 <azonenberg> The ~ -0.14 dB average S21 is mostly due to me using 1K ohm resistors, producing 21:1 attenuation

07:14 <azonenberg> but i couldn't find a good RF 950 ohm

07:15 <azonenberg> Easy to correct for in post, also i think it might be possible to tell the scope this is a 21x probe

07:15 <azonenberg> lecroy seems to be nice and flexible for this kind of stuff

07:46 <lain> :D