Amplifier Rampup Time for TX?
Posted: Fri Dec 29, 2023 3:42 pm
I'm periodically sending pulses with the standard bladerf C library. By "pulses", I mean continuous IQ samples of (1+1j)/sqrt(2) during the "on" time. These are generated at a sample rate of 2Ms/s, but are very short, 400 samples or so ~= 200us. I have 1024 generated samples within which are two of the ~200us pulses that I'm transferring. My bladerf buffer size is set to 8192 samples in the config call, so I zero pad the 1024 samples up to 8192 samples while keeping the 1024 signal samples centered in that overall buffer. Then I send, and...not much on the receiver, a HackRF running into GQRX.
Notably, all samples outside of the pulse interval are 0+0j. However, if I add in a CW signal into the entire 8192 sample buffer, I can much more clearly see the pulse in the spectrum at the receiver, along with that CW signal of course. This leads to the question: is there a ramp-up time for the output amplifier, or some output filter that needs to be excited before transmitting the actual signal? Are my pulses too fast, or am I doing something wrong at the receiver? My GQRX receiver is running the smallest FFT size at the highest frame rate to try and catch that ultra fast pulse.
Further info: if I tell bladerf to repeat that 8192 sample buffer many times in a row, I can see the pulses much better at the receiver. But I only need to send them every 1-2 seconds. All this leads me to think that either a filter has a time constant I have to overcome, or I'm not exciting the channel fast enough.
Thanks for any help.
Notably, all samples outside of the pulse interval are 0+0j. However, if I add in a CW signal into the entire 8192 sample buffer, I can much more clearly see the pulse in the spectrum at the receiver, along with that CW signal of course. This leads to the question: is there a ramp-up time for the output amplifier, or some output filter that needs to be excited before transmitting the actual signal? Are my pulses too fast, or am I doing something wrong at the receiver? My GQRX receiver is running the smallest FFT size at the highest frame rate to try and catch that ultra fast pulse.
Further info: if I tell bladerf to repeat that 8192 sample buffer many times in a row, I can see the pulses much better at the receiver. But I only need to send them every 1-2 seconds. All this leads me to think that either a filter has a time constant I have to overcome, or I'm not exciting the channel fast enough.
Thanks for any help.