RF Output - Gibbs phenomenon ?

[pmrp]

Hello Red Pitaya community !

I am just beginning to play with this wonderful tool (RP 125-14), mostly with basic RF signal generation & acquisition.

My project involve sending pulse-echo signals for ultrasound NDT applications. However, while playing with the oscilloscope app to generate 1us pulses (using 1kHz PWM with 0.1% duty cycle), I noticed a very high amplitude oscillations with a central frequency around 20MHz (see the screenshot below).

The setup is very simple: the OUT1 is directly plugged to the IN1 via a BNC cable & adaptors. All other inputs/ouputs are isolated with 50ohm terminators. Swapping between inputs and outputs does not change anything in the result.

Is it the usual behavior ? I would not expect the Gibbs phenomenon to be that strong, given the bandwidth of the RP's outputs. Would that come from the impedance of the BNC cable or something else ?



Thank you by advance !

[kasaudio]

Hello.

Is out1 also 50 ohm terminated?

[redpitaya]

it is, and all the specs for all the boards are easily accessible, also for comparison reasons, here:
https://redpitaya.com/rtd-iframe/?ifram ... dware.html

[Kaltobi44]

Did you find a solution for that ?

[redpitaya]

I would suggest connecting a load via a T connector near the input. It can be that 50 Ohm is not needed, in some cases 1KOhm is enough.