Hello, I have a DHO802, I bought it because I am not going to use the 4 channels and because it also saved me some money. If I set the oscilloscope to the 1khz test signal and activate the maximum memory depth of 25Mpts, the oscilloscope sets itself at 1.25 Gsa/s. In the trigger menu I activate the external synchronization input and I do not observe any variation of the 1.25Gsa/s. Of course, if I also activate channel 2 the sampling frequency does drop by half, to 625Msa/s and memory depth at 10Mpts. But it does this regardless of whether the external trigger is activated or not. My conclusion is that activating the trigger does not influence the maximum sampling frequency, only activating the two channels divides that factor in half. I hope I have helped you. Greetings