When I want to use reconstruction filters other than 250 kHz, 2.5 MHz, and 8 MHz, what should I do?

You can use external filters instead of those preset filters (250 kHz, 2.5 MHz, and 8 MHz) to prevent the unwanted image spurious.

Procedure :

1. Set the internal baseband generator of the ESG to output the ARB waveform you want to use; set ARB to On.
2. Set the Reconstruction Filter to Through so that the baseband signal's bandwidth is not limited.
3. Insert external low-pass filters between the I and Q Output’s on the rear panel of ESG and the I and Q inputs on the front panel to limit the baseband bandwidth.
4. Set the I/Q Source to Ext I/Q in [I/Q] key menu.