The low frequency limit of the 8569B is 10Mhz. Is there any way to lower it to 1Mhz or less either by some internal configuration change or by any add-on module ? Thanks.
You could use it a little lower but the frequency drifting and stability is about 50 KHz/hour and mixer spurious noises. It was not designed to go that low. If you need to measure lower frequencies, you can use another product based on your measurement requirements. You could post it, and see your choices to fit your budget.
Upconvert the incoming signal with the LO (+ isolator) with a double balanced mixer plus band pass filtering or use the Ailtech 757 principe: HP OEM comb generator mixed trough a directional coupler with the boosted (amplifier needed) LO and heavy bandpass filtering of the choosen band (for example (400 -500Mhz with a 100Mhz comb) 1Mhz will be 501... If you have the option ?? comb generator it is easy to implement inside with minor modifications.
Dave