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LeCroy LW420 Arbitrary Generator

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wishboneash:
I have a question for anyone who is familiar with the LW420 regarding the marker generators. I am trying to generate two frequencies at 50.000MHz and 49.995MHz. I am able to generate a proper 50.000MHz marker on one of the channels, but for the 2nd channel, I can't get it to generate the 49.995MHz marker (it allows some totally different frequencies like 66.xxx MHz and some other multiples unrelated to 49.995MHz). Is this is a limitation of the AWG in how it generates fractional frequencies using a common clock, or does mine have a problem? Unit passes all self-tests so that is not the issue. Perhaps a newer (than mine) firmware addresses this issue? Thanks for any insights.

MaxFrister:
I have a working LW420 but I haven't used the marker generators.  Tell me exactly what you are doing and I'll try it and let you know

wishboneash:
Excuse my late reply, just came across yours.
I am trying to generate markers for both Ch1 and Ch2 outputs.
Ch1 is outputting 50.000MHz and Ch2 is outputting 49.995MHz. I can't seem to get independent markers which are the exact right frequencies for both channels. Externally, I am mixing both these marker signals to get a 5kHz signal which is then filtered, amplified and used for driving some other circuitry. I can't use the Ch1 and Ch2 signals because their amplitudes are quite small (10s to 100s of mV) so the mixer doesn't work too well, hence the markers.
Thanks.

nctnico:
The markers are generated digitally and AFAIK both channels share the same clock generator. I strongly doubt you can have output frequencies on the markers that have your required precission. Likely you'll see them jitter when measured with an oscilloscope. An alternative is to use comparators on the output signals. Still I don't understand why you get small output amplitudes. You should be able to crank these up. Did you configure the anti-aliasing filter properly? IIRC you can set these manually on the LW420 to trade smoothness of the signal versus bandwidth.

wishboneash:

--- Quote from: nctnico on October 15, 2022, 07:36:35 pm ---The markers are generated digitally and AFAIK both channels share the same clock generator. I strongly doubt you can have output frequencies on the markers that have your required precission. Likely you'll see them jitter when measured with an oscilloscope. An alternative is to use comparators on the output signals. Still I don't understand why you get small output amplitudes. You should be able to crank these up. Did you configure the anti-aliasing filter properly? IIRC you can set these manually on the LW420 to trade smoothness of the signal versus bandwidth.

--- End quote ---

Yes, that's what I thought - it was using the same 400MHz clock for the markers. I can't use the Ch1 and Ch2 outputs for the frequency mixing is because I need the low amplitude signals from CH1 and CH2 for other circuits. It's a bit of a complicated set up unfortunately. I ended up using an external amplifier off one of the Ch1/Ch2 signals to generate the larger signal needed for the mixer (I need to adjust phase on one of the RF channel outputs only). Hope this clarifies. In any case, it's clear that this AWG can't generate arbitrary markers especially if the frequencies are fractionally related.

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