STEMlab 122.88-16 - DC coupled version

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STEMlab 122.88-16 - DC coupled version

Post by fbalakirev » Tue Jan 15, 2019 9:58 pm

It seems that newly announced STEMlab 122.88-16 SDR will have AC coupled inputs.

If that's the case, would there be an option or easy mod to make it DC coupled? I could see us interested in getting at least couple dozen boards if that's the case, otherwise we'll have to pass...

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Re: STEMlab 122.88-16 - DC coupled version

Post by Ste_Trat » Sat Feb 02, 2019 10:09 am

You could circumvent this problem by modulating the DC Signal / chopping it, with a AD633JR.
The DC component = Amplitude of the newly generated signal.

Another option is to use a DC to frequency converter.

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Re: STEMlab 122.88-16 - DC coupled version

Post by renegade264 » Wed Aug 26, 2020 12:23 pm

Hey, to revive a dead thread a little bit.

I have x3 122.88-16 SDRs and I need to modify both the ADC and DAC front ends to bypass the transformers as I need to generate low frequency square waves on the DAC and I need the frequencies below 300 KHz which is the cut off frequency of the transformers. Unfortunately I really require the x3 larger FPGA for a dual channel floating point processor and the 16 bit ADC for that extra 20 dB of dynamic range.

I will be using the MAX9321, on the ADC front end, this will convert the single ended input to differential, I believe this is the same chip they use on the 125-14 models, I will use two TSSOP4 adapter boards and sit them on top of the transformer and use copper wire and manually solder the necessary connections. On the DAC side of things I will again bypass the transformer, I don't think there is a way to utilise the both the positive and negative current sources for DC to 62.5 MHz operation. (I don't think the 125-14 uses both current sources either).

I will keep this thread updated with pictures about how this goes, in the next couple of weeks.

Best Regards Ren.

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