VSG60 Streaming Playback

[kaiser]

I’m experimenting some with using the SM200C to record signals, and then the VSG60 to play them back.

In general it works pretty well.

But I have one question — I have a signal that I’d like to record at 100MS/s.

My thought was that I could just play it back in the VSG60 at a supportable rate, like 25Ms/s or 50Ms/s. In that case the waveform would be slowed down by 2 or 4x, so I could just adjust my data rate lower by 2x or 4x and it should all work.

And it kind of does? It seems like about every 2 seconds I take a burst of bit errors. Then it’s clean, then I take a burst of bit errors.

Looking through the file structure, it should just be packed I/Q, so changing the rate with which I shove it out *should* work, right? Or am I missing something?

Thanks.

• This topic was modified 1 year, 7 months ago by kaiser.

Your logic seems sound to me.

2 things that I think could be happening.

1) Is the recording clean? Can you verify there wasn’t some sort of issue with the recording. The main issues being SSD write speeds not keeping up with the data rate, or UDP data loss. Are you using the I/Q recorder in Spike? It should indicate either of these issues. It will appear below the “Rate” label in the I/Q recorder if it occurs. It’s a hidden label by default.

2) Drop outs in the VSG60 output. Are you running the SM200C at the same time as the VSG60? If yes, that could certainly contribute. If you’ve been running other files at 50MS/s without issue, then I would lean towards #1

Is the recording only 2 seconds long? 🙂

If it’s a long file, are you using the “streaming” mode in the VSG60 software? If yes, that means it’s hitting the file all the time. Presumably you aren’t also doing other high speed file I/O while playing back on the VSG?

Thanks. We’ll investigate the network and SSD performance a bit. I don’t remember seeing an issue shown on the display, and we were looking for one.

The SM200C and VSG are on different computers, and the recordings are 20 seconds long. We are using the Streaming mode on the VSG60, and we aren’t doing much else with the computer, and that’s also why we tried bumping it down to 20Ms/s and 5MS/s playbacks, and we kept seeing the data error bursts (but on a correspondingly longer timeframe before the bit errors; so like at the same point in the file, which is why we’re goin to investigate the recording a bit more).

We were setting the SM200C into zero span mode, and then using the I/Q recorder thing on the bottom since that also produces an xml file with the recording details. Do the error labels show there? We can also try from the I/Q recorder dialog thing and see if its different; we just don’t get the XML file with the details. Is that by design?

I do not think there is any warning output with the zero-span recorder. The I/Q recording utility will show the warning (see picture)

Yes that is by design that the utility doesn’t provide an XML, I wanted to move towards a standardized format such as SigMF, but haven’t done so yet. The utility satisfied a number of customers that just wanted long term recording to multiple files and didn’t need the context file at the time.

The utility recorder is optimized for long term recordings and I think will ultimately be better for your use case. It can save to multiple files without gaps between the multiple files. The zero-span recording does not guarantee no-gaps between the files if you choose to output to multiple files (hopefully that’s not your issue). This allows you to load a sequence of files in the VSG60 “streaming” mode and be fully continuous.

I just did some testing here. My SSD claims 550MB/s sustained writes, but using your settings, will only sustain the 400MB/s (required for 100MS/s rate) for ~1 second before dropping to a lower rate of 250MB/s and thus eventually needing to drop data.

I did record the 1 second file at 100MS/s and played back at 50, and everything seemed fine as long as I halved the measurement rate.

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Thanks. Super helpful as always Andrew.

Just for reference it worked flawlessly when we used the I/Q recorder utility.

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