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Jeremy,
To convert to mV (voltage) you have to use the V = sqrt(P*R) Ohms law relationship. The system is 50 Ohm. This simplifies to
mV = 10^((dBm+46.9897)/20)
You can also derive an equation to go directly from I/Q to mV without needing to log/power the data too.
Use the 32-bit floating point values to avoid the need for an additional scalar.
Is the I/Q data 16-bit integer or are you using the 32-bit floating point data from the API? If you are using the 16-bit integer data, there is an additional scale factor you must account for.
Also, what value are you comparing it to in Spike? If you are looking at a modulated signal, you’re going to need to do a channel power measurement. If looking at a CW, then the instantaneous I/Q power will have more relevance.
dBm = 10*log10(i^2 + q^2) is the correct equation. Make sure it’s log10 not log2.
Look forward to your response.
Hi Devin,
The VSG60 does not provide indication or feedback that an ext reference is present, other than simply exhibiting a large frequency error (in my bench VSG60, the freq error is 38ppm without an ext ref to lock to). Maybe this freq error is enough to detect?
I apologize for the inconvenience.
Hi Tim,
Looks like we clamp at 0dB SNR in the software, so this is going to be a hard limitation right now.
The only workaround would be to generate your own waveform and transmit it using the Arb mode.
I have made a note to look into negative SNR’s and see if this is an easy add for a future release of the VSG software.
Thanks for the feedback.
Ed,
We have lots of customers using PyVISA to do this. We should have a PyVISA example in our SDK. It should help you jump start your project. Hopefully others chime in!
If you are willing to start a direct correspondence with us, please email me at aj@signalhound.com.
We’re going to do a little bit of research on our end to see if we can learn more about how our device performs in a VM.
If it’s possible on your end, I would be curious if running on bare metal makes these issues go away. Running bare metal may not be an option for you, but I think there is value in knowing if the VM configuration is the problem, or if there is still something else limiting the data rates.
Both -6 and -11 are related to network data loss. -11 is simply an indication of UDP packet loss, and assuming packet loss continues or is bad enough you will eventually see a -6 (device connection loss). -11 is generally bad enough that you can’t trust the I/Q data fully anymore.
Here are some troubleshooting ideas and suggestions,
– Ensure you have configured all the network settings we recommend in our network config manual. Ring buffer sizes, socket buffer sizes, jumbo packets, etc.
– Simplify your network to just SM200C directly connected to the PC. If stable, start adding additional equipment like your switch and determine when the issue starts.
– We recommend SFP+ for the full run. if you convert to RJ45 or SFP at any point, this is likely the source of your issue.
– Reduce the sample rate. You didn’t mention what sample rate you were using, but if it’s 200MS/s, try going down to 100/50/25. Any lower than 25 and the network rate doesn’t reduce, but it will perform on device decimation down to 25. This should put significantly less pressure on your network and hopefully contribute to a more stable system.
– If none of the above work, try swapping out fiber/transceivers to determine if there are any flaky ones. Definitely something we have seen in the past.I look forward to your results.
Eduardo,
You have requested the entire sweep. There are two ways to retrieve the value at a specific frequency.
Using the trace data you have already requested, you could also request the :TRACe:XSTARt? and :TRACe:XINCrement? which allows you to determine the frequency of each point in the sweep using the equation freq = start + index * increment. Then you just need to find the index into the sweep that is closest to your desired frequency.
Alternatively, you could look at the SCPI marker commands, place a marker at the target frequency, then readback the marker amplitude value.
Both methods would result in the same final result.
Let me know if you have questions.
Hi Jaime,
Unfortunately, that is not possible at this time. Right now we only support the generation of test models and some downlink RMC waveforms. We do not support the addition of specific PLMN information.
Let me know if you have follow up questions.
Unfortunately there is no way to save the waveform in the VSG60 software created in the various modes.
Everything else you said sounds correct. The signal in screenshot 2 looks like a valid modulated signal you can output with the ARB mode.
Let me know if you run into issues.
ABorel,
Based on your comments, I think you want to be using the digital modulation mode rather than ARB. You are specifying symbols rather than I/Q samples. To clarify, it’s common to oversample the constellation symbols by upsampling and filtering with an ISI free filter like the Nyquist filters. If you had done all of the upsampling and filtering, then you would want to use ARB mode.
What I would try instead, is feeding your integer sequence into the sequence editor in digital mod mode. You can either adjust your sequence to match the constellation mapping, or create your own custom constellation mapping to match the one you have been using. Then the software will upsample and filter for you.
Without upsampling and filtering, you are creating sharp transitions, which will be filtered out by both the VSG software digital filters and hardware reconstruction filter which have ~40MHz of bandwidth. I suspect the smoothing effect is from these filters.
Let me know if you have follow up questions.
Thanks for the update Kaiser. I have not set up this configuration yet to do any testing. I will use SM200C’s when I do get to this.
Sure, email any questions to
The digital mod mode also supports custom constellation creation with the “Define Modulation” button. Then you just select “custom” on the modulation type. You can save/load your created constellation or if you save a preset it should be saved/loaded as part of the preset.
Let me know if this doesn’t provide enough flexibility for your use case.
Luciano,
In the digital mod output mode we support pi/4 DQPSK generation, is this what you’re looking for?
Val,
If you have the waveform as a baseband I/Q file, or the ability to create a LoRa waveform with a tool like MATLAB, and the sample rate of the file doesn’t exceed 50MS/s, then yes you can use the VSG60 to transmit this waveform using the ARB output mode. Our software does not have native LoRa waveform creation capability, you would have to provide your own waveform.
Kaiser,
This is good information, thanks for the thorough reply.
What are typical sweep settings you are using? (span/rbw/etc). If I try to reproduce I want to get as close as possible to your setup. Thankfully we are about to release a high speed GPIO controlled switch, so it shouldn’t be too hard to simulate this!
Kaiser,
Fun setup. There’s a lot going on here, so maybe I can start with some high level ideas and questions.
– How are you switching between your sources? Are you using the smSetSweepGPIO function?
– If yes to the question above, have you done any monitoring of those GPIO pins? Any way to verify they are cycling through all your states and not missing one periodically? Whether it’s hardware/software, that would be extremely helpful to know.
– Am I to understand that the “sweep offset” sticks around for many cycles? So if you are cycling through all 20 slots, are all 20 slots now off by 1 for some duration until it corrects itself? Or is it just slot 10 that shows up in slot 9 for several seconds until slot 9 reverts?
– Does using just 1 receiver make the problem go away? Even with 16 queued sweeps?
– Is it always a specific slot, e.g. 9/10? Or random?
– Does the “sweep offset” happen on both receivers? Or just one?
– Let’s say you’re switching through slots 8,9,10,11. Does it now look like 8,10,10,11 for 15 seconds and then go back to 8,9,10,11?I’m trying to collect enough information that I could try to setup something here to reproduce, and narrow down the scope. I’m not aware of any outstanding issues with this functionality, but this is likely a more complex setup than most customers, and more complex than we’ve simulated here.
I look forward to your response.
Hi Val,
1) You want to make sure your IF bandwidth is wider than your signal of interest but not wide enough to include adjacent signals/channels. For FSK, this will mean knowing something about the frequency deviation and padding it. As for filter, yes, you want to know what the transmitter is using and match that.
2) We do not have any LoRa specific measurements. You might be able to use zero-span mode to estimate chip rates. My understanding is that its some sort of chirp like signal. That can be viewed with an FM v Time plot in zero-span, using markers to estimate chip rates?
Andrew