VSG60 Streaming GSM Recording

Hi, I have a question regarding the Signal Generator VSG60A. We have recorded a genuine GSM signal with the signal analyser BB60C and are playing this recorded message back through the signal generator VSG60A. We have the signal generator connected to a 10Mhz external reference and stream this recording for 100 seconds. We then test how much of the message is decoded by our equipment. Currently we are getting intermittent passes / failures on our automated tests using the signal generator. We have verified that our equipment is functionally working to spec using a different set of measurement devices. What would be the steps that we should take to check that the signal generator is playing back our recorded message to a good quality and in real time. We have found that turning the signal generator off for a period of time and then re applying power can increase the pass rate.

[Andrew]

Some general questions, suggestions, and ideas,

– Ensure you are transmitting at the same sample rate as the recording occurred.
– Depending on the settings used when the recording was made, it’s possible the noise floor of the BB60 is contributing to the transmission. Is the SNR good enough on the re-transmission?
– Did any compression occur during recording? aka IF overloads?
– Are you transmitting at the right power?
– Are you running both devices simultaneously? If yes, that could cause signal drop outs, or if both devices were active during the recording, the recording could be compromised (dropped samples). In general, not every PC is capable of running multiple of our high speed USB devices.
– Do you have anyway to verify the recording is good by inspection? (aka software inspection?)
– Do you have any known good recordings you can try to transmit with the VSG60?
– What is the make/model of your PC? Are you using any USB hubs?
– Is your recording on an SSD with necessary read/write speeds? I’m assuming you are using the streaming output mode in the VSG60 software which is going to read from disk in real-time.

Feel free to contact us at support@signalhound.com if you prefer direct email support.

• This reply was modified 1 year, 10 months ago by Andrew.
• This reply was modified 1 year, 10 months ago by Andrew.

Hi Andrew, thanks for the reply since this post I have been conducting some tests to verify these points. I did not create the recording so cannot fully verify that no IF overloads occurring when GSM was recorded but visually inspecting the signal with other measurement devices confirms that the signal is suitably clean.
I assumed the test PC’s that were purchased specifically for the VSG60A and the BB60C were in spec and from what I have seen they may not be. We purchased 3 Dell micro OptiPlex’s (3090, 5070) with 8GB of ram and 256GB ssd/nvme. I will post a picture from running winsat but it appears the read speeds do not meet the requirements for the VSG60A (in streaming mode). The later test systems are the micro OptiPlex 5000, these have 16GB of ram and faster nvme drives, we have seen the best results when using these test systems.
These performance issues have only surfaced recently as historically we have only used steaming mode in the VSG60 software but recently I have made tests using the ARB mode as to my knowledge is the only supported mode with single playback feature. As the recording is loaded using the old test systems the software hangs for a considerable amount of time before other actions can be performed. Changing dBm levels when RF on and MOD on are enabled also hangs the software. This does not happen with the newer Dell OptiPlex systems so raised a red flag.
We are currently in the process of updating the test PC’s and will see if this resolves the issue. For now is there anyway of playing a recording once through streaming mode instead of having it loop can this feature be added to the VSG60 software?

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Hi NMullin,

Thanks for the follow up.

I do not believe there is currently a way to play a streaming scenario only once. I will see if this is something that can be easily added.

I should at least mention, that it is possible to use the API to transmit a waveform. The API is an interface for programmatically controlling the instrument without need for the UI application. This would allow you to perform this task relatively easy if you are comfortable writing software. See link below for more information.

https://signalhound.com/software/signal-hound-software-development-kit-sdk/

Hi, Andrew —

We talked briefly a few years ago regarding the need for a way for applications to detect if there have been dropouts in the outgoing data stream ( https://signalhound.com/support/forums/topic/vsg60a-stability-in-cw-mode-versus-multitone/ ). Has any further thought gone into this?

Hi John,

No further progress has been made on this, I apologize.

[Author]

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