Question
User would like to demodulate a Tetra T1 uplink signal using K70 VSA option in an spectrum analyzer.
Tetra T1 Uplink Signal demodulation using VSA K70 option in Spectrum Analyzer
Answer
For this analysis one can take one R&S Signal Generator. In this case SMW200A (FW 4.80.041.57) was used using the standard T1 signal available in the Tetra modulation dialog.
Since this is a burst signal, it is firstly an important analysis is to check the signal in zero span to understand the length of the burst. For a stable signal it is advised to set the trigger using the IF Power accordingly.
For this case one R&S FSV3030 (FW 1.40) was used for the analysis. Using markers one can see that the burst length is roughly ~13ms.
As next step one can open the VSA K70 mode and start setting the demodulation. Based on R&S Application Note 1MA189 for Tetra Measurements user knows the demodulation format to be PI/4 DPQSK. Same Application Note gives a qualitative indication on the symbol rate, this has to be adjusted empirically to match the burst length which is known based on the Zero Span measurement run previously.
After this, one also needs to adjust the result length based on the length of the frame in symbols. If too long, the EVM will be quite high since the instrument is considering non-existing symbols for the demodulation.
At this point EVM results should be already quite good. If not, user is advised to run the auto level function and/or revise the triggering of the signal.
Additionally, one can recall a standard Tetra training sequence to be searched inside the demodulation, in this example Tetra_S1 was used,
The pattern search has to be activated accordingly inside the Signal Description menu,
Below the final results inside the K70 VSA Menu. EVM results are very good and the pattern sync is shown in green.
