BATC Forum

Hi guys,

I am looking for information on the Nyquist Filters used in this project. Over here in our part of the world a decision was made to use a Symbol Rate of 2222 m/s vs 2000 m/s.

This was determined based on the receiver performance at low symbol rates. The receiver was not reliable at 2000 m/s. However now that I have Minitouner I can see differences in MER and Constellation waveforms when I use 2222 m/s throught the FM Board. I am not sure about the DATV Express board but I am certain there are issues there too. What is causing me to look into this situation is centered around digital artifacts and dropouts when fast motion is detected by the camera. I do not see any of this at 2000 m/s.

So I guess what I am asking is this, have we exceeded the bandwidth of the 2000 m/s filter by running at 2222 m/s rate?
Can someone point me to a source to determine the coil and cap values that are closer to 2222 m/s rate?

Any thoughts?

The filters for 2MS are FFC1-6 and FFL1-4 on this diagram https://wiki.batc.org.uk/images/3/35/PdFM_V2_Sht_2.pdf. The values are listed at bottom right. To adjust for 2222KS, you should multiply the 2000KS vales by 2000/2222 (about 0.9), so for example FFC1 would become 82 pf.

There should not be any issues with the DATV Express board at 2222KS. If you are having problems with that, it suggests a receiver problem. What MER do you get at 2222KS from the Portsdown? If the MER is reasonable and you don't have Viterbi errors, the filters aren't your problem.

Dave