Stereo Tool

I recon that the transmitter has an effect on overshoots as well as the sound card. When I changed to my current transmitter which is capacitor coupled on the MPX input (The BW Exciter Board is DC straight) I had significant overshoots until stereo tool was calibrated. On my previous transmitter no calibration was needed.

True...the exciter and the sound card both play a big role in controlling overshoots. The BW and Marian are a gold standard in overshoot control but if there are other options, I'm always eager to learn. The fact that you were able to compensate for overshoots in your exciter by using ST's calibration settings is fascinating. It seems that every time I turn around, ST is finding another way to amaze me. I hope so many people buy the full version of ST that Hans will find it unattractive to be bought out by the big boys. I just want to climb to the tower top and holler "ST Rocks!" for all the world to hear.

Frequency response was the biggest problem with the transmitter. I had to adjust each slider to give exactly 75Khz on the Pira 75, so much adjustment was required e.g.. the 20hz slider is down -6db to -0.27db at 57Khz. As you can imagine the audio sounded very base heavy until the adjustments were made and stopped the overshoots too. Interestingly the tilt control show a perfect square wave without tilt adjustments, so capacitors were not the issue. Vericap diodes depending on the bias from the PLL can give a very un-linear frequency response, so calibration will be required in most cases if you are changing your transmission frequency significantly.

I checked the audio frequency sine wave flatness and found it to be about +.25db at 48500hz and +3.4db at 5.5hz...both easily correctable. Neither seemed to be having any ill effect on the audio or peak control, but it was interesting to see where my system came in. On square waves, the monitor starts doing bizarre things down around 5hz. Guess it's a good thing that program material doesn't have any 100% modulated 5hz square waves! I assume that the exciter was coming unlocked as the Low Signal lamp on the monitor was flashing.

Yes a DC spike is going to have a bad effect on the transmitter. It will send it out of lock in most cases unless the PLL can pull it back at a decent speed. At least with a coupling cap in the MPX input this would not happen.