What is code imbalance and how can I correct it?
Code imbalance is a condition that can occur when PSK modulating a carrier with a PN signal that has certain types of distortion. The primary cause of the imbalance is due to the fact that rise and fall times in the PN signal are generally unequal and nonuniform. Code imbalance is manifested by spectral lines appearing in the nulls of the PSK signal’s frequency spectrum. Under ideal conditions the nulls would be perfectly suppressed. There are other, typically less prominent, causes of spectral components in the nulls. At higher chip rates, ripples in a PN signal will often occur as a result of driving the non-linear input of a balanced mixer. For example, with our generators there is a ripple of about 5% present in the PN signal at 20 MHz chip rates. These ripples tend to spread a small percentage of the power from the spectral lobes into the null regions. A small degree of code imbalance is often not a concern in practical spread spectrum systems. And, in fact, shaping filters can su
