So Much Drama in the LPC

In the last year, I’ve had the same conversation no less than a dozen times about different units wanting 25k dedicated SATCOM nets.  Prior to this last year, I was never even allocated a 5k dedicated SATCOM net, so even getting a 5k dedicated net was a big deal.  The thing I really could not understand is why seemingly everyone thought they needed 25k dedicated nets.  I had at first dismissed the claims of the 5k nets being “unreliable” as unreasonable complaining.  After putting my best Marine on it and still not working properly, I realized it was an actual problem.  The thing about dedicated SATCOM is, it is not very complicated, and doesn’t have many options to choose from.

After talking through the problem, it was determined the issue was with the encoding scheme (voice CODEC).  After some research, we determined that our Harris radios supported two schemes: Linear Predictive Coding (LPC) and Mixed-Excitation Linear Prediction (MELP).  MELP is a the more advanced CODEC.  A radio configured for MELP is able to interpret incoming audio that is using LPC; however, a radio that is configured for LPC will not be able to understand incoming audio that is using MELP.

The moral of the story is, make sure if you are using 5k dedicated SATCOM you make sure you are using the same encoding on each end.