Reading a satellite modem’s statistics

When a satellite site has trouble, the modem’s own statistics usually say whether the problem is the space segment or something behind it. Reading them well saves you from escalating a LAN fault to a satellite operator, and from spending a day on a LAN when the link is degraded.

Signal quality

Eb/N0 or Es/N0 is the primary figure. Record what it reads on a clear day — without that baseline, no single reading means anything. A drop of a few decibels from baseline is significant; the relationship to error rate is steep, not gradual.

Error rates before and after correction

Most modems report both. The pre-correction rate tells you what the link is really delivering. The post-correction rate tells you what your traffic experiences.

The important case: pre-correction errors rising while post-correction stays at zero. Everything works perfectly, and your margin is being consumed. That is the early warning, and it is visible weeks before an outage if anyone is looking.

Lock status and history

Carrier lock, frame lock, demodulator lock. A modem that has re-acquired lock repeatedly has been losing the signal briefly, which users experience as intermittent faults nobody can reproduce. The lock counter is often the only evidence that anything happened.

Transmit power

If the system uses uplink power control, a transmit level that has crept up over months indicates degradation somewhere in your own equipment — a connector, cable water ingress, or a failing amplifier — rather than anything in space.

Separating link from network

If signal quality is at baseline and post-correction errors are zero, the satellite link is healthy and the problem is behind the modem. That single conclusion, reached in two minutes, redirects the entire investigation.

Trend these figures continuously rather than checking them during incidents. The value is in the comparison, and you cannot compare against a baseline you never recorded.