What dBc really tells you on an anti-jam datasheet
Suppression figures are quoted per jammer count for a reason. Reading ≥120 dBc without reading the number next to it is how integrators end up with the wrong array.
What the number measures
dBc means decibels relative to the carrier. On an anti-jamming datasheet it is the jammer-to-signal ratio the terminal can absorb while still holding a usable fix. A figure of ≥120 dBc says the terminal keeps working with interference twelve orders of magnitude stronger than the satellite signal it is trying to receive.
That is a suppression figure, not a sensitivity figure. It tells you how much interference the array can null away — not how weak a satellite signal the receiver can track.
The number next to it is half the specification
Suppression is always quoted per jammer count, and it always falls as the count rises. Our seven-element terminal is ≥120 dBc against one jammer, ≥110 against three, and ≥100 against six. Same hardware, three very different numbers.
The reason is the degrees-of-freedom budget again: every null you place costs the array some of its ability to place the next one. So a headline '≥120 dBc' means nothing on its own. Always read the pair — the suppression and the jammer count it applies to.
Comparing across vendors
Two terminals quoting the same dBc are not necessarily comparable. Check the interference type the figure was measured against — a number obtained with band-limited Gaussian noise is easier to achieve than one against a matched-spectrum jammer that mimics the spread-spectrum signal itself. Ours are specified across band-limited Gaussian, matched-spectrum, pulsed, swept and mixed interference.
Check the coverage too. Suppression across azimuth 0—360° and elevation −90° to +90° is a different claim from suppression only near the horizon, which is where the cheaper designs quietly limit themselves.
The numbers that get overlooked
Power consumption and weight decide whether the terminal flies at all. Output power and impedance decide whether it drops into your existing receiver without a redesign — ours are −70 to −60 dBm into 50 Ω, which suits most integrated receivers. And the constellation list decides whether you keep the redundancy you designed for, or quietly lose a system when the anti-jam front end goes in.