The eight checks

The eight checks

Every check states its own verdict, the number behind it, and a sentence of what that means. The overall verdict is the worst of the eight, and it must hold for sixty continuous seconds before it is reported.

Where a check cannot be judged at all, it says so rather than passing: "we could not check" and "we checked and it was fine" are different statements, and only one of them is a pass.

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1. Connected and producing

The caster accepted the connection and bytes are arriving. The number is throughput in bytes per second.

• "Connected, but the caster has sent nothing" — the caster accepted you and then sent nothing at all. On a network mountpoint this usually means it is waiting for a position: see Send GGA in Getting started. Otherwise the mountpoint may be published but not currently fed by its receiver.
• "Data arrived for N s, then the stream stopped" — a different finding, and one worth reading carefully. The station did deliver, and check 2 will still show the frames it delivered; something then ended the flow. That may be the receiver, the caster, or the network in between, and this check cannot tell you which — but it is not a station that never produced. One cause is close to home: many casters allow one session per account, so a second check started while the first is still running evicts it. Leave a gap between runs before suspecting the station.
• "Connection lost after N s of data" — the socket itself went away after the station had delivered. --check does not reconnect, on purpose: a drop inside an acceptance run is a finding rather than a nuisance to paper over.
• "Connected, but throughput is below the minimum" — something is arriving, but not enough to be a working observation stream.

2. RTCM 3.x format

Frames arrive, and their CRC checks out. The number is how many were decoded.

• "No valid RTCM 3.x frame yet -- wrong format?" — the stream is not RTCM 3. Some mountpoints publish a receiver's raw binary format, which this tool does not decode. The sourcetable's format column says which.

3. Reference position (ARP)

The station broadcasts its own coordinates, in message 1005 or 1006. Without it a rover has nothing to compute against.

• "No RTCM 1005/1006 within the 30 s allowance" — the station is not publishing its position. This is a genuine fault for a base station; report it to whoever runs it.
• "ARP seen earlier this run but not confirmed now" — it arrived and then stopped, which usually means the message is sent very infrequently.

On a network mountpoint — VRS, MAC, nearest-base — read this check differently: the reference position is computed near you and may move, which is correct operation there, not a fault. The instrument for that kind of service is the Network-RTK check (Pro).

4. Observations flowing

Every constellation the station is streaming must arrive at 0.5 Hz or faster. The number is how many constellations are at rate.

Note what this does not demand: a particular set of constellations. A station that sends GPS and GLONASS, and says so in its sourcetable, passes. An older station is an old station, not a broken one.

• "Some constellations slower than 0.5 Hz" — part of what it sends is arriving too slowly to position with.
• "No observations arriving at rate" — nothing usable is coming through.

5. Satellites in view

Counted against what this station advertises, not against a fixed number: the sourcetable says which constellations it serves, and the expectation is the sum of what those normally deliver.

• "Below expectation -- obstruction or partial tracking?" — fewer satellites than the station should see. Sky obstruction, a mask angle set high, or a receiver tracking only part of what it could.
• "Fewer than half the expected satellites" — a fault worth reporting.

6. Median C/N0

Signal strength across the satellites, as the median. Healthy is 40 dB-Hz or better; the check warns within 10 % of that and fails well below it.

This is the antenna and its cabling talking. A low median points at the antenna, its siting, a long or lossy cable run, or a failing LNA — not at the receiver.

• "Not measured: C/N0 is read from MSM4, 5, 6 and 7" — this stream's message types carry no signal strength the app reads. That is a limit of the reader on those formats, not a fault of the station, so it is a caution and never a failure.

7. Frame integrity (CRC)

The proportion of frames that fail their checksum. Healthy is fewer than one error in a thousand.

• "Elevated CRC error rate" — the link is corrupting frames. This is usually the network path rather than the station: a marginal mobile connection, or a caster under load.

8. Advertised versus actual

Compares the stream against the promise in the caster's sourcetable, in three directions:

• "Advertised message types are not being sent" — a promise not kept. A rover configured from this sourcetable will not receive what it was told to expect, so this fails.
• "Some types arrive off their advertised rate"
• "Sending types the sourcetable does not advertise"
• "Streaming a constellation the sourcetable omits"

The last three are cautions. Sending more than you advertise is not a fault in the stream, but it misleads whoever chose the mountpoint from the sourcetable, so it is worth telling the operator.

Advertising a constellation that is not currently streamed is ordinary and is not flagged — QZSS is advertised across Europe and visible from none of it.

• "No sourcetable entry to compare against" — the caster published nothing for this mountpoint, so the comparison could not be made at all. A caution, because nothing was checked.