Stations heard by X,
and stations which heard Y
aprs.fi collects monthly summaries of digipeater and
igate statistics. The info page shows both a table of
digipeaters and igates which heard the given station, and (if
the station is a digipeater or igate) which other stations
where heard by that station. The most recently updated entries
are shown using a larger font.
These statistics are usually somewhat correct, but
there are several caveats, and as you've probably heard –
there are lies, damn lies, and statistics.
- The APRS-IS network that
feeds the APRS packets from the igates to aprs.fi does
duplicate suppression. Only the first gated copy of a packet
traverses the entire network. All other duplicate copies
seen within 30 seconds after the first packet are dropped by
APRS-IS. A packet which is heard by multiple igates normally
gets credited only for a single igate.
- A lot of digipeaters do
not add their own callsign in the packet's path when
retransmitting a packet. aprs.fi cannot possibly know about
- A lot of digipeaters do
callsign substitution instead of insertion, replacing
original path components. A packet with a path of
OH7RDÖ,WIDE2-1 could have been a WIDE1-1,WIDE2-1 packet in
the first place, and gone through OH7RDÖ and another unknown
- The aprs.fi "first heard"
algorithm tries to go on the safe side: if it's not sure, it
doesn't count as directly heard. But even then, some
incorrect overly long paths are shown.
- Stations transmitting
invalid or fake coordinates will skew these statistics. If
the transmitting station claims to be 1000 km away (due to a
bad GPS fix), my best guess can only be that the station
actually is that far away.
- Items and objects are not
shown here, since they are usually far away from the
transmitter which transmitted the packets.
Read through that quote and I suspect that most of the packets
you're copying are either a) injecting directly to the APRS-IS
causing your RF receptions to be dupe-suppressed or b) have a path
that causes aprs.fi to have doubts about the reception based on
the above description.
The APRS-IS, from which aprs.fi draws its data, is not usable
for doing any sort of RF network analysis like "Stations heard
by". Although aprs.fi does make an attempt at it, it cannot be
relied on as being complete.
Lynn (D) - KJ4ERJ - Author of APRSISCE
for Windows Mobile and Win32
Hi, although my raw packets are being reported by APRS.FI, and
that I'm active, positions and stations that have clearly been
decoded on my RF port are suddenly not being shown under "Stations
heard by N7TTQ-9" nor "Stations which heard N7TTQ-9". Identical
stations heard identically up to the 29th were fine, then
nothing. I must have hit a button somewhere. Mind you prop has
not been good in the last few days but for example VA6ATA-1 I
clearly have heard and have even messaged but doesn't show up as
being heard by me nor vice versa.
Does anybody have any ideas?