DIGI_NED has a DX function build in. First of all you can get distance information through queries. This works with the command ?DX. It works like ?MH - with port number or call. It uses the entries in the MHEARD list, so when the MHEARD list is small the DX will also not give much.
DX with port number 1 returns for example the next 3 messages:
DX-P1 of all 263.3 km D0BRP DO4BH-1
DX-P1 of 24h 161,4 km DO4BH-1 PD0JBR-1
DX P1 of 1h 123.9 km PA3ESK-2 PE1ABT-15
The first is the best DX for all entries available in the MHEARD list. It shows the distance to best DX station, the call of the best DX station and second-best DX station.
The second and third lines are almost the same, but the second is for the stations received in the last 24 hours and the last for stations received in the last hour.
If there is no second best DX station then only one call is shown.
The duration over which is measured (all, 24h, 1h) is specified in the .ini file, this can be changed in steps of one hour.
Tip: ports are numbered 1 to 8, number 0 can be used to mean "all ports". This also works for the MHEARD command by the way We can zoom in on a station with "DX " for example
PD0JBR-1 138.1 km bearing 026 degrees
It shows distances and bearing from the digipeater to this station. Distance uses a great-circle calculation, bearing is based on a flat earth model. Bearing "0" is True North. The DX not only works on calls returned by DX command but on all calls in the mheard list. Like MH also port 0 is accepted to mean 'any port'. If there is no distance and bearing information the returned message will say so.
When a station is received which is the 'best DX' over a period of time then is will be announced by means of a DX bulletin which can be caught by a TH-D7 or TM-D700 radio for example. There is a threshold value defined in the .ini file, which specifies the minimum distance for DX.
Distances below this value are never DX. The period of time over which the 'best-DX' is determined is as specified in the .ini file. The rule with which this is specified is "dx_level:". This can be set for each port, because DX on for example 6 meters is a totally different distance then DX on 70cm.
With "dx_path:" the destination call and path can be specified which is used for the DX announcements. This can be set differently for each port.
After a DX announcement has been send a new announcement it will not be send if the same station is heard again within a period of time. This period is determined by the "keep_time:" parameter, the same, which is also used for duplicate checking. If after this period the same station is heard again and this station is still the best DX, then a new DX announcement is transmitted. If a better new DX is received within the "keep_time:" period (or after..) then is announced immediately. This mechanism only avoids duplicate transmissions of exactly the same DX message and does not delay new data.
Even in a AX25 environment where transmission failures not exist. It is possible to have errors in the DIGI_NED DX-list. Stations that are next doors can appear as thousends of kilometers away due to wrong position frames. These stations can be cleared by the digi owner using the '!clear < call >' command.