Sunday, December 20, 2009

APRS receiving performance graph

The graphs page of APRS igates and digipeaters now shows a new graph which tries to describe how well the station's receiver is performing by plotting the number of position packets received from a given distance during a month. There will be multiple lines, one per month, over the past few months. Here are a few examples:

OH2RCH close to downtown Helsinki, but there have been a few bad GPS fixes:

OH7AA fairly quiet on 144.800, peaks generated by stationary digipeaters:

OH6RDK is a digipeater without any activity within 20 km range (the receiver probably does work at that range, though):

VK2TV-4 has an HF receiver:

As usual, there are a few catches:
  • The graphs tell more about the amount of activity within a given distance, than the receiver performance at that range. A receiver in the middle of a big city might hear well from a long distance, but there is simply so much traffic close to the receiver that the linear Y scale of the graph hides the position packets from the distant stations. Maybe I should switch to a logarithmic scale, or would that be too confusing?
  • Stations transmitting invalid or fake coordinates will skew the stats. 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.
  • AIS support is still in the works, I need to add a method to configure the coordinates of the receiver.


VE6SRV said...

A log scale on the vertical axis would be a good thing where a digipeater is overwhelmed by a large number of packets at a specific distance.

A digi in a busy metro area would show a large peak close in, and the lower values would dissappear.

In my area, the traffic close in to the digis can be extremely low, and be drowned out by the other digipeaters far out on the horizon.

A log scale would still show the fine detail without being overwhelmed by the larger values.

VE6SRV said...

Found something interesting when trying to find the source of a huge number of packets...

I was looking at the CNP digipeater graph:

Where there are around 1200 packets at about 110 km away. Poking around looking for lots of noise around that range, I found VE6AQU with an interesting graph.

It doesn't explicitly label the graph with a negative distance, but the way the graph is drawn, one could extrapolate the value.


oh7lzb said...

VE6SRV: Looking at the info page's "heard by" list helps figuring out these cases. In this case, graph vs info. VE6AQU has only heard packets from VA7FF-14, 9 of those within past 48 hours, and 17 packets in this month (after I installed the monthly data collection). Iẗ́'s 5.2 km away, which falls in the 0 to 10 km slot, and the dot is drawn on 0. No stations further than 10 km away heard, so no way to draw a line.

I did figure out that the graph should be a bar graph, but they are hard to make readable when there are multiple months shown. There will be additional lines for 201001, 201011, and so on.

oh7lzb said...

VE6SRV: Looking at the info page of CNP, it's heard 516 packets within past 48 hours from FARS-2, which is 112 km away, which falls in the 110 to 120 km slot. 1200 packets will be nicely collected within a bit over 4 days.

LA3QMA said...

Very nice function :o)

VE6SRV said...

Okay, now you've got me wondering... I always tell people that I live in an APRS wasteland, very little activity on the air. Yet, when I look at the stats for my local i-gate, we have a top end of 10,000 packets on the graph. We probably have about 8,000 packets handled within 0-10 km of the digipeater this month.

Looking at other areas where they have heavy loading, and congestion, I don't see nearly the level. I have not seen anyone much over 1,000 before.

Of course, our i-gate can hear a long way, and we funnel everything for about 300 km around into it. There are a few i-gates in town here, but VA6KRM-10 wins the race most of the time. Other major centers have dead i-gates that don't do anything other than announce their presence.

That, and we also have a numbskull that beacons every 5 seconds when he's mobile every once and a while.

Is there a way to find heavy loading areas from the database? Just an idle interest.

oh7lzb said...

VE6SRV: So, is VA6KRM-10 the local igate you were looking at? The 'heard stations' / 'igated stations' list, and the /heard/ and /gated/ maps are the ones which should help.

VE6SRV said...

I know about the heard and gated maps, but they all are specific to that single station. I've been scratching my head trying to figure out how to look at network performance.

I don't look at individual stations when looking at how the network is running, but look at the overall performance. So, I spend a lot of time typing the callsigns of the neighboring digipeaters, and i-gates into the graph page to see what the other infrastructure in the area is doing.

What about this idea. Have a network performance page... it would put circles around the digipeater and i-gate stations that are relative to the amount of data being handled by that station.

It would be like looking at a map where a dot represents a hamlet, a small circle represents a village, a larger circle represents a town, and an even larger circle represents a city.

Looking at this map would show you the areas of heavy usage by infrastructure assets.

When we zoom out, you replace icons using shaded blocks, showing where there's a lot of traffic, but you can't tell who's handling the traffic.

In the Seattle area, they have at least 4 different APRS networks, VHF and UHF, and each has a 1200 and 9600 baud network. Looking at the map, it can be hard to know which digipeater is on 144.390 and heavily loaded, and which is on 144.350, and lightly loaded.

Also, having a circle around a an igate that is very small, or non-existent might clue some people into the fact that their i-gate is no longer functional, and they should look at it to get it fixed...

Tools for observing the network are very rare, and we really need to get people looking at the network, and understanding what is happening.

If you have a mountaintop digipeater that is heavily loaded, perhaps it might be good to look at replacing it with 2 or more digipeaters lower down so that the load is distributed, and more airtime is available for everyone in the area.

If you can show this to people, you might be able to effect some change for the better. You've got to drag the heads out of the sand once and a while!