[aprssig] Balloons abusing our network

Jason KG4WSV kg4wsv at gmail.com
Sun May 1 14:37:23 CDT 2016


On Sun, May 1, 2016 at 11:20 AM, Ron <ve1aic at yahoo.com> wrote:
>
> You have no clue.



> A device at 25,000 ft hits every digi within 300 MILES or more.

Wrong. It's less than 200 miles at 25k'.

https://en.wikipedia.org/wiki/Horizon

You need over 60k' to reach 300 miles, and a typical flight will be above
60k' for 30 minutes or less.



If you can hear a digi 300 miles away, your network is either sparse or
broken.

If you can't hear it, it is not part of your local network and what happens
there does not matter.

> At a rate of every 30-40 seconds its abusive.

Balloons should transmit on 1 minute intervals at minimum.

> NO Hops are required above a few thousand feet

Specific altitude required for path switchover depends on terrain, APRS
infrastructure at each end of the flight path, and other factors, but
generally above 20k' or so direct is sufficient, assuming the flight
hardware can support profile switching.  Payload recovery trumps
politeness, so a 1 hop path for hardware that cannot support profile
switching is reasonable.

FYI I've been in scenarios where I was directly under a balloon near
maximum altitude with 5/8 wave antennas on both the flight and mobile
stations, and I could not hear it directly because both stations were in
the null of the other's radiation pattern.

> and transmit rates should be set by speed, just like everyone else does
in their cars.

Wait, do I abuse your network because I don't use smart beaconing?  By your
definition every D700 operator is a network abuser. This is an absolutely
absurd statement.

It's also clear you don't have any experience with actual balloon
operations where something goes wrong (e.g. burst event causing antenna
damage) where the exact time slot of the transmission can be critical.
Regular updates are also extremely useful for updating the trajectory
analysis during the flight (which is estimated based on weather predictions
before launch).

> YOU should be glad that some people still care to maintain APRS Nodes and
networks so EVERYONE can SHARE it.

:|


Let's look at some definitions:

"Automatic Packet Reporting System (APRS) is an amateur radio-based system
for real time tactical digital communications of information of immediate
value in the local area."  -
https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System

Network: a set of nodes and links between those nodes.

I combine these two definitions and make simple definition of an APRS
network as: all stations that can hear my station, and all stations that my
station can hear. This definition includes any repeated packets.

If I can't hear it or it can't hear me, it is not local and not part of my
APRS network.  By definition.


If you can't hear the digi 300 miles distant, it is not part of your
network and none of your business.


>From the perspective of the APRS network (stations you can hear and
stations that can hear you) there is NO practical difference between a
balloon flight and a ham who forgets to turn off the D700 when stopped for
an afternoon of shopping at the local mall/home center/grocery.

In reality, since the balloon can hit all the digis in the local network at
once (assuming there are more than one), there is a significant chance that
the digis will all transmit that second hop simultaneously, there for
reducing the total air time as compared to a terrestrial station that can
only see a subset of all local digis, taking up two slots.

A balloon is JUST ONE STATION added you your local network.  If one station
beaconing a 1 hop packet every 60 seconds "abuses" "your" network then you
have problems and they aren't related to that station.



That's what is happening on your local network, which is all that matters
by the definition of APRS.  But since you're so concerned about that digi
300 miles away, let's do some analysis.

Let's define three adjacent APRS networks, call them A, B, and C. Let's
also say that A and B are adjacent and B and C are adjacent, but A and C
are not connected.

Let us assume that the network design and load of A, B, and C are
reasonable, such that adding an additional mobile station to any of the
three networks causes no significant change in the local network operation.

Now let us add three additional mobile stations X, Y, and Z, one each to
networks A, B, and C respectively.  Each user of network A sees single new
station X and only X. Likewise B users see Y and C users see Z.  Remember
we assumed that all networks are reasonably designed and loaded, and the
addition of a single station to any of those network does not negatively
impact the operation of the network.

At this point we have added one station to every local network.  The
network, local to A, B, C and overall, continues to function normally,
based on our assumption that each local network can handle an additional
station.

Now let us assume that all three of the stations added to the three local
networks use GPS to timeslot their packets.  Furthermore let us assume they
use the _same_ timeslot, and their packets are the same length.  This does
not change the previous analysis in any way - all local networks are
functional and undamaged by the addition of the three stations, so the fact
that the three stations are synchronized also has no effect.

Now assign all three stations the same source address. Again, this does not
affect networks A, B, or C in any way differently than previously noted.
This is identical to the scenario where a balloon at altitude can be heard
in the three adjacent APRS networks.

This analysis is a slight simplification, but it is not an
oversimplification and will hold true for any subset of an APRS
internetwork that meets the assumption that the network design and load are
reasonable.

-Jason
kg4wsv
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