[aprssig] [RFC] Power Source Data Extension

Kenneth Finnegan kennethfinnegan2007 at gmail.com
Sun Feb 12 03:27:18 EST 2017

As I continue to study the APRS symbol set this year, I've noticed a set of
symbol overlays indicating the power source for APRS stations, but their
documented application is limited to only a few base symbols and is
somewhat sporadic. Houses get all sorts of options for symbol overlays
indicating their power, but shelters get none.

In an effort to free the symbol overlay from trying to indicate both the
type of station and the type of power source for the station, I'm proposing
a new data extension to indicate power source.


Why was 50Hz vs 60Hz handled for houses? I'm a bit at a loss where that
would be an issue.


Power Source Data Extension

There has been a proliferation of APRS symbol overlays trying to encode the
power source for stations, which suffers from a few issues:

   1. Several duplicated sets of symbol overlays for power sources per
   station type (i.e. solar powered plane, solar powered car, and solar
   powered house)
   2. Prevents the symbol overlay from being used to convey more important
   information than the station's power source
   3. Is unable to represent more than one power source at a time
   4. Only gives the ability to indicate power source to a limited list of
   station types which have symbol power overlays defined

To correct these issues, I am proposing the definition of a new station
capability field to be included in the < capability packet or included as a
data extension in location or status comment fields.

PWR=[Unordered list of power source codes]

   - B - Battery
   - C - Coal, natural gas, wood, etc
   - F - H2 fuel cells
   - G - Internal combustion generator
   - H - Hydroelectric
   - N - Nuclear
   - S - Solar
   - T - GeoThermal
   - U - Utility mains
   - W - Wind

Multiple sources should be listed as several power source codes immediately
following the = with no seperator between power source codes. The list of
power sources is terminated by any character which is not an upper case
letter [A-Z].

The PWR extension is not meant to differentiate between different sources
for utility mains power. The availability of power codes such as geothermal
and nuclear are only for completeness, and should not be used by stations
which are simply paying their local utility company to operate these sorts
of power sources. This means that a power source like PWR=N would be very
unusual, since it indicates that the station is operating a nuclear power

Stations should indicate the power sources they typically have available,
which may not currently all be active. For example, an off-the-grid solar
site would beacon PWR=SB to indicate that they are a solar + battery
station, despite the fact that the solar panels aren't necessarily
producting power during the night.

This means that the PWR extension should never be used as a way to remotely
monitor power sources like whether a site has utility power or not (i.e. it
switching between PWR=UB and PWR=B). The correct way to monitor if a site
has power or not is to use one of the boolean telemetry fields to encode
the power state and beacon a telemetry formatter such as :MYCALL
:PARM.,,,,,AC Power.

The PWR extension may be foregone when the power source for a station is
unremarkable. For example, house stations only running on wall power (PWR=U)
or car mobile stations only running on internal combustion generator (PWR=G)
may forego the additional packet length taken to indicate the obvious.

This power source capability / data extension field deprecates the
following symbol overlays (with possible replacements indicated):

   - E^ = Electric aircraft (PWR=B)
   - S^ = Solar powered airplane (PWR=S)
   - E> = Electric car (PWR=B)
   - H> = Hybrid car (PWR=BG)
   - S> = Solar powered car/vehicle (PWR=S)
   - V> = GM Volt (PWR=BG)
   - E# = Emergency powered digipeater (PWR=?)
   - 5- = 50Hz mains power, house (PWR=U)
   - 6- = 60Hz mains power, house (PWR=U)
   - B- = Backup battery power, house (PWR=UB)
   - E- = Emergency power, house (PWR=?)
   - G- = Geothermal, house (PWR=T)
   - H- = Hydro powered, house (PWR=H)
   - S- = Solar Powered, house (PWR=S)
   - W- = Wind powered, house (PWR=W)

Many of these symbols would likely be replaced with something other than
what's listed; e.g. the overlay for a solar-powered house lacked the
expressiveness to distinguish if it's a grid-tied solar-powered house (
PWR=SU) or if it's an off-the-grid house with a battery bank (PWR=SB).

The distinction between 60Hz utility power and 50Hz utility power is not
made in this data extension since the possible application of where that
distinction would need to be made is incredibly small. For the very few
applications where mains frequency would be of any concern to other users,
APRS nodes may otherwise include a note on the power frequency. One
possible method would be PWR=U(50Hz); power capability parsers should
terminate at the '(' and need not process the frequency indication after it.

Kenneth Finnegan, W6KWF
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