[aprssig] timeslotting on HF ? was > 15. APRS trackers on 10m (Robert Bruninga)

Robert Bruninga bruninga at usna.edu
Sun Nov 27 13:52:27 CST 2005

>>> kmcaviezel at yahoo.com 11/27/05 12:32 PM >>>
> I agree that time slotting would be a good idea 
> if it were implemented seamlessly, but would
> be impossible and just a nightmare if we had
> to "assign" time slots. 

>Scott had a great idea- get the i-gating on the same
>page as the slot assignment.  If a ham transmits on
>his/her non-slot time, then there's no data i-gated,
>or better yet a "please use your assigned time slots"
>message on findu and aprsworld.
Time slotting on 144.39 will never work.  No need to
even try because there will always be 99% of other
digis, users and WX stations there not using it.
And CSMA between the digis works just fine there.

The only place where time slotting would work is
on a NEW dedicated frequency dedicated to only
one kind of TRACKER application where ALL 
devices use the algorithm.  This lets slots work
in the only place where they can work, on the
INPUT frequency of a system where the hidden
transmitter problem is most  prevalent.

Dont even wast time thinking about doing it on
the OUTPUT frquency (144.39)....where it so happens
that CSMA does work very well between the digis.

de Wb4APR, Bob
Starting from a clean sheet as it were, it seems to me
that an initial co-operation between hardware and
infrastructure parts of APRS (e.g. Pocket Track-esque
and Open Trak-esque PIC based units, aprsworld and
findu.com, 'client' software authors) could result in
a system wherein: 

a).  A ham with interest in HF APRS purchases and
builds a kit for a 10m (or other HF freq) tracking
unit, builds it, tests it, and included in the
instructions is an explanation of how disciplined HF
timeslotting is designed to work. 

b).  Then he/she signs up for as many as 3 slots per
hour, and programs the tracker to transmit only during
those exact slots, using the awefully darn accurate
GPS derived time.  

c).  Given the characteristics of HF propagation,
sometimes the packet will be heard at a gate across
town, other times a state or two away.   Since there
is discipline on the frequency, we're dealing only
with the vagaracies of HF propagation, not the random
QRM from another ham trying to transmit on the

d).  Slots could be 'churned' on a use it or lose it
basis.   If your 10m APRS time slot rig is 'SK' for
say 2 months, your slots are thrown open to others to

For me, I really like the way the low power Pocket
Track plugs away for days on a very modest amount of
power.  The problem is, it's a 'dumb' tracker (really
a deaf tracker...) and only works when it has the
frequency to itself.  Seems that timeslotted HF APRS
could add tremendous range to low power tracker units
way off in the hinterlands.  Because of the unique and
changing propagation characteristics of HF, it seems a
shame to bascially force a far-off user to jack up the
transmitting power to 100W when a 1W signal could get
the data through if the transmission wasn't battling
others.  Enabling low power reliability could lead to
easily backpackable units suitable for SAR teams on
foot, possibly offering much better visibility to the
command post than VHF APRS trackers, largely invisible
after they get behind a hill with no digipeater

This is just a concept.  The advent of low cost GPS
units can enable accurately time slotted packets to
share a frequency if the users and system are geared
up for it.   If the players here want to embrace it,
then we will have extended the state of the art.

- KMC ng0x Denver 

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