Cream of the Crop 3/Cream of the Crop 3.iso/comm/aprs30_2.zip/README.HF

Text File | 1993-10-31 | 7KB | 106 lines

                      HF APRS BOAT AND RV TRACKING NET

    We are currently operational on what I hope will become a national HF
APRS position and status reporting net.  The two frequencies so far are 7.085
and 10.151 MHz LSB.  Yes, I know that 10.151 is out of band, but the packet
signal (at -1.7 KHz) is not.  I use the LSB convention in specifying the freq
to be compatible with all other packet channels on the band.  If you are
really that concerned and have a bad radio which is not truely SSB, of course,
you can operate on 10.147.6 USB which is exactly the same frequency!  But
you will have to explain it to everyone who doesnt understand LSB and USB
offsets.  ALSO PLEASE NOTE that these frequncies assume an audio modulation
center frequency of 1700 Hz.  The AEA-PK232 uses tones centered at 2210 Hz and
some others may use tones centered at 2125 Hz.  Radios connected to a PK-232
need to be tuned 510 Hz higher using LSB and 510 Hz lower on USB.  The other
TNC's which use 2125 need an offset of 425 Hz.  The following describes
several notes about HF APRS operation.

     When you tell APRS that you are operating HF instead of VHF, it multiplies
all timing routines by two to make up in the difference between 1200 and 300
baud (and the factor of two improvement when not using a digipeater on HF).
So the net cycle time on HF is twice as long as on VHF.  One other thing it
does is to change your default ALIAS from the generic callsign of RELAY to the
generic callsign of ECHO.  Read the info on the ctrl-V command and in the
README.RPT file to fully understand the implications of the generic ALIAS of
RELAY used by all VHF APRS stations.  Obviously, for a nationwide HF net, we
do not want everyone digipeating everyone else's packets!  So the change to
the alias of ECHO is only important in that it REMOVES the generic ALIAS of
RELAY!  Of coure you can still digipeat your HF packets off of another station
but now you should specify exactly who, by callsign, NOT by the generic call
of ECHO.  (Except in real emergencies where you want to maximize the chance
of your signal being heard at the expense of nationwide collisions!)

GATEWAYS:  APRS has great applications through HF/VHF gateways.  By assigning
the generic APRS alias of GATE to the gateway function in any of the dual port
Kantronics or AEA TNC's, then any HF station can gateway in your local net and
any station in your VHF net that wants to be seen nationally on HF need only
specify the unproto path of GATE.  HF stations can probably use the VIA path
of GATE most of the time, because the slow HF operation could hardly clutter
up any local VHF APRS networks.  But users on VHF APRS networks should NEVER
use GATE on the VHF side of their gateways except under extreme caution.  This
is of course because there will probably be more VHF users in a single VHF net
than there will be HF users across the whole country.  So the HF net would be
totally clogged.  I am concerned about over-using the VHF side of the gateway,
and have included a mechanism to discourage the use of the GATE via path on
VHF.  That way a user will have to intentionally specify the GATE function
each time he wants to use it and there will be no way for him to forget about
it and accidently contribute to un-necessary QRM!

TYPICAL DUAL PORT GATEWAY SET UP:  So here in Annapolis, I have the two KAMS
each with an HF radio on the two HF frequencies.  The audio of their VHF
sides are tied together into a 1 watt radio on 145.79.  Both KAMS run with
the GATEWAY callsign of GATE so that any HF APRS packets using the VIA path
of GATE will be seen on our local 145.79 APRS net.  Similarly, any VHF station
on our local 145.79 frequency that uses the path of ...,GATE will go out on
HF.  The purpose of this gateway is to support the big picture APRS objective
of allowing any mobile station anywhere in the country to report his position
back to his home QTH.  If I am driving through ANY area in the country that
is using 145.79 for APRS and that has a GATEway station on either of the two
APRS HF frequencies, my 2 meter APRS position report has a good chance of
making it all the way back to my PC display.  All I have to do is to set my
mobile TNC outgoing path to WIDE,GATE,GATE,W3XYZ.  This way the closest generic
APRS WIDE digipeater will digipeate my report to the nearest GATEway. It will
in turn digipeate the report out onto the HF APRS net.  My Annapolis HF GATE-
way will then see the second GATE and repeat the packet onto the local VHF
net through the local W3XYZ digipeater, which will then reach my home.  Notice
that all of the other gateways will also transmit the packet, but only the
Annapolis packet will get digipeated via the W3XYZ digipeater.  For this
reason, an APRS gateway should have a low power VHF radio only capable of
hitting the nearest VHF APRS digi so that it does not QRM a large area.
Neat huh!

USING THE CTRL-V VIA COMMAND WITH THE DUAL PORT KAM:   The HF and VHF
parameters for the KAM Unproto command are separated by a slash character as
follows:  UNPROTO APRS VIA HFDIGI1,HFDIGI2/APRS VIA VHFDIGI1,VHFDIGI2 etc
To set up your KAM using the APRS ctrl-V VIA command, you need to remember to
include the second half of the command as noted above.  If you omit the second
half of the command, then the KAM applies the Unproto command identically to
both ports.  Since I want my KAM to go out on VHF via the local WIDE area
digipeaters (WIDE,WIDE) but I want the HF packets to go via any HF GATEway
node (GATE), I can do that via the APRS Ctrl-V command with the following:
    ...Enter new VIA path: GATE/APRS VIA WIDE,WIDE
Notice that APRS automatically inserts the APRS VIA for the first part of the
UNPROTO command and all I have to do is type the DIGI address (GATE here), but
for the dual port KAM, that I must type it in myself after the slash for the
second half of the command (for the VHF port).


CAUTIONS:  Obviously the shared HF APRS net cannot handle a lot of such cross
band position reporting, but if you are far enough away to have to use an
HF link to report your position, then nobody really cares exactly where you
are minute by minute, simply which town you are in is fine.  So mobile stations
using this gateway function should probably not beacon any more often than
once every half hour.  Similarly, HF stations such as boats and RV's I would
not expect to routinely report any more often than that either.  We will just
have to see how APRS grows.

OTHER BANDS:  I only have two HF radios, which is why I have not looked for
other APRS packet frequencies on the other bands.  I would avoid the QRM on 20
meters and would look next on the 18 MHz band for a good permanent APRS report-
ing frequency for the long haul round-the-world boaters.  Of course, an APRS
frequency on the 20 meter band would be fun for just working APRS HF DX and
seeing where those foreign stations are!  As of version 2.05, APRS can also
plot stations using only grid squares.  Any BEACON packet with the grid sq
enclosed in brackets at the beginning of the BText will be plotted.