Cream of the Crop 3/Cream of the Crop 3.iso/comm/aprs403x.zip/README.HF

Text File | 1994-01-03 | 9KB | 132 lines

                      HF APRS BOAT AND RV TRACKING NET

    We are currently operational on two national HF APRS position and status
reporting nets on 7.085 and 10.151 MHz LSB.  Yes, at 10.151 the packet signal
is 1.7 Khz lower and is in the band by 700 Hz.  I use the LSB convention in
specifying the freq to be compatible with other packet channels on the band.
Of course, you can operate on 10.147.6 USB which is exactly the same frequency,
but you will have just as hard a time trying to explain to the Guys on 10.147
that you are NOT interfering with them!.  ALSO PLEASE NOTE that these freqs
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.

NEW:  After the tremendous growth in APRS activity on 10.151 over the 1993
Xmas holidays while I was GPS mobile on a 1700 mile trip, it might be time to
start looking for a general APRS frequency on 20 meters.  This would give
all new stations a place to play with APRS and all of its features without
adding QRM to the RV and boater tracking function on 10.151 MHz.  Is there
anyone out there that can select a good APRS freq on 20M and start using it?
Both of my rigs are in use on 7085 and 10.151.  We will also eventually need
APRS nets on 18 and maybe 24 MHz.  Any pioneers?


HF OPERATIONS:     When you configure APRS for HF instead of VHF, it multiplies
all timing routines by 2 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!  In this
case, digi via ECHO)

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 into your local net.
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!

     To repeat:  The purpose of HF/VHF gateways is to permit VHF local area
APRS nets to see the movements of nationwide RV and BOATER mobiles.  For
example, when I go GPS mobile, I do not want to, and cannot leagally leave my
HF station running at home so my wife can follow my status.  But If I send my
HF mobile APRS reports via the local HF GATEway, then my wife can see me on
our computer which only needs to have a VHF TNC.  Please DO NOT GATEWAY from
VHF through a gateway ONTO HF!  (Unless you have good reason.)


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.  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 digipeat
my report to the nearest GATEway. It will in turn digipeat the report out onto
the HF APRS net.  My Annapolis HF GATEway 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 UNPROTO 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 "APRS VIA" again
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!  In fact, after seeing the growth of
APRS over the 93 Xmas holidays, I think it is time to find a 20m APRS freq.
That would be a good place to play, and leave 10151 clear for real GPS mobiles.
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.

HF TRACKING DEMONSTRATIONS:  To see the results of some actual APRS HF
tracking events, use Alt-R to REPLAY the 1st month of Naval Academy cruises
in the 93BLOCK1.HST file.  Those stations were transmitting once every 10
minutes or so.  My first HF mobile excursion was over Xmas holidays.  When
I returned 2 weeks later the file XMAS93.hst showed me all that was received
in Annapolis of my journey (before the computer crashed).  It shows good
tracking from Knoxville TN to Florence Alabama.