Shareware Overload Trio 2/Shareware Overload Trio Volume 2 (Chestnut CD-ROM).ISO/dir24/aprs503a.zip/README.HF

Text File | 1994-05-10 | 10KB | 156 lines

                      HF APRS BOAT AND RV TRACKING NET

HF FREQS:  MFJ/KAMS  AEA'S    Mode  NORMAL USAGE
            10.151   10.1515  LSB   Mostly East Coast so far (Calif late eves)
             7.085    7.0855  LSB   Mostly West Coast
            14.0963  14.0958  USB   Proposed new APRS DX freq

     The 7 MHz frequency has a lot of QRM, but is good for shorter range APRS
mobile during the day.  Both the 10 and 14 MHz frequencies were very carefully
chosen to minimize interference to all present users of the band and to
provide some measure of QRM reduction to ourselves.  Please note the SIDEBANDS
used.  These are important and here's why:

     By using 10.151 Lower Sideband, the packet signal RF energy is 1.7 Khz
lower and is inside the band edge 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.

     On 20 meters, by selecting the frequency of 14.0963 UPPER SIDEBAND we
are in effect radiating on 14.098 MHz.  This frequency is a full 2 KHz away
from the international CW Beacon frequency of 14.100 which SHOULD NOT BE USED
FOR PACKET.  The advantage of this 14.098 frequency is that it can also be
described as 14.0997 LSB for 1700 HZ packet or 14.1002 for LSB with 2200 HZ
tones.  These are exactly the frequencies that all other packet stations might
be trying to avoid if they do not understand the LSB offset!  In effect, we
are taking advantage of their missunderstanding.  To further clarify this
nuance, it is important to note that a packet station desiring to avoid the
CW BEACON frequency of 14.100 should actually never operate within 500 Hz of
14.1017 LSB with 1700 HZ tones or 14.1022 LSB with 2210 Hz tones!  Putting it
a third way, we would be crucified if we announced that we are operating on
14.100 LSB by all those who do not understand LSB offsets.  So we are just
calling it 14.0963 USB to avoid the controversy.  In any case, we are 2 KHz
away from the TRUE CW BEACON FREQ!

     If we use this 20 meter freq for casual APRS DXing and new user familiar-
ization, then we will remove some of the QRM from the 10.151 LSB national
APRS tracking frequency.  I expect this summer, 1994, to see a big increase
in the number of boats and RV's tracked.  In the future, we should also find
a single APRS frequency 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!

SETTING THE UNPROTO PATH 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 UNPROTO-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 UNPROTO 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 start populating the
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.   In fact, N2CZF (then in NJ)
was able to track me all day, just about everyday, for the two week period,
during daylight hours!