AERONAUTICAL FIXED TELECOMMUNICATIONS NETWORK
            AND OTHER WONDERS OF THE HF RTTY WORLD


Ever peruse the RTTY column in a SWL magazine or see a file
on a SWL BBS that read something like this: 13737.0  5YD
Nairobi, Kenya 50/425  Coded WX...?  And when you tuned it in
it looked like jibberish or a bunch of numbers and you
weren't sure that you had solid copy on anything but static ?
Well, here is a chance to learn a little about an interesting
but seldom discussed aspect of SWL-ing: Aircraft movement and
meteorological messages.

For starters you'll need a Shortwave receiver that is
frequency stable and a RTTY decoder. Perhaps a software
terminal program to link your computer to your decoder. Try
tuning in one of the following frequencies:

           13737.0   5YD     50/425
           13996.5   STK     50/425
           14600.0   CAK     50/850

The first station is in Nairobi, Kenya and usually runs a
string of RYRY's for a half hour or so around 0000 UTC. If
you tune in while there is no traffic being passed you will
find the MARK carrier signal to zero in on and occassionally,
atleast every 20 minutes, there will be sent a "channel
message": ZCZC KSA042 150220 CH DE 5YD NNNN.  This type of
message has two purposes. One it keeps the channel occupied
and two the message sequence number allows the receiving
operator a tally of all messages sent that date.  The message
reads:
               ZCZC      This is the beginning of a message
               KSA       Channel (K) Kenya to (S) Sudan (A)
                         The (A) denotes the only channel.
               042       Message number 42 sent this date.
               150220    Date and time of message origination
               CH        This is a channel message
               DE 5YD    From station 5YD
               NNNN      End of message.
Messages with other letters in place of CH have the following
meanings: DD, high priority; FF, flight safety (departure or
position); GG, flight safety (arrival);KK, general messages;
and SS,dealing with distress.

I chose the two stations for this brief because they transmit
to each other. 5YD in Kenya identifies its channel as KSA and
STK in Sudan uses SKA.  A service message is one in which the
communicators use to handle the business of communicating.
i.e. ZCZC KSA050 150227 FF HSSSYFYX 150227 HKNAYFYX SVC QTA
RPT SKA036 NNNN.  The following may help you understand.

               FF        Flight Safety related
               HSSSYFYX  Khartoum-Fixed station-Military
               HKNAYFYX  Nairobi-Fixed station-Military
               SVC       A service message
               QTA       Cancel telegram number..
               RPT       Report
               SKA036    Sudan to Kenya channel message 036
Location indicators are the hardest part to read.  Any that
begin with..H.. are Eastern Africa. HA is Ethiopa; HB Burundi
HC, Somalia, etc. Those that begin with .K.. denote the USA.
S for South America; L for Southern European countries. The
second two letters identify the specific airfield/facility.
Some American ones you will recognise: KLAX, Los Angeles;
KSFO, San Francisco; KJFK, John F. Kennedy, NY.  Those of you
already familiar with meterological stations might recognise
as old friends: KAWN, the USAF Automatic Digital Weather
Switch at Carswell AFB, Tx. or KGWC, USAF Gobal Weather
Center, Offutt AFB, Omaha, Ne.  More of these two later.

Now lets try a simple message and see if we get its meaning
without too much book searching or head scratching.  The line
of code reads: TAF FIMP 0207 09010KT 9999 3CU020 2SC050 TEMPO
8000 80RASH 5CU015.
     TAF       Aerodrome Forecast
     FIMP      F..Southern Africa IMP..Plaisance,Muritius.
     0207      Time of observation UTC
     09010KT   Wind is from 090 (East) at 10 knots.
     9999      Visibility is greater than 10 kilometers.
     3CU020    Amount of Cumulus cloud cover and base height.
     2SC050    Amount of Stratocumulus clouds and height.
     TEMPO     Temporary change noted/expected.
     8000      Visibility to drop to 8 km horizontal.
     80RASH    Significate weather forecast. Rain showers.
     5CU015    With increased and lowering CU cloud cover.
As you can see there is a change in the weather coming. Next
we will lightly touch on some other types of messages.  There
is the NOTAM, a message usually to warn of some problem i.e.
closed runways, NavAids out or down for service, etc.  The
DEP which is a departure message advising the next airfield
and others who, what, when and where.  The ARR message
announcing the arrival of an aircraft. The information within
the brackets on DEP and ARR messages is for use by Air
Traffic Control computers.

Now let's turn our attention to the big picture; the gobal
picture.  Try tuning in one of these:

KAWN      3230.0, 6903.0, 19325.0   50/850N
CFH       6330.0      75/776R
KGWC      6902.3      75/850N
JMG4     14880.0      50/850N   Note: Freqs, baud & shift
6VU73    13665.0      50/792N         may be different.



If your RTTY decoder has the UnShiftOnSpace (USOS) feature
try experimenting with it on and off during reception of any
message that has lots of numbers in it.  Messages with the
heading TTAA (upper level pressure,temperature,humidity,etc.)
are all numbers.  Almost continously KAWN and CFH are sending
routine aviation reports labeled SA.  Typically they look
like this: GFA SA 1555 40 SCT 120 SCT 250 SCT 45 181/52/36/
0000/CU ALQDS=
     GFA       Read KGFA  Malstrom AFB, Great Falls, Mt
     SA        Routine Aviation Report
     1555      Time of observation UTC
     40 SCT    Base of lowest clouds 4000 feet. Scattered.
     120 SCT   Base of middle clouds 12,000. Scattered.
     250 SCT   Base of upper clouds 25,000. Scattered.
     45        Wind speed.
     181       Wind direction. From the South.
      52       Temperature.
      36       Dew point temperature.
    0000       Pressure in hPa.
    CU ALQDS   Cumulus clouds all quadrants.
     =         Separation signal.
US meteological stations routinely omit the K on location
indicators while Canadian stations omit the leading letter C.
Station that are part of the global weather gathering service
like JMG4 Tokyo transmit data from other countries. These
message have AAXX in the heading (surface observation land
station) and use a five digit station index number. 47671 is
Tokyo International Airport.  Anything from 50000 to 59999 is
mainland China. 20000 thru 39999 includes all the Russias

Words like TEMPO indicate temporary changes; GRADU gradual
changes; NOSIG no significant weather and SKC sky clear.

We have only scratched the surface.  For some of you thats
more than enough.  For others who will want to know more I
recommend:  AIR AND METEO CODE MANUAL  Tenth edition. 1988
Compiled by Joerg Klingenfuss. $19.95 plus $1.00 S&H from
Universal Shortwave Radio  1280 Aida Dr. Reynoldsberg, OH
43068.
Two other books I recommend are: CONFIDENTIAL FREQUENCY LIST
Seventh edition. 1988 Compiled by Geoff Halligey $19.95
Gilfer Shortwave 52 Park Ave. Park Ridge, NJ 07656 Phone(201)
391-7887  and GUIDE TO UTILITY STATIONS Seventh Edition. 1988
$26.95 plus $1.00 S&H from Universal Shortwave Radio above.
Supplements due out April and August. Eight edition is due
out Dec.  1989

Submitted by Torkel Clark, N6KKA, 76057,1717.