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Dr. Ralph E. Taggart WBBOOT
602 S. Jefferson
Mason M/48854
Deadline Blues
OCcasionally, Weathersats is
' missing from the pages of 73. The
lirst lime this happened. I gal
anxious calls from people wanting
to know why the column was
canceled!
Not to worry. Every once in a
while, there's a 101 01 graphics
support for the column and it's not
ready by deadline. This accounts
for the lack of weareersers in
March . If the column is missing it
won 't do any good to berate the
poor editorial statt-s-berate the
COlumnist instead I
WB800T Station
This month is a run-through of
my own installation alOng with a
few comments on the evolutionary
trends in the station to appear in
upcoming columns."
Antennas
The primary WEFAX antenna is
a four-loot (1.2 meier) Melsat GA­
4 dish . The dish is spun aluminum.
It has a weather-sealed
O-ring feed assembly with a solid
coax support that terminates in a
Type-N connector at the rear of
the dish. The antenna is mounted
on a swing-arm assembly that
mounts to the side of the house
outside 01 a second floor window.
(Read about the anatomy of this
mount in Ihe August 1987 Weathersat
column.)
This antenna costs more than
other options, but it's built like a
tank. This unit has served continuously
outside lor almost ten years
and is completely trouble-free.
Considering all that can go wrong
with a WEFAX receiving system,
it's comlorting to have one item to
discount when trouble-shooting
the syslem!
I also have a two-toot (0.6 meter)
version of this antenna lor
portable work , such as providing
weather coverage for soaring contests.
This antenna shows a positive
gain margin, but the pattern
is too broad for regular use, which
resu lts in interference from adjacent
satellites at some look
angles!
Driving by the house, one may
assume I don't have a VHF antenna
system. The house, however,
72 73 Amateur Radio - April, 1988
View On Video Processing
is an historic Victorian piece with a
cavernous attic under all the
steeply sloping roof gabtes-all
the VHF antennas are in the attic!
The antennas are completely out
of the weather. Weather protection
more than compensates for
the incurred modest signal losses.
The primary VHF antenna is
the omnidirectionat "Zapper,"
" An IBM PCjr runs the
whole operation. It talks to
t he receiving/recording system
through . . . a standard Centronics
parallel-printer port."
described in Weather Satellite
Handbook (WSH), with a Hamtronics
GaAsFET preamp at the
antenna. The feedline is RG-58
loam which makes the tortuous
run down through the walls to the
basement station location. The
attic also contains the crossed
yagi featured in WSH, complete
with elevation and azimuth rotors.
This antenna has a Vanguard
JFET preamp and a feedline
arrangement id e ntica l to th e
Zapper. The bea m sits idle most of
the time , however, since most
polar orbit reception here is automatic,
and the omnidirectional
Zapper performs very well (see
the picture of the month).
Receivers.
The 1691-MHz receiving system
starts with a Microwave Mcdines
GaAsFET preamp mounted
on the dish feed , driving abou120
feet of Belden 8214 to get the signal
inside the house. A Microwave
Modules downconverter takes the
signal from there and converts it
to 137.5 MHz tor a long RG-58
cable run to the basement. John
Beanland at Spectrum International
in Concord, MA, sells both
preamp and downconverter. John
thoroughly checks cut all units
prior to shipment, because their
performance on leaving the factory
in Britain is not always up to
his stringent stand ards. A Metsat
GDC-4 converter receives a second
satellite, and is used for
portable work. VHF preamps are a
must lor long cable runs.
The primary receiver is a Van-
guard unit equipped with crystals
for 137.30, 137 .40 , 137.50,
137 .62, and 137.85 MHz. This
covers th e operational U .S.
TIROS/NOAA frequencies,
137.50 for the WEFAX IF and the
most common Soviet frequencies
. In addition to the standard
manual switching, mOOifications
permit the receiver to switch via
TTL logic lines.
A Rege nc y MX·5000 widerange
scanner is the search receiver
to look for Soviet activity on
non-standard frequencies. Its antenna
system is a discone and a
preamp, both located in the attic.
This system isn't for imaging bu1
just to spot new aClivily .
Automatic Operation
In the June '87 column, there
are some simple bu1 very effective
approaches to unattended satellite
reception. The one I use operationally
is somewhat more complex
but achieves great results.
Almost any computer that supports
such a port could be used. I
c hose the PCj r because it has
nothing better to do during the
day, and generates little AF hash.
The oerenet port con figuration:
- (1) The 8-data lines are used for
receiver channel selection.
-(2) One status line (input) looks at
the 2400-Hz tone deco jar output
that is connected to the receiver
audio output.
- (3) One control line (output)
switches in the WEFAX downconverter.
-(4) One control line is used to
switch power to cassette deck '1
while another control line doesthe
same for cassette deck 112.
The computer has a real-time
clock that provides constant access
to date and time. The operating
system is a simple BASIC program
built around a customized
version of the PREDICT program
from WSH . The customizing primarily
allows the system to keep
track of both operationa l NOAA
spacecraft. In addition, the program
contai ns the complete
GOES Central WEFAX schedule,
less the chans.
The operating program is a 001-
ance of dealing with both knowns
and unknowns. The "knowns "
are the transmission times for any
given WEFAX product, plus the
AOS and l OS times (on any given
day) torme NOAA spacecraft. The
" unknowns" are times and frequencies
for Sov iet spacecraft
passes. In operation, I select the
specific WEFAX products 01 interest.
For reasons to become evident
next month, I usually specify
the prime 1800Z quads for the full
earth disc in both IR and visible
light, but I can select anything
from the complete schedule. Barring
other imperatives, just prior to
the effective time of a WEFAX
quad, the system switches the receiver
to 137.50 MHz and switches
in the WEFAX converter. The
computer then monitors the 2400­
Hz tone decoder and starts the
recorder if a tone is present. II the
channel is inactive tor 3 minutes
alter the scheduled transmission
lime, the system switches back to
the VHF search mode. Otherwise,
recording continues unlilthe quad
transmission finishes.
Except lor scheduled WEFAX
transmissions, the system works
on VHF. Since it knows when to
expect the NOAA spacecraft, it ignores
137.50 and 137.62 MHz except
when it reaches the AOS lime
for a specific NOAA spacecraft. It
then switches to the appropriate
frequency and begins to monitor
the tone detector.
Early in a pass, the spacecraft
signal is noisy, marked by pulsing
of t he detector . The system
doesn't begin taping until the oetector
has a solid lock lor at least
15 seconds. Taping terminates
anytime within 4 minutes of the
calculated LOS time, when the
tone detector again becomes erratic
, indicating a noisy signal.
This alone saves a tremendous
amount of tape and makes review
01 tapes quite simple.
If there's no tone detector indication
within three minutes of the
predicted AOS time, the system
switches to the secondary trequency,
flipping back and forth for
two more minutes in search 01 a
subcarrier signal. It tapes wnatever
is found, otherwise the pass terminates
and the system returns to
the search mode. One may opt for
AM, PM, both AM and PM, or lockout
(no recording) for each of the
two operational spacecraft, giving
complete control over what is
recorded.
The system sequentially scans
all the primary Soviet frequencies
most of the time. It looks for 2400­
Hz subcarner signals. Any signals