Gift to

Antenna azimuth for ATS·3 from Washington DC:
X = 27.8 degrees
Y = 38.5 degrees
Azimuth = tan - 1 tan X
sin Y
SUbstituting :
Azimuth = tan - 1 tan 27.8
= tan - 1
Elevation ;;: tan - 1
cos X cos Y - .151
V 1 _ (c os X cos y) 2
Substituting:
Elevation = ta n - 1
= tan - 1
= tan - 1
sin 38.5
.527
.623
= tan -r t .846
= 40.23 degrees
Since Washington is east of the spacecraft, we add the
result to 180 0 • Therefore, the azimuth is 220.23 degrees.
Antenn a elevation for ATS·3 from Washington DC:
cos 27.8 co s 38.5 - .151
V 1 _ (cos 27.8 cos 38.5)2
.692 - .151
V 1 - .479
.541
.72 2
= tan - 1 .749
= 36.8 degrees
Geosynchronous satellite range in miles may be found by
the formula:
Range = 262 10 V 1.023 - .3 02 (c os X cos Y)
Once more, from Washington, the range in miles to ATS·3
can be comput ed as follows:
Range = 2621 0 ,,;'7 1 .""' 0"" 2"" 3 ----c. 3"0"2"(-c o-s--=c 2 7=-.""8 -c-o-s ""'3""8~. 5 )
= 2621 0 V 1.023 - .302 (.692)
= 26210 (.902)
= 23641 miles
In order for their axis synchronizations
to be maintai
ned-that is, the spacecraft's
angle in relati on to
Earth - t he satell ites are
sp in-stab il iz ed . The sp in
rate is about 96 rpm and
provides a noti ceab le amp
lit ud e-modu lated pul sation,
p arti c ul arl y fro m
weak signals.
As I mentioned ea rlier,
there are anoma lies in both
A TSor bits. ATS-1 is pre sently
expe rie ncing a nor thsouth
incl ination of about
10 degrees, w hil e ATS-3 suffers
from a similar incl inati
on of 8.5 degrees. These
disorders ar e uncontrol ­
labl e from Earth and w ill
52 73 Magazine· October, 1980
My ante nna, whi ch is
best descr ib ed as a foureleme
nt quagi, cost $4.80
and consists of three pieces
of wood and some alurninum
c l o t h e sl i n e . Thi s
antenna is linearly polarcontinue
to increase at a
rate of .86 degrees per year.
Be amwidth s of m o st
ground stat ion antennas are
in t he rang e o f 30 -40
degrees, so the necessity for
tracki ng does not yet exist.
Sip le stat io n (64° sout h
lati tude) now must meet
ATS -3 orbital sc hed u le s
since the spacecraft is over
the horizon dur ing its north
inclination.
Let's now address ourselv
es to an ATS receivin g
system. For one reason or
another, NASA has excluded
channels one and five
from ope rat ion, so we are
concerned only with three
re c ei vin g fr e q u en c ie s:
135.575 MHz, 135.600 MHz,
and 135.625 M Hz . Some
ground stations own mammot
h General Dyn am ics diversity-telemetry
receivers,
but for most o f us thi s kind
of equ ip me nt com e s
straight f rom fantasyl and
a nd is c e r t a i n ly n ot
necessary. The University
of Miami purchased some
in exp ensive crysta l-con ­
tro lled VH F sc anner s a
wh ile bac k, and the y co n­
ti nue to perfo rm satisfactoril
y .
AM aircraft receivers wi ll
not work. (The spin-stabili
zed ca rriers are somet
im es rec o gnizabl e o n
t hese re c eiv e rs .) O ld
tu nab le VHF monitor receivers
will not work very
well du e in part to th eir
poor sensitiv ity and unnecessarily
w ide i-f bandw
id t h. Su rp l us Gen er al
Electric and Motorola receiver
strips are great and
fi ll t he bill per fectly. Since I
already ow ned a Bearcat
210 sy nt hes ized scann er
(which does not tune to 135
M Hz), I dec ided to go the
converter route. M y converter
is designed so that its
i-f is exactly 100 MHz below
the input fr equency, all owing
me, fo r examp le. to
pu nch up 35.6 M Hz to receive
channel three.
W ith regard to ante nnas,
a simp le 88-inc h loop fed
with 75-0hm coax wi ll work
adequately. But remem ber,
there's a 168-dB path loss
betwe en th e satell ite and
your statio n, so you should
give you r rece iver all the
help it can get. If your co ax
run is long, an inexpensive
rf preampl if ier w il l help
tremendously. (The serious
listen er should pu rchase a
preamp anyway. Janel Labs
ha s t hem in st o ck for
$21 .9 5. A sk for M odel
137PB.)
ized and is mounted at my
QTH i n the ho r izont al
plane. The antennas on the
ATS satellites li kew ise are
linearly pola rize d, but th is
arrangement is of little consequence.
Radio signals in
t he V HF range are seve rely
affected by a phen om enon
known as Faraday Rotation,
ca using ultim ate recei ve
po la riz at ion s to be unpredict
ab le. It is rare that I
encou nter no signal at all ,
and then this situation lasts
only a minute or so. Most
ATS ground stat ions transmi
t and rece ive on circularl
y-pol arized antennas, of
both the hel ix- and cr ossyagi
variety. Althou gh this
solve s th e Faraday Rotati on
prob lem, an immed iate loss
of 3 dB is reali zed over an
antenna in the same plane .
You r next ob jective is to
point the antenn a in the
ri ght direction. You shou ld
be ' able to use the guess
method if your ante nna is a
loop or sm all yagi. However,
here are the geosynchronous
aim ing fo rmulas
for th o se of you with super
arra ys- as we ll as for the
mildly cu rious
Where X = th e difference
betw ee n sate llit e longitude
and site lon gitude in
degrees, and Y = the site
lati tude in deg rees:
Az im uth = ta n - 1 (tan XI
sin Y), and -
Elevation = ta n - 1 cos X
co s Y - .151 divided by
V1 - (cos X cos y )2.
Note: If yo u are in the
No rt hern Hemi sphere and
west of the spacecraft, subtrac
t your answe r fr om
180° . If yo u are east of the
space craft, add your answer
to 180 0
For examples, see the
box.
If you are in Washingto n,
or about 23,641 m iles from
ATS-3, and are co m municati
ng with a friend who se
statio n is likewise t hat
distance from the spacecraft,
you can expect a
sig na l de lay of ap p roxima
tely one fourth of a second
: 2 X 23,641 = 47,282