Hams in Space!

ABOVEANDSEYOND
CL Houghton WB61GP
San Diego Microwave Group
6345 Badger Lake Ave.
San Diego CA 921 19
Microwave Beacons
To round out last month's column on
waveguide mixers and microwave tormulas,
this month I'll covera typical 10
GHz microwave beacon . By changing
the RF source and antenna, you can
adapt the plans lor this beacon to other
microwave frequencies.
Unlike beacons on lower frequencies
such as 6 meters, microwave beacons
are not put up only to reveal CUfrent
propagation conditions. If you
heard a 6 meter beacon clearly, you
would rush to the shack and start operat
ing, looking for contacts on that
band. But it you heard a microwave
beacon from some remote location,
you would, instead, gel busy on the
phone to set up contacts.
The m icrowave beacon no t only
alerts you to band conditions, but also
serves as a piece of test equipment.
During contests, the microwave beacon
transmits a signal that stations can
use to check antenna alignment and 10
prove that their stations are functioning
normally. Most importantly, the microwave
beacon provides a reference
signal 1000al amateurs can use as a
transfer frequency standard. This way,
the custodian of the beacon can verify
frequency as accurately as he can (in
the band , of course) and setthe standard,
Frequency and Offset
In any large group, someone can
come up with a best metncc of determining
frequency either by wavemeter
or frequency meter. The method used
doesn't make any difference. When
you have lh is type of system in place.
all other stations can set their equip-
VHF and Above Operation
mentto copy the beacon. You can set
your system's frequency to either sideband
mix product, offset by your IF frequency,
This offset is determined by
whalever IF frequency you are using.
One standard is 30 MHz. For example.
if the transmilter is on 10.250 GHz, you
can copy on either 10.220 or 10,280
GHz , since both frequencies are in the
30 MHz offset due to the IF frequency.
When all local stations are copying
the same beacon , frequency determination
problems decrease , Until most
amateurs in an area can agree on [ust
where 10,250 GHz is, it can be a large
slumbling block. Even if a beacon is
slighlly off-frequency, everyone in the
local area using the beacon will be attected
the same . What matters is that
all stations in a local area know where
the beacon is and use it.
Antenna Checking
With a microwave beacon , you can
check your antenna direction pointing.
and test the sens itivity of your receive
system. Microwave antennas. especially
dish types, can have beam
widths of 3 to 4 degrees or less. This
makes accurate dish aiming very lmportent.
Copying a local beacon , you
can verify direction (compass bearing)
and vertical position. This helps elimi·
nate one more wobble in the system ,
Sensitivity can be verified by comoaring
results to past tests . or by placing
an attenuator in the system for further
tests. Useof a beacon has proved to be
a valuable asset, lelling you maka
quick assessments of system performance
. Quick varificalion can be everything
during contest weekand. See the
beacon schematic in Figure 1.
The Beacon System
Construction of a 10 GHz beacon is
quite simple. All you need Is a source of
RF, such as a Gunn oscillator, an teen-
Photo B. "All mode " (CW, SSB, and NBFM) 10 GHz transverter constructed by
VK2ALU Oscillator chain andamplifierisa G400K design feeding a X9 SRO(step
recovery diode) multiplier. The 10 GHz mixer section is a G3JVL design (image
reject mixer) with output on 144 MHz.
The antenna selected for beacon operation
must be compact, high-gain,
and omnidirectional to be of general
use What fills the bill is Ihe near amtification
system, and an antenna, The
CW identification system , described in
the June 1990 column, is just a simple
TTL kever with an EPROM loaded with
your calls ign. The unit repeats what is
loaded into the EPROM over and over
again, reseWing after each message.
The aud io output from the keyer is coupled
to the adjust terminal of a Gunn
oscillator po wer supply, imposing
wideband FM modulation on the Gunn
oscillator.
In most beacon setups the power
supply (unregulated DC) is remote to
the actual beacon , with the Gunn oscillato
r/power supply modulator and
kayer located within a common housing
with the microwave antenna. The
keyer is about the size of a pack of
cigarettes and the Gunn oscillator is a
compact structure about an inch and a
half square. A short section of plastic
drainage pipe is often used to house
the enti re system.
The Beacon Antenna
." , ~",
.,..
to.'
"0
'"
nidirectional waveguide slot antenna.
For 10 GHz, a waveg uide slot antenna
is less than a foot long; 6 slots (on each
sitfe ot the waveguide) exhibits 10 dB
gain. See Figure 3 for construction
details,
The top of the antenna is shorted
with a machined brass insert that closes
off the top of the waveguide. A
single waveguide flange connects the
antenna. The Gunn oscillator may be
directly connected to the antenna, or a
magnetic isolator may be placed between
the antenna and the Gunn oscillator.
The isolator helps reduce pulting
on the Gunn oscillator by allowing RF
to flow freely in one direction, which
provides high loss to refl ected RF
(VSWR).
The slots in the waveguide are verncal,
in the same plane as the length of
the waveguide. The radiated RF is hori·
zontally polarized. To receive horizontally
polarized radiation, your receive
waveguide must be vertical (the longer
opening of the waveguide). Having
you r waveguide vertically polarized
means having the long opening Of the
waveguide horizontal. If this sounds
confusing•
just remember the rule: The
..........
•
J '"'
"'E'"
o. w' _,.
' CO" ~
r:0'"
." ..'
' UO"0'<
r•
"
00 '
,.'IDE' '''''''''.m ..''...
/ "00"" '"'' ·"" '''''''''' wOO'''' ' '0.·.-
" • .". H"" '0" n • ""
uo." ,",,,tEo '" ...00. "0' '."0''''
-- .,,'." ..", "''''0''' .. 0< " ... , , ... . .
L
'0 ''''0' ,""w,' '0."0' ''''''''0 ""0" .,..'" "'"" ,. '"'"
.. '-0"' "u. '" " 'CE " " . " , ' 0 """'"",,. .. ', ...000 ""'11.'
PhofO A. Lyle PaNson VK2ALU of WolIongong , Australia. operating a 10368 MHz
transceiver on SSB, testing over 80 km to VK2ZAC (who can receive on SSB but
only transmit on NBFM). Note sighting telescope mounted below dish. A
Gassegrain subreflector feed is used allowing more effiCient illumination. The 20
inch dish is a searchlight reflector.
Figure 1. 10GHz beacon showmgCW IO'er andpowersupply. Regulator/modulator
audio from fO'er feeds to adjust terminal ofregufator for modulation on input on
regulator output voltage to Gunn osciflalor, which produces high quality wideband
FM on 10 GHz (See " Above and Beyond" in the June 1990 issue of73 for CW ID
delails).
73 Amateur Radio Today . March,1991 73