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Figure 2 Four quagi EME arrav wish 500h", coax feed (full quagi not shown in drawing)
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up the difference in signal stre ngth levels for
EME work. Four good long boom antennas
properly spaced, phased, and fed with 500
wens or more. will permit one to make many
routine. random EME QSOs on 2 meters .
The number of contacts possible with such a
statio n depends upon operator determination
and effort.
What is the lowest power station thai you
can have and still hope for an EME QSO?
Well. I have worked a couple ofstations who
were using a single long boom antenna and
runni ng less than 50 watts. In one such contact
, W2RS, running 50 watts into a single
Cushcrafl 32-19 antenna, answered my CQ. I
worked another station, ZD8MD. during a
sched ule. He was runni ng 25 watts toa single
32- 19. With higher gain antennas, such as the
42- 18XL and the 2M5WL, these contacts
could be easily repeated if peak conditions
happen to coincide with the schedule lime.
Preamplifiers
n "'e Al " U~ GEo' E~ T
A·QuAGI ( WE ARAAY
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FIgure 3. Coax phasing de/ads/or the 4 quagl EME array.
Your receiver's frontend noise figure must
be kept below 2 dB if you want 10 hear those
50 73AmateurRadio Today . March,l991
weak moon echoes. If your receiver's front
end is 001 that sensitive, do 001 despair. a
good low noise preamplifier between the antenna
and the receiver will perk it up to an
acceptable level. Such preamps can be
bought or built. They work best if they use
GaAsFET transistors. such as the MGF
1302. They also work better when mounted
at the antenna. where feedl ine losses cannot
deg rade Iheir performance. If antenna
mouming is used. some form of relay switching
and front end protection must be provided.
lest the preamp be blown OUI by the
transmitter power. Many of the solid-stale
" brick" amplifiers have preamps installed.
While these arc not usually the best (a preamp
with a low noise GaAsFET is the best) they
are usually good enough 10 let you listen 10
the larger EME stations when conduions
are good.
Avoid the use of bipolar transistor preamplifiers.
Even though some of these devices
can yield noise figures of less than I dB, they
are susceptible to imermodulation problems.
and in some locations can cause birdies 10
appear all over the 2 meter band. They may
work fine if you happen to live in the South
Sea Islands where there are no other RF signals,
but otherwise. avoid Ihem.
Coax Feedlines
On receive, feedl ine losses can be overcome
by installing the preamp at the antenna.
Feedline losses reduce the power transmitted
10 lhe antenna. and puning power into the
antenna, no! out of the transmitter, is what
counts in EME work. For example, 100 feel
of regular RG-8 coax will have nearly 3dBof
loss at 2 meters.
That means if you start with 100 watts
output from your amplifier. you will get only
50 watts into your antenna. Use the shortest
possible length ofhigh quality, low loss coax.
Your fccdline losses should be kept less than
I dB. As a rule ofthumb, Belden 99 13 is fi ne
up to 50 feet. Half-inch hardline is good upto
about 75 feel. Three-quarters ofan inch hardline
will work to 175 feet. Beyond that, you
will need the bigger Sluff. I use a 190 foot
length of I % ~ Heliax from the amplifier 10
the antenna. Its loss is less than four-te nths of
adD.
Be careful about connectors and power dividers.
Losses can increase ifa poor connection
occurs, or if water gets into connections
and power dividers.
Amplifiers
The minimum power you should consider
for EME work is about 150 watts. Some
commercial solid-stale brick amplifiers will
produce this. The output of IWO such bricks
can be combined to double the power output.
but this can be tricky. If you plan to II)' it. gel
the proper information 10 do it right. For a
more serious EMEeffort, power of500 watts
or more is recommended. Commercial amplifiers
are available with power outputs of I
kW and more, ifyou're ready for that. Many
EME operators have buill their own power
amplifiers. The A RRL Handbook is a good
reference fo r home construction . Sometimes
kits are available.
Remember, you do 001 need high power 10
start listening for EME signals, or to make
co ntacts with the large moonbounce stations .
Where, When. and How to Listen
EME work on 2 meters is primarily done
on CW, somerirnes on Sgg . but never on FM.
Signals are very weak echoes reflected from
the moon's surface. To hear such signals requires
a receiver with a reasonably low noise
front end (most commercial receivers are no!
good enough. but a relatively low COSIpreamplifier
can fix thai). A well-designed antenna
in good working condition must be pointed at
the moon. This can be done without elevating
the antenna if you can catch the moon during
the hour or so after it rises. or before it sets. In
fact. when there is EME activity. these are
the best times to hear EME echoes using a
rotatable antenna that cannot be elevated. If
your horizon is relatively clear and flat,
ground gain enhancement is possible during
rise and ser periods. Moderate EME activity
occurs often on weekends when the moon is