Optimized Small-Station EME
X-pol at 432 MHz
Joe Taylor, K1JTIntroduction
This paper describes the design and construction of a modest 432 MHz EME station forW2PU, the Princeton University Amateur Radio Club. The antenna and receiver front end
will also be used for radio astronomy instructional purposes in the university’s physics
department. For this project my departmental colleagues Dan Marlow (K2QM), Norman
Jarosik, and I have adopted a pedagogical approach characteristic of academic physicists:
our planning and construction has proceeded one step at a time, with frequent tests anddetailed measurements being made at each stage. As I write these words in June 2014,
we have not yet made EME QSOs. But construction of the station is well along toward
completion, and the station’s eventual EME capabilities are already well established. We
hope to have W2PU active on the moon in the near future.
Starting with a blank slate provided us a good opportunity to set goals, make design
choices consistent with those goals, and carry out a number of minor optimizations. We
hope that our design criteria and choices will be useful to others considering entry into theEME fraternity on the 70 cm band. We have aimed to satisfy the following goals:System noise temperature approaching the state of the art, at room temperature.
Tx power < 1 kW, and preferably much less. (No special licenses, no QRO++ !)Antenna: small, lightweight, rugged, and easy to point in azimuth and elevation.
No “Faraday lockout,” no one-way propagation.
Moderate cost, easy to build and maintain.
Station capable of EME QSOs with its own “twin,” anywhere in the world, whenever
the moon is available.

Anyone who has done EME knows that it’s not trivial to satisfy the first five of theserequirements, while also meeting the last one. We expect to achieve all six goals
reasonably well, and we can heartily recommend a similar approach to others planning anEME station.

Which band ?
144 MHz EME antennas are too big for our purpose. We have a 2.3 m dish, equipped for
an undergraduate advanced lab experiment observing galactic neutral hydrogen at 1420
MHz. In principle this dish could be outfitted for 1296 MHz EME; however, for a number ofgood reasons we decided to develop EME capability at 432 MHz instead. As illustrated in
Figure 1, achievable system noise temperatures are nearly as low there as at 23 cm.
Equipment for 70 cm is relatively easy to build and widely available “off the shelf”. Itseems that in many ways 70 cm is the most under-utilized of all EME bands, and we would
like to help reverse this trend.

Fig 1 – Typical contributions tosystem noise temperature, Ts,from the cosmic microwave
background (CMB), the Earth’s
atmosphere, the warm surfaceof the moon, galactic noise
entering through the main
antenna beam, and sky andground noise from anantenna’s side and rear lobes.
Antenna temperature Ta is acombination of all thesecontributions, appropriately
weighted by antenna pattern;
Ts is the sum of Ta and receivernoise temperature Tr. For
details see Reference 1.

What antennas, how much transmitter power ?
Linear polarization is the standard on 70 cm, so dual-polarization (“X-pol”) antennas should
provide the same major advantages that they do for 2 m EME. With random polarization
angles of incoming signals, adaptive polarization yields an average 3 dB improvement inreceive sensitivity, and much more in cases of large polarization mismatch2. However,X-pol Yagis with good performance are much harder to build at 70 cm than at 2m, and they
have not heretofore been widely used. The main problems are achieving accurate
symmetry in the X and Y planes of Yagi elements, and fitting the necessary feedlines,baluns, etc., into the available volume around the feedpoint.
A lunchtime conversation with Justin Johnson, G0KSC, at the 2012 EME Conference inCambridge persuaded us that with sufficient care, excellent X-pol Yagis could be built anddeployed for 432 MHz. With the help of Justin’s company, InnovAntennas, we decided toproceed in that direction. After a few iterations we settled on a basic antenna design that
we call 15LFA-JT: a 15-element, dual polarization Yagi about 3.5 m long, rear-mountedand built on a 25 X 25 mm hollow fiberglass boom. Simulation with NEC4 shows that anarray of four such Yagis should provide 22.4 dBi gain in each of two orthogonal linearpolarizations, with extremely low side- and rear-lobe responses.

The link budget for EME communication1 can be summarized in the following equation for, the received signal-to-noise ratio in dB:(1)
Here and are the received and transmitted powers expressed in dBW (dB above 1Watt); is the Earth-Moon-Earth path loss in dB, assuming isotropic antennas; andare gains of the transmitting and receiving antennas in dBi; and is the received noise
power in dBW. For average moon distance the path loss can be written as(2)
Received noise power is equal to, whereconstant, is the system noise temperature in Kelvins, andHz. Thus, in units of dBW,

Joules/K is Boltzmann’s
the received bandwidth in(3)
Let’s assume equal gains
for the transmitting and receiving antennas, aswould be the case for our station communicating with its “twin”. We can then calculate thetransmitter power required for any specified system noise temperature, bandwidth, and, using the equation.

(4)

Communication in the JT65 digital mode is nearly 100% reliable3,4 when
bandwidthHz. For a typical system noise temperaturetransmitter power for
dB is

dB inK, the requireddBW,(5)or 66 Watts. Audible self-echoes and CW communication with a twin station require
something likedB in 50 Hz bandwidth — and thus about 10 dB more transmitter
power, or 660 W at the antenna. These numbers are fully consistent with the goals
outlined in the introduction.

Model 15LFA-JT Yagi
To allow us to verify the antenna design and make some initial test measurements,
G0KSC sent us materials for a pair of 15LFA-JT Yagis following his design. Some
important construction details can be made out in Figures 2 and 3. Reflectors anddirectors are 1/4-inch aluminum rod, each one passing through the boom center tomaintain full polarization symmetry. Element positions for the two polarizations are offset
by 30 mm along the boom. Long sides of the LFA driven elements are made from 10 mm
brass tubing with 1 mm wall thickness; the U-shaped end pieces are made from 8-mm
brass tuning, cut to 45-degree angles and hard-soldered at the 90-degree corners. Theseend pieces fit snugly into the long straight sides, and are soldered in place after final

tuning. The forward side of each LFA loop is split with a 6 mm gap filled with a nylon
insulator. We drilled all the way through the brass and nylon and tapped the holes for 4-40
machine screws. Ends of the RG142 feedlines are stripped, fitted with eye lugs, treatedwith liquid rubber sealant, and secured to the feedpoints with 4-40 screws. The screws areaccessible through 6-mm holes drilled through one side of the boom, immediately above
the feedpoints.

Fig 2. – A pair of 15LFA-JT rear-mounted Yagis on a simple mount with azimuth and elevation
control. Separate feedlines carry signals for horizontal and vertical linear polarization from each
Yagi to a power splitter. Light-duty dacron ropes serve as forward guys, to prevent boom sag.

Fig. 3. – Rear view of a single Yagi
showing construction details aroundthe driven elements. The brass loops
are fed at the center of their forwardsides, inside the hollow boom. RG142
coaxial feedlines pass out to the rear.
All elements are held in place withtight-fitting holes and a few drops offiberglass resin.

Antenna tests
One of the most sensitive indicators of how closely a real antenna resembles its computermodel is a plot of return-loss versus frequency. Therefore, after assembling each Yagi wemade a number of return-loss measurements, following advice from G0KSC to takeadvantage of two “tuning controls” for each polarization: the telescoping ends of the driven
loops, and the length of the first director. Adjustments to both were made in steps as small
as 0.5 mm; in practice, this required us to cut several extra D1 elements with slightlydifferent lengths, to find the best match. We checked carefully for evidence of feedline
radiation possibly caused by connecting coax directly to the driven loop. We found none.
With optimum tuning we obtained return losses better than 25 dB over the range 427 – 437
MHz, in excellent agreement with the simulations. Compared with some designs, theseYagis are relatively wideband antennas.
We are well aware that measurements of angular power patterns are difficult without aprofessional antenna range, but nevertheless we attempted such a measurement using
purely amateur-radio techniques. The test signal was an amateur beacon transmitter
located in Philadelphia, 42 miles away. We drove the antenna at constant rate over a full360 degrees in azimuth, and then repeated in the opposite direction. With the receiver
AGC turned off and the upper-sideband bandwidth set to 5 kHz, audio output from thestation’s TS-2000X transceiver was sampled in a soundcard at 48 kHz, squared, andaveraged over 1-second intervals. The averages were recorded along with the readout
azimuths. Plots in Figure 4 show the simulated and measured azimuth patterns for ourphased pair of 15LFA-JT Yagis, for horizontal polarization.

Fig 4. – Simulated (left) and measured (right) azimuth patterns of a pair of 15LFA-JT Yagis stacked
horizontally, in horizontal polarization. The stacking distance was 1.2 m.

We believe the measured asymmetric sidelobes are likely the result of a permanent steel
ladder, the top of which is only about 1 m away from the forward ends of the Yagis when
they are pointed toward the horizon and close to the direction of the beacon. This nearfield distortion should disappear when the antennas are elevated, especially after the arrayis raised to its final position at the top of its mast (see Figure 2, at left). Other than this(presumably temporary) distortion, the measured array pattern closely approximates thevery low side- and rear-lobe responses of the simulation, especially when allowance ismade for likely multi-path propagation (reflections from nearby structures) at low signallevels. The completed array should have excellent performance.

Our next test of the temporary two-Yagi array was a measurement of Sun noise. Software
was written to control the azimuth and elevation positioners in an Off-On-Off pattern inazimuth, centered on the Sun’s position. The offset positions were set atdegrees. Once again, we recorded 1-second averages of the receiver output
power. Results after normalization to the mean off-source power level are plotted inFigure 5. Expressed in dB, the on-to-off-source power ratio was found to bedB

(6)

Fig. 5. – Measurements of Sun noise with apair of 15LFA-JT Yagis. The dotted line
represents the expected value forwith
432 MHz solar fluxSFU and system
noise temperatureK.

EME receiving setup
On several occasions we have operated the W2PU station in SWL mode, with the antenna
pointed at the moon. We find EME receiving performance to be consistent withexpectations. The first such measurements were made with the TS-2000X receiver and asingle polarization — that is, without benefit of adaptive polarization. Some results areshown in the WSJT waterfall spectrogram of Figure 6. Note that K5DOG (at DF=900 Hz)
was using a modest array of four M2 model 432-12EME antennas and about 400 W
transmitter power. His signal was easy to copy (dB) with our temporary twoYagi setup.

Fig. 6. – Waterfall spectral
display for a sequence of
15 two-minute intervals
during the 2013 ARRLEME contest. One can see
decodable EME signals
from an unidentified station
at upper left, near DF =–800 Hz; OH2PO, –700
Hz; LZ1DX, +150 Hz;
K5QE, +500 Hz; andK5DOG, +900 Hz.

As another test we operated the W2PU station remotely over the April 26-27, 2014
weekend. This time we used the LinkRF IQ+ receiver5 together with Linrad and MAP65
software, as will be our norm — but again without enabling adaptive polarization, because
only one of the Rx preamplifiers was installed at the time. Despite moderately poor
conditions (degradation –0.9 dB, moon 28 degrees from Sun, high libration rate), we easily
copied EME signals from additional stations in Europe, North America, and Japan.

Worksheet for System Noise Temperature
Optimizing the receive performance of an EME station requires careful attention to allcontributions to system noise temperature. Unlike the situation for a well-designed 23-cm
station using a parabolic dish and circular polarization, a 70-cm setup with a Yagi array
necessarily has a number of lossy, ambient-temperature units in front of the firstpreamplifier. I highly recommend the use of VK3UM’s EME Calculator software, oralternatively a simple spreadsheet6 like the one copied below, as an aid to minimizing ina step-by step manner.

Tsys Worksheet
4 ft RG-142
Power splitter
3 ft LDF 4-50A
T/R relay
LNA1 (DB6NT)
10 ft LMR400
100 ft LMR240
10 ft RG58
LNA2 (ARR)
LinkRF IQ+

Gain(dB)
-0.32
-0.05
-0.04
-0.05
23.00
-0.27-5.20
-1.00
20.00

Tr at antenna feedpoint
Antenna and feed losses
Sky noise (main beam, on ecliptic)
Side and rear lobes
Total antenna noise, Ta
System noise temperature, Ts

0.06

Frequency (MHz)
Lossless antenna gain (dBi)
Solar Flux at 432 MHz (SFU)
Tx power at antenna (W)

432
22.40
44.0
100

EME path loss (dB)
G/Ta (dB/K)
G/Ts (dB/K)
Y Sun (dB)
EME S/N in B=2500 Hz (dB)
EME S/N in B=50 Hz (dB)

261.6
5.5
1.6
9.9
-23.0
-6.0

NoiseFigure(dB)

Noise Contribution0.50
9.00(K)
22.2
3.6
2.9
3.7
30.8
0.1
3.9
1.5
0.9
0.5% Total
18.7%
3.1%
2.5%
3.1%
26.0%
0.1%
3.3%
1.2%
0.7%
0.4%

0.94

70.0

59.2%

4.0
20.0
25.0
48.4
118.4

3.4%
16.9%
21.1%
40.8%
100.0%

0.40

Spreadsheet items highlighted in yellow are input by the user; all remaining numbers arecalculated from the input data. As displayed above, the spreadsheet properly reflects ourpresent setup except that it lists antenna gain
dB, the value for our planned fourYagi array.
We have not yet done a particularly good job of minimizing before-the-preamp
contributions to system noise. For example, the 22 K contribution from RG142 feedline
segments can certainly be reduced; this small-diameter cable is needed only for about 0.3m, inside the hollow booms. On the other hand, the estimated 48 K contribution fromantenna noise is likely to be overly pessimistic, especially at higher elevations. Overall, webelieve the numbers are conservatively realistic. Two stations equipped similarly toW2PU, using four X-Pol Yagis similar to the 15LFA-JT and power 100 W or more, shouldbe able to work each other by EME more-or-less any time the moon is available.

References
1. J H Taylor, K1JT, “Earth-Moon-Earth (EME) Communication.” ARRL Handbook forRadio Communications, Chapter 30 (2010);
http://physics.princeton.edu/pulsar/K1JT/Hbk_2010_Ch30_EME.pdf
2. J H Taylor, K1JT, “MAP65 Version 2: A Panoramic, Polarization-Matching Receiverfor JT65.” Proceedings of the 15th International EME Conference, Cambridge, pp.
101-108 (2012); http://physics.princeton.edu/pulsar/K1JT/K1JT_EME2012.pdf.
3. J H Taylor, K1JT, “The JT65 Communications Protocol.” QEX (September-October2005); http://physics.princeton.edu/pulsar/K1JT/JT65.pdf.
4. J H Taylor, K1JT, “Open Source WSJT: Status, Capabilities, and Furure Evolution.”
Proceedings of the 12th International EME Conference, Wurzburg (2006);
http://physics.princeton.edu/pulsar/K1JT/K1JT_eme2006.pdf.
5. See the LinkRF web site, http://www.linkrf.ch/IQ+.html.
6. The Excel spreadsheet is available at
http://physics.princeton.edu/pulsar/K1JT/W2PU_432.xlsx.

© 2014 by Joe Taylor, K1JT