Introduction
A year ago I would not have believed it to be possible to work over a hundred different EME stations in a span of 8 months, all with just two short yagis. I have worked ham radio satellites for a number of years now, and have recently become active in 144 MHz EME (Earth-Moon-Earth) radio contacts. Each one of these contacts is exciting, since it involves signals carried all the way from my backyard, to the moon, and then back to some distant point on earth. Since I don't have much physical space for antennas, I have had to spend much time optimizing my small JT65B / WSJT9 EME station for maximal performance (with the valuable assistance of the W6YX team). I have listed many of the optimization tips below. By following these guidelines, it should be possible to work many dozens of EME stations, even with a small station.
I have ordered the optimization tips spatially, to preserve clarity and flow. The tips start with antennas, then move to the feedlines, then to the transceivers, then to the computer and software, then to the human side of operating the software and attempting EME. For each tip, I have included my own personal "ranking" as to how important they are. Some are nice-to-have (Very Useful), whereas others are so important that if you skip them, you will certainly miss out on many contacts (Critical!!). As with all lists, this one too will be subject to change. It's based on what I consider important after learning enough to contact the hundred-plus EME stations so far; I'm far from finished learning, so no doubt the list will change in the future.
Enjoy!
Dave KB5WIA
Hardware: Antennas: Gain
Importance: Very Important
Use the maximum antenna gain possible. Why? EME signals are weak! Every additional dB of gain you can obtain from the antennas will help out. Use modern antenna designs, pay careful attention to the manufacturer's recommendations for spacing and mounting, and avoid interactions with crossbooms, other antennas, or the feedlines.
Hardware: Antennas: Polarization
Importance: Very Important
Use linear polarization. Why? On bands 432 MHz and below, the convention is to use linear polarization, not circular polarization. Circular polarization results in a 3dB reduction in signals of linear polarization. Unless you are using dual horizontal / vertical polarization, you will need to wait for Faraday rotation to line up signals for optimum reception, this will take from a few minutes to an hour or more. Patience is a virtue with EME.
Hardware: Antennas: Preamplifier
Importance: Very Important
Use a low-noise preamp (LNA) at the antenna if possible. Why? By boosting the signal immediately after the antenna, you can reduce or eliminate the effects of cable losses on your received signals. Keep the preamp at the antenna, since any loss between the antenna and the preamp will add directly to your noise figure.
Hardware: Rotator Type
Importance: Important
Try to use a two-axis rotator. Why? If you don't have elevation control on your rotator, you are going to be limited to attempting EME with the moon close to the horizon, typically where most environmental RF noise is located. By being able to elevate your antennas towards a high moon elevation, you can significantly extend your moon operating time, and therefore improve your chances of EME contacts.
Hardware: Feedline Quality
Importance: Important
Use the lowest loss feedline you can afford with a minimal number of connectors. Why? Again, on EME, every dB counts. You do not want to lose signal in the feedline. Note that if you have a LNA at the antenna, the effects of feedline losses on receive are minimized. Unless the amplifier is at the tower, however, using high-quality low-loss feedline will prevent your transmitted signal from being wasted as heat.
Hardware: Separate Feedlines and Sequencer
Importance: Very Useful
Use separate RX and TX feedlines with a dedicated sequencer if you can. Why? Having a dedicated RX feedline will let you split off some of the received signal to a SDR (software defined radio) if you desire. Having a dedicated TX feedline and sequencer will let you bypass the preamplifier and SDR entirely on transmit, to prevent system damage.
Hardware: Transmitter: Stability
Importance: Very Important
Avoid frequency drift in your transmitter. Why? Transmitters will change in frequency as they heat up, and JT65B transmissions can generate a lot of heat. Frequency drift can make decoding impossible, or force both stations to have to turn on AFC which results in a modest reduction in coding "gain". By having a stable frequency (install a TCXO if necessary) you can improve chances of decodes.
Hardware: Transmitter: Power
Importance: Very Important
Have the ability to use as much power as possible to complete the contact. Why? Since every dB counts, the more power you have, the more chance of successful decodes at the DX station. A 600W amp will improve your signal at the other station by 3dB over a 300W amp, all other things being equal. A 1.2kW amp will improve your signal by 6dB.
Hardware: Receiver: Noise Blanker
Importance: Important
Use your receiver's noise blanker. Why? EME signals are very weak, and using your receiver's noise blanker can help remove interfering signals that could reduce your receiver's sensitivity. If your noise blanker has variable settings, use a "light" setting to prevent blanking out the desired signals.
Hardware: Receiver: Software Defined Radio (SDR)
Importance: Very Useful
Use a SDR if possible. Why? With an SDR and
MAP65 software, you can monitor the entire EME sub-band (144.105 to 144.165) at once, allowing you to immediately spot stations that your antennas can hear. This can multiply your chances of a successful EME QSO, since you will be less likely to miss seeing another station calling CQ. Quality SDR's are relatively inexpensive these days. [Example: The
FunCube Dongle Pro+, can be installed with
Linrad and MAP65].
Environment: Obstructions
Importance: Important
Be aware of nearby objects that will block the antenna's view of the moon. Why? If the antennas can't see the moon, they can't see EME signals! Obvious factors are mountains and neighboring houses. Less obvious factors are trees, which can significantly attenuate the already weak EME signals.
Environment: Background Radio Noise: Your own home
Importance: Critical!!
Turn off all devices that cause RFI. Why? Any devices adding to your baseline noise level will directly reduce your sensitivity. For weak EME signals, a simple defective switching power supply can completely destroy your ability to hear other stations. Almost every home has devices that cause radio interference. Turn off circuits one-by-one to find these devices. Eliminate the noise by shutting them down, replacing them, or adding ferrite chokes to the input/output leads.
Environment: Background Radio Noise: Nearby Noise
Importance: Very Important
Know your surrounding radio noise levels. Why? You can't eliminate RFI coming from your neighbors, but you can avoid it. Watch your meters as antennas are raised above horizon, and take note of how different antenna directions and elevations relate to your ambient noise levels. Plan for best operating conditions when the moon is high enough that your antennas can be up and out of the noise.
Environment: Ground Gain
Importance: Important
Understand ground gain and how you can use it to your advantage. Why? You can pick up an extra few dB by capturing the signals reflected off the ground at low moon elevations! This is potentially equivalent to doubling your power output, or doubling the size or number of your antennas. Of course if you have high RFI at the horizon, you can't take advantage of your own QTH ground gain ... but you can still use the DX station's. Simply use the Astronomical Data in WSJT9 or MAP65 software to monitor the DX station's moon elevation. Very often you'll see signals come up when the DX station has low moon and is experiencing ground gain effects.
Protocol: Communications Mode
Importance: Important
Plan to operate with mode JT65B rather than CW or voice when starting out. Why? EME signals are extremely weak, and a small EME station will only be able to hear (by ear) the largest of the EME stations. This pretty much entirely rules out SSB voice communications, and also rules out CW communications. The
JT65 modes by Joe Taylor K1JT provide 10 to 15 dB better signal-to-noise than CW, and are what make small-station EME possible. (That being said, once you have experience, go ahead and try for the thrill of working the big stations by CW. It's not easy, but it's possible!).
Computer: Sound Card Interface
Importance: Important
Ensure that robust audio signals are reaching the computer's sound card. Why? You want to have your radio's audio signals significantly above the background noise level of the computer's sound card. Feeding too low an audio level to the PC will result in more difficult decodes.
Computer: Clock Synchronization
Importance: Critical!!
Ensure your computer clock is accurate to within a fraction of a second. Why? If your clock is off, you will have difficulty identifying valid decodes (which will have a dT of approximately 2.6 seconds). In addition, your CQ calls will not be published by the automated spotting network
LiveCQ.eu, which uses the dT value to differentiate between EME and tropo spots.
BKtTimeSync by IZ2BKT works well to keep your clock synchronized, set your time server to pool.ntp.org with a sync of every 15 mins.
Computer: Read the manual
Importance: Absolutely Critical!!
Read the WSJT9 manual. Once you've read it, read it again. Why? The
WSJT manual is a great resource that covers in great detail how the software works and how to use it. Small stations need every advantage they can get, so don't shortchange yourself by missing out on knowledge that's located in the manual.
Computer: WSJT9 Software: Sampling Rate
Importance: Very Important
Ensure no sampling rate errors. Why? If your computer soundcard has problems with sampling rate, you will have significant problems decoding stations, and other stations may have significant problems decoding you. The sampling rate values in the lower left of the software should be in the range of 0.9995 to 1.0005.
Computer: WSJT9 Software: Noise Floor
Importance: Important
Adjust the slider on waterfall to zero the RX noise floor. Why? You need to keep the decoder working within a reasonable signal range. Adjust the slider to zero depending on your ambient RF noise conditions.
Computer: WSJT9 Software: Waterfall Speed
Importance: Very Important
Adjust the waterfall speed in the WSJT9 software to "3". Why? JT65B is a visual mode, so you need to optimize your software display for the best visual signal-to-noise possible. Using a slower waterfall speed will help you identify EME traces. Also be sure to select "Flatten Spectra" in the SpecJT options, it's not set by default and helps improve your ability to see signals. These steps are often overlooked, so spend time adjusting the waterfall settings for maximum visual sensitivity; a properly optimized waterfall will have snow and a light green tint to it.
Computer: WSJT9 Software: Sync Value
Importance: Critical!!
Set the Sync Value to 0 or below. Why? Values equal to or less than zero set maximum Sync sensitivity. If you do not have maximum sensitivity, you will see traces but miss decodes. All values from 0 and below are technically equivalent, so any number -1 or less will work. Some operators set a large negative number here, just to avoid the chance of accidentally clicking this value upwards past zero.
Computer: WSJT9 Software: Deep Search
Importance: Critical!!
Turn Deep Search on. Why? Deep search decoder provides an additional +4dB of coding gain. Without it you are seriously limiting your chances of a successful EME contact. Once you become familiar with discriminating real from false decodes, turn Aggressive Deep Search on for further sensitivity. And remember that for Deep Search to work, you must have an updated call3.txt file (see below).
Operating: Practice files
Importance: Critical!!
Practice using WSJT9 software using the
practice JT65B .wav files. Why? It's very important to know how to use the software. WSJT9 is powerful and not immediately intuitive, but with practice (and careful attention to the free manual) you can be comfortable using it. Learn how to use the Freeze, the Tol, the AFC and the ZAP functions. Learn how to read the short-hand signals for RO, OOO, and 73. If you don't know how to use the software, there is no point in attempting EME.
Operating: Your call in the call3.txt file
Importance: Critical!!
Make sure you're in the other party's call3.txt file. Why? If you're not in the other station's call3.txt file, you're effectively losing over half (-4dB) of your transmit power via the missing coding gain at the receive station. Be sure to register at
Make More Miles on VHF and add your call to the call3.txt database. It's hard to stress this enough:
be sure to register your call, grid, and check the box that says you're an EME operator.
Operating: Update your call3.txt file frequently
Importance: Critical!!
Be sure to update your own call3.txt file immediately after installing WSJT software, and frequently thereafter. Why? If the other station's call and grid is not in your Call3.txt file, you'll lose -4dB of coding gain, equivalent to more than cutting your antennas in half. The default call3.txt file in the WSJT9 download is very much out of date, so frequently download the latest call3.txt file from
www.mmmonvhf.de or
www.livecq.eu/call3. To keep your own call3.txt file up to date without losing the calls you've manually added, use
wsjtmerge.exe to merge the new call3 to your existing call3.
Operating: Check your call3.txt file for every QSO
Importance: Critical!!
Always make sure other station is in your call3.txt. Why? Many stations who you see on the moon may not have added themselves to the mmmonvhf.de database, so they won't be in your call3.txt. You don't want to accidentally lose that 4dB of coding gain! If you are calling another station, check to be sure they're in your call3.txt file by looking them up in the "To Radio" box of WSJT9 software.
Operating: Know how to adjust for Doppler on 432 and 1296 MHz
Importance: Critical on 432MHz and above!!
Be sure to follow the proper Doppler adjustment convention on 432MHz and above. Why? If you don't adjust for Doppler, you may not be looking in the right place and may miss callers entirely. In the Main WSJT window, click View > Astronomical Data. The "Self Dop" value is how many Hertz away from your transmit frequency you should be receiving. This is offset is also referred to as your self echo frequency. You may use your RIT or split A/B VFO to achieve this. (On 144 MHz, Doppler will not shift received signals out of the audio passband of your transceiver, so it's not as much of a concern.)
Operating: Start thinking in dB
Importance: Very Useful
Stop thinking of signals in terms of S-meter readings and instead in terms of dB. Why? Decibel units, displayed for decoded signals in the WSJT9 and MAP65 software, have real-world value! For example, if you just barely work a station at -27 dB signal strength, then you can imagine if you double your antennas (adding 3dB) you could have worked that station much easier at -24 dB. Or, if you see on a spotter that your CQ was decoded at -25 dB and you're running 300W, if you went to 600W (3dB more) you'd likely have been decoded at -22 dB. Thinking in terms of dB helps put many aspects of EME operation into perspective.
Operating: Best days to operate
Importance: Important
Learn how the moon's position in the sky during a month affects EME activity. Why? Some days have many EME operators who are calling CQ or listening to the moon, other days have very few. If you try to operate on high activity days, you will significantly improve your chances of hearing or being heard. The moon's orbit is inclined relative to the earth's, so the moon alternates from being low in the sky to being high in the sky every two weeks. There are many more operators out in the two weeks of high moon elevations. Similarly, at new moon (next to the sun), many operators avoid EME, as well as when the moon is near high galactic noise sources. Such physical conditions don't diminish a small operator's chances of EME nearly as much as the reduced turnout of EME operators does. [Reference:
The MMMonVHF EME Propagation Predictor has a nice graph of moon declination]
Operating: Best hours to operate
Importance: Important
Learn how EME activities vary during the day. Why? You will have much more success finding stations when they're a) awake and b) can see the moon! For example, Europe has many active EME operators, but they naturally will be mostly asleep at 2300z to 0600z. In addition, as the earth rotates "underneath" the moon, some regions will lose moon visibility and some will gain it. Activity on EME will ebb and flow during the day according to sleep and visibility patterns.
Operating: Understand the impact of the degradation value
Importance: Important
If you're a single polarity station, don't worry much about the Degradation number in the software. Why? The calculated degradation in the moon signals varies by just a few dB for most days of the month. On the other hand, your signals can vary up to -20dB due to polarity mismatches between you and the DX station. Since the effects of Degradation are small with respect to the effects of Faraday Rotation, don't let the Degradation values scare you away from operating.
Operating: Finding active stations
Importance: Very Important
Use the
LiveCQ.eu spotter to find active frequencies and relative signal strengths. Why? Unless you are running MAP65 and can monitor the whole EME band for yourself, it's fruitless to try to scan across the band tuning for JT65B signals; they're too weak to hear. If you stick to LiveCQ.eu, you can see who is "on the moon" in real-time, what their calling frequencies are, and how strong they are heard at other stations. Use caution when looking for stations calling CQ via an EME chat (ie.
N0UK EME Logger). Chats may have very small stations advertising calling CQ (that you're unlikely to hear), or operators with incorrect settings, or operators who announce calling CQ but then discontinue without updating the chat.
Operating: Recognizing EME traces
Importance: Very Important
Recognizing EME traces is a useful skill. Why? It allows you to tighten the decode window around the particular trace, improving decodes by eliminating interfering signals. EME traces have a characteristic start (:00 seconds) and stop (:50 seconds) times, a characteristic brightness (varying brightness over time), a characteristic width (about 3 to 5 Hz), and a characteristic period (every second minute). Skill in identifying potential EME traces (and differentiating them from noise) will help you to find signals.
Operating: Traces that won't decode
Importance: Very Important
Know what to do when seemingly strong EME traces don't decode. Why? Strong EME signal traces that don't decode are most commonly caused by three things: 1) the message is part of a QSO between other parties (ie. N1XYZ observes W6YX KB5WIA CM88 OOO) and does not invoke Deep Search. 2) operator error on the other end. 3) operator error on your end. If you recognize an EME trace and it unexpectedly does not decode, it should be a big clue that you need to go back and check your settings!
Operating: Recognizing false and true decodes
Importance: Very Important
Knowing the difference between true and false decodes is important. Why? You don't want to waste time calling a station who never called you in the first place! When you see a decode, ask yourself: a) do I expect to see the other station calling me? b) does the other station see the moon at this time? c) does the dT of the signal match an EME signal (2-3 seconds)? d) does the width of the trace match an expected EME signal (3-5 Hz)? If in doubt, simply wait one more cycle and see if the same decode comes up. The odds of a false decode are slim, and the odds of two identical false decodes are virtually nil.
Operating: Persistence
Importance: Critical!!
Be persistent when trying to contact another EME station. Why? EME propagation is not like terrestrial VHF! EME propagation changes from minute to minute, is often unpredictable, and can include "one-way" propagation. Just because you call someone five times and do not hear back from them does not necessarily mean that they cannot hear you, nor that you will not hear them on the next cycle. Sometimes it takes many cycles of calling before conditions (ie. Faraday rotation) line up favorably for you to make a contact.
Operating: Don't be afraid to call CQ
Importance: Very Important
Call CQ as much as you can. Why? Just because you don't see other stations calling CQ yourself, or on the Internet, doesn't mean that there aren't other stations listening to the moon. It is guaranteed they will never hear you if you don't call CQ! Call CQ often, since there are very frequently many more stations listening than you will be aware of.
Operating: Chat rooms
Importance: Important
Don't become reliant on chat rooms to complete your QSOs. Why? First, exchanging any information about your QSO prior to completion will invalidate the QSO. Secondly, if you have to depend on the other station telling you about the QSO status via the internet, then you aren't doing EME communications. It's fine to announce that you're calling CQ in the chat room, and to give the other station a signal report after the QSO is finished. Finally, all hams can relate to the unexpected thrill of having a DX station unexpectedly replying to your CQ -- don't let internet chat rooms diminish this joy!
Summary
It's quite possible for ham-radio operators to make contacts via the Earth-Moon-Earth path, even with a smaller station of no more than a 10-foot yagi and 100 watts of power. However, since with small stations there is very little margin for signal reductions, no stone should be left unturned when attempting to optimize the station.
My own experience has shown with the above optimization tips, a small station with two ten-foot yagis and 500 to 1000W of power on 144MHz is capable of working at least 100 different EME stations in a relatively short period of time.
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