Saturday, June 29, 2013

A Checklist for Optimizing JT65B and WSJT9 144MHz EME Stations


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.



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, 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 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 or  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 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 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, 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!


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.

Sunday, June 23, 2013

ARRL Field Day 2013 - Satellite Fun

The annual Field Day was June 22-23rd this year, and as usual there was a lot of activity on the satellites!!  With so many satellite operators trying to access the limited number of sats at once, it certainly was a challenge to make two-way contacts this weekend.  Below are some observations from a few passes.

The FM satellite SO-50 was near saturation on the 6/22 1827z pass, with only the strongest stations able to get through and capture the transponder.  Stations heard  included K6MMM, W6YX, W6TO, KO6TZ, K6CLX, and K6AGF.  I didn't hear too many stations complete QSO's due to the congestion, but some lucky stations made a few contacts.

Satellite FO-29 was very busy on the 6/22 1831z pass.  I copied stations W7PIG, W6YX, K6MMM, AI6RE, KU6S, W7SU, W7AIN, and N6HN.  Activity across the FO-29 transponder was spaced out pretty well, and a number of stations were able to make two-way contacts.

Satellite AO-07 was hammered pretty hard on the 6/23 0002z pass!  Not many stations were able to get in through the congestion, but I copied WA2DPI, W6YX, W7SAA, W0GQ, K4BFT, KO6TH, K4FEG, W6ARA.  Screenshots from my SDR's view of the transponder downlink are below (you can see what AO-07 normally looks like on an SDR in this earlier post:

The middle four panels show significant distortion across AO-07's passband, notably many parallel zigzaggy lines.  Trying to copy any single station via the analog radio (FT-817ND) was really difficult, as the satellite transponder was probably reacting to the wildly varying input power levels coming up from below

Satellite VO-52 was really congested on the 6/23 0255z pass.  I copied K6MMM, W6ARA, and W6YX, and a few other stations.  Screenshots of the transponder during the pass are below.  (See my earlier post for what VO-52 normally looks like through an SDR).

In the first three frames above you can see some strong stations and some tuner-uppers.  The middle three frames show distortion of the whole passband, probably due to the number of stations trying to get into the transponder at the same time.  The last two frames show how the transponder activity has tapered off as the satellite footprint left the majority of the field day sites, with just a few stations remaining on the satellite.

Overall, it was a lot of fun to listen to the satellites during this Field Day weekend!  Sometimes the satellites are pretty quiet, so it was nice to hear so many operators trying to make contacts and complete QSOs.

Monday, June 10, 2013

VHF Contest - Mt Diablo

For the 2013 June VHF Contest, I again traveled to Mt Diablo to set up a QRP station.  The equipment I used this year included the Yaesu FT-817ND transceiver, connected to three yagi antennas.  For six meters I used a new Diamond A-502HB short-boom two element yagi.  For the two meter band I used the 4-element Arrow VHF antenna, and for 70cm I used a Diamond A430-S15 15-element yagi.  All three antennas were attached to a Buddipole 18' telescoping mast, and the mast was guyed to the bed of my truck.  The antennas were spaced so that the entire array could be rotated by hand.  New this year was 223.5 MHz FM, using a Yaesu VX-6R radio and a an Arrow 220 1.25m 5-element yagi on a photo tripod.

The radios were running on solar power, via the 6.4Ah LiFePO4 battery and PowerFilm solar panels that I've used previously.  With the bright summer sunshine both days, there was no problem with the solar power keeping up withe the load from the radios.  Typical power output from the panels was around 5 to 10 watts -- I didn't need any more than that to keep the battery topped off.

The new antenna system seemed to work pretty well!  I started the contest Saturday around 1:30pm, on a very hot day (98F!) in the summit parking lot just below the Mt Diablo main summit.  The higher gain of the antennas (compared to the Elk and HO Loop from last year) seemed to help make it easier to contact the DX stations.  Running QRP, it was good to have the extra gain.

Along with me this year was Henrik KK6BQU (operating low-power nearby), and Gary KE6QR and Dave N6ORB were already set up in the same parking lot.  Activity was fairly heavy on Saturday, and at sunset Henrik and I packed up and headed back to the campsite at Juniper Campground.  As we were packing up, the Mt Diablo Astronomy Club was setting up quite a few telescopes in the parking lot -- a number of them had questions about what were were doing with all the antennas!

Sunday was more contesting, starting around 9am and continuing to the contest end at 8pm.  Overall, preliminary totals indicate 248 unique contacts on the four bands this year.  By band, I counted 90 QSOs and 25 grid squares on 6 meters, 80 and 12 on 2m, 21 and 6 on 1.25m, and 57 and 8 on 70cm.    There were sporadic E openings to the mountain states on Saturday, and into Canada and Alaska on Sunday. 

Highlights included making contact with N7NW in Washington on 6 meters (who I had contacted by EME two months ago), hearing W6PH operating from Lone Pine, CA (on the other side of the Sierra Nevada), hearing new stations in the contest for the first time, and working the contest regulars.  It was also nice to see Henrik enjoying his first VHF contest, and nice having the company up there!

Wednesday, June 5, 2013

EME and Antenna Patterns

I'm trying to further optimize my small EME station.  Based on the noise plots in the posts below, it's easy to see that raising the antennas to higher elevations will significantly decrease the radio noise that they "see" from the surrounding houses.  What I have noticed over the last six months or so is that by raising the antennas out of the noise (and pointing them slightly away from the moon), I can get significantly improved reception of EME signals.  This is because the main lobe of the antenna array is fairly broad, so even if the array is not pointed directly at the moon, there's still enough gain to receive signals.  Similarly, the steep sides of the main lobe help to selectively null out much of the surrounding terrestrial radio noise.

So, if the reception of moon signals at low moon elevations can be improved by pointing the antennas above the moon, does this have any negative effect on the transmission of signals to the moon?  If so, how much?  Is there a way to find out?

I have found that an easy way to test this is to call CQ, and monitor the reports of my received signal strength at a distant station.  The site makes this relatively easy, as members of the MAP65 spotting network automatically upload signals that they have received from the moon.  In my case, station KB8RQ has a very good receive system and (when online) automatically will report my signal, in real-time, as it's received.  KB8RQ also has the advantage of using an adaptive-polarity dual-receive system, which helps to eliminate the effects of signal strength variability due to Faraday rotation.

By alternately raising and lowering the antennas every second CQ cycle, it's possible to do A/B comparisons between the two antenna angles.  There's a significant natural variation in signal strength on EME signals, but over time it seems possible to do some rough calculations as to whether one antenna elevation is significantly different from another.

My first test was to alternate a +0 degree elevation offset with a +7 degree elevation offset.  The offset is the number of degrees in elevation above the moon.  I was able to record received signals at KB8RQ over the period of about half an hour of calling CQ (with three brief interruptions as new inits from Hungary, Germany, and France replied to the CQ calls!).  Plotting the reported signal strength over time gave the following plot:

In the plot above I've recorded the signals received at the DX station.  The pink colored dots are the +7 degree elevation and the blue colored dots are +0 elevation.  From the plot, visually at least, there's not much difference between the two.  Both are highly variable and both are "about" the same.  Mathematically, it's possible to compare each cycle with its adjacent one, and see if it was "better" or "worse".  This is the value in the delta column, and with a mean delta of 0.31 dB and a standard deviation of 4.06 dB, the statistics confirm that there's no apparent difference in transmit signal between having the antennas pointed straight at the moon, versus pointed 7 degrees higher than the moon.

What about higher elevations?  Some draft antenna gain modelling of the M-squared (M2) 2M7 yagi antennas by W6YX suggests that it should be possible to raise the antennas 15 degrees above the target with only a -1dB penalty in signal.  The plot below shows the predicted gain of the 2M7 antenna in both the Horizontal (H) and vertical (V) planes:

My second test was therefore to alternate calling CQ at +0 and +15 degree elevations above the moon.  Results from this test are below.  

The second test indicates, again, a relatively small difference in transmit signal strength between having the antennas pointed at the moon versus raised 15 degrees above.  Mathematically, the pairwise comparisons indicate that elevating the antennas results in -1.6dB signals with a standard deviation of 3.2dB.  This actually fits very closely with the model predictions!

Subsequent tests the next day indicated similar results:
In the above plot, elevating the antennas 15 degrees above the moon causes a decrease in the received signal strength at the DX station of -1.7dB with a standard deviation of 2.7dB.  This fits nicely with predictions and the previous day's data.

In addition to KB8RQ, station S52LM in Slovenia was reporting signal strengths at the same time.  The S52LM station has less receive capability than KB8RQ so the signal strengths are lower:
This plot shows similar results to the last two:  relative received signal strength is down -1.7dB with the antennas elevated 15 degrees.  What is also of interest is that there are fewer total decodes with the elevated antennas (5 decodes at +15 degrees versus 8 decodes at +0 degrees).  This is probably a result of the slight signal loss pushing these (already marginal) signals past the limit of MAP65's Wide Graph detection (about -25dB).

Overall, what does this all mean?  Basically, it provides some early evidence that it's okay to aim the antennas well above the moon, in order to reduce the effects of the surrounding terrestrial noise and improve received signals, with little impact on the transmitted signal itself.

How much should the antennas be raised away from the moon in my situation?  It really depends on the moon's proximity to the surrounding terrestrial noise.  If the moon is at 20 degrees elevation, then raising the antennas +15 degrees will get them to a part of the sky with approx -3dB less noise, substantially increasing receive capability, with only an estimated -1.7 dB reduction in transmit signal strength.  If the moon is at 50 degrees in elevation (already in quiet sky), then there's no benefit to aiming the antennas off of the moon.  I haven't tested it yet, but based on the +7 degree tests, the calculated shape of the main lobe, and the fact that the +15 degree test shows a -1.7dB reduction, I suspect that a +10 degree elevation offset will not have a measurable impact on transmit signal strength.  My gut feeling is that using a "permanent" elevation offset of +10 degrees will allow me to take advantage of lower noise levels without any significant impact on TX signals.

(much thanks to W6YX for the M2 2M7 draft antenna plots!)