WELCOME TO 6M EME!
6m Longest Path Comes of Age
W7GJ EME antennas on AZ/EL mounts (L to R): 16x17 el for 2m at 27' high, 11 el for 6m at 70' high, 4x9 el for 6m at 32' high
INTRODUCTION
What do you do on 6m during the solar cycle minimum, when conditions most places around the world are like they always are in western Montana? Don’t put away the 6m equipment for 10 years - make long path contacts instead! I mean REALLY long path contacts - like 800,000 km! Many 6m stations or DXpeditions assume that they don't have a station capable of EME (Earth-Moon-Earth communications, or "moonbounce"), and therefore never consider trying it. But many who are willing to try it are surprised to learn that they actually do have the capability of sending signals to the moon and back. Working REAL long path on 50 MHz is now very possible and unquestionably brings magic back to the "Magic Band"!
In the three decades since the first 50 MHz amateur moonbounce contact between the teams of Dick Allen (W5SXD) and Joe Muscanere (WA5HNK - now W5HNK) in Texas, and Connie Marshall (K5WVX - now K5CM) and Sam Whitley (W5WAX - now K5SW) in Oklahoma, the playing field has changed dramatically. That historic contact utilized a pair of 8 yagi arrays, each aimed at the horizon! Previously only an option open to a very few of the world’s largest stations, moonbounce contacts are now within reach for most well-equipped 6m stations. Until recently, an accomplishment such as making a moonbounce contact on 6m EME was about an "S Unit" or two beyond the reach of most stations. And when it comes to something like 6m moonbounce, where signals are just on the threshold of detectability, 5 to 10 dB is a HUGE amount! However, several very significant developments have combined to make this out-of-this-world type of 6m propagation practical today.
1) Computer-optimized antennas have significantly improved both receive and transmit capabilities. The difference between the old ubiquitous 5 element beam of 30 years ago and the computer-optimized long boom 5 element yagi of today is substantial, and noticeable even during non-EME contacts! And for those who are not inclined to homebrew antennas, there are now some manufacturers of very high performance computer-optimized 6m antennas. Remember, you only need to aim the antenna at the horizon to work EME when the moon is rising or setting!
2) Recent developments in equipment have incorporated 6m into many new HF transceivers (some of which, such as the Elecraft K3, are even already set up for digital mode operation on 6m!), and the band is also included in a growing number of new HF amplfiers. Inexpensive power tubes from Russia have made it very easy to develop "legal limit" type of power output on 6m, and new inexpensive transistors provide excellent performance from very affordable receiver preamplifiers. The ready availability of such equipment has made it very easy to assemble a first class 6m station using “off-the-shelf” equipment. In fact, many well equipped HF stations also already have all the 6m equipment they need for 6m EME!
3) New weak signal digital signal processing software that can be run by Windows computers has further narrowed the gap. The very specialized weak signal mode of JT65A (included in the WSJT computer program developed by Dr. Joe Taylor, K1JT) provides an improved sensitivity of more than 10 dB compared to CW, the previous mainstay for weak signal work. This innovation has turned very difficult weak signal accomplishments like 6m EME into very real possibilities for many hams. Any station that can transmit PSK31 can operate on JT65A mode. WSJT Version 5.9.7 with a complete English language User Manual is available for free download. User Manuals in many other languages are also available here. In addition, to help bring new users up to speed, I have prepared a list of JT65 tips.
The
author operating 6m
EME. The desktop computer monitor displays JT65, while the
laptop monitors the receiver audio using Spectran.
4) And, of course, it doesn’t hurt one bit that many households have switched to either cable television or to satellite reception of television signals, and old 49 MHz portable phones are rapidly being displaced by inexpensive 900 MHz and 2.4 GHz portable phones. The 6m band has long held the reputation as the most difficult amateur band to operate safely without causing interference. However, now many of these most vulnerable household appliances are being improved through newer technologies, making the 6m ham band much more attractive again!
COMMON MOON WINDOW
The most basic requirement in order to contact somebody via the moon is that both stations must be able to see the moon at the same time and aim their antennas at it. Since the moon is visible to roughly half the earth at any particular time, it is possible to contact stations halfway around the world…that basically means you can contact someone anywhere in the world using moonbounce. And because the moon rises and sets every day, there are at least two times each day when you can aim your antenna at the moon without elevating it off the horizon. It is very easy to predict when you will have a "common moon window" with a station somewhere else in the world, and to see what days look like they will have the best conditions for EME. My newly revised GJTRACKER program for Windows is free for download and quickly calculates future EME schedule possibilities.
DECLINATION CHANGES
Everyone knows that because the Earth is tilted on its axis, the sun appears to move north and south in the sky over the course of the year, as we orbit the sun. Similarly, the moon moves north and south in the sky as it completes its monthly orbit around the earth. This apparent deviation (referenced with respect to an imaginary plane going through the earth’s equator) over the course of each month is called the “declination”. One result of this changing declination is that the length of the “common moon window” between two locations on the earth changes every day. What this means for moonbouncers is that you are provided at least one time each month when the moon is on the horizon for both stations at the same time, so both stations can keep their antennas on the horizon while they both are aiming at the moon.
STATION REQUIREMENTS
In short, a station with 1 kw output, a sensitive receiver or external preamplifier, ability to run the JT65A weak signal digital mode, good low loss feedline, and a good single yagi (over 1.5 wavelengths long) is an excellent candidate for successful 6m EME contacts. My first 6m EME contact was using a homebrew 7 element yagi only 20' above the ground. After a number of attempts during my moonrise, I finally completed a CW contact with SM7BAE who, in addition to having the largest 6m array in the world, was very patient. But that was in the days before WSJT and JT65A! Although there still is nothing easy about 6m EME, using JT65A instead of CW definitely increases the chances of success considerably!
Such a single yagi station should now be able to complete contacts with other similarly-sized stations when the moon is on the horizon for both stations. The simplest way to specifically assess your capabilities and target other stations you can work, is to use the very convenient "EME Calculator" that is found on the "EME ECHO MODE" screen of the WSJT program (in Version 4.9.8 only). Whether or not your station is already wired with a computer interface unit that will allow you to operate digital modes, you can certainly download the WSJT program and run the EME Calculator!
I usually suggest that a station have an antenna with 14 dBd gain if he is interested in reliably working similarly sized stations. That 14 dBd gain can include ground gain, if he is primarily interested in operating on the horizon. With 1500w output and 14 dBd from my single long yagi, I could detect my echoes more than half the time when pointed skyward and could often hear my own CW echoes weakly during good conditions. Of course, when the moon passed through my ground gain lobes during moonset or moonrise, signals were significantly louder.
If you want to be able to contact
stations smaller than yours, or run
less power yourself, you will have to make up for the gain on your end
with a larger antenna. With my array of four long yagis, I have
completed contacts with numerous single yagi stations running between
400 and 600w, and with some single yagi stations using only 100w.
There currently are dozens of steerable four yagi stations around the
world, which makes it easy for single yagi horizon-only stations to
make EME schedules.
The
author standing at the base of his four yagi 6m EME array, manually
positioning the antenna after untying it.
GROUND GAIN - USE IT TO ADVANTAGE!
Many stations assume they have no EME capability because they cannot elevate their antennas to track the moon. However, as discussed above, there are certain times of month when two stations both can “see” the moon without elevating their antennas. Actually, there is a very real advantage in keeping antennas aimed at the horizon! An antenna that is aimed at the horizon has “ground gain”. This is extra gain that can often make the antenna perform more like twice (or even 4 times) as many antennas! This extra 3-6 dB only is available at certain elevations, and depends on the local terrain, the ground conductivity and the height of the antenna above the ground. The signals reflected up to the antenna create “ground gain lobes”, and when the moon passes in front of one of these lobes, the signals can be greatly enhanced. That is exactly how smaller stations are able to complete moonbounce contacts - they keep their antennas aimed at the horizon and wait for the moon to move into their ground gain lobes.
Figure
1
-
Ground Gain Lobes of Typical Single Beam Antenna 3.5
Wavelengths Above Ground
Notice that the first two lobes shown for my single yagi in Figure 1 have substantially higher gain than the third lobe. The third lobe is roughly equivalent to the “free space gain” of the antenna (how the antenna would perform if it were elevated and pointed skyward). I have completed 6m EME contacts with many single yagi stations while the moon was in their second ground gain lobe. In the example shown in Figure 1, the second ground gain lobe can be seen as having over 4 dB more gain, compared to the third lobe, and only about 1.5 dB less gain than the lower "main" lobe! Actually, for a number of reasons (discussed below), the second ground gain lobe sometimes even works better for EME than the main lobe!
The closer the antenna is to the ground (or some other object or antenna below the antenna that looks like ground), the higher the ground gain lobes are raised. Conversely, the higher the antenna is above the ground, the lower the ground gain lobes. It also is not unusual for an antenna that is only a few wavelenths high to have an excellent lower ground gain lobe if the distant horizon is actually a negative horizon (such as looking out over the ocean). This situation frequently happens when a station is located on a hill, or the smooth terrain is flat or dropping away in front of the antenna.
Beams that are stacked vertically only exhibit these same types of multiple ground gain lobes when both antennas begin to approach the same height above ground. This usually means that the center of the stacked array has to be higher than 4 or 5 wavelengths above the ground to have these same kinds of strong multiple ground gain lobes. For antennas closer to the ground than that, each beam has ground gain lobes at different elevations, so they cancel out and/or “smear” into a single broader ground gain lobe. Figure 2 shows a typical vertical pattern for my 4 yagi array centered at approximately 1.75 wavelengths above the ground.
Figure
2
-
Ground Gain Lobe of Typical Stacked Beam Antenna
Centered 1.6 Wavelengths Above Ground
You can see the advantage that a single yagi offers for EME - the two very good ground gain lobes offer twice as many chances for the moon to line up with a lobe while the antenna is aimed on the horizon. For an antenna that is used on the horizon, one single long yagi serves as an excellent EME antenna.
CONDITIONS AFFECTING 6M MOONBOUNCE
6m is perhaps the worst and most unreliable band for EME, because of all the things that can adversely affect the propagation at 50 MHz. You can easily understand why conditions may change rapidly, and success may result only after numerous failed attempts. Since signals are usually only marginal anyway, attempts at EME should be scheduled to try to avoid as many of these disruptive factors as possible. For that reason, most of the 6m EME activity happens during times when conditions appear to be most favorable, and people generally do not waste their time running schedules during poor conditions.
1) One of the most common challenges faced by 6m operators - especially if they keep their antennas on the horizon - is local noise. Power line noise, interference from strong local broadcast stations, industrial noise sources, automobiles, household appliances (thermostats, motors, computers, etc.) - all can make it difficult to hear weak signals. Ideally, attempts at EME should be scheduled when local noise is at its minimum.
2) Aside from local noise, there are numerous types of phenomena in the atmosphere and ionosphere that can interfere with 6m signals as they travel out to the moon and back again. Es, F2, aurora, generally disturbed geomagnetic field (a high Kp index or even a high A index) have all been found to adversely affect 6m signals. Local temperature inversions can “trap” signals along the earth, rather than allow them to head out toward the moon. Many of these adverse effects are difficult to predict in advance, while others can be avoided by picking the correct time of day, or watching space and local weather forecasts. In many cases, elevating an antenna (or using the second ground gain lobe on a single yagi aimed at the horizon) will reduce these adverse effects, by sending the signal through less atmosphere/ionosphere. Of course, the geomagnetic interference is far less, and the conditions are best outside the peak of the solar cycle!
3) Faraday rotation is rotation of the polarity of the signals as they pass through the ionosphere. Often the polarity repeats itself in about 15 minutes, but it can be “stuck” for long periods (especially during periods of low Kp index, or when both EME stations are in darkness), in which propagation will appear to be “one-way” or wrong for both stations. This is something which cannot be controlled or predicted, but needs to be anticipated.
4) Perhaps the most predictable factors related to EME conditions involve those related to the orbital motion of the moon. Every month the moon moves close to the earth (perigee) and away from the earth (apogee). The difference in signal path loss between these two spots is over 2 dB - a very significant difference. On top of that, the moon also moves through quieter and noisier parts of the sky. At 6m, this background noise can be significant and can mask the weak signals you are trying to detect. The combination of these two factors, compared to the ideal situation of the moon being at perigee and in front of a quiet sky, is called the amount of “degredation”. An estimate of this degredation is shown on the JT65A screen, as well as in my GJTRACKER moontracking program.
SCHEDULES
Currently most 6m EME contacts are made by setting up schedules with other stations in advance. Because of the relatively small number of stations active at any given time, and the various operating and propagation conditions that have to be taken into consideration, this usually seems to make the most sense. Schedules are usually set up via email, or through dedicated real-time websites such as the N0UK JT65 EME , the ON4KST 6m CHAT or the ON4KST EME CHAT pages. Because almost all 6m EME activity uses the weak signal JT65A mode, which does not tolerate QRM, most frequencies are agreed to well in advance, and frequencies with known or expected activity are avoided. In addition, there are other local band use plans and government regulations that further restrict the use of digital modes and/or EME weak signal operation, so a suitable frequency often has to be coordinated in advance, depending on where each of the stations are located.
ACTIVE STATIONS
With the advent of JT65A mode, there are a growing number of stations capable of operating 6m EME. Also, with the declining solar cycle, an increasing number of 6m DXpeditions are adding 6m EME to their toolkits. Over a third of my Magic Band countries have been worked using EME, and many of those (i.e. CY9DH, ES8X, OJ0LA, V36M, 9U0A, 7P8NK, EA8/G8BCG, D44TD, 9A8A, OX3LX, GJ8BCG/P, ZL8R, KH0/KH2K, CN3A, V51W, 9N7JO, P29NI, TO5E, IS0/I0JU, 6W1SE, OM3RRC, DX0JP, J68AS, ST2RS, YA1RS, 4X/ZL1RS, N8S, etc.) have been from 6m EME contacts with DXpeditions or portable operations. Having completed with over 150 different EME stations in almost 90 different DXCC, it is very difficult to provide a current list of the active EME stations. Let it be said simply that there are dozens of 6m EME stations around the world with steerable four yagi arrays, and of course many hundreds who are capable of EME with horizon-only antennas. One effective way to find potential schedule partners is to watch for "spots" of stations (on internet 6m activity pages or on the DX Cluster) being heard via the moon.
THE FIRST STEP - TESTING FOR ECHOES
If you are interested in determining if your station is capable of 6m moonbounce, you can start by simply listening for your own echoes. Just send a few dashes on CW when the moon is near the horizon passing through your ground gain lobes on a day with very low degradation, and see if you can hear your signals returning from the moon approximately 2.5 seconds later. Don’t become too discouraged if you don't hear them right away, or if they are not very consistant - as you can see from above, there are lots of things that will cause them to come and go! If you can detect your own CW echoes, you most certainly can contact similarly sized stations under similar conditions.
If you are set up for digital modes, the easiest way to test for echoes is to use the WSJT “EME ECHO MODE”. Echo mode will automatically test for your echoes and display a record of precisely how strong they were.
RESOURCES
The following are some links to provide a starting point for those interested in specifics regarding some of the subjects discussed above:
6m Preamplifiers:
http://www.hamtronics.com
http://www.elecraft.com/PR6/pr6.htm
HF/6m kw power amplifiers:
http://www.hfpower.com/new/a1000.htm
http://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=102&encProdID=47ZAY%2Bq1XfE%3D&DivisionID=65&isArchived=0
http://www.icomamerica.com/amateur/amps/index.html
Dedicated 6m power amplifiers:
http://home.cshore.com/lunarlink/
http://www.command1.com/products.htm
http://www.intertronicsolutions.com/amateur/
http://www.pollak.sulinet.hu/elektro/pa_rev/pa_rev.htm#high_vhf
Computer-Optimized 6m Antennas:
http://www.m2inc.com/index2.html
http://www.tridentantennas.co.uk/Frames/Mainframe.htm
http://www.directivesystems.com/antenna4.htm
http://www.yu7ef.com/
Free moontracking program to calculate common window times and degredation:
http://www.bigskyspaces.com/w7gj/tracker.htm
Free WSJT digital communications program for JT65A mode weak signal work:
http://pulsar.princeton.edu/~joe/K1JT/
Interface units between computer and radio to operate digital modes:
http://www.westmountainradio.com/
Free programs to simply display received audio spectrum:
http://digilander.libero.it/i2phd/spectran.html
More information about 6m EME and using digital modes:
http://www.bigskyspaces.com/w7gj/JT65checklist.htm
http://www.bigskyspaces.com/w7gj/JT65.txt
http://www.bigskyspaces.com/w7gj/
http://www.on4ant.com/
CONCLUSION
Although 6m EME is very challenging and unpredictable, it also is very fulfilling and exciting when it works! And, for me, it is a very welcome alternative to ionospheric propagation, which comes along far less often out here in Montana! If you want to experience some real magic, even when you think the 6m band is "closed", consider giving 6m moonbounce a try! You just might be very pleasantly surprised at the DX you can work! See you off the moon!
On 6m EME, the Magic never ends...
This page last updated
on 12 January, 2009
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