2m EME

2m ground gain


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 The text, hereafter, should provide the rationale for the strong moonrise echoes perceived with the 2M12 from this QTH.
  The type or making of the antenna is irrelevant for the analysis. Its heigth above the ground and its free space gain, however can be taken for
a similar analysis. 

  Although most values are quoted with two decimals, you should not be bothered by such an accuracy! In practice,... 

  Let's start with the computer simulations of the 2M12 in free space.


Fig.1: 12M2 E-plane pattern. For a horizontally polarized antenna this corresponds with the radiation pattern in the horizontal (azimuth) plane.

Fig. 2: 12M2 H-plane pattern,. For a horizontally polarized antenna, this corresponds with
the radiation pattern in the vertical (elevation)  plane. 


         According to the manufacturer, M˛ Enterprises and the above simulation, the 2M12, a 12 element on a nearly six meter long boom (2.87 λ long)
            has a free space gain of 12.85 dBd or 15.1 dBi.

            This corresponds to half-power beamwidths of 32° for the E- and 36° for the H-plane.


            Now, by taking profit of the property called ground gain, the free space antenna gain figure can be grossly exceeded and this for signals arriving from certain elevation angles.

            Indeed, the constructive play of the direct and ground-reflected waves will split up the main broad vertical lobe (36° @ -3dB points)  into several smaller sublobes with
            decreasing peak amplitudes, appearing at distinct angles, as shown in the elevation-plot, hereunder..


Fig. 3: The azimuth pattern of the 2M12, taken high in the 2m band and
for 5° elevation.

Fig. 4:
The important elevation pattern of the 2M12, showing the different
predicted vertical side lobes.



Lobe #















dB relative to max gain (see reference line)
















appearing @ x degrees above horizon


             Table 1:  derived from figures 3 and 4 and again valid for the 2M12-antenna sited at 10m above ground, overlooking (nearly ideal ) flat (farmer) ground.



The first major peak has a gain of 18.85 dBd or 6dB higher than the 2M12 in free space ! (see the 0dB reference line level of figure 4)

I.e. this antenna gain, originating from one single antenna pointed at its horizon, exceeds the effective gain of a real stack of four 2M12


From the important H-plane pattern, one can see distinct radiation peaks at angles of about 3°, 9°,  15°, 22°, 28°, …etc.

In between, deep nulls are seen at radiation angles of about 6°, 12°, 19°, 26°, 33°, …etc.


Turning the above into practice:

-an interested moon-listener at this QTH, switching on its receiver at moonrise, will benefit from an antenna with a slightly higher than nominal
free space gain. (13.87dBd)

-several moments later, the best chance for receiving strong signals will be reached (at radiation angle or moon elevation) since this
corresponds with the radiation angle of max. gain. (18.85dBd)

Other effective radiation angles for moon-communication will subsequently follow at and 15°. (with gains of 17.85 and 16.85 dBd)

With the moon climbing higher and higher in the sky, minute by minute, it is simply a matter of waiting till the moon arrives at these beneficial
elevation angles.

They are alternated by nulls in which the signal strength drops by several dB!  At least, we are warned this will happen!


Please note that these three, predicted gain peaks (@ 3°, 9° and 15°) fall closely to one another, all within a gain range of 2dB.

Moreover, the three first radiation peaks provide gain values that remain at least 4dB (four dB!!) higher than the calculated 12M2’s free
space gain of 12.85dBd.



The interested EME-listener (without elevation control) at this QTH should therefore continue monitoring the different random frequencies
between 144.040-144.060 MHz at moon elevations upto 16-17° for best results. (with the assumption, he's a CW operator)

This elevation angle corresponds to roughly half of the vertical half-power beamwidth.


BTW: The 3d lobe at 15-16° is very dominant at this QTH since it has allowed the copy of consistent EME signals on several occasions.

Even with the moon at an elevation angle of 22°, signals from fellow EME-ers have been heard. (just 1 dB higher than the12M2 free space
antenna gain)


From radiation angles of 9° upwards, we’ve noticed improved S/N-ratios, making the smaller signal S (with higher elevation from the ground gain)
stand out better into a proportionally lower noise level N.

Environmental noise drops markedly at these higher elevation angles.   


From the 5th lobe onwards, all benefit of the combined space and ground reflections is lost and a proper elevation system is required to
continuously communicate via the moon.


With great thanks to Lionel, VE7BQH for the simulation with Brian Beezley’s, YO 7.5-Yagi Optimizer.



Hereafter, I've grouped some pictures of stations, I've worked now on several occasions on 144MHz EME with the single 12el (2.87λ long) at 10m agl, in CW and on random.

Click on the picture to increase its size.


KP40        RU1AA          KO48
4x 15el XPOL                 16x 14el XPOL

SV1BTR           16x 7el XPOL

 G3ZIG 8x 15el

IK3MAC 24 x 23el logloop hor
 + 24 x 10el vertical yagies
SP7DCS 16x 8el


RU1AA has now been worked from both his home and contest QTH. The QSO from KP40 came as a surprise since it was unknown during the QSO...

He was just weaker than usual and this could have been due to Faraday rotation or other reasons...until I received his direct QSL!
This is one of the "joys" of completely random EME, CW or FSK operation.

Moonrise ground gain also works with WSJT! (of course)

Last weekend, on 27-01-2007, I was kindly surprised to work a number of stations on WSJT.
My past record on WSJT, only shows Sam, RN6BN worked on several occasions with a best level of -9dB.


The big surprise came in the form of ZL3TY in RE57.
I had worked ZL1BVU in CW for my 2m WAC, achieved in 1992 but the QSO with ZL3TY betters my ODX to 18636km. Not bad for a single yagi!

I first heard  ZL3TY calling CQ on his announced frequency on the EME-chat, with a solid level of -18dB, judge for yourself: .
The mp3-file starts weakly but as time goes on his signals get stronger and stronger and the multiple tone FSK can be heard very distictly!
You can even hear a meteor burst or some other reflection...!

The screenshot hereunder summarizes a part of the JT65B QSO-flow:  (the 73 were not pictured)



the report (-23dB) is typical for most of the QSO's performed here with the JT65B-protocol.

Joe Taylor (th author of the program) explains in his WSJT-manuals that the JT65B-decoder when decoding "both calls" or "both calls + OOO"

to require a level of -24dB, which can get as low as -26dB since the decoder threshold is +/- 2dB.

Likewise but even exceptional, a -22dB will also fail to decode!

This threshold will be lower when the deep search feature is activated.
As can be verified in my log and the screenshots, no QSO's have been made with this deep search feature activated...
Recently, it was verified that the deep search decoder could produce "calls" and "calls + OOO"decodes as low as -28dB and -30dB.
The deep search decoder is however prone of false decodes which will have to be recognized by the operator.


For shorthand messages, such as "RO", "RRR" or " 73", the threshold levels are much lower.
The JT65B-protocol is several dB's lower for these messages, meaning eg. the QSB down can be worse compared to the calls but still result in a decode.


The presence of the 4th ground gain lobe on moonrise


Last Sunday, on 15-04-2007 , I discovered that the fourth ground gain lobe on my moonrise to be present and effective enough to produce valid QSO's.

The fourth lobe corresponds with a moon elevation of about 22° as can be seen in figure 4, above.

By using Sam, RN6BN's loud transmissions, I could easily spot down high elevation angle EME  reflections, as can be seen in the following table:

Sam sometimes indicates his transmit polarisation, by including this in his CQ-call. This is a worthwhile indication for the 2m-experimenter.
Example: CQV RN6BN KN9 would indicate, he's transmitting with vertical polarisation. (the V in CQV)
The missing '5' of his WW-location (KN95) is due to amount of CQ-characters, contained/defined by the WSJT-protocol. (up to 13characters are possible)


Time (UT) Tx-polarisation Moon elevation (°) WSJT signal level
In QSO with
0548 CQ H 16.5 -8  
    16.7 -10 ON7EH
    17 -16  
  CQ V 17.6 -14  
    18.1 -20 UA9UIZ
    18.5 -14  
  CQ V 18.7 -13*  
  CQ H 19 -10*  
0608   19.3 -9  
    19.5 -8 DD0VF
0612   19.7 -11  
    20 -9  
    20.3 -7 Not noted
    20.6 -11  
    20.8 -10  
0622 CQ H 21.1 -8  


The moon elevation angle where super-station RN6BN was worked, corresponds with the moment, I usually quit moonbounce operation.( around 17°)

This time, I decided to continue monitoring Sam's signals and this is shown in the above table.

After my QSO with him, Sam changes to the orthogonal polarisation (vertical) to work (nearby) UA9UIZ.

In the middle of this QSO, at about 18° of moon elevation , I noted the lowest measured value (-20dB ) of the measurement session.


After the QSO with UA9UIZ (as after my QSO), we note again a Tx-polarisation change.

As before, there is no significant signal drop by orthogonal polarisation switching , indicating the polarisation to be close to slant (+/- 45°) polarisation. 

Near to 20° of moon elevation (and beyond) , the signals from RN6BN remain VERY comfortable at and around -10dB.

This proves the:

- 4th moonrise ground gain lobe to be effective and permitting QSO's as predicted by Lionel, VE7BQH's simulation, see higher.
- the ground in the surrounding farmer fields to be close to ideal and very much corresponding to the simulated ground properties.


The indicated relative levels were started with 0dB noise reference. (+/- 1dB)
The covered azimuth angles during the observation period cover the lowest possible noise levels at this QTH so very representative.
With no doubt, the conditions were exemplary between our both stations that moonrise.


The following document explains the 1st Fresnel zone geometry at this QTH and shows one possible set of direct and reflected waves.



WSJT echoes visualized!


Last night, April 30th , I was taken by surprise by my own echoes while calling I6BQI.
First really strong, the next period weaker. Judge for yourself: see the circled white dots in the WSJT-waterfall plot at a frequency of about 1520 Hz.




 Most remarkable was the high degradation value of -4.2, which is far from optimum for low signal EME communication!!  
The moon elevation of abt. 4° is close to the 1st and most significant vertical lobe of the 2M12 2.87WL antenna at this QTH!