The text, hereafter, should provide the rationale for the strong
moonrise echoes perceived
with the 2M12 from this QTH.
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.
According to the manufacturer, M˛ Enterprises
and the above simulation, the 2M12, a 12 element on a nearly
six meter long boom (2.87
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
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
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
will benefit from an antenna with a slightly higher than nominal
-several moments later, the best chance for receiving strong signals will be
reached (at 3° radiation angle or 3° moon elevation) since this
Other effective radiation angles for moon-communication will subsequently follow at 9° 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
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 (@
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
(four dB!!) higher than the calculated 12M2’s free
The interested EME-listener (without elevation control) at this QTH
should therefore continue monitoring the different random frequencies
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
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)
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
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.
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...
just weaker than usual and this could have been due to Faraday rotation or other
I received his direct QSL!
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
The big surprise came in the form of ZL3TY in RE57.
first heard ZL3TY calling CQ on his announced frequency on the EME-chat,
with a solid level of -18dB, judge for yourself:
the report (-23dB) is typical for most of the QSO's performed here with the
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.
For shorthand messages, such as "RO", "RRR" or " 73", the threshold levels are
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.
Sam sometimes indicates his transmit polarisation, by including this in his CQ-call.
This is a worthwhile indication for the 2m-experimenter.
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.
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 indicated relative levels were started with 0dB noise reference. (+/- 1dB)
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
Most remarkable was the high degradation
value of -4.2, which is far from optimum for low signal EME communication!!