Iniciación al EME en 6m con una estación sencilla

Preparando nuestra próxima expedición a la isla Coetivy (Seychelles), nueva IOTA AF-119, que va a tener lugar entre el 16 y el 21 de noviembre, no he querido dejar pasar la oportunidad de poder transmitir en la banda de 6m, al tratarse de un DXCC muy raro en dicha banda, sólo activo una vez anteriormente hace muchos años.

Pero como 6m es una banda que probablemente esté cerrada para hacer DX (ojalá me equivoque y la TEP despierte en los próximos días!), el interés está en tratar de hacer QSOs con rebote lunar, lo que se denomina EME (Earth-Moon-Earth).

Hasta ahora lo del EME me parecía algo totalmente fuera de mi alcance, seguramente por el desconocimiento del tema, pero Steve HA0DU me ha enviado una guía que preparó para un colega en el Caribe donde explica desde cero, y de una forma muy entendible, cómo poder hacer EME con una estación relativamente básica, tratando de aprovechar los momentos en que la luna está más próxima al horizonte.

Creo que es muy interesante compartirlo por aquí, y a pesar de estar en inglés, quizás pueda animaros a probarlo y, quien sabe, a lo mejor contactar con S79C en 6m en EME ?

6M EME WITH A „SMALL” STATION

A short tutorial for potential EME operators.

First of all, I think EME is often over-mistified and considered something very difficult and time consuming. Wrong! If you ever operated any digital modes on HF, you can do EME as well. There are certain settings which you need to keep, but otherwise it is just like working someone on PSK31 or RTTY. Most of the job is done by the computer. Without any serious programming/computer knowledge I made over 40 QSOs on 6m EME, including big guns like W7GJ and G8BCG, but also small pistols like VK0JJJ or FO4BM.

What do you need for 6m EME from an island surrounded by salt water?

  • A radio. Todays most popular rig, the K3 is probably not tailored for 50 MHz, but the addition of a PR-6 preamplifier can improve it considerably.
  • An antenna. Your 6 element antenna is good enough. Since you do not have elevation, you should concentrate on the roughly one-hour periods just after your moonrise, and just before your moonset. This is called „on-horizon” EME, and I think about 150 different stations were successfully worked this way by the big guns. In the vertical plane, the antenna has so-called „lobes”, in which most of the power is transmitted (and reception is enhanced), so you may experience changes in signal strength. This is normal, and this is one of the challenges of EME.
  • An amplifier. As the rule of thumb says, bigger is better, as far as power is concerned. If you have anything above 500W, you must try (don’t forget JT65A is a continuous-duty mode, so your transmitted signal is permanent for about 48 second TX periods.) Be careful, better put an extra fan to the cooling fins of the amp to keep it at a convenient temperature.
  • A computer. Most modern laptops have fairly good soundcards, so practically any laptop (=any computer) will do. The computer’s clock must be set within half a second to a timebase, even setting manually to GPS time is OK.
  • A software. The famous WSJT software is free. Any version will do it, WSJT 7 is just as good as WSJT9 or even WSJT10 (but the version should have JT65A, be careful, JT65HF is not good for EME!) . Your initial screen should look like this (WSJT9 pictured):

1

Take note of the following initial settings:

  • To radio: (bottom left): Type in a call if you have a sked. If you are calling CQ, you can leave it blank.
  • Grid (bottom left): Type in the grid of the sked partner.
  • Sync -30 (bottom center): Don’t ask me why, but -30 is the best setting for EME…
  • Messages TX1-TX6 (bottom right): These messages are generated automatically, when you push the „Gen Msgs” button (bottom center)

The procedure of setting is relatively simple:

Start with Setup – Options.

2

Enter your call ZF1EJ and grid locator EK99ig. The next thing is to set PTT and audio in/audio out ports. I can only tell that on the “black” screen of WSJT you see the audio settings of your computer, and you should pick the ports which correspond to audio in/out there…
Then on the main screen of WSJT, set Band to “50 MHz”, Mode to “JT65A”, Save to “Save decoded”, and Decode in JT65 to “Include average in aggressive deep search”.

In the lower part of the screen, enter the sked partners callsign in the “To radio” field, and their grid in the “Grid” field.
In the lower center, set Sync to -30 (by clicking on the number field with your right mouse button).
Then click on the “GenStdMsgs” button, and your main screen shall look like the shot above.
Click on “Monitor”, and if you connected your radio well to the computer, you should be in receive mode (in the right bottom green field “Receiving” is read).

Settings of the radio: depending on the type of your radio, and how your radio is connected to the interface, you use USB or DIGI mode. For weak-signal receprion, you should turn AGC off, bandwith to 3 kHz and TX power to drive your amp to a safe power level, which your amp will handle for about 50 seconds without playing a sparkler…

Setting of the antenna: You just set your antenna to the direction of your moonrise (on October 23, this is 100 degrees).
The program is using alternating TX/RX periods of the two partners. When I TX, you RX. I start TX at 00 second of the minute (but it takes the signal about 2,5 seconds to be reflected from the surface of the Moon, so you should “see a trace” from about 03 second of the minute. Then receiving goes on for about 50 seconds, and at second 52-53 of the minute, the “Decode” button will glow blue, and decoding will take place.
See the screenshot below, which shows you a typical screen during reception. On the right, SpecJT can be seen, with the traces of the signal received. You can see two parallel lines there: that is the „RRR” message I received at 2242 from G8BCG.
OPERATION

The basic idea of these modes is that the two stations are transmitting known messages in alternating periods to each other. „1st” means the station transmits in even minutes: 22:00, 22:02, 22:04 etc. „2nd” means the station transmits in odd minutes: 22:01, 22:03, 22:05 etc.

At the beginning of the sked you push the “Auto is Off” button, which will turn to red, and will display “Auto is On”. This means your computer will control the TX/RX periods automatically from now on.
But what should you transmit? In a sked, we both start transmitting the TX1 message (I transmit “ZF1EJ HA0DU KN07“, while you transmit “HA0DU ZF1EJ EK99“, in our respective TX periods). We also have to agree, which is your TX period, and which is mine, to avoid transmitting together and then receiving nothing J. I recommend you TX in the first period (tick the „TX first” tickbox ont he main screen).

3
The subsequent transmissions are governed by what we receive from each other. Pressing the F5 button will bring up the procedure and “what message to transmit?” of WSJT, and it is very clear. If you receive my “ZF1EJ HA0DU KN07” message, in the next period you start transmitting the TX2 message “HA0DU ZF1EJ EK99 OOO”. Remember, decoding will happen at second 52-53 of the minute, so you have about 5-6 seconds to switch from TX1 to TX2 (by clicking in the circle at TX2 on the right side of the screen). I will continue transmitting TX1 until I receive your TX2 message, when I do, I will switch to the next one, which is TX3, that is, “RO”. You keep transmitting TX2 until you get my “RO”, then you switch to TX4, that is, “RRR”. I keep transmitting TX3 until I get your “RRR” – and if I do I open a bottle of champagne, because the “official” rule is that receiving the “RRR” completes the contact. I will obviously transmit “73” to you, but it is not necessary that you receive it. Of course this can happen the opposite way, so if I receive your TX1 message, I will switch to TX2, and so on…

73 Steve HA0DU

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