EME / Moonbounce for a beginner?

Discussion in 'Satellite and Space Communications' started by G1VVP, Mar 29, 2010.

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  1. KC8VWM

    KC8VWM Ham Member QRZ Page

    Unlike the sats and working on HF, EME is especially technically challenging and yes it can even lead to much frustration. Some stations don't make a contact even after a year of trying.

    The rewards are many if you manage to experience success but it doesn't come easy. EME is not for someone who wants to simply flip a switch and expect to start making contacts.

    My Best,

    Station KC8VWM Mooncam view - 03/28/10 02:15 GMT

    Azimuth 120 degrees - Elevation 31 degrees


    [​IMG]
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, that's sure true. My first EME work was on 70cm back in the late 1970s. With 1kW output power to four stacked 19 element K2RIW optimized yagis fed with 7/8" hard line I could not hear my own reflections. Thankfully, some others could and after about a month of trying I finally made my first contact (CW) -- then I was hooked. I screwed around for more than a year before I heard my own echo.

    WSJT makes all this easier now...but it's still not even close to a "plug & play" mode of operation.
     
  3. W9GB

    W9GB Ham Member QRZ Page

    EME "Moonbounce" -- Wikipedia
    http://en.wikipedia.org/wiki/EME_(communications)

    The Earth-Moon signal path loss over the 770,000 kilometer return distance is extreme (around 250 to 310 dB) depending on VHF-UHF band used.
    WJST / modulation formats; Doppler shift effects; amount of TX power available and high-gain antennas (> 20 dB) are components that are typically used in assembling an EME station.

    My first EME contact (CW) was with KA0Y's 40 foot EME dish in 1984 .... it is quite an experience .. tracking the moon with a Heathkit H-100 computer!

    w9gb
     
  4. WA9SVD

    WA9SVD Ham Member QRZ Page

    Current satellite work is NOTHING like EME. As you state, satellites CAN be worked with nothing more than H-T's. (I've made several sat contacts with two H-T's (2 Meter mono-band H-T for the uplink and a 440 MHz-1.2 GHz dual-bander for the downlink) with (aftermarket ) whip antennas.
    EME is a WHOLE different ballpark; particularly with a "modest" station, the signal levels from EME can easily be 20-30-40 dB LESS than that received from an Amateur satellite, (even when using computer assisted detection for EME) and a directional antenna will be an absolute necessity. Accurate aiming of the antenna will also be critical; you can't just point the antenna in a "general direction" and expect results, as you can often do with the 'birds. Unless a person has proper tracking rotators and software abilities, terrestrial success will be limited to the moon being only a few degrees above the horizon, so a clear horizon view will be a consideration. If there are objects in the way (dense forest, buildings) chances of making a contact (or even reception) are greatly reduced.

    EME is probably THE ultimate "weak signal" challenge.

    Good luck to all that try, and keep us posted!
     
  5. KF5FEI

    KF5FEI Ham Member QRZ Page

    I think maybe my point was missed. If you are unfamiliar with construction / use of directional antennas and aiming them at moving objects, satellite work is a good way to start out, especially if you don't have someone in the area who can help you out with the EME stuff.

    Doctors don't start off doing brain surgery -- they dissect dead people first, then work up to simple surgeries and later, more complex stuff. The easiest path to disappointment is to blindly jump into something way over your head and expect instant gratification.
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    If there were birds like AO-40, AO-13, or AO-10 still in operation, that would CERTAINLY be true. But with the LEO birds, aiming an antenna and getting a response merely requires hitting the "broad side of a barn."
    Surely, if one DOES have an AZ-EL rotator system, one can practice tracking the Amateur satellites with even a small directional antenna. But it's nowhere near the precision required for EME work.
    I do agree, however, that with a directional antenna, (preferably a highly directional antenna) the birds can be a place to start. And as is true in any of our Amateur Radio endeavours, "if you can't hear 'em, you can't work 'em."
     
  7. G1VVP

    G1VVP Ham Member QRZ Page

    After reading the last few posts I realise I will have my work cut out. Voice contact was my original intention but I see this may not be a consideration with relatively simple equipment.

    There's certainly no harm in trying. I have plenty of aluminium and should be able to make a reasonable yagi antenna in excess of 13 elements.

    Thank you WA9SVD for your confidence in me. :)

    73 all.

    John
    G1VVP
     
  8. WB3BEL

    WB3BEL Ham Member QRZ Page

    Working EME on 2meters using WSJT is not all that hard. If you have about 100+ Watts and an 8 or so element yagi on 2wl boom you can work the big guns when conditions are favorable. When you start out you don't need a super low noise preamp. If you don't have some TX power you don't need to hear weak stations that you can't work. You might make a few contacts with 50W but 160W brick amps are pretty affordable and will help a lot. You still will have to fight for every contact but it's fun to get started with what you have.

    If you want to build a decent yagi check out the DK7ZB designs:

    http://www.qsl.net/dk7zb/start1.htm

    As far as getting your feet wet with the technology using WSJT I can strongly recommend trying meteor scatter. The program is the same just using a different mode FSK441a for meteor scatter versus JT65B for EME.
    You get used to the tools and meet some of the guys you might hear later on EME.

    If you want to make an EME contact you certainly can with simple equipment and antennas.
     
  9. KC8VWM

    KC8VWM Ham Member QRZ Page

    "A cut and paste report - JT65 EME moon bounce reception at station KC8VWM"

    144.125 MHz.

    *** 043500 3 -18 2.0 0 3 * CQ K6MYC DM07 ***

    Hmmm.. EME conditions are in pretty good shape from California to Oklahoma tonight. :)

    Martin, DK7ZB has some excellent "low noise" EME antenna designs and his 12 element Yagi design is probably the most popular antenna build I would recommend to get started on EME.

    What I like in particular about the "German engineered" DK7ZB antenna designs is the fact these are actually "real world" antenna's. They are not just simulated computer model designs that only look good on paper. These designs stick with actual DL6WU's real world optimized antenna design principles. Not just plug and play antenna modeling data. One of the better designs in terms of real world antenna's with a proven and tested history.

    My Best,
     
    Last edited: Mar 31, 2010
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    "Voice" isn't gonna work for e.m.e., about 99% of the time, even for the best equipped station with hundreds of elements and kilowatts.

    I understand the Arecibo (Puerto Rico) radiotelescope dish will be activated for a period of time coming up, on 70cm (not 2 meters). That antenna has so much gain that SSB contacts might be possible, if they choose to do so; but it's one of the few antennas ever activated in the amateur bands having that kind of gain. With enough antenna gain, FM e.m.e contacts are possible! But the gain required is enormous and beyond the scope of amateur setups, so on "one end" of the circuit it will take a radiotelescope-type antenna.

    Some info on the Arecibo dish: http://www.naic.edu/public/the_telescope.htm
     
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