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EME anyone?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF4ZGZ, Jun 10, 2021.

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  1. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    33fthawaii7.jpg

    That my fellow OM's is a 33ft. radio telescope.
    How hard would it be to convert it to EME use?
    There is a reason I'm asking. It may be available if someone wants it.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Only the feed system that illuminates the reflector and possibly the transmission line to that would need to be changed, assuming the dish already has elevation/azimuth control.
     
  3. K2AR

    K2AR XML Subscriber QRZ Page

    It depends. If it is a prime focus focus feed it should be relatively easy especially with a patch type feed where you can have multi-band operation with the right design. If it has a cassegrain type feed then it gets a bit trickier with developing a feed to get good sidelobe reduction. Reusing an existing waveguide system limits at what frequency you can operate at. Also with that antenna size, it will not be efficient to use on 2M and 70cm but will be good to go at 1296 MHz and up. The antenna in my profile photo was originally a prime focus 60 ft. VHF/UHF antenna with a 10KW VHF used for satellite navigation. A yagi array will outperform it but wouldn't meet the power requirement so this is what they came up with back in 1962. Now it has been modified as a cassegrain feed for S and X band operation. Back in the early 1980's, I worked at a ground station that had a 42 ft cassegrain C-Band antenna that was the spare for the site. I made a coffee can feed for 1296 MHz and lashed it next to the existing feed and while the sidelobe performance wasn't that good, it did work for EME contacts on CW and a couple of SSB contacts with 250W.
     
    Last edited: Jun 10, 2021
  4. SM0AOM

    SM0AOM Ham Member QRZ Page

    If the mount is servo-motor operated in the azimuth-elevation planes, the conversion work for EME use would be to replace the feed antenna at the prime focus with a suitable design for the band in use, usually some form of dipole with reflector or horn.

    Lower bands than 70 cm would be impractical.

    Guidance for EME station dimensioning can be found by
    consulting the VK3UM EME calculator.

    On 70 cm, the required power to hear your own echoes in a 100 Hz bandwidth would be about 150 W, and on 23 cm about 50 W. Both assuming "good" preamps and feed systems.

    73/
    Karl-Arne
    SM0AOM
     
  5. KY4GD

    KY4GD XML Subscriber QRZ Page

    Does it come with mobile mounting brackets?
     
    N9SD, S21RC, AK5B and 1 other person like this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Even better: Will it work okay in my attic?
     
    KD2UHD, WB5YUZ, N9SD and 2 others like this.
  7. AK5B

    AK5B Ham Member QRZ Page

    Do you have any foil insulation or much HVAC ducting up there? IF the answer is "none at all" you should be good to go. Some modification to your roof may still be necessary, though.
     
  8. AK5B

    AK5B Ham Member QRZ Page

    For local pickup only---or will they ship?
     
    KY4GD likes this.
  9. KY4GD

    KY4GD XML Subscriber QRZ Page

    I just flashed to an image of a house with hydraulic jacks splitting and lowering the roof, to reveal that antenna.
     
  10. W4HWD

    W4HWD Premium Subscriber QRZ Page

    Thats about how big the home satellite dishes were in the 80s.
     
    KD2UHD, KY4GD, AK5B and 1 other person like this.

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