Doppler shift on 432MHz EME

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by ON6KE, May 15, 2018.

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  1. ON6KE

    ON6KE Ham Member QRZ Page

    Hi,
    my name is Gus, I'm 64 and a HAM for 43 years who spent 99,5% of the time on HF. I'm a bit done with HF especially now that we are near the bottom of the solar cycle.


    I'm interested in 70cm EME and now gearing up to get everything together.
    I have a question regarding Doppler shift.


    When operating JT65B on 70cm what do I do when a station calls me? Do I stay on my original frequency?
    I assume I do otherwise the other station will have to chase me each time when I TX on the Doppler shifted frequency.

    When operating JT65B on 70cm what do I do when a station calls CQ? Do I take into account his Doppler shift?

    Questions questions. :)

    Hope to hear from you guys.
    73, good DX

    Gust ON6KE
     
    Last edited: May 15, 2018
  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    If you are calling CQ and a station answers you, you do not change frequency.

    If you want to respond to a station calling CQ, you can calculate the Doppler and correct for it if you choose. It does not need to be perfect. You just want to stay within the receive passband of the station you are calling. So usually +/- 1KHz is fine. If you are calling a DXpedition with many callers you also want to spread out and not call right on the other stations frequencies so you have a better chance of being decoded.

    That said, it is my opinion that starting out on 144 MHz is much easier than 432 EME. There are many more stations and more superstations. Once you learn the the basics a transition to 432 becomes much easier. With 100+Watts and one medium,2 to 3 wavelengths, boom-length Yagi you can make some EME contacts on 144 MHz.
     
  3. ON6KE

    ON6KE Ham Member QRZ Page

    Hello Harry,
    thank you very much for your input, it is much appreciated.


    I've been thinking about 144 a lot but the point is that I'm an apartment dweller with a really small terrace.
    A 3 WL Yagi on 144 is way too long, I won't be able to swing the antenna azimuth wise from my 85 through 280° window. To be able to do that I would have to seriously elevate (EL) the antenna. I'm on the third floor and it's a 4 floor building, lucky for me the people on the 4th don't have a terrace. Even a 2 WL Yagi won't swing if I don't first elevate it to about 40°.

    I haven't got my amplifier yet so in the end still going for 144 is possible. Going /P hasn't been withheld as an option for several reasons.
    Oh well I will yet again have to think it over again.

    Again thank you.
    73, good DX.
    Gust ON6KE





     
  4. WB3BEL

    WB3BEL Ham Member QRZ Page

    Well I am sure you can make a few contacts even with 2 WL. A pair of 2WL would be better, but it's worth a try.

    /P is a good idea. It will get you away from all the awful noise that buries EME weak signals.

    Anyway good luck with your experimenting !
     
  5. ON6KE

    ON6KE Ham Member QRZ Page

    Thanks. :)
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    Remember, (especially at 70 cm) you have to not only account for Doppler, BUT you also have to adjust your aiming, since the moon IS a moving target, and you are using antenna(s) with relatively narrow beamwidth.
     
  7. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    The best way to start out in EME is by "picking up" (receiving) stations first. The transmitting part can come later.

    You will have to know where and when everyone is transmitting to do this.

    To find out where everyone is coordinating and operating EME in real time, you can use this online EME chatroom link posted below.

    EME stations will announce the frequency and tell you exactly when they are actually transmitting !

    https://www.chris.org/cgi-bin/jt65emeA

    Bookmark it in your favorites !
     
    Last edited: Jun 23, 2018
  8. K6CLS

    K6CLS Ham Member QRZ Page

    Chris.org is for 2m EME.

    For 70cm and above, the chatrooms on http://hb9q.ch
    Are most popular

    Hint, look at the upper right corner for "create a new account" and "login"
     
  9. K3RW

    K3RW Ham Member QRZ Page

    Is JT65B still a dominant mode for 70cm? I thought others were using JT4, JT9, etc.
     

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