Track Movement of Milky Way With Amateur Radio Telescope

Discussion in 'Amateur Radio News' started by W0PV, Oct 2, 2019.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: abrind-2
ad: L-MFJ
ad: L-Geochron
ad: Left-3
  1. W0PV

    W0PV Ham Member QRZ Page

    Many radio amateurs are also keen on astronomy so they may enjoy this recent article by David N2LVD in IEEE Spectrum. Click on the bold blue text headline link below for all the details.

    73, John, WØPV

    Track the Movement of the Milky Way With This DIY Radio Telescope - Detect galactic hydrogen using roof flashing, a paint-thinner can, and a software-defined radio


    A young friend recently spent a week learning about radio astronomy at the Green Bank Observatory in West Virginia. His experience prompted me to ask: How big a radio antenna would you need to observe anything interesting? It turns out the answer is a half meter across. For less than US$150 I built one that size, and it can easily detect the motions of the spiral arms of the Milky Way galaxy. Wow!

    (A real CAN-tenna :) )


    At my instrument’s “first light,” I was able to detect the neutral hydrogen line with just a little squinting. After getting more familiar with the HDSDR software, I figured out how to time-average the signal and focus on the spectral plot, which I adjusted to display average power.

    This plot distinctly showed a hydrogen “line” (really a fat bump) when I pointed my horn at the star Deneb, which is a convenient guide star in the constellation of Cygnus. Point at Cygnus and you’ll receive a strong signal from the local arm of the Milky Way very near the expected 1420.4-MHz frequency. Point it toward Cassiopeia, at a higher galactic longitude, and you’ll see the hydrogen-line signal shift to 1420.5 MHz—a subtle Doppler shift indicating that the material giving off these radio waves is speeding toward us in a relative sense. With some hunting, you may be able to discern two or more distinct signals at different frequencies coming from different spiral arms of the Milky Way.


    Don’t expect to hear E.T., but being able to map the Milky Way in this fashion feels strangely empowering. It’ll be $150 well spent.

    by David Schneider (N2LVD)
    Last edited: Oct 2, 2019
    K0WJ, AA9G, W5KUL and 31 others like this.
  2. K8ERV

    K8ERV QRZ Member QRZ Page

    WoW! I hope they are not listening to us.

    TOM K8ERV Montrose Colo
    WD8JFT, W7XLR, KT7R and 1 other person like this.
  3. G3SEA

    G3SEA Ham Member QRZ Page

    Cool ! :cool:

    N1GKE likes this.
  4. DL3PB

    DL3PB Ham Member QRZ Page

    Excellent job, OM David!
    Though I'm not really into ultra-high frequencies nor astronomy, I enjoyed reading, how you solved the according issues.
    Always fun to see, what can be done 'at home', when you focus on a certain challenge.

    W7XLR, KC7HDE, N1GKE and 1 other person like this.
  5. K5SOP

    K5SOP Ham Member QRZ Page

    Great article John!!
    KC7HDE and N1GKE like this.
  6. KC2SIZ

    KC2SIZ Ham Member QRZ Page

    Remember to ID every 10 minutes
    W5KUL and KC7HDE like this.
  7. KA2KQM

    KA2KQM XML Subscriber QRZ Page

    Very interesting article David! Would be great to hear additional details of your setup ... did you use an L band preamp? What NF? What feedline/length and downconverter did you use before your SDR? Great work!
    KD2KOS likes this.
  8. AB9TX

    AB9TX Premium Subscriber QRZ Page

    Now try a little Earth Orion Earth...
    KC7HDE and KD9MKZ like this.
  9. W1YW

    W1YW Ham Member QRZ Page

    Here's a pic of the horn that Ewen and Purcell used to detect the 21cm (1420 MHZ) hydrogen line. This was on the top of the Harvard physics building....

    They had more gain but also far noisier receivers:)

    'Doc' Ewen became a big player in the microwave and 'dish' revolution of the 60's and 70's.

    W5KUL, W7XLR, KC7HDE and 1 other person like this.
  10. W1YW

    W1YW Ham Member QRZ Page

    The 'horn' shown in the OP is likely a monopole inside a rectangular can, with a horn opening .

    "TIME AVERAGING" is called 'integration' in radio astronomy, and is key to detecting celestial sources: it beats the noise down by the square root of the total time. The problem is that the OP is doing 'drift scans', so this sets the time averaging to less than a few minutes. Bright sources show up, dim ones are in the noise:)
    W5KUL, K4AGO, KC7HDE and 2 others like this.

Share This Page