Simple 70cm SAT / EME / RA / SETI receive only system

Discussion in 'Satellite and Space Communications' started by KK4NSF, Sep 13, 2019.

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  1. KK4NSF

    KK4NSF Ham Member QRZ Page

    For quite a few years, I've been a fan of all things related to Space / Astronomy and related subjects.... in addition to my Ham Radio hobby. Unfortunately, since I live in an older suburb with tiny yards, and am surrounded on all sides by trees, power lines, and other houses, a fixed station is out of the question. SO... I built a portable receive-only system, that is easy to pack, easy to carry, and easy to set up, but a little more capable than an HT with an arrow Yagi. Below are a few pics of it.

    The antenna is an OWA 6el Yagi, with approx 10.2 dB gain. I used the drawings by KG4JJH, and only modified it slightly, mostly to accomodate available materials. The aluminum came from Home Depot, and the insulators were cut / drilled from a scrap block of bullet resistant acrylic I had in the shop. It shows a 1:1.2 to 1:1.5 across the entire 70cm band, and came up with an almost perfect 50 ohms impedence with just a little tweaking. More importantly to me, it's pattern is very clean. It's a great design.... available here: 6 EL Yagi Drawings.pdf

    My next addition will be a 2m yagi of the same design, and a longer 70cm yagi to get a bit more gain for EME. Since the receiver has two antenna inputs, it may be a 70cm / 2m combo, switchable between the two.

    The receiver is an SDRplay RSP2pro, mounted with Velcro directly on the antenna base.... thus eliminating long coxial runs. Instead, I used a long USB cable that goes from the receiver to a laptop computer. Without the associated coaxial losses, there is less need for a LNA..... at least that's the theory. ( Here is the SDRplay web-site: )

    The mount is a Vixen Porta Mount 2 that I bought about a decade ago for astronomy. It allows 360 degrees AZ, and -45 to +90 degrees ALT movement. It is perfecly balanced (note the weights on the base) so it moves with just a touch, but stays put where you aim it. The antenna BASE (upon which the reciever and a yagi are mounted.... which attaches to the mount) is a long Vixen Shoe, also used for my astronomy.

    Since those photos were taken, I've added ALT-AZ setting circles.... but to be honest, I rarely use them since the beamwidth is ~25 degrees. I also have an Equatorial Mount for RA work.

    So how does it work? For portability, I could not have asked for more. The whole thing easily fits in a small car back seat, and takes just a few minutes to set up.

    For satellites, it works great! I've found it is a lot of fun to track and listen to the spacecraft as they fly over! Since it only operates on 70cm, I can obviously only hear the 70cm downlinks. Even so, I find it to be sort of addictive. A 2m yagi is in the works!

    On EME Receive-Only.... it actually does work, sometimes. I've managed to hear a few of the powerhouse stations, and seen a number of weak-signals on the waterfall. Given the small size / relatively small gain of the antenna, I consider it a big success to even be able to detect a signal at all!

    For RA, it's great! The atmosphere at 70cm band is virutally RF transparent, and thus is a good frequency for listening for Fast Radio Bursts. So far I've not heard one, but I have logged / charted several interesting emissions. The SDRplay has a good recorder function that can be used much like a strip-chart recorder.

    For SETI- no aliens yet. BUT if I hear one while listening to the EME signals, I'll let you know ;)

    nasa4.JPG nasa3.JPG nasa2.JPG nasa1.JPG
    N7UJU, KS1G, K4BAD and 3 others like this.
  2. K4BAD

    K4BAD Ham Member QRZ Page

    Great pictures! Maybe,with a little more work,you can add a transmitting capability.
    Receiving EME sits is quite an accomplishment!.
    73 K4BAD Harry
    N4DJC and KK4NSF like this.
  3. KK4NSF

    KK4NSF Ham Member QRZ Page

    Note: the link to OWA Yagi drawings is incorrect. It's for the 2m version I'm working on now. The 70cm version can be found here: 6 EL Yagi Drawings.pdf

    Thanks, Harry.

    About adding transmit capability..... I'm looking into it. To make it work well, I'll need a transceiver that plays well with HRD or similar software, and fits on the antenna boom. I'll keep you guys apprised of my progress.
    N4DJC likes this.
  4. KS1G

    KS1G Ham Member QRZ Page

    Nice job! I've also thought about remoting a small SDR, or SDR + RPi at the antenna and just run Cat6e back. MUCH cheaper than LMR400!

    I don't think you'll find a 70cm transmitter (other than an HT) that will fit on your mount. Since you have the RX side already, any of the HF--70cm radios with CAT control should work. For operating car-portable, the relatively short feedline length will not cost you too much signal. But looking forward to how you tackle this!
    N4DJC and KK4NSF like this.
  5. AI3V

    AI3V Ham Member QRZ Page

    Have you considered sending the stations you heard on eme a swl qsl card?

    I think they would be more than happy to qsl, as it would be quite an accomplishment indeed to receive eme signals with such a modest set up.

    KS1G likes this.
  6. KB4MNG

    KB4MNG Ham Member QRZ Page

    That is really an impressive looking set up, I bet you turn heads. Can't imagine why you havnt gotten into transmitting.
  7. KK4NSF

    KK4NSF Ham Member QRZ Page

    thanks. It does turn a few neighbor heads, since I often use it in a nearby park.

    About transmitting: For now, I'm still perfecting the antenna and field set-up. A longer yagi is in the works, as is a 2m /70cm combo antenna. With the two RF inputs on the SDR, switching bans will be one push of a button on the laptop.

    Remember, it is a bit easier to receive than transmit... and right now, the rig needs a bit more gain to do what I want it to do. Once that's sorted out, I'll look into adding transmit capability.

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