Low cost 10Ghz EME Rx System

 

  • 1 – Low cost 10Ghz EME Rx – The LNBF
  • 2 – Modifying the LNBF
  • 3 – Tuning the LNBF
  • 4 – Pictures and PlotsNOTE: This is not intended to be a definitive “how to” article, but may serve as a guide for those interested in receiving 10GHz EME signals at minimum cost and complexity.

    Why 10Ghz

    Several reasons. First, low cost commercial equipment designed for TV satellite reception is available. Second, there’s a reasonable amount of EME activity compared to the other bands above 1296MHz. Third, there’s a beacon – DL0SHF – which (when it’s operational) can easily be received by this simple system. Fourth, most of the world uses the same frequency allocation so most of the activity centers on 10.368 GHz. Japan’s allocation is different though and they are on 10.45Ghz. That’s still a lot better then the situation on 13cm. Fifth, you can see/hear/decode signals with a very small dish. Dish diameters under 3ft will work quite well and receive quite a lot of 10Ghz EME signals.

    So what’s the low cost system

    There are three options at outlined below. Each step is a little more complicated (and expensive) then the previous one

    Stage 1 – An unmodified LNFB, An RTL-SDR dongle and a small (~1m) dish

    Total cost here is around $35 plus the dish. Assuming you are pointed at the moon and you are running SDR software that controls an RTL-SDR dongle, you should be able to see sun noise and if you look at 618MHz +/- 0.5Mhz and you may see 10Ghz EME signals on the waterfall plot if any strong stations are active. You won’t be able to decode any digital signals, but there is a small chance you may be able to copy CW from one of the “big guns” on 10Ghz EME. You will be able to see sun noise.

    Stage 2 – As above, but with an LNBF modified to take an external reference signal

    This maybe adds another $10-$20 to the cost and some time to tune the LNBF for best NF. If you feed the LNBF with a higher stability signal at 25MHz (e.g TCXO) it will it easier to find and stay tunes on a signals. If you use WSJT-x with the RTL-SDR you still may not have enough stability to be able to decode anything digital, but at least the signals won’t drift too much once you’ve found them. If you are lucky, have CAT control of the RTL-SDR via suitable SDR software, you might get a decode if the rate of change of Doppler shift is low or you can track it using the software, assuming the reference oscillator is at a stable temperature. Doppler shift can change by as much as 100Hz/minute at 10Ghz at times with the moon in transit (max elevation). It can drop to under 10Hz/min near moonrise and moonset.

    Stage 3 – A modified LNBF, a radio with CAT control and a reference signal around 25.477MHz

    This can add another $100-$200 to the cost (not counting the radio!). It will bring the IF down into the 70cm band, where you may have good receiver capability with a high performance rig. In that case you can use your main radio along with WSJT-x software to see the 10Ghz EME signal. If you use WSJT-X and configure it to control your radio’s receive frequency via a CAT link, you can then track Doppler. If you are using a stable LO signal (preferably GPS referenced) it should be relatively easy to find signals and you will be able to decode digitally encoded signals (usually QRA64 or JT4 encoded) from moderate power EME stations. I decoded QRA64 signals from the A21EME dxpedition (they were running 50W to a 1.5m dish) with an 85x91cm offset fed dish. There are probably 10-20 10Ghz EME stations (maybe more) that you could copy with this system.A modest (90cm) satellite dish will cost around $100 if you have to buy a new one, or it might be free if you find someone looking to get rid of that “ugly satellite dish” bolted to their house. You need to be able to accurately point the dish, but to start out you can probably get away with optically sighting on the moon and manually moving the dish every few minutes. The 3dB beamwidth of a 90cm dish is of the order of 2 degrees, so you need to point it with and accuracy of 0.5 degrees or better.

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