Thread by @M0SKN_SA5IKN

Recently, tens of #amsat ops made their 1st #moonbounce QSO. The thrill of #EME with a biggun creates an illusion of similarity to other modes. EME is different. How small a station you can hear? This thread elaborates on accurate predictions. No magic, only Physics! #hamradio

2/10 #EME is the only field in #hamradio that allows reliable predictions of station sizes that one can work. No smaller station beyond this prediction can be contacted under any conditions! You cannot bend the theory. The link budget can be expressed in Signal-to-Noise ratio-SNR

3/10 SNR represents the ratio of System Gain to Noise Temperature. #WSJTX in Q65 computes SNR in the bandwidth B=2500 Hz. That is the report that you exchange with each other. We want to maximise it by increasing the numerator and decreasing the denominator
#hamradio #moonbounce

4/10 But how can we know the values for Signal and Noise to predict the lower limit of who we can contact via #EME? We can feed the formula for SNR (see image) with specs for our equipment and known astronomical data.
#hamradio #moonbounce

5/10 The system noise Tₛ is of special interest. Everything in the signal path contributes to it: every cable, connector, relay, LNA, antenna, etc. We can estimate these. For the sake of clarity I'm not touching on galactic noise and other noise sources. #hamradio #moonbounce

6/10 Example for 70cm #EME. RX station: short (3 wavelengths) 15el Yagi 14.8dBi, LNA G=15dB NF=1dB, 2x6ft LMR240, FT818 NF=4. TX station: 75W, 2dB loss, 2 short (2 wl) 11el Yagi 16.6 dBi total. Can the RX station copy the TX station?
#hamradio #moonbounce

7/10 No. RX station can't copy the TX station even in ideal conditions. SNR<-37dB. How many Yagi does TX station need to add to be copied by RX station? Q65-60B allows reliable decodes under SNR=-27. To reach target SNR the TX station must have 24 such Yagi in ideal conditions!

8/10 This was a real life example. The RX station is SA5IKN Greencube setup. The TX station with 2 Yagi is Dave's @KG0D_Dave station.Dave kindly allowed me to use his data.

https://twitter.com/M0SKN_SA5IKN/status/1614665437622554624

#hamradio #moonbounce #amsat

9/10 You can make #EME performance predictions too and even without going through equations. I highly recommend to use VK3UM EME Calculator.
#moonbounce #hamradio

https://twitter.com/FG8OJ/status/1628497110780837888

10/10 Wrapping up. If you've done your first #EME QSO using QRPp, 99% of credit goes to big gun. Yet, the remaining 1% is plenty, don't underestimate your contribution (some would never do it)! But if you want to do some real EME yourself keep learning. #hamradio #moonbounce

PS: I wrote this thread for novices and deliberately made a number of simplifications. Even though I hold a PhD in Theoretical Physics, I'm no expert in this area. I strongly recommend papers by Prof. Joe Taylor K1JT and Prof. Alan Katz K2UYH for more in-depth knowledge
#hamradio