Feb 25 11 tweets 9 min read
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
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.
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?
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.
9/10 You can make #EME performance predictions too and even without going through equations. I highly recommend to use VK3UM EME Calculator.
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

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# More from @M0SKN_SA5IKN

Jan 31
This is a simplified guide describing a bare minimum (!) for #EME operation of WSJT-X in Q65-60B on 432 MHz. A few settings are TRX-specific. Consult to your rig's manual for those

Step 2: Install WSJT-X and open Settings
1) Fill in "My Call" and "My Grid"
2) Tick "Enable VHF and Microwave submodes"
3) Tick "Decode after EME Delay"
Step 3: Navigate to Radio tab
2) Choose your serial port and baud rate
3) Choose CAT as PTT
4) Mode and split operation depends on your rig. A minimum non-destructive set: Non and Fake it, respectively
You test CAT by a button
Jan 31
Bernd DL7APV asked me to QSP to the #AMSAT community that he will QRV this coming Thu, Sat, Sun and listen especially for #satellite setups. Use your chance to make your first ever #EME QSO - biggest challenge in #AmateurRadio 🌗

See how this can be done⬇️

Jan 28
If you work via #GreenCube, try #EME with big guns. I promise, you will be amazed! As a proof of concept, I made a quick #moonbounce QSO with DL7APV with just a Yaesu FT-818, 40W, 1dB NF LNA and 15 el Diamond antenna held by hand! Easy QSO. Read on🧵
2/9 There are a number of extremely capable #EME stations on 70cm: DL7APV, HB9Q, NC1I. If you are enjoying decode rates above 80% on #GreenCube, don't wait and try #EME. You will likely complete your first QSO over the Moon faster than on the congested #IO117
3/9 I used my portable #Greencube set: Yaesu FT-818ND - 40W amp / 1dB NF preamp - Diamond A430S15 14.8dBi on wooden extension, held by hand and pointed visually. With a low NF frontend you can go with a 7el Arrow
Nov 1, 2022
LNA / preamp is an unpopular topic of the portable SAT discourse. Noise figure (NF) is assumed to be low due to absence of long cables. But what if NF of the system inherently is not top tier? Any benefit in using LNA with FT-817 & FT-818? 🧵
NF & MDS are determined by the quality of the signal chain and the venerable FT-818 is not a star in that department. Under exact same conditions (antenna, cable etc) a very weak signal readable from IC9700 would not be copyable from FT-818. 2/7
The comparison of NF & MDS of IC705, IC9700 and FT-818 assumes favourable IMD performance of the FT-818 with a 500 Hz filter. In the field this is rarely true and even less so with a passband of 3 or 2.7 kHz in SSB. 3/7
Oct 17, 2022
When operating SAT-portable, the automatic Doppler correction of 2xFT-818 can be conveniently performed by a #RaspberryPi Zero W running #Gpredict and #Hamlib. Proven solid and reliable in DXing over the last 2 years. Read on for details 🧵