u/switch161

I don't want to shame any dev that puts out code that works and brings people joy. But I will definitely have a giggle when I notice something like this:

r = rtlsdr_read_eeprom(dev, buf, 0, EEPROM_SIZE);
dev->force_bt = (buf[7] & 0x02) ? 0 : 1;

This is in librtlsdr (blog mod) rtlsdr_open and makes sure that when you set a certain bit in EEPROM it will always turn on the Bias-T for you and not allow you to turn it off.

Pretty nice, but wait a second...

Why are they reading the whole EEPROM for 1 bit?

I checked, there's no reason.

Then I patched it out and tested with time rtl_biast -b 0:

Unpatched: 1.12s

Patched: 528.12ms

Now rtlsdr_open setups a lot of stuff, so I can understand that it takes a while. But about half of that time is wasted.

After all they're reading 256 bytes of EEPROM. That's one I2C write, and one I2C read per byte, delivered as USB control command to the device.

Fortunately for us nobody is calling rtlsdr_open in a hot loop. Right?

I recently saw someone on r/Fedora asking how long it's good to have an install - theirs being ~600 days old.

$ cargo run -- days
2610

That's just over 7 years :3

I'm curious how long some of you have had your OS installed.

TL;DR: Never done satellites before. Botched together an antenna to receive ARCTICSAT-1 with partial success.

I saw this morning that people were receiving SSTV with adorable cats. I've never tried to receive satellites before, but always wanted to. And I can't say no to those cats!

So I checked and saw that there would be a pass at 20:00 UTC over Central Europe, so I wanted to give it a try.

Now, this is not my first antenna, but my other one is a stove pipe for 1420 MHz and I also have a junk audio cable on my wall for HF. I decided to try to build a Slim Jim, because I don't have any cores to wind transformers, and the slim jim is impedance matched. I also looked into other matching methods this week and the offset feedpoint with a stub seems like a good way to test my knowledge.

First attempt at it failed because I didn't connect my NanoVNA correctly, thus measurements were off and I cut it way too short. Apparently you can't just chop of centimeters on an antenna like this! Who could've known? Or maybe this antenna is just too difficult for a beginner?

I gave it another try, but this time soldered the connector in place where it "should" go. The Slim Jim is a folded dipole, I only have thin (1mm) copper wire, so I fixed it to some cardboard. After some tuning I got it to be reasonable resonant on 435 MHz. Then I hung it up in my window to test. The second I opened SDR++ I saw good transmissions (CW, USB) and they had doppler shift! Checked gpredict and found out it's the repeater on the ISS. Holy, that was easy! I thought I would receive some more weather stations, not this 😄

My plan was to use the Slim Jim as the driven element of a Yagi-Uda, because some directivity surely would be good for satellites. This is my antenna!

https://preview.redd.it/1snz3r1t0l1h1.jpg?width=4128&format=pjpg&auto=webp&s=c870918370011aec497d456724cb9dc01e62a9e6

So just one reflector and director. The parasitic lengths are for a regular Yagi-Uda, but of course I didn't make the Slim Jim the right length for a Yagi-Uda. Also it's off to one side because I thought that the lambda/2-element of the Slim Jim actually has to be driven element. And that part to the right is just the impedance match. Not sure if my thinking is right, but I was racing against the clock! Also having the connector over at the right was a pain!

The SWR and impedance match was actually even better with the parasitic elements. With the Slim Jim you're supposed to move the feed point to adjust impedance, but I didn't want to resolder the connector, so I just made it slimmer 😃 My thought was that since it was a bit on the inductive side it needed more capacitance, which you can get my moving elements closer (I think). It worked well. Also duct tape over the stub did something, and for me it worked out.

Okay, so now I'm sitting in my garden at 20:00 UTC and the app I have tells me the overhead pass will be at 21:00 UTC. I messed up and at 20:00 UTC it's over Eastern Europe, probably not visible behind neighboring houses. Well I'm gonna try.

https://preview.redd.it/64s5x5bh1l1h1.jpg?width=2322&format=pjpg&auto=webp&s=4802dc10bade459bda4486941cd8089d67f2da3c

(Ouch my arm hurts from holding this)

I got lucky and FO-29 was also just overhead. At this point I'm not listening and just recording baseband, trying to aim at FO-29. ARCTICSAT-1 is somewhere behind bushes, but I did see it in the waterfall!

https://preview.redd.it/hi56iq572l1h1.png?width=1918&format=png&auto=webp&s=3f5b44eeb53a615de7ba1071694181924cfa4a2b

Once I'm back inside I check the recording and there's plenty of chatter on USB - doppler shifted. So that's from FO-29. And at ARCTICSAT-1's frequency there's FM modulation that sounds like SSTV! I didn't even aim at it and it was so low.

I go back and wait for the next pass at 21:00 UTC. This time I will aim straight at it. There's a signal, but it doesn't look like FM. I think my antenna got out of tune. Well it's late and I will take this first adventure into amateur satellites as a win! 😄

Well, I would have tried ARCTICSAT-1 again tomorrow, but if I'm not mistaken it's already dead 😿

PS: That SSTV is probably too choppy to decode, right? I tried QSSTV, but can't make it work. I might try my own decoder at it at some point, but that decoder isn't finished yet.