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by ab1jx
Tue Apr 16, 2019 10:33 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Hi ab1jx , I guess running Apache will up the load when active - I must say that I just connect to dump1090_mutability's internal server (after setting openstreetmap as the map tile source- still get google artifacts though!) at ip/dump1090/gmap.html and let my desktop do the heavy lifting. I've no...
by ab1jx
Tue Apr 16, 2019 9:06 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Yeah, it's not bad. I just had some OTG adapters show up in the mail so I moved the dongle and antenna over to a ZeroW that wasn't used much. I'm running just dump1090_mutability and Apache, no FlightAware or any of that. Standard internal wifi adapter, running on one of 2 jacks on a MonoPrice 2.5 ...
by ab1jx
Tue Apr 16, 2019 6:37 pm
Forum: Troubleshooting
Topic: Does cloning an SD clone the Pi's MAC address?
Replies: 20
Views: 1095

Re: Does cloning an SD clone the Pi's MAC address?

It seems unlikely that the DHCP server only uses 3 bytes to match an IP. Systemd has made the role of /etc/machine-id (a D-Bus thing) more prominent, perhaps your DHCP client uses that ID when it talks to the server. Of course, there are special motions to go through in case you want to re-generate...
by ab1jx
Tue Apr 16, 2019 5:50 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

HI abi1jx I wouldn't worry too much about the loading on a Pi-zero - this is mine currently:- I'm using a 10Mbit enc28j60 spi ethernet adapter - note this is even fast enough to stream to the "full" SBS data to another machine running "socket3003" although I was not running piaware at the time so n...
by ab1jx
Tue Apr 16, 2019 1:27 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Good job stuffing wires. I never used SMA for much, then I discover I've got a couple right beside me, not in use. My dongles so far have MCX connectors but I have a couple cute little center loaded antennas I bought as external antennas for a Huawei cell modem that have SMA on them, adapted to some...
by ab1jx
Mon Apr 15, 2019 7:49 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

[ I found that putting it on top of a metal cabinet (about a foot above) greatly improved it. I think it's moved the radiation pattern upwards a little, giving more gain over my surrounding hills where it's useful. My message rate jumped about 30% instantly when I put it there. Before that it was j...
by ab1jx
Mon Apr 15, 2019 7:35 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

I had a look, the PLUS version has the 1090 MHz filter. I think I would go without the filter, as the receiver can be used in different directions, so I start probably with a broad-range receiver. Some cell phone stuff and the "little big city" close by here, too... How do you connect your handcraf...
by ab1jx
Mon Apr 15, 2019 5:49 pm
Forum: Troubleshooting
Topic: Does cloning an SD clone the Pi's MAC address?
Replies: 20
Views: 1095

Re: Does cloning an SD clone the Pi's MAC address?

Interesting. I wrote the MAC address from the upstairs one on paper, brought it downstairs and compared, last part is different. So the Android DHCP server is only looking at the first (manufacturer) part of the MAC. That seems like a big security hole. And for anybody with a bunch of identical hard...
by ab1jx
Mon Apr 15, 2019 4:22 pm
Forum: Troubleshooting
Topic: Does cloning an SD clone the Pi's MAC address?
Replies: 20
Views: 1095

Does cloning an SD clone the Pi's MAC address?

I don't care about the MAC address, except my DHCP server (Android phone) puts them both on the same IP address, which doesn't work very well. I cloned the SD in my upstairs Pi and put it in my downstairs Pi. All of a sudden the internet seems terribly slow. But only on the Pi, my phone and laptop a...
by ab1jx
Mon Apr 15, 2019 4:01 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

I have 2 of these https://www.nooelec.com/store/sdr/sdr-receivers/nesdr-mini-rtl2832-r820t.html which come with an antenna for $18.95. I've also got a cheaper one that was about $12. And one under $10 still in China on its way. All with antennas and remotes for DVB-T. (There's no DVB-T here in the U...
by ab1jx
Sun Apr 14, 2019 4:45 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

I can't find it, I'm ready to call it a wrap and build it. I'm sometimes hitting the odd state where the radiation pattern is a ball and useless. This turned out the way I expected. as_planned_geom.gif I can't rotate it any way I want, but there are the top (or bottom) collinears on the right and le...
by ab1jx
Sat Apr 13, 2019 6:38 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Oh, writing antennas in C is fun. Mirror the Sprut antenna, the impedance is too high. So wire 4 of them in parallel to bring it back toward 75 ohms. Except that didn't quite work, NEC says 5.88010E+06 now for the impedance, how can that be? The radiation pattern looks reasonable. Maybe I missed and...
by ab1jx
Sat Apr 13, 2019 2:54 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

OK, here's my tin can collinear I built a couple years ago from the drawing on Sprut's page. I didn't spend any money on it, just used what was kicking around. 1090_sprut_collinear.jpg To start make a big clearance hole in the bottom of the can, but not so big your insulator won't cover it. The tria...
by ab1jx
Fri Apr 12, 2019 4:25 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

It's too long for ADS-B on 1090MHz. You need to trim it down to 68mm. Rather than trim it down, if the tip comes out, just cut a new tip out of some kind of wire (paper clip straightened out?). We have some interesting stuff in the 850 MHz range https://www.radioreference.com/apps/db/?sid=736 so yo...
by ab1jx
Fri Apr 12, 2019 2:31 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

I'm trying (not very hard) to find out what a Franklin antenna is but I think it's just a collinear, and it was used for AM broadcast (650 KHz - 1.6 MHz). Franklin: https://www.oldradio.com/archives/stations/sf/radio019.htm It was apparently a 2 element collinear. Which at that frequency is about al...
by ab1jx
Thu Apr 11, 2019 6:35 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

This is what I was thinking of about baluns. This is from the 2009 ARRL Radio Amateur's Handbook. A balun can be made using coax cable but only for specific frequencies since you need to use 1/4 or 1/2 wavelength and that corresponds to a single frequency. In this case 1090 MHz is all we want anyway...
by ab1jx
Thu Apr 11, 2019 12:28 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

I was playing with antenna ideas (that's why I got my ham license after all). I modeled Sprut's collinear in NEC, I don't remember what the gain is, about 4 db I think. But the termination of the bottom is sort of an ugly solution. So I thought what happens if you just mirror the top part, and it lo...
by ab1jx
Tue Apr 09, 2019 6:11 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

This one I posted on Facebook. I'm on my laptop, the dongle's on a Pi. I'm getting it over wifi from the Pi across the room. It's not right on my phone though, some screen size issue. Maybe it's an Android Firefox issue. I don't see the map on the phone, maybe it can't do CSS layers. It works on a K...
by ab1jx
Tue Apr 09, 2019 5:02 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

OK, I installed it on a Pi, and I don't have the ugly extra lines. Picture tomorrow when I bring up my adsb antenna. Quite efficient, I see about 15% CPU usage on this Pi 3B. From my notes: Having given up on the debs (they built but wouldn't install because I once had dump1090-fa installed). Get th...
by ab1jx
Tue Apr 09, 2019 1:23 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Works better when the antenna isn't lying on the floor. But this is a laptop, I have to put it all down when I stand up.
dump1090_osm_apache2.jpg
dump1090_osm_apache2.jpg (150.04 KiB) Viewed 3573 times
by ab1jx
Tue Apr 09, 2019 1:14 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

That's what I wanted really, not to spend a year reinventing Dump1090. dump1090_osm_apache.jpg This is maybe an older version that works with Open Street Maps. Just got it working, not sure what the extra lines are for or really why there are so few planes. This fork is from https://github.com/mutab...
by ab1jx
Mon Apr 08, 2019 7:05 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

If you're interested in dump1090 without Google (and there have been plenty of privacy, etc. issues with them) see https://forum.flightradar24.com/threads/10232-How-to-Install-dump1090-mutability_1-15-dev-on-RPi I haven't tried it yet. It uses Open Street Maps. The direct Github link is https://gith...
by ab1jx
Mon Apr 08, 2019 1:54 am
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

Having fun. I don't think the ads-b designers had working in C in mind so there's this 112 bit binary number and sometimes you seem to need odd groupings of bits. Which can change depending on earlier bits in the message. So I treated each hexadecimal digit individually and put them all into an arra...
by ab1jx
Sat Apr 06, 2019 10:16 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

This page http://www.radartutorial.eu/13.ssr/sr24.en.html goes into a lot of low level detail
Image

Also see https://mode-s.org/decode
by ab1jx
Fri Apr 05, 2019 10:19 pm
Forum: C/C++
Topic: Making sense of ADS-B checksums & bitfields
Replies: 52
Views: 5885

Re: Making sense of ADS-B checksums & bitfields

OK, I'm going to steal the checksum routine from dump1090, it's open source after all. I was never into checksums and crypto, all that stuff. From dump1090.c uint32_t modesChecksum(unsigned char *msg, int bits) { uint32_t crc = 0; int offset = (bits == 112) ? 0 : (112-56); int j; for(j = 0; j < bits...

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