I did rtl_power on my setup and realized that I had a 1066 mhz peak even bigger than my 1090 signal.
I bought a 5.foot.usb-a extension cable and moved the FA pro stick as far away from the computer as possible. I also lined the sides and top of the shelf my computer is on with aluminum foil to make a mini Faraday cage. With both changes I had a 6 dB reduction in noise, which was gigantic.
I have 2 setups at my house and with these changes this current set up went from seeing 40 percent of the planes that my better setup (open sky) can see to 90 percent.
What was causing the 1066 mhz spike? My computer memory. Afaik the 1090 filter isn’t narrow enough to block 1066 mhz.
It may be worth a $5 trial of a 5’ USB extension cable to see if you get improved signal.
What computer are you using – a Raspberry Pi, or something else? Also, the FA pro stick is in a plastic case, no shielding (unless there’s shielding inside the case). I have a 15 ft USB cable to go from a Raspberry Pi on a closet shelf up to an RTL-SDR dongle, LNA, and antenna in the attic. Seems to work well.
I think I have a 3-ft cable between my feeder and my Airspy Mini, but I also have a few other devices on the same shelf. I hadn’t thought about interference from memory reaching that far (inverse square law and all), but I’ll set up a cage and see if there’s an improvement.
people have asked about setup. I have it running on an intel nuc. ddr4 memory.
@jimMerk2 I was thinking about a much longer USB cable but I was worried about voltage drop over 15 feet. I guess that isn’t an issue? I know with unstable or too low voltage you can drop signal or destabilize MLAT.
@abcd567 it wasn’t plugged into the computer directly – I had a 1 foot usb extension cable, but it was laying right next to the computer. So that’s why I got the 5 foot one to get it much further away. I killed a FA Pro stick in the past plugging it directly into the computer – too much tension from the USB part being fixed and the coax cable on the other side. The USB extension cord gives it some play. I have Ultrafeeder running as a Podman (Which is basically docker but not docker)
@fhmiii See what happens. Do a rtl_power before and after and see if there’s meaningful differences. If you feed the CSV into gemini, chatgpt, etc it can make you a graph of the data.
I was just going to let it run and see if the average number of reported positions increases. I’ve played around with settings and data dumps and all that over the years, but I’m just not a Linux guy. So a simple, “Do I get more positions?” is all I’m interested in.
I grabbed the gain (-g) from graphs1090 since I have it on autogain. I think it’s actually 28.something but it’s smart enough to move it to the right one or one close to it.
change -d if you have multiple devices like a 1090 and a 978.
I have -e set for 15 minutes but change it to what you will.
perfect. I got a cable matters cable b/c they seem a bit higher quality/have decent shielding.
and just because I bought some ferrous chokes and put them at the USB-a computer end since they are cheap. (they stop transmission of stuff via the external part of the cable). I figure they can’t hurt. I actually put them on everything – my antenna where it inputs the stick, the USB power supply cord for the bias T, as well as the USB extension cable. Probably overkill. (Well, more than probably I’m sure…)
Which ferrous chokes do you use? The small clamp-on type or the big ones that you wrap the cable around?
BTW, on the long USB cable (16.4 ft), I tried rtl_test and noticed that occasionally I do drop USB samples at 2.4e6 sample rate. When I previously have run rtl_test with the RTL-SDR dongle, it was always plugged directly into the computer and never lost samples at 2.4e6. Course, 2.4e6 rate is kind of important because that’s the rate that dump1090-fa uses. So there is some hit to performance with the long USB cable. However, apparently it’s good enough for reliable MLAT.
Wonder if a powered USB hub would help. I know the power is supposed to be constant no matter if it’s computer or powered hub but my guess is the powered hub may solve this.
The effectiveness of CMCs (Common Mode Chokes) using ferrite toroids, and clamp-on types, vary from mix to mix. The mix is important because of the frequency (range) they are supposed to suppress. In addition to the ferrite mix, the cable type and number of turns used matter.
While I’ve never used one at this frequency, a ground-loop breaker (a.k.a. Galvanic Isolator) could be an option as well.
Both CMCs and ground loop breakers are easy to build. Lots of info on how to build them on the net.
Yeah, I’ve bought several things from ONN and they were all good.
Regarding RFI on ADS-B 1090 MHz, I notice that when some LED lights are turned on, it just about wipes out distant FM stations. I gotta believe that 1090 MHz is also affected. If this is the case, probably common mode chokes are needed on these light fixtures.
I don’t know if LED generated RFI will go that high (1090 MHz), never looked into it. I do have an FM DX autologger feeding RabbitEars and nothing bad has been noticed.
LED bulbs can be nastier on HF. I use dollar store LED bulbs and so far all is good. Before the switch to dollar store bulbs, I used Walmart house brand LED bulbs, all good as well.
My preference, and first try, is to have the CMCs on the computer, RX, and antenna sides before going to other places.
It doesn’t need to. There are plenty of other freqs inside - the crystal typically runs at 28.8MHz from which the LO is generated is a great place for noise to get in.
