Sorry to interrupt, I know you are slapping another set of graphs together for the next post. That 480Mhz USB noise spike - does it go away (or at least attenuate) if you use a good shielded short USB cable in between the radio and USB hub youβre using?
Very good points and findings with the shielding.
HA! I hadnβt thought of that, Itβs a USB3 hub with a very short premium cable to my computer. Good thing to check though. Maybe Iβll put the SDR on a short extension to get it away from the hub.
It didnβt make too much difference in my own tests sometime back no matter how well shielded or how many toroidals I slapped on, but curious what you come up with while youβre setup and on a roll. Oddly enough, mine show larger spikes at 960Mhz than 480. I canβt explain that other than it must be that plate in my head. 
Filters:
Since the filter tests are done with the FA 1090 antenna on the roof and require the splitter to get simultaneous readings I needed to get a baseline with the splitter.
The splitter is actually 2 3-way splitters on the same board. The top 3 connectors are one splitter and the bottom the other. I terminated everything to make it as quiet as possible.
So⦠First, a baseline with the splitter and FA 1090 antenna and no filters at all. Both SDRs are the shielded NESDRs and I verified that they have the same response curves.
With the addition of an unshielded RBOX 1090 filter:
And the shielded RBOX 1090 filter:
Now hereβs the FA 978-1090 filter:
Antennas tomorrow maybe. If the weather cooperates.
Letβs seeβ¦ High speed 480 mbits/s would be 240MHz and the 4th order harmonic of that would be 960MHz. Depending on the length of the cable, that could be a nice 1/4Ξ» antenna
Iβll be testing the USB stuff after lunch. Iβll also throw a VHF-UHF antenna on the SDR and wave it over the hub and cables to see if it picks up anything.
Thereβs just too much ambient crap to do any meaningful USB interference analysis. Butβ¦stupid meβ¦ Iβve got a bunch of copper screen in the garage so maybe Iβll make a Faraday cage.
Just a thought - the splitter will have a common ground and (depending on the isolation) allow noise generated by one dongle to enter the other.
Could you repeat this scan with: a) both dongles powered, b) one dongle unpowered (but otherwise identical)
I think I understood. If I didnβt I can easily repeat any test.
NooElec NESDR NANOv3 Shielded Splitter (Left) Dummy Load
NooElec NESDR NANOv3 Shielded Splitter (Right) Dummy Load
NooElec NESDR NANOv3 Shielded Splitter (Left) (Right Unpowered) Dummy Load
The blue reference trace is while the right side is still powered. Yellow is the current measurement.
Same setup as earlierβ¦
@Nitr0 Turns out the spike at about 480Mhz was actually at 476.something. Turns out there are UHF transmitters about 3 miles south of me that I forgot about. I also forgot to check the RF TV channel assignments instead of the logical ones.
Anyway, I created a Faraday cage which helped a lot. I was able to remove the copper foil shielding from the SDRs (which helped their heat dissipation) and get the same results.
I also scored a NooElec LNA which Iβll be testing to see if using the LNA gives better results than using the SDRβs amp.
OK, here we go. A Cage Match betweenβ¦
The 3 antennas are mounted such that their main elements are about 1m above my roofline. 3 RG-142 downleads, 3 FlightAware 978-1090 filters, 3 NooElec Nano V3 SDRs, 49gb gain. The SDRs and filters are in a Faraday cage.
Iβm using a modified dump1090/view1090 that displays RSSI and Distance summaries and the stats were captured within 0.5 seconds of each other.
V-Lad
Aircraft: 59 RSSI: Max -16.2+ Mean -28.1 Min -35.8- MaxD: 206.3nm+ βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
The Mutant Spider
Aircraft: 57 RSSI: Max -14.1+ Mean -27.4 Min -35.4- MaxD: 192.8nm+ βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
The Big Green Stick
Aircraft: 75 RSSI: Max -10.1+ Mean -25.2 Min -35.6- MaxD: 253.3nm+ βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
I think we have a clear winner!!
Thatβs awesome! The only suggestion I would make would be to now try switching the cables at the antennas to prove that the advantage wasnβt created by that particular cable/filter/SDR combination. Basically you would be isolating the antenna itself as the variable.
Thoughts?
Yeah, I should have stated that I swapped SDR and filters around to make sure that they were all equal. The downleads I tested right after I made them and again before I lashed them down and raised the antenna platform.
Forgot to mention, I have an Airspy R2 due in tomorrow so Iβll update the SDR post above with some graphs and Iβll do some aircraft stats after i read through the HOWTO for the Airspy and dump1090.
Nice!
Scientific method, FTW!
Great!
Well done, and in a very methodical & scientific way. 
That is what I have always said that our DIY antennas do NOT outperform Flightaware antenna, and V-Stub is somewhat better than Spider, but still less than FA Antenna. My indicative ratings based on my field tests / plane count were Spider 60%, V-Stub 70%~80%, and FA Antenna 100%.
My FA antenna 100% and my DIY CoCo 100%
That is great.
You are one of the few lucky ones who could make a CoCo right.
The dimensions, details & photos of your CoCo deserve to be posted in this thread:
Β
