FlightAware Discussions

RF Scan of Various Combinations of Dongles, Filter, and LNA

See this also:

Generic DVB-T (Black), No Filter

 

Generic DVB-T (Black) + RB24 Filter (Blue)

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We’ve been doing a bunch of testing in other threads and @abcd567 kindly offered this thread to continue various testing efforts.

My plan was to get several antennas up on the roof this week and to start doing some comparisons but I soon realized that I need to get baselines on some pre-antenna components before testing any antennas. Given my high-RF interference environment I decided to start with making a few things…


From the left…

  • FA 978-1090 Filter
  • RBOX 1090 SDR. Unshielded on top, shielded on the bottom.
  • RBOX 1090 Filter, Unshielded on top, shielded on the bottom.
  • NooElec NESDR NanoV3 SDR, Shielded on top, unshielded on the bottom.
  • gtj0’s super-duper dual 3-way resistive delta shielded splitter.

Why the shielded versions??? Heh, here’s why…


That’s my ambient environment with an unshielded NESDR, 33db gain and the FA 1090 antenna on the roof.

First let’s talk about SDRs…
The following graphs were taken AT THE SAME TIME (well almost since I had to get screenshots a few seconds apart). I had 4 SDRs connected and 4 Spektrum windows open. Aso all settings were the same… sweep 24.0 - 1200.0 MHz, 200Hz bandwidth and 33db gain.

Here’s an unsheilded RBOX 1090 (with built-in 1090 filter) with a dummy 50Ω load:

and here’s the shielded RBOX:


It’s actually kinda weird because the VHF interference is gone but the UHF grew a bit.

Here’s the unshielded NESDR (no built-in filter) with the dummy load:


That’s MUCH better.

and here’s the shielded NESDR:


That’s very nice. Going forward, I’m going to use the shielded NESDRs.

Next post… RBOX 1090 Filter vs the FA 978-1090 Filter.

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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 you’re using?

Very good points and findings with the shielding.

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HA! I hadn’t thought of that, It’s a USB3 hub with a very short premium cable to my computer. Good thing to check though. Maybe I’ll put the SDR on a short extension to get it away from the hub.

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It didn’t 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 you’re setup and on a roll. Oddly enough, mine show larger spikes at 960Mhz than 480. I can’t explain that other than it must be that plate in my head. :slight_smile:

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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.


You can see that the splitter itself still leaks a little but the filters will be between the splitter and the SDRs.

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.


Pretty ugly.

With the addition of an unshielded RBOX 1090 filter:

And the shielded RBOX 1090 filter:


It helped a little.

Now here’s the FA 978-1090 filter:


Still a little VHF leakage but quite acceptable!

Antennas tomorrow maybe. If the weather cooperates.

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Let’s see… 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 1/4λ antenna :slight_smile:

I’ll be testing the USB stuff after lunch. I’ll also throw a VHF-UHF antenna on the SDR and wave it over the hub and cables to see if it picks up anything.

There’s just too much ambient crap to do any meaningful USB interference analysis. But…stupid me… I’ve got a bunch of copper screen in the garage so maybe I’ll make a Faraday cage. :slight_smile:

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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 didn’t 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 earlier…

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@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 I’ll be testing to see if using the LNA gives better results than using the SDR’s amp.

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OK, here we go. A Cage Match between…

  • V-Lad the Impaler (@abcd567’s V-Stub)
  • The Mutant Spider (@gtj0’s 1/4λ Spider with doubled radials)
  • The Big Green Stick (The FlightAware 1090 MHz ADS-B Antenna - 66 cm / 26 in)

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.

I’m 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+
───────────────────────────────────────────────────────────────────────

The Mutant Spider

 Aircraft:  57  RSSI: Max -14.1+ Mean -27.4 Min -35.4-  MaxD:  192.8nm+
───────────────────────────────────────────────────────────────────────

The Big Green Stick

 Aircraft:  75  RSSI: Max -10.1+ Mean -25.2 Min -35.6-  MaxD:  253.3nm+
───────────────────────────────────────────────────────────────────────

I think we have a clear winner!!

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That’s awesome! The only suggestion I would make would be to now try switching the cables at the antennas to prove that the advantage wasn’t 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.

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Forgot to mention, I have an Airspy R2 due in tomorrow so I’ll update the SDR post above with some graphs and I’ll 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. :+1:
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%.

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My FA antenna 100% and my DIY CoCo 100%

That is great. :+1:
You are one of the few lucky ones who could make a CoCo right.

@SweetPea11

The dimensions, details & photos of your CoCo deserve to be posted in this thread:

Coco (Coaxial Collinear) Antenna - Tips & Tricks