Архив за 17.09.2016

Comparison: Four ADS-B Antennas

Comparison: Four ADS-B Antennas

Should you fork out $45 for a FlightAware antenna?
Quarter wave (2.7 inches / 6.88 cm) or Half-Wave (5.41 inches / 13.76 cm)?
How does Nooelec's 5dBi antenna perform?
To find out, I used four Raspberries with PiAware and four SMARTs (review link, manufacturer link).



Antennas tested



1. Nooelec 5dBi ADS-B antenna, $6,
2. Large FlightAware antenna, $45,
3. Telescopic supplied with SMAart, extended to half-wave on metal plane cost: $0,
4. Telescopic supplied with rtl-sdr.com dongle, extended to quarter-wave on metal plane, cost: $0.




Location



Outdoors on a first-floor windowsill, top of antennas at the same level, height above ground 4 meters, overlooking local international airport and Europe - USA flight corridor.
Same vertical plane, but not in the same horizontal location; polar plots might reflect slight positioning differences, but for all intents and purposes except serious hair-splitting, differences are negligible.

Results


Maximum range at 250 degree indicated on plots from Planefinder, all data from FlightAware.





Large FlightAware antenna was best performer, unsurprising considering its humongous size and $45 price tag. To get the most position reports, it is the antenna to buy.
Half-wave came in second, 22 percent difference in total reports received versus FlightAware antenna.
Nooelec's 5dBi high gain antenna is a solid performer for $6, 44 percent less position reports than FlightAware's significantly larger antenna.
4. Quarter wave antenna had worse performance than any other competitor. Cutting black solid antenna supplied with Chinese dongles back to an interim solution, but it's a solution nonetheless.

Draw your own conclusions, data is above.

ADS-B Testing Notes

There is a huge community out there who love anything connected with airplanes. Yours truly included, who thinks that leaning forward in St. Maarten into a departing 747's jetwash is great fun, and a good night out is listening to Approach, Ground and Tower from a hill. If you snigger, stop reading, this post is not for you.
Because ADS-B performance relies on equipment, and I do ADS-B performance comparisons, it is necessary to elaborate on setup details. This is a technical, and somewhat boring post, but required for full and absolute transparency. Furthermore, individuals (and manufacturers) might be interested in how I reached a particular result.




Back-end computing



I already had a Pi 2 and a Pi 3, on different Amperage power supplies, in different cases, with different lengths of Ethernet cable, and system variance was below 2 percent.
ModMyPi came on board and agreed to supply two identical packages (many thanks, review here), so same Pi 3 and power supply and MicroSD card and Ethernet cable could be used.


Two percent rule



Results, pro and contra, should be viewed knowing that system variance is maximum two percent.
Comparative values showing less than 2 % difference could be down to setup, manufacturing tolerances, and a host of other variables which are impossible to eliminate in a real-world environment with more than 20 individual components.
2 % figure has been achieved with two factory-fresh premium dongle sets from two different manufacturers.
Retested the main (red) ModMyPi setup with the latest v.3 dongle from rtl-sdr.com before the Pro Stick review went online, and variance was less than 1 %.


Data aggregators



All data from feeding FlightAware, because:
1) most popular with like-minded community,
2) ease of use,
3) verifiable and easy to present findings (printscreens).
PiAware version 2.1.5 used, as the latest version with WiFi support just came out, and the previous iteration works just as well. Wifi would have ben easier to setup, but
1) extra variable, and
2) placing a 2.4 GHz transmitter right next to a sensitive receiver might influence end results.
Simultaneously feeding Planefinder for range polar plots, which are much more detailed than FlightAware's.


Baselining


I planned to use chinese generic dongles as didn't want to abuse the goodwill of premium dongle manufacturers, but variance was in the neighborhood of 3-4 %, unacceptable for reliable results. Initial testing has been performed with indoor antennas and two SMArts.
These two SMArts used for baselining had to be opened for reviews and photos, so Nooelec kindly sent two factory-fresh dongles.
Rtl-sdr.com also sent two new v.2 dongles (previous generation), so I could do back-to-back comparative testing.
Neither dongle sets were opened, modified or tinkered with. Two dongle sets enabled me to double-check results and to cut time in half.
On both setups, figures differed ranging from 0.2 % to 1.7 % with same brand same model dongles over 12 hours minimum.
Dongle pair from rtl-sdr.com had 0.3-0.5 % less variance, and lowest value observed was with them, plus the SMArts are used for other experiments, consequently two previous generation rtl-sdr.com dongles will be used as comparison baselines, one in the Pi3/Pi3 and one in the Pi 2/Pi3 setup.


Splitters



Two-way splitters used, so same antenna can be utilised.
Tried and tested four-way splitters with four SMArts, and results were unreliable due to four-way splitter.


Connectors and adaptors


The bane of my existence. Imagine setting up, checking reception, and finding that no data is coming in. Power fault? Card corrupted? Antenna shorted? LNA died? PiAware reinstallation?
9.9 times out of 10, the source is a faulty connector, an F-type or SMA not fully screwed on. Or no contact because SMA Male pin is too short. Splitter is F-type, but dongles are SMA or MCX, so F-Type to SMA pigtails and adaptors from Nooelec after splitter, because they have never failed so far, and tried to use pro gear as much as possible.
Had to use homemade gear with RG6 coax and F-connectors, same length down to millimeter level.
Impedance mismatches exist, so antenna comparisons won't be 100 % accurate. I can live with that, and this fact will be noted in any upcoming review.


Coax, mounts, antennas



To keep results real and to approximate a general user's profile, two identical cables and mounts supplied with the Nooelec SMArt, RG59 50 Ohm, length 6.5 feet / 2 metres.
Metal telescopic antennas supplied with RTL-SDR dongles, extended to the first joint. Half-wave on a ground plane, which is a sweet tin, antenna bases as close as possible.
Bought and tested a FlightAware antenna, but performance improvement in range and received signals does not justify the $45 price tag compared to stock antennas on a magnetic mount.


Timeframe



FlightAware counts a new day at 0100 local time, but I can't be always up to change receivers; so I log results and do printscreens close to bedtime, double-check stations and connections afterwards.
20 or 23 hours of data collection period did not change percentage numbers due to local flight patterns.


Your results won't be the same, but will be very close



Location, antenna, positioning, weather, plus a great number of other variables mean that your ADS-B results differ. If you see 157 mile range with a receiver, don't expect that buying the same receiver and components will get you 157 mile range.
This is a comparison setup, with one singular purpose: to find out ADS-B performance of various dongles and / or antennas.
Compared findings with other enthusiast living literally on the other side of the globe, and my results for SMArt vs Mini 2 + were very close, despite significantly less position reports and shorter timeframe.


I'll always listen when you got something to teach



More dongles than I can locate, four Raspberry Pi microcomputers, professional antennas, connectors, preamps and the joint goodwill of Nooelec, rtl-sdr.com, ModMyPi, Adam, plus my purchases and time.
The more I know, the more I realise I know nothing, therefore please share your opinion, tips, tricks, any observation, here as a comment, on reddit, on rtl-sdr.com, on a FlightAware forum, or by sending an email (address in Manifesto).
Many thanks in advance, and I can't express my gratitude to all contributors who made this comparison possible, from manifacturers supplying equipment all the way to enthusiast Joes and Janes buying my books.

Avoid Rip-Offs Part 3

Part One here, Part Two here, read up if unfamiliar with RTL-SDR dongles, aim remains the same: providing an overview what not to buy or spend money on.
I'm constantly amazed by the ingenuity and sheer cheek of sellers. A generic dongle costs $8-ish from China, rtl-sdr.com's v.3 dongle covers 100 kHz to 1.7 GHz with direct sampling and costs $25 with antennas.
Just so you know.


Is this the new rtl-sdr.com dongle for three times the price?





For fairness, it comes with two adapters and small USB extension cable; also available around the 60 dollar mark elsewhere. From case and specs, it looks and reads like the latest v.3 dongle in previous case (four screws) in a different color.

BatterElec? What? For 25 dollars?



I'd be laughing if it wasn't so sad, then I started crying on Amazon UK...
$111 direct sampling receiver:



Interestingly, the same is available for $57, which is still daylight robbery, but the trend seems to be to offer these receivers at grossly exaggerated prices:



Graphics might change:





Not only "Full band" receivers, plain old R820T dongles are selling for eye-popping prices:



Save 53 %, sixty-two dollars for a receiver which can be bough for less than $10:




Just because it's small, it doesn't have to cost a lot: the following size can be bought from Nooelec here with much better specification.



Just because a dongle has an aluminum enclosure, asking 60 bucks for a product which costs $30 with 2-year warranty is a bit excessive:



The old E4000 scam is here to stay, $27 dollars.



Please, please, don't spend more than $10 on a generic dongle, or on any product which comes with a small black antenna, especially not $35:


If you want value for money, order new rtl-sdr.com v.3 dongle or Nooelec products from manufacturer, but never ever from online auction sites unless it's the manufacturer's outlet. Why? New v.3 costs $25 from rtl-sdr.com with a few extra bucks for shipping.
This is not value for money:



If you know of any more ripoffs not mentioned above, comment here or drop an email.
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