Thursday, 31 August 2017

Fine tuning noise floor testing methodology

A dongle's noise floor represents a value in decibels for a particular frequency and gain setting.
Measuring the noise floor of any RTL-SDR dongle is beneficial for the following:
- establishing whether any modding or attempted improvement resulted in the expected outcome,
- comparing dongles as long as the same testing equipment and commands used.
Comparisons are NOT recommended by the software developer, kmkeen on rtl_power's webpage, yet it's commonly done by reviewers, including me, as 1) numbers are easy to comprehend, and 2) resulting graphs look cool in a post.
Not being content with the accepted methods, and looking for a reliable way to test 30+ dongles, went ahead with following experiments, using the same rtl-sdr.com blog v.3 as test subject - full size dongle with thermal pads and metal case, all other dongles are smaller / lighter. Nooelec's Mini 2 / 2+ Al donges are the two exceptions, but they're far from widespread and do not ship with thermal pads, takes ages to warm up.
Equipment was two digital thermometers taped to metal case to monitor temperature changes, and the same pigtail / resistor throughout the test.
Values in Celsius.

Hot vs Cold


Assumption: a colder dongle has a lower noise floor. Fully warmed up dongle after one hour at full gain at 38 degrees, cold dongle at 24 degrees when finishing scan, 5 minute pass:




Result: depends on frequency. I listen to airband and shortwave with an upconverter, chew numbers below:



Higher up, situation is slightly reversed with a hot dongle having a slight advantage.

Reaching thermal equilibrium


All dongles need to warm up to operating temperature to be able to compare apples to apples, question is, for how long?
To find out, full gain whilst videotaping thermometers, then compiled values against time:



25 minutes is a safe bet, 30 minutes is more than enough - smaller dongles e.g. SMArt and Nano 3 reach operating temperature much faster, Nano 3 is on the ball in no time.

Time required for a scan


Keenerd recommends "It is important to let the scan run for at least 15 minutes. Any less and repeatability suffers". Fair enough, went by this advice for years, but a full noise profile (at 0-5-10-15-20-25-30-35-40-45-50 db gain) takes 11 measurements, that's at least three hours with a warm-up run. Absolutely fine for an individual dongle test, would take ages with multiple dongles.
Assumption: results do not significantly change as long as dongle is warmed up properly.
To test, 30 min at full gain, then 1-2-5-10-15-20-30 minute passes, data below (click or tap for full screen):


Full data set on demand, apart from a few frequencies, I did not see any major difference which would justify spending hours for a noise test.


Reliability and repeatability


Noise floor testing is fun, as long as testing environment and equipment follows the golden rule of comparisons: only one variable, which is the dongle used. This is impossible with multiple connector standards, then environmental and circumstantial factors will change results:
- Dongle position: even a small push on a crowded table with multiple RFI sources around skews by 0.2 - 0.5 dB. Ran multiple tests, LCD screens and especially power supplies for smartphones / tablets wreck results, the closer, the worse.
- Connectors, starting from USB port. If you replace one variable, it must be noted.
- Ambient temperature. Premium gear (SMArt, v.3, XTRs, etc) are very sensitive. Just because you can have a receiver for less than $30 in a week on the floor, do not underestimate what contents can do.

What I'll go with


Warm-up run at 50 gain for 15 minutes, v.3 was within 2 degrees of operational temperature by this stage.
Secondary at 45 gain for 5 minutes.
Tertiary at 40 gain for 5 minutes. 25 minutes elapsed, more than enough, apart from ADS-B nobody uses dongles at 40 dB on the slider anyways.
Measurements at 35, 30, 25, 20, 15, 10, 5, 0 dB gain for three minutes each.
Total time: 49 minutes for one dongle.

I know nothing


Agree? Disagree? You know a better way? Know more than I do? Help me, and many others, contribute, comment, share your wisdom.
I want to hear from you. Let me, and countless readers know how to do better.
No man is an island.

Tuesday, 29 August 2017

Group ADS-B test: 19 dongles

19 RTL-SDR dongle variations tested with identical Raspberry Pi 3 based ADS-B stations, sharing the same antenna and filtered preamp.

Disclosure


Post features my purchases and manufacturers' review samples, couldn't have done this comparison without support many thanks!
Links open in new tab, maker, main distributor, or Amazon affiliate links given to check at-door cost, do your research to save money.
Images go full screen when clicked or tapped, more info on testing environment here, my approach in Manifesto.
Subscribe on Twitter @rtlsdr4everyone with the blue button top left of screen to get notified of updates and new posts.

Tested and works


Approximate prices for bundles as of August 2017, from left to right:



1. Nooelec Nano: unavailable from Nooelec or Amazon, occasionally shows up on eBay. 
2. Nooelec Nano 2+ : $23, manufacturerAmazon USA.
3. Nooelec Nano 3: $33, manufacturer.
4. Nooelec Nano-P: $24, Amazon USA.
5. Nooelec Mini: $19, manufacturerAmazon USA.
6. Nooelec Mini+ Al : $30, manufacturer.
7. Nooelec Mini 2: $19, manufacturerAmazon USA.
8. Generic R820T2: $10 or less from eBay, don't pay more.
9. Nooelec Mini 2+ : $23, manufacturerAmazon USA.
10. Nooelec Mini 2+ Al: $23, manufacturer, Amazon USA.
11. Nooelec SMArt: $27, manufacturerAmazon USA.
12. rtl-sdr.com blog v3: $25, manufacturer, Amazon USA.
13. FlightAware Pro Stick: $17 for receiver only at Amazon USA.
14. FlightAware Pro Stick Plus: $19 for receiver only at Amazon USA or $25 worldwide from rtl-sdr.com store.

All dongles are used with the exception of Nano 3 and unmodded, exactly as you'd find them in the envelope.

Tested and doesn't work


Incapable of receiving 1090 MHz aircraft signals, no matter what:




E4000 chipsets: Nooelec XTR+, Outernet (discontinued), SMArt XTR and SMArTee XTR. E4000s have a gap at 1090 MHz, this fact is clearly stated for new SMArt XTRs.
EzTV 645: refuses to cooperate due to FC0013 chipset, no surprise there.

Testing rig


Two Raspberry Pi 3s from ModMyPi (Starter Kit reviewshop), antenna splitter into Uputronics 1090 Mhz Filtered Preamp (reviewEurope shopUSA distributor) to get as much data as possible in the shortest time, 6 feet / 2m 50 Ohm RG-58 coax from a Nooelec SMArt bundle connected to a FlightAware antenna (Amazon USAcontributor comparison vs other pro antennas).
Data collection period at least 20 hours, performance judged by total position reports according to FlightAware, ranges and maps from planefinder. Guide how to use both here.
Reliability was 100% with all components, unplug power, switch dongles, plug in power.
Personal comments dot the text in italics, as I love each and every dongle in the arsenal for one or two (3,4,5...) particular reason.

Results are relative

Update 1:
Two dongles tested on the same day to find out which one performs better. Consequently, Totals are only valid between two dongles, as they change due to traffic density day to day - see SMArt vs v.3 below as an example.

Calibrating


Establishing a baseline was necessary to check whether testing rig performs as it should.
Two rtl-sdr.com v.3 for four consecutive days to see day-to-day changes, 0.78%, 0.90%, 0.8%, then 0.57% difference in Totals.

Four Nooelec SMArts, one pair with 0.16 percent difference before commencing testing, retested other two SMArts midway, 0.65% between them.
Two R820T2 generics had 1.36% difference in Totals, 136 vs 140 nm maximum range.
Don't get too excited below 2%.

Perspective


At cruising altitude and speed, 5 miles more range means an extra 30-40 seconds capability, if that, to track a commercial flight at 33,000 feet doing 550 knots. Furthermore, maximum range primarily depends on antenna location, consequently I evaluate pairs based on Total received reports, but include maximums and maps if warranted. A higher Total always means better range, but only up to the point of geographical limitations.


Nano vs Nano-P


Same R820T chipset, -P denotes PAL connector standard:



Unsuitability of PAL for ADS-B pops up now and then on online forums, fortunately, this Nano-P can't read: 23.69% more Totals.

Mini vs Nano-P


Same R820T chipset, different size:



3.05 % more with Nano-P.

Nano 2+ vs SMArt


Question asked for small-space applications:



17.95% more Totals.

Nano 3 vs SMArt


Latest and smallest Nano against its big brother, with and without heatsink:



Two tests, without heatsink SMArt collected 49.70 % more data, attaching supplied heatsink lowered ratio to 43.69% and case temperature by approx. 4 degrees Celsius.



Doubt anyone will improve FA ranking with a Nano 3, designed for an entirely different purpose.

Thoughts on Nano dongles

Nano-P is only a Nano in the name, twice the size of a thoroughbred. True Nanos are small, comparatively and absolutely:



PCB surface area contributes to heat dissipation, which becomes problematic beyond a point; in envelope heatsink is advantageous and highly recommended for Nano 3, the smallest RTL-SDR dongle ever.
Know that all Nanos as designed for, and marketed as the ideal solution for space-restricted applications, all perform extremely well for their intended purpose - I had a nailgun vs hammer analogy in mind, but you get the point anyway.
For maximum receive performance, full size dongles are a must, so onto big boys now.

R820T2 Generic vs Nooelec Mini 2


Bog-standard $8 R820T2 off eBay against a seemingly identical Mini 2.



1.27% percent higher Totals with generic.

Mini Al+ vs Mini 2 Al+


Both with TCXO, both in metal case without thermal pads, chipset is the main difference:



0.44% after 23 hours is very close, safe to say both are of equal performance.

Nooelec Mini vs Mini 2


Chipset question revisited, some say the R820T2 in the Mini 2 is better for ADS-B.



2.90% more with R820T chipset.

Mini 2+ vs SMArt





7.79% more with SMArt. Despite being smaller, thermal pads for heat transfer do a good job.

SMArt vs rtl-sdr.com v.3


Top two premium general use dongles on the market.



Two v.3s and four SMArts tested, and I mean extensively:
Day one: 12.91% more with v.3, was a scorching day, 25 degrees on the Emerald Isle results in people dropping on the street from heat exhaustion.
Day two: v.3 still 8.06% more Totals on a cooler day.
Day three: third SMArt against same v.3 used yesterday, ambient temperature 10 degrees less than two days ago, v.3 3.36% better.
Day four: 3.2 % more with v.3 again:



Day-to-day differences: fourth SMArt and v.3 for three days:
Friday: 37846 / 35836, 5.60%.
Saturday: 37121 / 34414, 7.86%.
Sunday: 40262 / 37302, 7.93%.
Rtl-sdr.com blog v.3 consistently more - why? From what I can see, larger surface area for sure - I've noted that there's a direct correlation in connection with comparative performance and ambient temperature, e.g. SMArt performs better on cooler days.


rtl-sdr.com v.3 vs FlightAware Pro Stick Plus


Frankly, I didn't expect this to work, cascading preamps and two 1090 MHz filters in the signal path, buy why not?




Pro Stick Plus 16.06% more positions reported at 2145, on an already amped and filtered rig.
Reran this comparison to be on the safe side, 11.90% more over 23 hours with blue stick, map with max ranges:



Perfect day, experience being a snail humidity combined with massive fog, 213.93 nm range is best I ever got, haven't broken the 180 barrier before.
Had to triple-check, 68,908 vs 64,704, 6.49 % more with blue Pro Stick, slight advantage, but it's visible:



Why? Solve the following equation: n1+x2+42+x4 over traffic density equals what? Result = Pro Stick Plus dependably outperformed the best unamped dongle.

V.3 vs Pro Stick




16.91% more with orange Pro Stick. Did not pursue this any further, as earlier comparison showed the Plus is better on its own.

Conclusion and buying advice


Best value: $8 generics from China. Build a Coketenna, be merry for less than $10 - a $150-dollar rig won't get you 15x more fun. Or 15x more data.
Best ADS-B receiver only: blue FlightAware Pro Stick Plus. On its own, or in this test, continues to amaze.
Best ADS-B receiver only with general use in mind: orange FlightAware Pro Stick. Onboard LNA for $17 is priceless for weak data signals - if ADS-B, weather satellites, pagers etc are your game along with casual listening, get an orange FA Pro Stick.
Best plug-n-joy bundle: Nooelec SMArt. Longest supplied coax cable on the market, shortest of three supplied antennas good for ADS-B, quality in every detail - less than 1% between four dongles, need to say more? Thirty dollars for a SMArt bundle is an uncontested long-term investment in radio.
Advanced $20 receiver-only: rtl-sdr.com v.3. Hands down the best performing dongle without onboard amplification, and the discerning ADS-B enthusiasts' choice due to bias-T: adding an antenna-mounted Uputronics LNA is easy.
Zombie dongles: Nooelec aftermarket case offers unparalelled physical protection, stock on Mini+ Al and Mini 2+ Al,  fits all generics, dongle doubles as a short-range weapon against rabid dogs with two-year warranty. I always carry a Mini2+ Al when I go somewhere rough without no sit-down toilet in sight.
Small and performs: Nooelec SMArt receiver only. Nanos' size and inconvenient MCX or PAL connection standard are unwarranted when a SMArt is better in every aspect for terrestrial users.
Mobile / portable use: Nano 3. Any other dongle will run circles around it when and if numbers matter, but no other dongle attached to a mobile station or smartphone is so easy to use.

Which one would I spend my own money on?


Put my money where's my mouth is, ordered a Pro Stick Plus before publishing, well in advance preempting "Out of Stock" misery. $25 dollars / $20 euros from rtl-sdr.com (lowest price I could find for Europe delivery) is money well spent.

End of a beginning


No stone was left unturned to find the best performing RTL-SDR dongle for 1090 MHz ADS-B use; however, results reflect my location, testing equipment, air traffic density, plus many factors.
FlightAware Pro Sticks, either one, were significantly better than the best unamped dongle, rtl-sdr.com's v.3 - onboard LNA matters a lot when the objective is eking out the last ounces of performance.
Look at the whole picture: neither FlightAware dongles come with any antenna nor cable, so any bundle will be better out of the box, as they will be usable right away.
Choice is yours: Premium dongle bundles come with bells and whistles for less than $30, generic for $8 rewards with best aircraft for money ratio after a three-week wait, any Nano is an engineering marvel, a Nano-P will pass a hard-eyed customs inspection in Burma, Plus models from Nooelec assure 2-years' restful nights, and so on.
Pros and contras exist for all dongles.


Point is: buy what you feel will be good for you. Undecided between this or that, go for both, or get any RTL-SDR dongle you can afford: performance ultimately matters little, as any dongle will put a smile on your face, and that's the most important thing, much, much more than percentage differences.

Sunday, 14 May 2017

ADS-B easy antenna picture guide, testing and some wisdom

It all started in February, when commenced testing antennas with four ADS-B stations - read my struggles in the Diary. Warning: very long and detailed post.

The Coketenna picture guide details steps how to build an easy ADS-B antenna for less than $1 or from junk materials with only a knife in less than 10 minutes. Complicated measurements? No, use dongles as a template:



ADS-B Wisdom offers some advice how to optimize, monitor and upgrade a station should you wish to jump into the ADS-B hole. Remember: antenna location matters the most.



Long term testing with four stations, each with successively more advanced components, took over a month. Post only features 10 day's data, setups from $8 to $135, filtered and unfiltered dongles.


Enjoy.

Thursday, 19 January 2017

Today's Menu

First of all, the mother of all dongle comparison, testing almost all RTL- SDR dongle varieties on the market is underway, here's a teaser, right-click to download as a Full HD desktop background:



Subscribe on Twitter by clicking on the blue button (top left) to get notified of the latest updates.

Today's menu:

Line of sight: visual demonstration shows what line of sight means, useful for ADS-B and Outernet use.

USB cable quality has a profound effect on received signals, much more than you expect.

Testing Uputronics' 1090 Mhz Filtered preamp was a definitive highlight in the last few weeks.

Easy homemade beginner ADS-B antennas lists three easy-to-do antennas using supplied mount or $1 worth of coax cable.

New guide for Building an ADS-B station with a Raspberry Pi 3, concepts are the same for PC users.

In retrospect, I could have avoided the bumpy road, learn from my mistakes.

An open letter to radio manufacturers details why and how the radio industry needs to improve, right here and right now.

Traditional or software defined radio? Make up your mind after reading the post.



Tuesday, 3 January 2017

Ripoff special: Targeted Ads

Jan 03, 2016

You'll receive targeted ads as per your browsing interests, no surprise that I had the following coming up:



Up to 70 % off is the oldest trick in the book, but lets's see if the claim is true:



Wonder of wonders, Nano-P for £30.70, when it retails for £18.95 on Amazon UK.

Just don't.


Monday, 26 December 2016