Thursday, 1 December 2016

Thumbnet N3 First and Final Impressions

I was really looking forward to the N3, and got the review sample on Monday.
Started with noise profiling, which looked promising:



Proceeded to do noise profile with a switched mode supply, as it was the only one available, but figures and graph looked almost identical.
Did ADS-B testing for 36 hours, N3 had 4 percent more position reports than an rtl-sdr.com v.3.

Emailed Thumbnet for voltage reguriments, got the following answer, quoting:


Recommended power supply 5v regulated +/-10%
Minimum supply 4.5v
Maximum ” 6v (recommended)
Although it will tolerate up to 10v for short periods
(the limit is heat dissipation in the LDOs and the 10v rated
dielectric of the decoupling caps)
Never exceed 10v
NEVER apply a reversed polarity supply.
Damage may result to the N3 or (through overcurrent) the power supply circuits

I did test that and was happy that the N3 took four 1.2 rechargeables, and 4 regular AA batteries. I can only assume, because there was no feedback from the dongle.
Onto noise profile with batteries last night, all is well, then a blackout, laptop and two screens gone. I managed to massage laptop back to life, but as it stands now, one of the USB bus seems completely gone, I'm down to two USB ports, happy that the motherboard seems intact.
I presume the N3 is smoked as well, won't risk anymore by trying with the remaining USB ports.
It is entirely possible that it was my fault, but I checked power leads this morning with a clear, un-panicked head and all was well.
I wished to do further testing, then looked at the N3 this morning with such hatred I'll simply send it back.
I don't know the reason why I had a blackout, why half of my laptop smoked away, an event that has not happened with 20+ other dongles and countless accessories over the last three years. And frankly, I don't care, because the equation is no N3 = no risk.
I wish Thumbnet good luck with the N3.
Update 1: Thumbnet is very supportive with this fault, I am awed by their customer service. I'll add more info as is comes in, this moment, I truly don't know what could have caused a blackout.
Update 2: Went through setup with a fine-toothed comb, maybe wires inside power connector caused fault. Thumbnet is the definition of "concerned", on the ball. From what I've seen and think, the N3 will be great when Thumbnet adds self-protection to the N3, like overvoltage, polarity and short-circuit protection. Until then, I won't touch an N3.
The possibility of an RTL-SDR dongle wrecking a computer never came up before:

Damage may result to the N3 or (through overcurrent) the power supply circuit.
rtl-sdr.com v.3 has fuse, and I've never had issues with any other equipment. And I test lots of gear.
I have nothing against Thumbnet or the N3, in fact, I hope they will recall all shipped units and make a new one with proper protection, and at that joyful moment, we will have a great dongle, with "killer N3" strengths - build quality, F connector, great data performance and silky audio. The N3 now is a great dongle with major internal weaknesses.
New one should be a safer one. I'm looking forward to it.



Thursday, 24 November 2016

New posts: Outernet antenna and LNA at antenna

Nov 24, 2016

Been building antennas for Outernet use over the last couple of days, succeeded to get well over 3dB SNR required for downloads.

Easy homemade Outernet Antenna

A truly portable a cheap - less than $1 total cost - antenna.



Also did some more tests of the Pro Stick Plus - versus other receivers and with different antennas.

Enjoy.

Sunday, 20 November 2016

The wait is over - Thumbnet N3 shipping

I've just got the following email from Wade from Thumbnet:

"Hello Akos.

I got your N3 production unit out yesterday.

(...)

Feel free to review, write and post anything you care to."

I've been drooling over the manufactuer images for a while, final product looks sweet:




I've also received more images:





Can't wait.

Sunday, 13 November 2016

ADS-B: Pro Stick Plus vs LNA at antenna

Update Nov 13, 2016: added info to images due to comment.

Common wisdom is to place LNAs at the antenna.
Let's test a FlightAware's Pro Stick Plus against Premium dongles with LNA at the antenna, with long coax cable length.
Which setup gets more reports?

Test details



- Pro Stick Plus as the highest performance pure ADS-B receiver for $21, review here,
- rtl-sdr.com blog v.3 and Nooelec SMArt as top premium dongles available now, had same ADS-B performance in a previous test,
- Janilab LNA with external power, gain set to 19 dB, for $25 incl. worldwide shipping,
- two 45 feet / 15m RG 59 Mil-STD coax into splitter, Nooelec pigtails and adapters,
- two Raspberry Pi 3 from a ModMyPi Starter Kit, so identical back-end computing, system variance less than 2%.
Antenna is a half-wave telescopic commonly available with dongle bundles, on a metal tin. Normally, I get around 20,000 position reports with this antenna and short coax lengths.
No user involvement, and no gain adjustment in PiAware.

Results

rtl-sdr.com v.3 used on Day 1, Nooelec SMArt on Day 2. Totals indicated.







Polar Plots:




Frankly, I'm just as surprised as you are, as I've only seen the results when double-checked which IP address belongs to which receiver combo.
15.17% percent more position reports with a Pro Stick Plus, which costs half as much as a premium dongle and preamp. Granted, it will be pretty much unusable for general use due to filtering, but the same 1090 MHz filter also does wonders for ADS-B reception.
Significantly less position reports than usual; other FA feeders in my area did not experience such a downturn, so the only explanation is long coax length. Minimize coax length for best signal, or completely eliminate it with direct connections.

It's only one test


Your location, preamp, antenna, cable and retina is different from mine. The "LNA at the antenna" mantra comes up so often that I wanted to see what happens for ADS-B use. That's all.
The fact is that a receiver built for a specific task with a preamp and filter, costing $21, beat a combo built for general use costing $46. Adding a filter for $20 might narrow the performance gap, but spending $66 when the same job can be done for $21 seems a bit stupid. If you can run coax to a remote location and mount an antenna there, you should be able to run Ethernet cable and mount Pi3 with PoE at the antenna. Ethernet cable is so much cheaper than coax.

Tuesday, 8 November 2016

Unavoidable

I'm writing posts at the moment, and concurrently testing lots of equipment.
This blog is supported by the following manufacturers:
- Nooelec,
- rtl-sdr.com,
- Adam,
- FlightAware,
- Outernet,
- Thumbnet,
- ebay seller novakx,
- ebay seller Janilab.

Some of the makers above offer similar products, so comparisons are unavoidable. And necessary. And the purpose of this blog.
I can't help it, so I'll tread on quite a few toes in the near future.

As a teaser:


- Outernet kit is great fun, unbelievably easy to use,
- rtl-sdr.com broadcast FM filter works quite well,
- Pro Stick Plus is astonishing, but only for ADS-B,
- LNA4ALL has a competitor from novakx, 
- FlightAware antenna still beats everything else, at a cost and size,
- homemade ADS-B antennas are great.

Plus many more, I'll try to catch up with posting, doing justice takes time. Watch this space, follow on twitter @rtlsdr4everyone for news.

Stay tuned, 

Akos


Saturday, 15 October 2016

More than half million




Thanks to readers, supporters, and everyone who believed that radio should be for everyone.


Sunday, 25 September 2016

RTL-SDR dongle generations

Sept 25, 2016


This is absolutely my arbitrary classification.



Post heavily features Nooelec and rtl-sdr.com dongles for one simple reason: they support this blog and send me review samples.
Details in Manifesto, links open in new window, tap or click images for full-screen glory.
Subscribe to twitter feed @rtlsdr4everyone to receive updates (blue button on left).


Basics



The RTL2832U chipset by Realtek, responsible for converting analog signal received by antenna into a digital form, is the same in every RTL-SDR dongle - hence the "RTL" in the name. All dongles use this chipset, irrespective of cost, size, or accessories.
I distinguish generations primarily by tuner chipset, then secondarily by additional characteristics. Exotics not generally available are not discussed.




Generation One



R820T and E4000 chipsets.



Still with us in various shapes and forms, E4000 no longer available for cheap, R820T is here to stay, because 1) warehouses are probably full of them, and 2) quite a few folks prefer its waterfall cleanliness.
Check the number of spikes in image below:



Countless eBay sellers entice customers with this chipset, often at ridiculous prices (read Avoid Ripoffs Part OneTwoThree).
Nooelec still sells the Mini, my first receiver for $19, and a smaller version called Nano for $19, and the Mini+ Al for $30 is available, looks dear until you realize that the metal case alone costs $12, and dongle comes with TCXO.
R820T is also used by the Soft66RTL3 for $40, features a built-in upconverter and band preselector; read review here before ordering one (summary: don't).
E4000 tuners are a completely different cup of tea, chipset no longer manufactured, better performance on some frequencies and with extended signal reception range. $32 buys you a Nooelec XTR with E4000

Generation Two



R820T2 chipset offers better receive performance across the tunable range - it's the recommended chipset at the moment.
Blue $8 generic chinese dongles, and all current premium dongles feature this chip.
Nooelec sells R820T2 models as well, full-size in the Mini 2 for $19, small size in the Nano2 for $20.
The R820T2 was the last technological milestone, all later developments focus on additional features (some say unnecessary gimmicks) without improving the "brain" of the dongle.
Consequently, a bog-standard R820T2 generic will be very, very close in ultimate receive performance to a premium dongle costing twice as much - those features and warranty cost.


Generation Three



TCXO, Temperature-controlled oscillators make your life easier, entered frequency is spot on, dongles don't change frequency (called drift) with ambient temperature variations.
Do you need TCXO? I was happy without it, as warm-up takes a few minutes, then drift stays the same. For example, SDRPlay doesn't officially come with TCXO for $150. TCXO is good to have, but shouldn't be a deal-breaker.



In Nooelec nomenclature, all "Plus" models come with TCXO, such as the Nano 2+ for $23, Mini 2+ for $21. An E4000 with TCXO is also available, called XTR+ for a whopping $38.
All rtl-sdr.com dongles are TCXO equipped.


Generation Three and a Half



R820T2 and TCXO with LNA on board, should be a separate category, because FlightAware's ProStick is the only one, intended for aircraft data collection on 1090 MHz, but underlying PCB is essentially a Generation Four rtl-sdr.com dongle without metal case and thermal pads.
As explored earlier, despite sold as an ADS-B receiver, it is an excellent RTL-SDR dongle at a fair price of $17.

Generation Four



Parts from TV tuner heritage eliminated by removing LED and IR tuner, passively cooling the dongle with thermal pads and a metal case.



Rtl-sdr.com offered the first dongle with this architecture, instantly establishing rtl-sdr.com as a dongle manufacturer. Great telescopic antennas supplied for $25 cemented well-deserved reputation.


Generation Five


In 2016 summer Nooelec's SMArt comes on the scene in a ground-breaking USB friendly shape for $28.



Lowered noise, quality accessories, heatsinked plus thermal pad, R820T2 with TCXO, detailed review here.


Generation Six


Further efforts to reduce noise, and adding features. Basics (R820T2 TCXO) remain the same.
Only dongle in this category is the latest v.3 from rtl-sdr.com for $25.


Addition of easy direct sampling to access HF frequencies and improvements to lower noise, plus a few other goodies such as software-selectable bias-T. Review soon.


Antennas



The easiest way to spot older generation dongles is by antennas offered.
Two common options: small, black fixed-frequency one or silver telescopic.



Always go for the silver telescopic, small black is nearly useless for listening to radio. Works as an ADS-B antenna if cut back a bit and good to check that a dongle works, but pretty much that's it.
Nooelec SMArt and rtl-sdr.com come with their own antennas, read relevant reviews for an overview.


Connectors



MCX, PAL and SMA are common.


MCX is used on most dongles, small push-in type. PAL is generally found on older Gen 1 or Gen 2 dongles. SMA is the radio industry standard, all premium dongles and SDRs use it. F-type (not shown above) is the TV cable standard in the States and widespread worldwide as satellite TV connector, but not really used on RTL-SDR dongles.
Connector type only affects compatibility with other accessories, pigtails and adapters are widely available for 2-6 dollars for various connector standards.
Some people say that PAL is inferior for GHz frequencies, I've had no problems with it, even for 1090 MHz ADS-B use. It is widespread in Europe as the standard TV coax connector.


Remote controls



If a remote is supplied, the dongle uses TV tuner architecture, and features an onboard IR receiver.
Silver remote in the image is most common, the black one is a curiosity, comes with Nooelec's XTR plus E4000 TCXO dongle.
Remotes actually work for using dongles as TV tuner for DVB-T, which is not available in the USA, but widespread around the world.


Warranty



Online marketplaces (eBay, Amazon, alibaba, AliExpress, banggood etc) generally offer 14 or 30 day warranty with sub $10 dongles, caveat is buyer pays return shipping, which can be more than the original purchase price.
6 month is standard with rtl-sdr.com dongles.
Nooelec offers two-year warranty with the Plus models.


Manufacturing quality and dependability




No exact figures publicly available at the moment, but I'd wager that 99.9% of RTL-SDR dongles are made in China. This means nothing, as the majority of consumer goods, from $1 toys to smartphones are manufactured there, but quality control varies widely.
Chinese generic dongles used to fail, but recent ones seem to tick along nicely - even when assembly standard in not up to scratch.



I recommend Nooelec and rtl-sdr.com dongles and equipment for one simple reason: they work. Yes, they cost 10-15 dollars extra, and if you're new to the hobby or money matters, $15 seems an unnecessary expense, but additional features and supplied accessories outweigh initial savings.
My experience - which seems to be shared  by quite a few individuals in the RTL-SDR community - is that Nooelec and rtl-sdr.com dongles are also very, very reliable. Even when I rarely read about equipment failure on a forum, next post is usually an update that the relevant manufacturer sent out a brand new one free of charge.


The future?



Efforts to add more customer-enticing features are underway.
Thumbnet recently announced a new receiver based on the RTL-SDR platform; called N3, distinguishing feature is external power for lower noise. Shipping around October, will cost around the $25 mark.
Demand for affordable radio receivers is increasing, but the steady supply of $8-10 generic dongles with R820T2 chipsets make introducing a new dongle with more features, or altering the underlying architecture a risky endeavour. Rtl-sdr.com pulled off this feat with the new v.3, but pretty close to the limit of what's possible on a small printed circuit board.
Size is one of the limiting factors choking further development; cramming more components into a device the size of a cigarette lighter (new v.3) or reducing dimensions (Nooelec SMArt and Nano series) is possible, but eventually, dissipating heat becomes problematic - run the new v.3 with bias-T on for a few hours to feel what I mean.



More expensive SDR manufacturers (e.g. SDRPlay above) offer larger device sizes, partially to prevent heat-induced performance degradation with a larger printed circuit board. Reduced sensitivity due to excessive heat does not affect regular listeners or dependability at the moment with RTL-SDR dongles, and purists, or those seeking the last ounces of performance always have cooling options.
I foresee the following features to trickle down or become mainstream within the next two-three years:
- software-selectable LNA: the ProStick, for $17, has a constantly-on LNA at the moment.
- filters: a constant and recurring argument against RTL-SDR dongles is no selectivity. Just like frequency drift, this will be remedied soon. The Soft66RTL3 has filters on board, which work quite well (the rest doesn't).
- software-selectable bias-T: latest v.3 offers this feature.
- upconverter: direct sampling is great, but a proper upconverter is better.
- 12 or 16 bit: higher dynamic range would be nice.
I know it's on your lips, some of the features above are found in the SDRPlay, AirSpy or HackRF. Problem is, all cost in excess of 100 dollars, and each come with unique weaknesses: SDRPlay has no bias-T, AirSpy platform isn't integrated into one box, and the HackRF is more or less on the same performance level as a 10-dollar RTL-SDR dongle (which I won't hold against it, it's not designed or marketed as a radio receiver).
We'll see. Dongle development times are shortening - barely a few months passed between announcing Nooelec's SMArt and rtl-sdr.com's v.3, and there's still potential left in the RTL platform.
What will we get for Christmas?