Monday, 19 September 2016

Direct Sampling vs RTL-SDR with Upconverter vs SDRPlay for HF

Let's hear the difference between a generic chinese RTL-SDR dongle modded in 5 minutes, an RTL-SDR dongle with upconverter, and an SDRPlay on frequencies below 30 MHz with 20 foot of wire.
Background information and testing notes in the Manifesto, underlined text are links, bring you to a new page in a new window. Click / tap images for full-screen glory.


In the video



Direct sampling modded generic chinese RTL-SDR dongle: $8 from eBay, push a wire through a hole (detailed picture guide here link), connected to an outdoor wire.
Premium RTL-SDR with Upconverter: Nooelec SMArt (review link) with Ham-It-Up v 1.3 Upconverter (review link) in a metal case, yours for ~80 dollars from Nooelec (manufacturer link).
SDRPlay: All-in-one DC to daylight software defined radio receiver. $150 or thereabouts (review link, manufacturer link).


Alternatives



The AirSpy platform consists of a receiver and an upconverter. Can't comment on performance as I don't have one. Reviews praise excellent performance (such as this one, link).
Chinese all-in-ones: most of them are rip-offs, direct conversion receivers in nice wrapping (post how to avoid them link). Some of them feature an upconverter for 40-50 dollars, not tested so can't comment - I won't spend 50 dollars on a product with 30 day warranty when I've seen what's inside a chinese dongle (see images here, link).


Software choices and testing methodology



SDRUno for SDRPlay, SDRSharp for RTL-SDR with upconverter and direct sampling, because:
1) beginner RTL-SDR users will likely start with SDRSharp, so a familiar software environment can be presented,
2) two separate programs let me to use SDRPlay's dedicated software on one screen, and SDRSharp for RTL-SDR based dongles on other screen,
3) SDRUno requires a restart when removing a dongle, and I'm not immortal.
Hunting for signals: Find a station with SDRPlay, adjust gain and LNA for best audible audio, record, find same with RTL-SDR based setup, adjust settings for best audible audio, record, find same with a direct converter, record. Or the other way round. Switching between receivers took less than a minute.
I'll be the first to admit that I'm nowhere near proficient with either SDRSharp or SDRUno; nobody is, save the guys who's written the software. I simply adjusted available settings to enjoy a particular broadcasting station, then recorded results.
Broadcasting stations only due to availability, plus moral issues with ham SSB or CW conversations.
Personal moaning: how much I hate SDRSharp, especially after this: constantly crashes. Wanted to record more, but given up after two days and the umpteenth computer restart. SDRUno was stable as a rock.


Testing setup



Two 20 foot / 6.5m multi-stranded 1mm diameter copper wires strung from a first-floor window.
SDRPlay and RTL-SDR with upconverter sharing the same antenna with the SMArt's supplied antenna cable and mount, antenna wire wrapped around base screw.
Wire for direct conversion dongle wrapped around RG6 coax center conductor on one end, other end of center conductor goes directly into direct sampling RTL-SDR dongle.
Above antenna configuration takes less time to sip a cup of tea: throw wire out from a window, wrap antenna wire around center conductor, connect other end to receiver. Done.
Yes, grounding, capacitors, antenna isolation, better antenna to receiver connection, metal shielding, devoting time to software intricacies, a dedicated antenna tuner, an LNA4HF, bandpass filters, soldering, living in the Australian Outback, a T2FD, inviting NASA radio engineers over to dinner and listening to suggestions, a better sunspot cycle, plus countless other variables will undoubtedly increase receive performance.


The video



First: Direct sampling modded generic chinese dongle (frequency in SDR#), then
Second: Nooelec SMArt with Ham-It-Up v1.3 versus (125+frequency in SDR#), then
Third: SDRPlay (frequency in SDRuno).
Repeat.
Same stations, displayed frequencies are off due to drift and no TCXO in generic dongle and SDRPlay.



If doesn't play here, copy-paste the following YouTube link:

https://www.youtube.com/watch?v=g7qa8nQbIPge


Conclusion



Direct sampling works to an extent, such as a <insert crappy automobile name here> is better than walking. Inserting a wire into an RTL-SDR dongle can be done in a few minutes, and provide an opportunity to listen to stations below 30 MHz.
Using an upconverter, such as the Ham-It-Up v1.3 here, is better in most cases, but an upconverter costs around $50.
The SDRPlay is a great receiver, however, it costs $150 - you get what you pay for.

RTL-SDR Travel Kit with Pi 3

I'm just back from holidays, and as usual, been carrying a lot of equipment.
Here's what worked:



Latest rtl-sdr.com v.3 dongle



The workhorse during the trip, not only due to testing, but because it receives everything out of the box, without an upconverter. I'm writing a detailed post at the moment, as a teaser, let me state here and now: look no further, order one.



Cable length is my only grief, not an issue as I carried a SMArt mount as well.


Nooelec SMArt



USB friendly shape and longer supplied cable made life and setup so much easier; a go-to solution when I didn't want HF or felt the need to enjoy local commercial FM.


Raspberry Pi 3 with powerbank



Used for ADS-B signals by creating a local WiFi hotspot with Nooelec's 5dBi antenna, sharing information to my tablet or smartphone. Completely portable with 20,000 mAh battery bank, see a plane on the beach and have detailed information with a few taps.



Nerdism galore: you'll survive without knowing which streak in the sky does what, but every moment is transformed into a planespotting event with a mobile ADS-B station.


Antennas



1. Huge telescopic: came with v.3 from rtl-sdr.com, extremely versatile.
2. Nooelec 5dBi ADS-B antenna: works extremely well as a general receiving antenna for local action, screws right onto either premium dongles. Secret favourite, looks like a WiFi antenna, can be used anywhere.
3. Medium telescopic: comes with Nooelec dongles. Used this for years, good if you don't chase faraway signals. Adjustable length is good for airband and to feel smart doing 75 divided by frequency for quarter-wave calculations.
4. Nagoya knock-off from eBay: extendable telescopic, works great, saves time rummaging around in bag for magnetic mounts for RTL-SDR dongle antennas.


Baluns



Nooelec One Nine takes a few seconds to screw on, insert wire / antenna connector into terminal, done.




Space-saving, light and efficient kit



Two receivers and two magnetic mounts provide backup, antennas above cover all frequencies except weak signals on HF and the Gigahertz range.
For HF: recent v.3 in direct sampling mode, larger extendable telescopic with SMArt's magnetic mount and cable, balun One Nine via barrel adaptor.
Grab n' go: SMArt with smaller telescopic on magnetic mount, or with 5dBi. I used the 5dBi plus SMArt combo extensively, because finding a magnetic mount is just one more item on the to-do list, right after locating the aloe vera gel and putting out swimming gear to dry, whereas plugging in said combo takes 3 seconds. And looks cool.

ADS-B: Either receiver with Nooelec 5dBi antenna with RasPi 3 and power bank.


Pointless to carry



For me, or when size or weight is at a premium.
Upconverter: Heavy and cumbersome to assemble, especially when v.3 in direct sampling mode does the job on strong stations, and weak signal's incessant noise wasn't on the wish list for evening listening.
Dedicated T2FD shortwave antenna: used for testing weak signal reception, finding a syphatetic tree and erecting antenna in the dark is not an experience I'll likely repeat. Large v.3's extendable antenna on magnetic mount snaps onto balcony steel railing - done.
Additonal dongles: Had a Nano 2 Plus, Mini 2 Plus, and two generic chinese dongles along to test v.3 against competition. All performed well, and I love the Nano 2 Plus for its small size, but finding MCX to SMA pigtails or adapters was annoying after a while.
Homemade 9:1 Unun: Nooelec's One Nine is smaller, easier to connect, and nearly same performance.
Long Wire: takes up little space, but hanging it from the balcony was an extra worry. Huge telescopic on SMArt mount with v.3 in direct sampling mode was great; SDRPlay with UnUn and long wire was better, but too much hassle.


Costs



Two receivers: one rtl-sdr.com v.3 dongle and one SMArt package provides the best two receivers out there, two magnetic mounts and five antennas. Both receivers have their unique strengths and weaknesses, so I carry both. $55 seems a lot, until you're faced with the evening meal tab in a tourist restaurant.
Raspberry Pi 3: backup to main laptop, and affordable enough at $60 with accessories to leave in the car without second thoughts. ModMyPi's kit contents really work in the real world, travel adapter and 6.5 ft / 2m microUSB cable was handy.
Battery bank: $20 from eBay, soaks up sunlight to power Pi 3 above if left in back window of rental car. Rarely needed evening recharge.
Balun One Nine and connectors: maybe $15 together, makes a small difference for HF reception. Probably unwarranted, but small enough not to think whether it will fit in the bag.
Total: $150, give or take depending on where you live and supplier, which is not too bad for a computer with WiFi, two software defined radio receivers and five antennas covering DC to daylight and most man-made communication forms.

Review: Nooelec 5dBi High Gain ADS-B Antenna


Review: Nooelec 5dBi High Gain ADS-B Antenna


These are the big brothers of the previously reviewed 3dBi antenna bundle; only larger with more gain, cost 2-3 dollars more on the manufacturer webpage. Antennas in the pack are also available separately for around 6 dollars.
5dBi gain means that claimed figures are in the territory of FlightAware's $45 large antenna. Separate post here comparing four antennas, results versus FlightAware antenna:



22 percent less position reports from an antenna costing nine times less and measuring four times less.
They are larger than 3dBi brothers, with corresponding performance improvement:




As a general receiving antenna



Works extremely well for daily use; large enough to receive local and medium-strength signals, small enough to be unobtrusive.
Worked flawlessly on handheld general communications receiver due to shared SMA connector standard, and on handheld transceiver. Furthermore, both look identical to larger WiFi antennas, so no questions from onlookers.




Conclusion



Quickly became one of my favourite antenna for daily use due to versatility, small size and decent performance. Fits into an airport screening plastic bag or into your pocket, and the whole kit costs around $16 for two antennas and two adapters for generic dongles with older MCX connectors.
Highly recommended.

Sunday, 18 September 2016

rtl-sdr.com v.2 dongle versus bus

Torture testing goes this far, rtl-sdr.com's metal case survives.


A bus. 30,000 pounds, 15 metric tons, or thereabouts, but works.



New v.3 has the same case. No, I won't try this again, 'cause my heart was crying.

Saturday, 17 September 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.