Архив за 19.09.2016

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.

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