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FM Audio Transmitters — Portables and Car Hands-Free

FM Audio Transmitters - Portables and Car Hands-Free

I'm using FM transmitters for years, both portables and vehicle versions, and pretty much used the majority of types on the market, so here's how they work and which ones I recommend.

How FM transmitters work?


Output audio from a device via FM transmission standard: you set a frequency on FM transmitter, units sends signal on that frequency, home / car / any FM radio can receive said signal just like if sending device was a radio station, but it's easier to visualize this with an rtl-sdr dongle:



Before you have dreams of taking over the neighborhood, portable FM transmitter was a foot away from receiver, they are good for personal use but with a very limited range.

Bluetooth or FM transmitters?


Bluetooth is a different standards, concept explored here in detail, some FM transmitters also incorporate Bluetooth, more on that later.

Power


Standalone units have a built-in battery, good for 3 to 6 hours of operation, charging via micro-USB cable (supplied) and 5V (smartphone or tablet standard, also computer's USB port or by battery banks).



Car / vehicle models are powered by the vehicle's 12 or 24 Volt system, perfectly usable in trucks, buses, RVs, as long as vehicle has a cigarette lighter adapter. Power requirements might be also shown on the actual unit, if not, don't despair, will work. In practice, I haven't come across a permutation of 60+ vehicles and numerous transmitters which didn't function together as they should.

How to use


Find a frequency where there's only hissing or static without any audible radio station, that will be your target frequency. Next, set FM transmitter to same frequency by pressing buttons, hissing goes away, replaced by quietness, until you put on your tunes.
Both radio and transmitter must be on the same frequency, however, if a strong local station is also on that frequency, a portable device will not be able to overpower it. Full size car FM transmitters can best most local stations save for the strongest ones.

Connecting to sender device - 3.5 mm headphone out


Also called Jack output for plugging in headphones or earphones, round hole on the side of sending device, examples: Amazon Fire tablet on left, Samsung tablet in the middle, smartphone on right, same hole, indicated by arrows:


On several phones and other portable audio devices, FM transmitter might be facing the wrong way:



Solution is called 3.5 mm Male to Female stereo audio extension cable, around $6 on Amazon, this also enables better transmitter placement, and lessens the chance of damaging phone if dropped. Dispelling urban myth: adding an extension cable did not generally improve signal strength, at least an extension cable didn't make matters worse, so get one.

Standalone FM transmitter - older version:


Looks like this in search results and in real life:



Costs anywhere around 3-5 dollars on eBay and on various online marketplaces, found a version for $10.4 on Amazon USA, but I'd buy the later model below for 2 dollars extra.
Built-in battery, charges via supplied cable, units shows charge remaining, which is nice, but only lasts for 3-5 hours.

Upgraded portable FM transmitter


If you need a portable FM transmitter buy this, successor to the version above, bought mine for $13 from Amazon branded Doosl, thought it also comes up under various other names:



Battery life: 6-8 hours, forget claims of "can play for 10 hours". Maybe if volume is turned down, at a lab temperature, real life is 6-8 hours. No power indicator.



Signal strength is significantly better as visible in image above, thicker red = better if Reader is not used to spectrum analysers.
Audio quality: Finding a frequency which is far away from strong radio stations helps a lot, takes a few minutes, don't just set the first frequency coming in relatively quiet. After adjustments, quality can be nearly Bluetooth level, but much quieter, need to turn volume up on head unit, susceptible to strong stations coming through, still, light-years ahead of cheaper version.
Personally, I use this Doosl on a daily basis for months now, and it's excellent as long as there're no nearby strong station.

Car FM transmitters with Bluetooth


Plugs into 12/24V socket, most come with Bluetooth and work as a cheap hands-free system.
Phone connects to device via Bluetooth, yoke puts out an FM signal, tune to it on radio unit as described above and Bob's your uncle.
USB ports: 5V output for smartphones and other electronics, great for charging on the go. Normally I get in the car, hear "connected" and off I go.
With an external USB thumb drive, same port can also play MP3 files, some models have multi-format capability such as aac, flac, wma and so on.
AUX-In: connect an external device via cable. Useful for passengers with a no-Bluetooth device,and plugging in a cable is easier for less gadget-friendly people.
Buttons: the more, the better. Pick up a call is usually the middle button, change track, volume up and down, change audio source.

I'll list versions by type and spice with personal observations, your mileage will certainly vary.

Thin finger-sized


$4 off eBay, avoid:



Worked as a charger, caller could barely hear me, buttons too small, side port USB means that on a rough road surface unit will come out of cigarette lighter adapter, for a few dollars, good for doomsday backup.
Similar versions abound on Amazon, I won't link to products because I wouldn't buy a small version myself.

Square with round button in middle


Off eBay, the less than $5 category, avoid:


Why avoid? FM quality was horrendous, taking calls by pressing on the middle button means unnecessary stress so it'll pop out of socket, adjustments are a pain in the hand, need to constantly look down.

Middle size with full feature set


Small enough to fit in a pocket, yet large enough to adjust essential features, versus a full-size for comparison:



Takes microSD card for music, charges two devices at the same time or one phone and music from USB drive. One extremely handy feature is large green rotary button in the middle for calls and adjustments.



If I had to replace the existing one I'd buy the version above for $17 from Amazon, same feature set and similar price.

Full-size: possibly the best in-car FM transmitter with Bluetooth


The one recommended by me, and thousands of Amazon revievers, universally loved for a reason: works for $17.



Don't take my word for it, Amazon customers gave 4.5 stars out of 14,646 reviews.
Chinese woman tells me "pairing" very second I start up car, then charges phone, plays music off USB device, easy to use.
Audio call quality is excellent, can talk away as with a factory handless system, in fact, callers did noy notice any difference versus several factory $$$ systems.

And many more

Unless you only want to occasionally use an FM transmitter, either the standalone or plugged-in versions, it's literally cheaper to go for the more expensive options in the $10 to $20 dollar bracket.


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Review: Nooelec Rattlesnake antenna kit

Three antennas with magnetic mount and coax for $16:



Review and observations are based on over half a year's use, summary: order from manufacturerAmazon USA, or eBay right away. Rattlesnake kit is the best value aftermarket antenna package I ever came across. Period.
Direct competitor on price ($15 on Amazon) is rtl-sdr.com's antenna kit, separate review here.

First impressions


Heavy, feels good when opening the envelope:



M5: Screw standard referring to outside diameter of screw, yepp, same standard used with dotcom antenna kit on paper, but antennas are not cross compatible.

Magnetic mount


Holds fast on car even on a highway, in fact, the strongest magnetic base I came across in the RTL-SDR universe, small (supplied with basic dongles) or medium size (e.g. in the SMArt bag, also with advanced Plus models from Nooelec) are much less powerful.



Supplied cable is 2 meters / 6.5 ft of 3C-2V, 75 Ohm coax, not RG-58 as promised on product page:



Feels the same as SMArt's RG-58 in hand, terminating in an SMA Male connector, screws right onto any receiver / preamp / upconverter with SMA female: for example, all four of the SMArt family, rtl-sdr.com V3, Pro Sticks, SDRplays, AirSpy range.



Handheld scanners e.g. Icoms also use SMA female, mag mount screwed right onto an IC-R5. Uniden users, or those with a Baofeng can also utilise the pack, but you'll need appropriate SMA Male-Male barrel connectors - one piece costs less than $2 on eBay.
Adjust telescopic antenna supplied to frequency of desire (1/4 of wavelength with mount on a metal surface, or whatever you fancy, here's a handy calculator) and off you go - check local laws and/or get a licence before messing up the airwaves, you can be heard a serious distance with 5W output power on a Baofeng.

Telescopic antenna


22.3 cm collapsed, 118.7 cm extended, angled joint:



Quarter-wave between 63 MHz and 336 MHz, not that it won't work lower or upper - the $150 Tecsun PL-680 shortwave / broadcast FM / airband receiver has a shorter 88cm built-in antenna.
Most action happens in the range telescopic covers perfectly: broadcast FM, airband, AIS, local utilities, and don't forget shortwave, fully extended with new Ham It Up Plus, mount on windowsill, plethora of SW programming, even hams fisting away came in.

Stubby with blue bands


Officially for digital terrestrial television (DVB-T/T2) and GSM, capabilities I'm less interested in than politics, antenna indoors received local programming:



Where's my jaw? Thick part diameter 15.05 mm, total length 96.91 mm, also worked quite well in the 400 Mhz range.

Stubby without blue bands - the black one



Officially, antenna can "receive a wide range of VHF/UHF signals with ease", same can be said of my body, a wire coathanger or a nine inch nail, so a bit more information would be appreciated from Nooelec. Moaning aside, 74.92 mm total length, close to ideal 1/4 wave (68.8 mm) on ADS-B.



Versus a pro Jetvision antenna: 31,503 Totals, Nooelec 23,995, 31.2% more with pro antenna, so folks who don't check daily take first thing in the morning will be more than happy with performance. I simply screwed on the black Rattlesnake during a recent outing and could see aircraft over 100 nautical miles away.

What I don't like


No official SWR plots from Nooelec, coax cable is 75 Ohm, not 50 Ohm standard used with transmitters and pro gear, when all other components are prosumer level. SMArt family bundles come with proper 50 Ohm coax, but not compatible with this kit due to different antenna screw standard.
And, as a sideline suggestion, would it be so hard to process all those orders by making the antennas and base SMA connector standard?

Competitors


Antenna kits supplied with legacy Nooelec receivers, or chinese $8 dongles will not let you hear as much as with the Rattlesnake bundle, other Nooelec telescopic antennas are smaller, black thin ones with basic kits are excellent to scratch top part of back below neck, almost utterly useless for radio signal reception.
Nooelec's own SMArt family bundles (SMArt, SMArtee, SMArt XTR, SMArt XTRtee) already come with the same length of coax, which is better RG-58, but the mount is smaller with less holding power, and telescopic antenna is shorter.
Rattlesnakes or rtl-sdr.com antenna kit? Love both, having three kits each on the on the table, I'd rather pay same money for a Rattlesnake, as they feel more quality and dependable. Rtl-sdr.com antenna kit is great for experimenting, and to get max SNR due to telescopic dipole config for a specific frequency, but Nooelec gear is just easy, go anywhere, throw mag mount with antenna on roof, forget it's there, no hassle nor doubts weeks later. Dotcom kit is primarily for indoor apartment / city dwellers, probably designed for a certain customer base. It works fantastic in that role, mine is attached to living room window and functions well.
Buy both. I simultaneously enjoy advantages of each kit, dotcom's cables work with Rattlesnakes, SMA connectors mate with little effort, dotcom cable is thinner so less whoosh thru window with snake mount on roof, dotcom suction cup attaches to window easily and holds firm, two telescopics enable me to fine-tune a signal I've seen with the Nooelec telescopic.

Who is this antenna kit for?


Anyone with a radio receiver or transceiver. $100 and up 12-bit receivers such as AirSpy and SDRPlay range do not ship with an antenna, same can be said of many experimental boards. Any Baofeng will function with the stock antenna, but there's a massive range increase if antenna is tuned to the operating frequency, which is possible with a telescopic.
Sixteen dollars plus shipping on Amazon USA. 13 euros. 21 Canadian. 914 rubles. For 2 meters of coax with connector and magnetic mount, go cheap on eBay and try to find a mag mount for less than $8 dollars, then search for three antennas. Good luck.
Magnetic mount and large telescopic antenna is worth the money alone, two stubbies are bonus.

How I use it


Keep plastic bag, cable and antennas fit into it, throw in a an RTL-SDR dongle and an OTG cable, ready for exploring the airwaves with a smartphone or tablet. Note to Nooelec: make it a bigger bag, so a Ham It Up in a metal case, or an SDRPlay would fit in as well.

Would I buy one?


Absolutely.

Portable Bluetooth Audio Signal Receivers

Receive an audio signal up to 50 feet / 15 meters - best replacement for wires, also work as hands-free in a vehicle. Hands-on guide and five types tested and compared: cheap from China, for Hi-Fi, and midrange and expensive hands-free. Regardless of locale and prices, these four types cover most flavors on the market.



What Bluetooth Receivers are: small, most commonly less than a lighter-sized electronic devices, which connect to your smartphone / tablet / computer via Bluetooth, and output audio signal received to whatever device they're plugged into.

How they work


Turn Bluetooth on, turn on receiver, lights flash, ready to pair with your device: unit will show up instantly.



That's it, audio will be routed to Bluetooth receiver. Hint: it's better to turn on Bluetooth on phone first, then the receiver. I haven't come across pairing problems, devices were operational within seconds.

Receiver or transmitter?


You wanna hear what you play on your phone: A receiver will receive an audio signal from a Bluetooth equipped source and put it into the device which it is plugged into, just like a cable did in the 90's.
Transmitter: sends an audio signal via Bluetooth to any Bluetooth-equipped device. For instance, if you have a TV / home theater system / anyhing with sound output, a transmitter can send that signal via Bluetooth.
This post details receivers, for sending a signal from a non/Bluetooth equipped device, get a TaoTronics combined transmitter / receiver just like I did for my parents and be merry.

Example - upgrade existing earphone / headphone to Bluetooth-equipped


Say you have an ol' trusty headphone you paid top dollars for years ago, but it only comes with a regular cable.



Any earphone or headphone can be upgraded to Bluetooth status, and it's much cheaper than buying a newer model with built-in Bluetooth.

Example - home HiFi / stereo with Bluetooth receiver


Head unit, like most, has an AUX-in at the front, or RCA connectors in the back, so Bluetooth receiver can be connected:



On more serious home theater units, and on car amplifiers, you'll have two connectors in the back, often called Line level RCA input in user manual, use an RCA - 3.5mm cable.
In practice, transitioning from walking to car to home mode with constant music playing is seamless, as only the appropriate Bluetooth destination on device needs to be selected (you can rename multiple receivers of course):




Example: In the car or mobile use


Majority of affordable car stereos have an AUX-in port, which is a hole at the front, Bluetooth receiver goes in there, such as:



Same procedure again, plug in Bluetooth signal receiver, power it on, select aux in with source button, voilà, your tunes are coming through car speakers.
Knowing that in most jurisdictions you'll be quartered and burned crispy on a stake for hand holding a mobile phone, buying a Bluetooth Hands-Free is a good investment.

Where to buy?


Amazon if available, eBay for rest of the world. One major issue with eBay recently (2018 Fall / Autumn) is exorbitant shipping times, often a month or more on the China-Europe axis, which is not gonna improve come Christmas and Chinese New Year.
Personally, living in Ireland, I subscribed to Amazon UK Prime for two-day shipping; in reality, that means 3-5 days and always less than a working week.
Brand-name, or more than $10 products cost nearly the same, and they are here from Amazon quickly with generous free returns policy.

Power and portability


Built-in batteries: good for 4 to days of standalone operation, really depends on model and physical size, larger has more battery inside = more juice, works longer. Charging via micro-USB power cable (always supplied in pack), which is the standard on every Samsung / Huawei / HTC, practically every smartphone uses same charger standard with the exception of iPhones (supplied micro USB charging cable works with USB iPhone chargers, the other end of the cable is the same USB):



At home, I just keep receivers always connected to charger, as they won't be moved around. On the road, if 8-10 hours isn't enough, battery banks will also charge devices if you have no power outlet nearby.

Maximum range


In an ideal scenario, receiver can "see" the source of signal, so about 50 feet / 15 meters maximum.
At home, playing music or taking calls was seamless once the receiver and source was in the same room, even one room away quality did not suffer, bringing thrash out and signal starts to disappear. Know that residential results depend on wall materials, radio signal can permeate drywalls better than a brick wall.
In vehicle, no problems encountered, even in large coaches (called RVs Stateside).

Features


Microphone: most models come with a microphone, so can be used as hands-free in a vehicle. Two microphones are better than one.
Buttons: some units come with volume up / down, take call / pause / play track, skip forward or ahead buttons, think about which way you'll be using the device and select a model accordingly.
AptX: better sound quality claims IF source and receiver both support the standard, Wiki here.
CVC: external noise suppression, also written cVc, 4.0 and 6.0, higher is supposedly better, info here. If ya plan to use receiver as a hands-free, CVC is great, makes a world of difference.
Bluetooth 4.0, 4.1 and 4.2: higher number is better, shows improvement, backward compatibility, so a 4.2 receiver will work with a 4.0 sender smartphone. Generally, if device has Bluetooth, it will work.
Audio quality for music: tried all tested models in several vehicles, streaming music and podcasts from my phone and couldn't tell the difference.

Basic model


Around $3-4 shipped from eBay, on Amazon USA, found it for $2.68 from CreazyDog, $5.88 for a Jahyshow, and various other versions up to seven dollars, pretty much the same:



Use several of these, as they simply work, even when connected to a battery bank for extended operation, built-in battery lasts for 4-7 hours, never less than 4 hours.
On button with backlight, long press to pair, shines blue when paired, one press to stop/play source music or take/end incoming call. That's it. Job done.
Built-in microphone, in a car, caller could hear me and I could hear caller via speakers, no more I ask for $3, was happy with them until spurred on by functionality bought more expensive models.

Less than 15 dollars for Home HiFi


Mine is called Golvery, sold as Friencity in the USA for $12, this is primarily for home stereo music listening only, no built-in microphone, but comes with RCA adaptors:



Feels good in the hand, connects instantly, battery life is significantly better than the basic model, 8 hours easy.
If you need the extra RCA cables for home HiFi definitely get this, or a similar model.

20 dollar price bracket


Numerous versions with better features, volume and track buttons, a good representative would be the MPOV below, spent $20 on this. Taotronics also sells a seemingly identical model for $16, which doesn't come with a side power button.



Comes in a nice box with Jack-Jack cable if you wish to place it away from radio, normal adapter for direct plugin, and charging micro-USB cable.
Added features are noise cancelling technology CVC, that works fantastic, less "Can you hear me?" CVC cancels drone of engine or a swooshing of a window down. Difference between this and basic version above is someone calling you and knowing an easy and understandable conversation to both parties will be possible.
Battery life: 8 hours easy, or more, lasts a working day. Official promise is 15 hours.
Two signal sources: connect a tablet and a phone at the same time, or any two Bluetooth-equipped devices simoultenously. Say you're watching a video on laptop  with headphones+Bluetooth adapter combo and phone is on charger long forgotten where, can pick up call without rummaging around. Or travel with partner in car and both of you can connect to head unit.
Daily use: power on via side button, one hand movement, instantly connects to paired devices, no lag.
Backlit: buttons are white, middle flashes blue indicating it's connected to source device.
Extremely light, also use this around the house with headphones.
Volume and track buttons are extremely handy, all-in-all, well worth the money.

$30 price bracket: Taotronics

26 dollars on Amazon USA for top of the range feature set:


Where does the extra money go? Excellent battery life, noise canceling cVc 6.0 standard, callers in a car said that audio quality was better versus the MPOV.
Sightess operation e.g. in your pocket are easier, as volume buttons are on the side, but no backlit buttons, plus supplied cables are also shorter than those coming with the MPOV. I can live with that, as caller audio quality overrides niggles for me.

And many other choices


Amazon and eBay is full of various flavours and makes of essentially these receiver types, whichever model you choose, decide on one that suits your lifestyle, and personal preferences: pushing a button might be favored, backlighting, size, and so on.

Maximum USB cable length

Question often comes up, Answer: 27 feet / 9 meters with RTL-SDR dongles:



For testing, I tried four separate RTL-SDR dongles in image above: rtl-sdr.com v3, Nooelec Mini 2, Nooelec E4000 SMArtee and regular Nooelec SMArt.
USB connector cable is crucial, as mentioned in a previous post detailing stuff I'm happy with, blue 5 feet / 1.5 m USB connector with ferrites were used. Tried several USB connectors over the years, these worked best, 27 feet / 9 m connectors totaled 5 dollars off eBay.



Computers were a Lenovo and a ThinkPad, identical results, all computers provide 5V to USB devices, so host computer should not matter.

Noise pickup


Nope at these extreme lengths, in fact, better with once section of USB cable as receiver is moved away from computer, didn't see any noise pickup from 5 feet /1.5 m to 27 feet / 9 meters.

Try not to use coax below 20 feet / 6 meter


If distance between antenna and receiver is within these lengths, substitute coax with USB cables. Cheaper, and since signal received is immediately chewed into digital ones and zeros, there's no chance of electrical noise pickup by coax cable.
Doubtful? Check printscreens of various lengths, top image without any USB cable connection, then adding one section (5 feet / 1.5m) at a time.
Really, I can't see any changes between the second image from top (one section) and the last image on the bottom (5 sections).




RTL-SDR Dongles Image Gallery

Studio Photos of over 20 RTL-SDR dongles on the market:


More than 200 high-resolutions PCB, case and comparison images by clicking here.

Nooelec Ham It Up Plus upconverter / noise source

An upconverter lets you hear signals below the tuning range of RTL-SDR dongles, so signals less than 30MHz, that's the entire shortwave / medium wave / longwave spectrum will be audible with a suitable antenna. Works by adding 125 MHz to received signal, so a station on 3MHz will show up at 128 MHz, which falls into the tunable range of every RTL-SDR.



Plus in the name for $65 with free worldwide shipping means it contains a noise source for experimenters: antenna and filter tuning is possible out of the box if you have the knowledge and necessary equipment.




I use Ham It Up upconverters for years, so post contains references to predecessor called v1.3 BareBones, without Plus in the name, PCB board still available for $40 at manufacturer website. Official shop on Ebay also available, check that PCB board version is v1.30a2, and seller is nooelec:


We're still talking about the predecessor, which can be bought also for much more, ripoffs at $63 and $105 available:



That's a good sign, if something is in demand, opportunists will try, just use the Official Nooelec Order page to avoid spending more than necessary.

Official Prices


Ham it Up Plus in metal enclosure, subject of this review: $65 plus shipping from manufacturer.
Ham it Up Plus, PCB board only: called Barebones, $50 plus shipping from manufacturer.
Upgrading an existing Ham It Up is easy: enclosure kit for 1.3 and higher sold separately for $16, 125 MHz TCXO upgrade kit is a tenner, noise source kit is another ten dollars. If you got a v1.3 in a metal case you'll only need to drill one more hole to accommodate one more SMA connector, but at least Nooelec thought of punters who love soldering.

Ham It Up Generations


Let's look at differences, original version with surface-mounted 100 Mhz oscillator, the first I bought from Nooelec and reviewed five years ago, unpopulated noise source:



Version 1.3a1, you won't meet these any more, the basis for further improvements, fix 125 MHz oscillator, included here for identification, this is not the latest model:



Version 1.3a2, now what we call the Ham It Up v1.3, distinguishing feature from predecessor are addded screws for easier case mounting:



Version 1.30b1, the latest model also called Plus, easiest to categorize by two SMA antenna connectors above passthrough switch.



Connectors


SMA female, package comes with barrel connectors to connect SMArt family, rtl-sdr.com v3, SDRplays, AirSpy, nominally everything for enthusiasts.




Power options



Needs 5 Volts via USB Type B cable, which is not supplied, nor can be ordered from Nooelec, big thick square-ish cable for printers, probably used for dependability, USB-B connectors work, SDRPlay also fancies the standard.
Unfathomable, cannot understand, makes me constantly wonder why there's still no micro-USB port (read: Android smartphone charger plug), or mini-USB (bigger brother, GoPro or Uputronics). All above are 5V, more readily accessible, users can buy a smartphone charger paractically anywhere, whereas you gotta hunt for a printer USB cable.
Just in case, PCB got positive and negative inputs just in case you want to run it off a battery bank, properly labeled. Personally, I just run the upconverter off a $15 power bank, probably not as good as dedicated batteries, but certainly better than a switched-mode power supply or occupying USB port from host computer, and enables easy mobile operation.

Performance



Manufacturer site details two claims, quoting:

" Input, output and LO filters configured for substantial sensitivity and selectivity improvements" and "Ultra low-noise linear power regulator (LP5907), with voltage noise under 10 µVRMS!"

I can neither confirm nor deny those claims, what's clear is that in the sub 30 Mhz region the Plus is better than the predecessor; I tended to hear more with the Plus, often substantially more, to the point that a faint signal came in loud and clear - but it must be noted that shortwave reception is very much down to external factors such as atmospheric propagation, so look at the following knowing that switching upcomverters took 15 seconds, same station / dongle / everything:



Regardless of the possibility of tester error, with the same gain setting on the dongle, newer Plus has a noticeably noisier waterfall.
What's not tested: reception range supposedly extends down to 300 Hz, so it's theoretically possible to listen to time signals and other low frequency signals, stations I wasn't interested in as I had no equipment capable of receiving it, hence I have no suitable antennas for proper reception.
Noise source: well, I simply had no time to dwell into the quagmire of "How to use it?", at first glance, I'd need a directional coupler, and a few weeks off on a beach to soak up the topic and sunkissed margaritas, so this will have to wait. However, just like a sunroof or a towbar it's good to know the possibility is at hand should it be needed.

Worth it?


Certainly worth the extra few dollars over the regular version, if for nothing else, it's the latest Ham It Up with extra goodies.
Question gets a little complicated once we throw cost and the availability of higher-class all-in-one SDRs into the equations, and I mean the SDRPlay RSP1: total reception system cost including three antennas is around $140 with an RSP1A, but that's $140, not $50 for Plus board only.
If you already have an RTL-SDR dongle, true sub-30 MHz capabilities are $50 away, hint: order the Rattlesnake antenna pack for $15 and enjoy three antennas, free worldwide shipping and lots of interesting signals for years to come.

About Software Defined Radio and RTL-SDR

What?

Software Defined Radio: computer or smartphone does signal processing, not individual and expensive components as with traditional radios. The cheapest way into radio reception, best bang for the buck.
RTL refers to chipset converting analog radio signal to digital form.
RTL-SDR dongles are digital TV tuners re-purposed for radio signal reception; with a special driver and free software, up to 2.4 Mhz worth of signals can be seen and heard - completely different experience than a traditional radio, where you only see and hear the tuned frequency. Think of looking at a waterfall through a telescope (Traditional Radio) or enjoying the whole scenery (Software Defined Radio).


Why?

Receive majority of human radio communications for cheap. Sky is not the limit; listening to the International Space Station orbiting 400 km above is an easy catch, plus more, popular uses:
- Listen to shortwave stations from other side of Earth,
- CB radio,
- VHF amateur radio,
- Broadcast FM, aka morning talk shows,
- Real-life weather satellite images as they come down from satellite, user image as an example,
- Voice of local utilities / security / taxi companies,
- Position reports from ships, trains and aircraft.
And so on, there are no gaps or locked frequencies with Software Defined Radio, no limit to what you can receive, hear, or decode.

How much?

Cheapest RTL-SDR receiver from China costs $8 from eBay, fantastic value if you're handy with wires for better reception. A better, and highly popular choice is rtl-sdr.com's V3 bundle ($27, manufacturer, usually sells out on Amazon fairly quickly), however, antennas in that pack are designed for indoor use only, and you'll get much better reception with an outdoor antenna. To Dad, friends or any acquittance I want to talk again, I recommend Nooelec's SMArtee bundle ($32, manufacturer, Amazon USA) for overall quality, 2-year warranty, excellent customer support, and most importantly, long cable to place either of three antennas indoors or outdoors.



Many other RTL-SDR dongles are available for specialist purposes and different budgets up to $50, you get what you pay for.


What about software?

Multiple choices, all free, popular for Windows 7, 8, 10:
- SDR Sharp, or SDR#, easy to use for beginners with lots of plugins for particular purposes,
- SDRConsole for an Office-like environment, if you use Excel or Word on a daily basis you'll feel home in no time,
- SDRUno, bit of a learning curve (my guide here) to get the most out of any RTL-SDR receiver.
Alternatives for Mac or Linux exists, I use neither platform, so aficionados comment below what's good.

What can I receive? How does it look like?

Frequencies between 27MHz and 1700 Mhz are yours for the taking with an $8 generic dongle, insert a wire in 3 minutes (called direct sampling) and get shortwave signals (below 30 Mhz). If you don't know what's a Megahertz, think of your car radio, that receives between 88 to 108 Mhz, so reception capabilities are enormous with any RTL-SDR.
User interface of SDRSharp for example, you'd only see 96.4 on a traditional radio:



See a signal represented by a hump or line (lots of different types out there), click on it, hear signal. Left hand side allows fine-tuning for better reception. Surely, procedure involves learning how to use a particular software suite, but nobody starts with writing macros in Excel straight away, isn't it?
Smartphone apps look more or less the same.

Complicated? How does it work?

No. A complete novice will get to "happy days" status in less than an hour, and that's a pessimistic estimate.
1. Install software.
2. Connect three components together: computer, dongle, antenna, then
3. Place antenna close to a window, or outside if you can. Nick a metal cooking pan from kitchen if you can, place magnetic mount on that.
That's it, double click on software shortcut on Desktop, hear an invisible world.

Technical mumbo-jumbo

Complicated words such as impedance matching, wavelengths, ionospheric propagation, line of sight and so on are for enthusiasts, maybe you, definitely later on. Play with software, shorten or lengthen telescopic antenna, see what happens. If curious, google how radio signal reception works. Do your thing, exploring with success is the biggest reward.

Transmit

No RTL-SDR can transmit, e.g. you can't talk to your buddy, mess up the neighbor's day by mimicking a car keyfob, or get in touch with buddy in Australia for $8. Skype, Viber, pick up the phone, get an UV-5R walkie talkie if wanna talk locally.
Some Software Defined Radios can transmit, we're talking many hundreds of dollars and in-depth software, programming and radio knowledge, sleepless nights of pure dedication.
If you really want to transmit, get in touch with your local ham radio society, easier and cheaper if you value your time.

I want to listen to the police, emergency services, firefighters

Not an easy task without some serious programming, and whilst it's apparently doable, easy and legal in the States, I have no interest, nor experience in the topic - what's the challenge with strong local transmissions anyway?
If police freqs keep you awake at night, you might be able to listen to them if they're analog, but most of the free world (drinkable water, McDonalds, careless walk home) gone digital ages ago. Not to mention, I heard from experience, emergency services are really boring.
If you're reading this from a less than fortunate region of the world where dictators reign, think twice, it's easy to end up on a lamppost, sent to a labor camp, or get stoned to death if you get caught.

WiFi, Bluetooth

No, RTL-SDRs are not WiFi or Bluetooth adapters.

I want to listen to cellphones or mobiles

Those frequencies are fully digital and encrypted, due to software limitations it's not really possible.

I want to receive digital TV

No problem, RTL-SDR dongles are primarily TV tuners, but due to different standards, the only RTL-SDR dongle which reportedly works in the USA is the ExCAP 645 - all others work for digital terrestrial TV, also called DVB-T, Freeview, Saorview, etc. Buy a $1 OTG cable and TV on an Android Smartphone is possible in less than 10 minutes:




Older (read: even $8 dongles) come with a remote.

I want to use RTL-SDR on my smartphone

No bother. Lots of apps exist for both Android and iPhone, visit your relevant platform store and search for "RTL-SDR", you'll be amazed.

I want to see aircraft position data.

You're not alone, called ADS-B, snapshot at my airspace as I write this, cheapest dongle with worst antenna on my windowsill indoors, can only get better than this:



Ordinarily, you get data of aircraft you can see with the naked eye with an $8 dongle straight away. If you want to reach out and increase range and data received, better gear is needed. I also love anything connected with aircraft, so this site has tons of info on ADS-B.

I want to listen to aircraft and pilot talk

Easy, specific frequencies for Tower / Approach / Ground can be found online within a minute, or seen in software without internet connection. For a taster how pilots and controllers sound like, go to the Live Air Traffic Control website.

I heard it's illegal

Receiving signals is tolerated in most developed countries as long as you don't act on the received information, to be on the safe side, ask around, read legislation, exercise common sense, or best of all, talk to local law enforcement. I've written extensively about the proper approach earlier.
Circumstances matter. Home town police did a courteous house call when I put a blatantly obvious huge antenna out on the roof, left within 10 minutes after being invited in seeing I'm a harmless radio enthusiast.
Please, do not use, operate or view any radio device in, at, near, or in close proximity to airports or aircraft without permission, unless you left home with the desire of four very twitchy policeman escorting your backside for a cavity search.

I got no money but want good receive performance

When I started all I had was $10 to spare and some free time, so had to go down the "make do" route. I still maintain, and deeply believe that money is not an issue, knowledge is. Having a slight clue what's happening from the very second radio wave hits the antenna to the joyful moment you see a transmission on screen has got more to do with the matter between your ears, not with equipment.
Order an $8 dongle, then in the two weeks until it arrives from Shenzen / Hong Kong: read, read, read. Speaking home, this page got lots of info, browse around, from easy mods to antenna positioning, or read posts on rtl-sdr.com, or google away. Reddit group is open to anyone, manufacturers lurk around helping as much as they can answering questions, RTL-SDR Facebook group full of helpful folks, all the info you'll ever need is out there. If stuck, comment below, I'll do my best to help if you have a question.

Review and Comparison: Nooelec SMArt XTR and SMArtee XTR

Start with a legendary chipset, combine it with an advanced RTL-SDR platform, send three antennas and top it up with 2-year warranty: end up with a Nooelec SMArt XTR featuring the E4000. Yes, that E4000.


Review: Nooelec SMA Connectivity Kit

8 pigtails for Software Defined Radios and amateur radio equipment with standard SMA female connectors, 6" / 15 cm RG-58 cable with eight different connectors on the other end:




Costs $25 at manufacturer, same price on Amazon.

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Good buys off eBay and Amazon




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