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FM Audio Transmitters - Portables and Car Hands-Free

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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.


Page contains Amazon Affiliate links, you pay the same, and you help me maintaining this free ad-free website.

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