Why do electronic devices show signal strength in bars instead of dB?

[nd2023]

Considering devices that show signal strength have to sample the strength in dB and then convert it to the arbitrary "bar", why not just show the strength in dB? The Insignia portable HD radio shows strength in bars, which is nearly useless for me. I'd rather see the field strength in dBu. I jailbroke my iPhone and one of the things I changed is to display all signal strengths in dB. A -50 dBm and a -90 dBm cell signal is "5 bars" but it's a big difference in reliability for data. Same thing with Wi-Fi, a -80 dBm signal is "1 bar" but it's usable, a -90 dBm signal is not usable, but it's also "1 bar". A -40 dBm Wi-Fi signal can provide much faster speeds than a -65 dBm signal, yet both are "3 bars". Having a dBm reading lets me find the spot where the signal is strongest (or for radio, lets me null out a strong signal). Bars also shouldn't measure battery life, ideally the display should be the voltage or number of remaining milliamp-hours, or a percentage.

Bars should be places to get drunk, not measures of signal strength.

 

[jesseg]

It's not in dB because that's easy to measure, and people (non-engineers) actually understand though bars means little from a technical standpoint.

Probably just goes back to some ancient cell phone that sold well with it, and people liked the bars, and so they kept it.

Ehh, at least in Android 4 you get a ramp with a "bar" for each pixel column. hehe.

 

[Studio1]

Receivers with properly calibrated signal strength readouts are not common, and are not cheap.
Jesse makes a valid point. Numbers mean little to non-technical people, who make up 95% of all domestic electronic equipment users, so they do the next best thing - bars. They're easy, cheap and give a 'relative' indication:

1) no signal
2) a little bit
3) enough
4) more than enough
5) you are only 3 ft from the tower. ;D

I have a Technics ST-505S tuner which, if you push a button, gives a signal strength readout in 'dB' - which is absolutely meaningless.
Sure, the numbers go up when the signal is stronger, and go down when it gets weaker, but all it really means is that when it says 3dB, there
is twice the amount of signal than when it says 0dB.
No doubt it relates to some particular level, but what that is exactly is anyone's guess.

On a professional piece of equipment however I'd expect to see numbers with meaning. Calibrated and dBm or dBuV scales.

 

[HadYourPhil]

Bring back the tuning eye!

 

[nd2023]

Even if it isn't calibrated, dB still means more than bars. If you have a known signal strength, and the readout from the device, you can figure out the strength of any signal.

People can easily figure that numbers closer to zero are better, even if they don't know that +3dB means twice the signal.

 

[ProducerGuy]

Simple answer: Most people don't understand dB as a measure of signal strength. Hell, most radio people don't even understand it fully.

 

[Goat Rodeo Cowboy]

This question is just one more example of how mass-marketing and mass-production for a consumer population that simply wants CHEAP. If I pick up a device and it claims to be giving me information in the "dB" format, I take that as a message that supposedly there is some calibration and accuracy involved.

Go to Frys or Radio Shack or anywhere else that sells components and you will find you can buy a small circuit board that you can wire up to your flash light, your bicycle, or your treadmill and the little lights or bars will light up and pretend to tell you something. You can buy these devices from 99-cents to maybe $6 or 7 and the device doesn't care what the impedance of the circuit is or anything else.

Then price a meter... a mechanical device with that little arm that waves at you. IF the vendor has them, they will ask you what kind of response time and "weighting" you want. (Broadcast VU meters and telephone company dB meters sitting side by side and hooked up to the same circuit will wave at you with completely different styles and anxiety.)

I wanted to add a decibel meter to a church sound system a couple of years ago. I quickly realized I was looking at a $75 to $200 project. Bars on the other hand I could have done for $10 or less. But buying the Rosetta Stone language course to learn how to speak "bars" was too expensive.

 

[rfry]

Receivers using the Silicon Labs si4734 DSP chip usually have an indication of signal strength on the display, labeled as "dBµ." However it is a measure of the voltage at a sample point within the receiver, and not an accurate measure of the field intensity of the arriving radio wave. So, for example, a display showing 60 dBµ does not mean that the arriving field intensity is 1 mV/m.

Several of the Tecsun PL series radios use this chip, and they cost around $60 on EBay.

Below is a link comparing some measurements made of known fields with indications for them on a PL-310.

http://i62.photobucket.com/albums/h85/rfry-100/Tecsun_PL-310_Signal_Readings.gif

 

[bilco]

As Usual, R. Fry is right on the money. Accurate FI takes more than just a readout. The relative bars mean little on any but the very best receivers. They often measure total RF getting into the radio. When I drive up to one of our multiple FM sites, all the bars on my radio are lit, even if I'm tuned to a station many miles away. Sure, as a radio engineer I'd appreciate the relative readings of dB in it's various forms, but I'm not willing to spend the money on routine radios for that purpose and I doubt 98 % of the public would. If I want acurate Field Intensity readings, I have multiple thousand dollar FIM's to handle that.

 

[nd2023]

Receivers using the Silicon Labs si4734 DSP chip usually have an indication of signal strength on the display, labeled as "dBµ." However it is a measure of the voltage at a sample point within the receiver, and not an accurate measure of the field intensity of the arriving radio wave. So, for example, a display showing 60 dBµ does not mean that the arriving field intensity is 1 mV/m.

Several of the Tecsun PL series radios use this chip, and they cost around $60 on EBay.

Below is a link comparing some measurements made of known fields with indications for them on a PL-310.

http://i62.photobucket.com/albums/h85/rfry-100/Tecsun_PL-310_Signal_Readings.gif

I have the Tecsun PL380 and it has a dBu meter. I figure that it reads 20 dBu lower than the actual field strength.

It shouldn't be too hard for most consumer devices to measure a voltage and convert it to dB to give an estimate of the field strength. That estimate is better than "bars".

 

[WNTIRadio]

Remember when VCR's had clocks and timers, and lots of people left them to blink "12:00" all the time?

Seriously, it's a nice option for us geeks to have, but you think Joe Gottaphone or 15 year old Susie Textalot is going to care or know what a dB is????

 

[ProducerGuy]

I can set my phone's signal meter to dB and the battery readout to mV. Never even considered it.

 

[spunker88]

I've been using Mobile Signal Widget on my Android phone and love it. It shows the actual dBm signal value and also shows accurate signal bars based of the dBm. I find the signal bars on my to be pretty inaccurate. The typical signal levels are from -65dBm being strong to -115dBm where it drops coverage. Yet it takes a signal of around -90dBm before the factory signal drops below 5 bars.

On my MP3 player the Sandisk Sansa Clip Zip, I loaded Rockbox an aftermarket firmware which shows the dbu signal on the FM radio. The factory firmware has no signal indication. Its a Si4703 chip used for FM and I find its dbu measurement to be similar to what the Tecsun radios with the Si4734 report.