LoRa/LoRaWAN tutorial 5: Decibel, dBm, dBi, dBd
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- čas přidán 21. 09. 2018
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This is part 5 of the LoRa/LoRaWAN tutorial.
In this video series different topics will be explained which will help you to understand LoRa/LoRaWAN.
It is recommended to watch each video sequentially as I may refer to certain LoRa/LoRaWAN topics explained earlier.
In this video I will explain what the decibel is and what the purposes are of the units dBm, dBi and dBd.
A deciBel (dB) is a unit of measurement used to express the ratio of powers, sound pressures or others things on a logarithmic scale.
The deciBel was invented by Bell Labs and named after Alexander Graham Bell.
In this tutorial the deciBel is used to express the ratio of electrical powers (meaning Watts).
A = 10 x log10(Po / Pi) dB
Where Pi is the input power and Po the output power.
Convert deciBel to power ratio:
Po/Pi = 10^(A/10)
The logarithmic scale is used to avoid very big or very small numbers, meaning the ratios. Using decibels is easier to work with.
For example: A power ratio of 1,000,000 (1 million) can be expressed by 60 dB.
A power ratio of 0,000001 can be expressed by -60 dB.
A power ratio of 1,000,000,000,000,000 (1 quadrillion) can be expressed by 150 dB.
A power ratio of 0,000000000000001 can be expressed by -150 dB.
A power ratio of 1,000,000,000,000,000,000,000,000 (1 septillion) can be expressed by 240 dB.
A power ratio of 0,000000000000000000000001 can be expressed by -240 dB.
dB is a ratio it does not represent an absolute value.
If we use a reference input power of 1mW (Pi=1 mW) the unit is expressed as dBm.
A = 10 x log10(Po / 1) dBm
Po/Pi = 10^(A/10)
P = 10^(A/10) mW
Unit dBm represents an absolute value because it uses a fixed reference value 1mW.
Rule of 10s and 3s:
10 dB = x10
-10 dB = ÷10
3 dB = x2
-3 dB = ÷2
Prefixes can be used with SI units.
SI is French for Systeme Internationale which means International System of Units.
Fore example:
-138dBm = 16 aW
-14dBm = 0.04 mW
Other notable deciBel notations are: dBi and dBd (these also represents ratios)
Antenna manufacturers are using these units to measure antenna performance and is useful for comparison purpose.
Manufacturer A has an 868MHz antenna, its gain is 3 dBi
Manufacturer B has an 868MHz antenna, its gain is 2.5 dBi
dBi refers to the antenna gain with respect to an isotropic antenna.
This is an hypothetic point source antenna, that radiates its power uniformly in all directions.
Radiation or antenna pattern reflects the strength of the radio waves from the antenna in different directions.
dBd refers to the antenna gain with respect to a reference dipole antenna.
The radiation pattern of a dipole antenna looks like a donut.
The relationship between dBd and dBi:
dBi = dBd + 2.15
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my CZcams channel:
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The presentation used in this video tutorial can be found at:
www.mobilefish.com/developer/...
#mobilefish #lora #lorawan - Věda a technologie
One of the "very best ever" found in CZcams with great presentation.
Crisp, Clear, Simple etc etc etc etc one of the best video youtube will ever have
Best dB explanation I've ever seen 👍
Thanks for taking the time to make this!
I have been working out for last 3 days to learn LoRaWAN....and finally got this channel.....Probably the best one.
Excellent illustration.
Good explanation and easy to understand, thanks a lot😊
thank you so much for this video. never been crystal clear before. this is the best video on this topic so far. i humbly request you to make more videos on several more topic like in this way.
Nice to hear that finally explained! Can't tell you how long I have been wondering about that.
I have to admit with others that you are one of the best RF teachers I have ever seen! I studied and worked in Bangladesh, Germany and USA just to let you know that I have seen a lot of RF teacher and engineers in my life!
Thanks for the compliment, but please be advised I am not a RF engineer or electronics engineer. I am interested in this technology and spend a lot of time to grasp it. To share my knowledge with others, I have therefore created this tutorial series.
why they did not teach us like this in Engineering school ?!!!
I graduated at 2007 and this is the first time i totally understand dB, dBm
thank you
i was looking for this, thank you very much!
Well done sir- you have a gift for explaining things clearly.
Excellent video. Crystal clear explanation.
The explained examples help to make this an intuitive learning versus a learning by rote. Thank you.
Thanks a lot for this *excelent* video! I never found it better explained. :-)
Thank's, i really enjoyed your explanation!
Thanks for the great video explaining about dB, dBi, dBd. I do not really understand this for long time.
a very great explanation!
thank you bro!
Awesome!
Easily and perfect explanation!
Thank you for taking the time to make this.
Thank you, it all start to make sense now.
VERY useful information . god bless you man
Thank you Sir, easy and simple way to deliver the information
Excellent teaching on fundamental topics .
is the first time that I understand this matter, thank you!!!
Thnks for your effort! Very good and understandable explanation!
hats off to the makers of this video. cannot b simpler than this
Thanks.
Tremendous video... Thanks my concept has been cleared..
Thanks for very good explanation!
Crystal clear... thanks a lot for your share
Great Stuff !!! Bravo
Thank you sir for giving excellent knowledge in better ideas
Very well explained. thank you
very interesting & informative ...thank you sir
awesome lecture!
Very nice sir..
great video serie
Incredible video. For years I have been trying to wrap my head around understanding db. This video makes a great explanation. Now it is almost clear as mud. Do you have a link to more of these 10 & 3 multiplication examples?
there is another rule that can also be applied. 2*3*5 [mW] vs 3+5+7 [dBm] for example 17dBm =50mW { 5*5*2=50 ----- 7+7+3=17)
Gold.
Very nice.
a gem
good...thanks
incroyable thank
Minute 0:25, there is an error in the second example (Cable), The input power and the output power is in [mW], hence A(loss) will be in [dBm] not in dB
Thanks
Thank you everyone explains it badly and like I know what there talking about but you explained it good thank you now I understand that it is a ratio. 👍
So is the higher the dBm the better the signal
And could you increase the dB / dBm by using operational amplifiers
Does body loss in dB can be converted to dBi? While dBi is actually reference to isotropic antenna. Thanks in advance
Thank you I thought it was way more complicated than it really is
me to! Thank goodness for youtube.
@14.32 can you please explain how the equation dBi = dBd + 2.15 comes? Is that correct?
bright side !
What is dbic in circular polarised antenna.or.how one specify a circular polarised antenna measered with std. Lineor dipole.
🙏🙏🌹🌹
What does mean of 0 dBi with respect to radiation pattern of an antenna?
I am a little confused by one point. As the radiated patterns of the isotropic antenna and dipole antenna, dipole antenna's gain is 2.15dB bigger than the isotropic antenna in the horizontal direction. Why does dBi equal dBd plus 2.15, not dBd equals dBi plus 2.15?
isotropic antenna has equal gain in all directions where a dipole has a null off the ends and (more gain/energy) off the broadside. take a balloon and point your fingers together your fingers form the null and balloon expands (gain) out
Sorry, sir, is there a journal, if so, can I send it by email?
pleas respon me
dBi = dBd + 2.15. Should this not be dBd= dBi + 2.15 based on blue and red diagram/ pattern shown? @14.27
what means By ALOHA
See:
www.wirelesscommunication.nl/reference/chaptr06/aloha/aloha.htm
DB is a ratio. Not aabsolute
DBM is absolute value.... mW
Isotropic v dipole
Sir, very useful information.. I request you to make a video like how to read the datasheet of the Antenna.
Here is the Example: www.johansontechnology.com/datasheets/0868AT43A0020/0868AT43A0020.pdf
In the datasheet Antenna Gain:-1.0 dBi represent minus values so it represents loss?
Asmat, thanks for the input. I am working on several videos about antennas and I am explaining most often used antenna parameters used in datasheet. I have missed negative antenna gain, oops.But I will explain this in my tutorials. THANKS!
@@Mobilefish I appreciate your quick response on this.. looking forward to see your video on this..