Fast Easy Guide to Decibels dB vs dBi in 6 Minutes

Decibels (dB) can be slightly confusing. Here is a simple short video explaining. Callum.
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[richb.]

Antenna manufactures love to use the DBI rating for their antenna's because it makes the antenna look 2.1db better than it actually is. Since none of us have antenna's in outer space using an isotropic rating is pretty much useless. Any time you see an antenna rated at dbi subtract 2.1 right off the top.

[Siskiyous]

I am sorry it took me a week to watch this. What a straightforward way to untangle the dB - We need a dBC measure.

[Steve-GMHUU]

Good explanation. Often bugs me when someone states states 10dB. I think dB with reference to what? Isotropic radiator power, dipole, mW, Volt, etc. This can be important. For example, +6dBmV is a doubling of voltage whereas +3dBmW is a doubling of power. With antennas, PAs, feeder, we are usually interested in power but for small signals in radio equipment it is often voltage that's important. To save folk looking it up: dB (power) = 10 x log (power_out/power_in). dB (voltage) = 20 x log (voltage_out/voltage_in). So, if power out is 200mW for 100mw in, we should say the gain is +3dBmW. If power out is 100W for 5w in, the gain is +13dbW. If RMS voltage out is 100mV for 50mV in we should say gain is +6dBmV. Also, be wary of antenna manufacturers who say things like their antenna has 1.5 dB gain. If they mean +1.5dBi, this is 2.15 - 1.5 or 0.65dBi less gain than a dipole. So, you might think you are buying an antenna that gives you more gain at a particular angle/direction but may actually perform worse than a basic dipole.

[JesterHellsingborg]

Thanks...have an amazing weekend...enjoy family time 🤙💚🙏

[DKONV]

I always use green Marker on green Boards! Happy Weekend Lord Callum...😉💯🙋‍♂

[brentjohnson]

Great discussion on “bananas” ! Haha. All the best!

[markramsay]

Great Video Cal as always. If anyone is using dB in any exam I really recommend making up some of their own examples for adding and taking away dB. It is not a difficult concept, but it is odd if you have not come across it before. I found doing a load of simple calcs helps at loads. Mark, 2E0MSR

[gaptastic]

It's logarithmic scale, no? But I did like the affix identifier explanation. Thanks Callum!

[acestudioscouk-Ace-GACE]

Thanks for the video Callum! Decibels is a subject which ties people in knots, I found it a little easier when I understood that it's a really useful way of comparing a really wide range of numbers, like when you start talking of plus or minus 30dB compared with 0dB.

[PatAutrey]

Field day is coming up pretty quick and I'm kind of concerned about operating in close proximity to other radios I was wondering if you have any recommendations to protect the radio so it doesn't get damaged I am using a 991 Yaesu

[davidhtims]

I am commenting here to seek an antenna solution. My location is in a shallow valley. It runs north and south for about 100 miles. The east and west ridges are 500 to 800 feet above my location. My property is 130 feet wide north and south. East and west is 600 feet. What antenna has a high takeoff angle to help clear the hills?

[luiscosme]

@5:41 You said 13 is 2. Where did the 2 come from like magic?

[mikeladd]

Any chance you can explain smith charts.

[deankqadj]

You have helped clear the dB mystery for me. Thanks for taking the time to explain!!

[southernexposure]

Thank you for the video and explanations. I've watched about a dozen dB videos and I can parrot a lot of what each says and each explanation is almost the same. I still have a few questions and I bet you're the only one who can touch me with some understanding of my questions.
Mainly (that is to say my highest proprity at this time is) I'm trying to make an RF probe with which I can measure the output of a one transistor crystal oscillator, and then measure the subsequent stages to see the gain. I think I'll have to put amplifier stages in a box before I put the VOM leads at the oscillator output so I can get a reading on the VOM. I don't want to make one watt of RF power before I see the meter needle (digital meter reading etc) increase to zero.
My question on that is how many stages (I suspect using small plastic RF capable transistors) of amplificaton do I need in line between the transistor output and the meter lead to get an indication on my VOM. I do understand that 0 dB is equal to 1 mW RF power. And I understand that doubling the power is 3 dB gain and all that other stuff about the S-Meter readings.
Oh I don't care at this time about technical accuracy I just want the get a meter indication that I can see.
My next question is secondary and relates (I suspect to Audio dB). I just got a few new VOMs and they have a dB scale. The manual says how to add a number to the AC meter reading get the actual dB. Is the the measurement made by placing the meter leads on the speaker terminals while the speakers are being played? I'm guessing that's right.
Thank you very much for your time.

[Mystik-Kitty]

THANKS CAL for the great video!! SO NICE to watch you! This is Kathryn from Alaska, now living in Texas! Just got my 9 band Butternut erected at the new home, and perhaps one day will be able to DX with you! 88s! de KL4QZ (ps: still going strong with my DXC Classic for portable HF!!)

[zeebraeend]

That's very clear indeed. Thank you

[aeron-mwofs]

The wife has quite a lot of dB's .

[DonzLockz]

dB is still hard for me to understand, expecially minus dB on my wifi signal on my router.🤔

How many "dB years" do I need to understand dB?😂

[charleswoods]

Funny little discovery I made; I seem to get better audio quality (in single sideband) by lowering my output power in the transceiver. Also, better DXing!