Isotropic Antennas - dBi vs dBd - and Negative Gain
Рет қаралды 4,158
Күн бұрынHow can an antenna have a NEGATIVE gain - and still work great? I often quote gain in NEGATIVE numbers. What is that - and why do they work? Let's unpick dBd and dBi and why we need these numbers to benchmark our antenna results.
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@rrrandommman 2 ай бұрын
You so often make videos on radio theory topics I've been meaning to get my head around, you're a credit to the community, 73.
@DXCommanderHQ 2 ай бұрын
Hey thanks!
@robertabbott7770 2 ай бұрын
kept staring at the dot - We love Lord Callum - We love Lord Callum - We love Lord Callum !!!🤣🤣
@rrrandommman 2 ай бұрын
We love Lord Callum. @_@
@DXCommanderHQ 2 ай бұрын
HAHA.. Crazy! You've been watching too many of my videos!!
@grahammoucka7270 2 ай бұрын
"poke a balloon in the middle" 🤯 such a simple explanation to understand 😂 thanks!
@DXCommanderHQ 2 ай бұрын
You bet!
@snokones 2 ай бұрын
But this is why i keep two antennas. I have my 12.4m Signature, That i absolutely love. And a 135' Doublet fed with 600ohm. If one doesn't get the contact, the other will.
@DXCommanderHQ 2 ай бұрын
Perfect!
@j.p.thearmoredchef 2 ай бұрын
Fantastic explanation!
@DXCommanderHQ 2 ай бұрын
Great :)
@BrokenSignal 2 ай бұрын
Love this, very good videos explaining dB!
@DXCommanderHQ 2 ай бұрын
Much appreciated!
@sunn1011 2 ай бұрын
I love when you draw things! Have you ever thought of raffling off those sketch books for charity? They are works of art technically.😊 Thanks again for all that you do!
@DXCommanderHQ 2 ай бұрын
Good point.. I keep meaning to do something with them...!
@maciejkowalczyk23 2 ай бұрын
thanks Call 73!
@DXCommanderHQ 2 ай бұрын
Any time!
@Rubedo777 2 ай бұрын
R..iii..ght errr I’ll take your word for this Cal 😵💫 I’m really p.poor at anything maths… I’ve just got plus minus times divide understood, coz I’m thick I suppose… 🧐 still passed my G0 licence though way back when I was just an harmonic 😆 🤣 💙
@DXCommanderHQ 2 ай бұрын
You are funny!!
@migalito1955 2 ай бұрын
I've always wanted to build a 2 element 40 meter Yaggi. I have the space for it, but often I am just too busy elsewhere. I used to build up to 4 element vertical 10 meter Yaggis like a rope ladder and I used a 12.5 calculated impedance at the feedpoint to make them very short in boom length. I then used a folded dipole as the driven element to alter impedance back to about 50 ohms. They worked really well, unfortunately the technique does not scale up to 40 meter size easily. You guys, have likely already had the fun of building one but I need a piece of the fun pie too & antennas certainly are fun to make effective....
@DXCommanderHQ 2 ай бұрын
Well.. It would scale - you just need a huge tower - and some extra money! PS - Great technique for the impedance transformation!
@paulsengupta971 2 ай бұрын
What about building a 40m Moxon?
@migalito1955 2 ай бұрын
@@paulsengupta971 You know, that actually is a good idea... i like it.
@migalito1955 2 ай бұрын
@@DXCommanderHQ Spot on with my wallet is to thin for the towers needed.
@paulsengupta971 2 ай бұрын
@@migalito1955Alternatively, do what Callum has done, create a vertical two element beam using quarter wave ground plane verticals, either phased or passive.
@m0aze611 2 ай бұрын
Hi Callum, trying to access your website via iPad or iPhone and I get a notification that it couldn’t establish a secure connection to the server. Maybe an Apple Safari thing dont know. Regards Mike
@DXCommanderHQ 2 ай бұрын
Hmmm. We're through CloudFlare.. It might be a glitch.
@k9eihamradio 2 ай бұрын
Cal. Thanks for showing the dBb ruler, or dB relative to bananas measurerer. :) Ha!
@DXCommanderHQ 2 ай бұрын
HAHA
@rickbattle5706 2 ай бұрын
Is it legal in the UK to stick your fingers in a balloon? Goodness, I must be missing out. Great Video as usual. KB3NG
@DXCommanderHQ 2 ай бұрын
Yes, new legislation was passed last year!
@DonzLockz 2 ай бұрын
So, more banana's are better?🍌😂 Thanks Callum. ;)
@DXCommanderHQ 2 ай бұрын
Yes Sir!!
@rayb228 2 ай бұрын
Helpful, now i'll have to watch the Db vid AGAIN. Maths defeats me especially when - x - = + and then there's 3.142........where does it end.........Wigglies and Bananas. Good Grief !
@DXCommanderHQ 2 ай бұрын
Ah.. 3.142. At least you know off by heart!
@paulsengupta971 2 ай бұрын
I just thought a downside of using dBb (relative to a banana). Are we talking about distance/length or are we talking about calories? How many dBb does a pie have relative to a banana?
@rayb228 2 ай бұрын
if UK try SLIMMING WORLD RADIO , Sir ;-)@@paulsengupta971
@paulsengupta971 2 ай бұрын
Everything's relative. Especially in Alabama. New measurement, dBb. Relative length to a banana. As for poking fingers in balloons and bulges changing shape, my belt does that to my stomach.
@DXCommanderHQ 2 ай бұрын
HAHA!!
@stargazer7644 2 ай бұрын
The Sun is a pretty good isotropic radiator.
@DXCommanderHQ 2 ай бұрын
Oh yes! It's just a million times bigger than this planet..!
@ke8wlw 2 ай бұрын
First. Good afternoon cal
@DXCommanderHQ 2 ай бұрын
Good bananas day!
@jeffmerlin2580 2 ай бұрын
1:09 Fill the balloon with water, then the analogy works. 🙂 Water in incompressible, air is not. Anyway, that nitpicking. Nice video, good explanation.
@DXCommanderHQ 2 ай бұрын
Yes OK.. I would like you to see your hand compress air :)
@jeffmerlin2580 2 ай бұрын
@@DXCommanderHQ If you're as old as me, you've probably done that with a bicycle pump. 🙂
@jest.s50si83 2 ай бұрын
Heii Call🫡 I'm steal here and watchig you👻 My friend
@DXCommanderHQ 2 ай бұрын
Hello old friend!!!
@Siskiyous6 2 ай бұрын
I dislike dBi because it changes with height and the quality of the ground, using it for comparison takes the thoroughness of a man like Cebik, I would say no one else ever explains their comparison in enough detail for it to be even worth reading.
@DXCommanderHQ 2 ай бұрын
Well dBi NEVER changes, that's the point.. Everything else does though! :)
@paulsengupta971 2 ай бұрын
Antenna fiends change. Entropy. Something to do with putting up antennas while drinking cups of tea.
@Siskiyous6 2 ай бұрын
@@DXCommanderHQ my bad, I am a terrible editor, I meant dbd
@williamkizer3445 2 ай бұрын
Real explanation very cool 😎KQ4OHB
@DXCommanderHQ 2 ай бұрын
Thanks 👍
@dondonaldson1684 2 ай бұрын
Then there is dBDXC 😂
@DXCommanderHQ 2 ай бұрын
Oh yes!!
@JayN4GO 2 ай бұрын
Dbi needs to be canned. Dbd and dbd over average ground more reasonable. These companies will never understand that true gain sells. Innov meh they’re getting better. Not quite there yet.
@petemillis4666 2 ай бұрын
dBi does not "need to be canned". Reference to a theoretical isotropic radiator is a perfectly scientific and valid comparison. What needs to happen is that amateur radio ops / hams need to partake in self learning and critical thinking, and gain a decent understanding of the comparison to various reference antennas.
@JayN4GO 2 ай бұрын
@@petemillis4666 there shouldn’t be 3 imaginary made up reference points to base scientific theories. Make the shit realistic
@dondonaldson1684 2 ай бұрын
@@JayN4GO"dBd over average ground" isn't realistic. I understand your point but as soon as "average" is brought in to the discussion it infers statistical mean, standard deviation and variance...