How to best explain what is a balanced and what an unbalanced antenna?
The classical balanced antenna is a simple dipole.
The signal enters here and comes out there.
Both legs are the same length.
Preferably half wave length.
So if you want an antenna for the 40m band,
that's about 7MHz,
this length has to be 20 meters. Give or take few inches.
An unbalanced antenna e.g. would be a wire with 20m length,
which has the feedpoint not in the centre, rather at the end
That would be an unbalanced antenna.
A.k.a. half wave endfed.
Endfed because it's feeded on the end.
This is called center-fed.
Because it's fed in the centre.
Also unbalanced are vertical antennas.
Which is fed at the bottom.
And has radials.
And we have the so called 'feeders'.
Or in Croatian I call em connectors,
so I don't know whats the technical terminus for that in Croatian.
The most known feeder for antennas is coaxial cable.
It has a center conductor, an dielectric and a shield.
Also the signal comes through the center
and comes back via the shield.
And as you can already see it's not balanced.
Two simple wires would be balanced.
Where the signal comes in and out symmetrical.
Often used a so called 'ladderline'.
It's the wire that has those plastic spacer in between them.
So it can keep a healthy distance between those two wires.
So why is it balanced?
As the signal goes out it electromagnetizes the copper
and as it comes back it creates an polarized field
so they cancel each others out.
To understand the problem with attaching antennas
we have to talk about 'impedance'.
Basically said, impedance is the resistance. Most radios work on 50 Ohms.
So, our radio has 50 Ohms.
And our coaxial cable has an impedance of 50 Ohms.
And you have to transform the antenna to match the 50 Ohms of the radio.
I can't recall but I think a dipole has 200 Ohms.
I am not certain, but you can look that up in the internet.
To attach this 200 Ohms to the 50 Ohms we got
we need a transformer.
And those transformers are called BalUn and UnUn.
So we can transform the impedance so our station can use it.
If the impedance does not match, we get high SWR (unused power from antenna).
That's a pretty basic explanation. If you want more scientific ones, check the internet.
I don't want to make a 45minutes video, I want to share basic knowledge quickly.
As we already found out, coaxial cable is unbalanced.
A dipole is balanced.
To match those, we need a transformer called "BALUN".
Because we assume this is 200 Ohms,
and this is 50, we need 4 to 1.
4 x 50 = 200.
I often use my radio...
with coax...
and then comes a tuner...
and then comes a transformer....
and then an endfed dipole.
It's a dipole fed by the end.
So we got 50 Ohms...
That's my tuner...
A tuner is needed to match the impedance to our 50 Ohms.
So if you got a resonant antenna...
you can fix this by using a balun.
And a balun will do it for that band because it's a resonant antenna.
It will transform it to 50 Ohms.
But if we have an antenna
which is in my case a 25m long wire
I use that wire on all bands, meaning it is not resonant.
For none.
So it has a high impedance.
But I can lower the impedance through a so called 9:1 UNUN.
It's an unbalanced unbalanced transformer.
I attach an unbalanced coax to an unbalanced wire.
The wire is unbalanced because its fed by the end and not through the centre.
And the impedance here is around 500 Ohms, give or take.
As I already told you, don't nail me on the numbers!
But with this UNUN we can lower the impedance so much,
so the antenna tuner is able to match the impedance to my 50 Ohms.
So I can setup my antenna and use all bands
with just one wire I can transform the impedance so much that my tuner can handle it.
Here we also have a coaxial cable.
And here.
There is a third option.
We take the station
attach the coax to our tuner
and we attach a wire directly to the tuner.
The wire is not resonant in any band, not a halfwave (random wire)
and ground the tuner.
Also we can use the station
Coax
attached to a tuner
and on the tuner you attach
a balanced feeder.
The ladderline we talked about earlier.
To it we attach a dipole.
Which is not resonate.
So in that case we need, assuming our dipole has 200Ohms impedance,
with our 50 Ohms coax, a 4 to 1 BALUN.
Because we attach a balances wire to an unbalanced coax.
With this combination we can use that dipole.
If we want to avoid that ugly ladderline,
and want coaxial cable instead,
up there we must install a 4:1 BALUN.
To attach a balanced dipole to a unbalanced coax.
I often hear people saying they need a balun to reduce common mode current.
Common mode current is this:
we have a coax that is connected to something.
During transmitting it can happen that the current which comes back
goes through the shield of the coax and our cable is radiating.
This is called common mode.
Current.
To prevent this, we need a so called COMMON MODE CHOKE.
This is mostly a thoroid
on which you wind coaxial cable.
How much windings you need, you have to find out yourself.
I found a nice page with a spreadsheet where you can see how much you need.
I'll put the link into the description.
There you'll find what type of thoroid to use, which coax and how many turns for which band.
And finally, there is a so called AIR MODE CHOKE.
People often call it UGLY BALUN.
But a BALUN has nothing to do with it.
I don't know why people say BALUN to it, a BALUN is something different.
You take a PVC pipe
and then some coax
and wind it around.
This prevents current to flowing back on the shield.
So to conclude. If you got a station.
Which is connected to coax.
You have two possibilities:
Either you use a resonant dipole
preferably half wave length
and you feed it via 4:1 BALUN.
Or you take a random wire length
also a dipole, feed it directly with a ladderline
or coax
and this goes to the radio.
If you use a ladderline, you don't need a BALUN
and if you use a coax, you need a BALUN.
Or do it as I do, use a tuner
which is connected to my radio via coax,
and then the coax goes to the 9:1 UNUN
and to this UNUN I attach a random wire length
and I got another wire to act as a ground/Counterpoise
and I can work all bands.
Although such a setup is not as efficient as a dipole,
you set it up very easy and very quickly
and you can change bands without leaving a cozy shelter or tent.
I also got a so called Linked Dipole.
It is a simple dipole with a BALUN in the center.
The legs are linked together and can be connected or disconnected.
So I have a resonant dipole.
If I go on 40m I connect all links, If I go on 20m, I disconnect those two.
And I can use a shorter antenna for the according band.
So thats roughly it. I hope you learned something.
And that those terms are more clear now,
when making future videos about hamradio.
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