Balun, Choke, Counter-poise....

Hi all,

I've been struggling with the differences between the three, so a simple description would be great please.......I think I get that the choke is an isolator which ends resonance, but I'm lost on the Balun and Counter-poise chaps.

Thanks

Simon.

Balun = balanced to unbalanced use is where you feed and unbalanced tramission line to an antenna, the antenna is balanced (the length of the antenna corresponds to a wavelength that the antenna is tuned to) this allows for low reflected transmit back to the device transmitting.

counterpoise i have no idea, ill google and see what i find and perhaps update my reply on what a balun is 

This is from memory, been a few years

Update from wikipedia, i was not that wrong it turns out

"A balun /ˈbælʌn/ (from "balanced to unbalanced", originally, but now dated from "balancing unit")[1] is an electrical device that allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either line.[2] A balun can take many forms and may include devices that also transform impedances but need not do so. Sometimes, in the case of transformer baluns, they use magnetic coupling but need not do so. Common-mode chokes are also used as baluns and work by eliminating, rather than rejecting, common mode signals."

go to wikipedia to see more and there are links in the articel, i am too new to post links.

Counterpoise forms part of the antenna.
It is fitted to the earth ??? side of the balun/unun.
Next 9:1 or 49:1 and so on.
9:1 for a random length of wire.
49:1 for a resonant length of wire.
And there's more but our Victor will be along soon to put me right as i am not good at explaining things lol.

There is more than one definition of counterpoise. In short it's something for the antenna to work against. If you have 10 mins, David Casler describes better than I could..

Hi Simon,

Cor, this is going to depend on who you ask.....


The 'choke' does pretty much what it sounds like. Usually used to try and stop unwanted signals coming through, it never totally stops it but rather restricts it and hence 'chokes' the signal path. I say 'signal' as it can mean any electromagnetic signal from mains hum to RF.
Confusion arises because many think of any inductive wound lump as a 'choke' so the word gets used for many things.


Balun, often mispronounced (balum????) but means an inductive method utilised to couple a "Balanced" load to an "Unbalanced" one and hence Bal-Un. For example the coaxial output and coax cable used from the back of your transceiver is an unbalanced load and if you were pumping that into a balanced antenna such as a dipole (or doublet, more confusing interjection) you'd need to convert it into a balanced feed. Really depending on your point of view it could be called an "Un-Bal" but that doesn't roll off the tongue as well.


Counterpoise - a dirty ugly word used by Ham operators. Honestly joking aside it gets used for too many things and is essentially anything placed on the 'ground' path of an antenna. A length of wire, an artificial earth, a ground mesh, ground radials, radials in the air but essentially something trying to 'counter' (the opposite direction) RF current to 'poise' (balance) the antenna load. Even if the antenna doesn't have radials or some such your coax, radio, microphone and even you can become the 'counterpoise'!
(I won't get into Kirchoff's circuit laws but that's ultimately what it's about.)


That's about the basics but due to some simplification or misunderstanding more confusion arises than is absolutely necessary.

A commonly used choke would be an inductive lump used to prevent stray RF currents such as Common Mode Currents (CMC) coming back down a coax cable. Think 1:1 Guanella with windings around a ferrite toroid or 'winding up' some coax around a cylinder to place in the antenna feed path sometimes also disturbing the RF return path on an end-fed.

A Bal-Un is often used on a dipole setup particularly at HF frequencies but unusually not a lot with VHF/UHF antennas. Where's that Bal-Un on your Yagi beam which uses a straight or folded dipole?? 


There's way more confusing elements to it all depending on who's selling it, whether that is "information" or prying you out of money for a 'magical box' with a winding of wire and some ferrous material inside. (Hidden by 'potting compound' to make sure you don't copy it.....ahem, waterproof it.)
Then there's the "auto transformers" (not Optimus Prime  ) which 'convert' complex impedances such as the typical end-fed 9:1, 49:1, 64:1, etc.

There'll always be those that do the "Wrong! Wrong! Wrong, Wrong!" exercise making you feel like you're being swatted in the face with the wet end of a dildo at each utterance of the word 'wrong'. Often accompanied by how many years they've been an Amateur Radio operator or espousing some mathematical reasoning making their numbers fit observations rather than prove anything.


No wonder it's all flipping confusing!


So apologies for not giving a straight forward answer because really these things are hardly straight forward at all.

I know, I've been there and have now chucked it all out of the window instead running a way too short, non-resonant, ladder-line fed antenna system without a choke, Bal-Un, transformer or other such in sight! Instead I have a simple tuned LC (inductor & capacitor) circuit hooked up to a 50 ohm winding of coax to link couple my radio to the antenna. Simple, straight forward, works, yet dismissed by so many.
(Many will argue the 'link-coupling' performing similar tasks.)

But then I'm not after the apparent 'best-of-the-best' type solutions and will leave such confusion to those that pursue those avenues.


Part of the 'fun' of radio is getting it all working to make that contact and there are many solutions to it all. 
Just enjoy the ones that work for you and never slam anyone for having a different method.


Yeah, I know, that's probably not helped much......or maybe it has.

All the best,
Victor

I said our Victor would be along soon.

Simon
Why do you ask ???.
What you up to come on spill the beans lol.

I'm hoping that he's looking to expand his horizons into HF Alan, maybe eyeing up or getting a new rig....

Plus all the confusions that comes with HF antennas!

Got a book coming today "Hf Antennas for Everyone".
Amazon best price RSGB want more for it.
Will let you know what it is like.
https://www.amazon.co.uk/gp/product/1905086598/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1

Hey Victor, your making those long posts now like I used to.  Keep up the good work, you've come a long way.

Lets see if I can break this down from a different point of view.

Chokes.  These have one purpose, they raise the impedance of one part of the antenna system (typically the feed line) to make it less desirable for the RF current to flow there, in essence manipulating where the current that is trying to radiate will naturally flow.  That is all a choke does.

There are two varieties, resistive and reactive.

Resistive chokes are almost always ferrite based, although other materials can be used as well.  They make several varieties depending on the coax used, snap on, put on before putting on one of the connectors, and some large rings that you feed smaller diameters of coax through multiple times.  This is my preferred method of choking, and I put beads on a coax before connecting one of the ends.  As a personal preference, I use heat shrink tubing to hold said beads into place.  It comes out with a very clean look that is easy to miss if you don't know what you are looking at.

This method of choking uses pure electrical resistance to prevent common mode currents, i.e. it converts said current directly to heat, just like an electrical resistor.  This type of choke also tends to be very wide banded, and some designs can cover the entirety of the HF spectrum.

Reactive chokes, which I think are far more common as they are often a coil of coax wound to specific dimensions.  A lot of people see them as easier and cheaper than ferrite chokes (although in my experience it really aren't).  They also tend to be very narrow banded, and if you get the dimensions wrong can cause more problems than they fix.

Unlike the resistive chokes talked about above, these use reactance.  This is a bit more difficult to explain.  You may have heard of "resonance".  In the hobby space, "resonance" who's variable is "X" is X = 0, or no reactance.  The goal of X = 0 is to allow as much current flow into the antenna as possible.  When it comes to reactive, or air would chokes, we actually seek out the opposite.  We want X to be as high as possible.  In common 5 turn air wound chokes, X can get as high as 8000 or even higher, which is very high compared to other parts of the antenna, thus preventing current flow through said choke.

Baluns are devices that force RF currents on two wires into balance.  Typically used when connecting an unbalanced feed line into a balanced antenna, but can be used at other times as well.  Baluns will be either "voltage baluns" or "current baluns", and sometimes one works better and other times the other will.  In most cases, baluns are also used as impedance transformers.  For example, you have an antenna that has a feed point impedance of 200 ohms, a 4:1 balun will convert the coax 50 ohm input to the antenna's 200 ohm input.

There is another type of device called an unun, or unbalanced to unbalanced impedance transformer.  These will convert impedance but not force balance.  Many people call these "baluns" even though they don't actually force the balance that baluns are required to do.

Another misuse of the word is when referring to reactive chokes above.  Many people call them "air baluns" or "choke baluns".  They are technically not baluns as they don't force both wires that feed the antenna to be in balance.

And finally the word "counterpoise"...  This, I can write pages on but I'll try to be somewhat brief.  I'll break it up into counterpoise (traditional engineering) and counterpoise (modern hobby).

Originally, counterpoise referred to a very specific device that was meant to do something very specific.  A more accurate name is (was?) capacitive ground system.  It was an elevated radial system that was close enough to the earth that it could use "capacitive coupling" to electrically connect the antennas ground system to the earth itself.  Think of it like a magnet mount antenna, the magnet, in addition to holding the antenna in place, provides an electrical path for the currents on the shield of the coax to connect to the metal chassis of the vehicle, and thus make said chassis a "ground plane".  There is no DC connection here, but RF makes the jump.

As a counterpoise is intended to be one plate of what is essentially a capacitor, it has a requirement.  It has to be close enough to the earth for a connection to be made, which for the CB band is no more than about 2 feet off above the earth.  On the plus side, as it is just one side of a capacitor, it doesn't have to be resonant.

So now onto the counterpoise (modern hobby).

Well...  I asked what a counterpoise is to different people on this forum once, I got 14 answers, and they were all different.  So yea, counterpoise can apparently mean whatever the person using the word wants it to mean.  In general, most people tend to settle on one of two general lines of thoughts.

1) Anything connected to the shield of the coax at the feed point

2) Anything that counts as the antenna's "other half"

In addition to this, there are many small variations, for example, some people consider the outside of a coax shield as part of a counterpoise, while other people don't.

I have also seen other descriptions and uses of this word, including an on ground radial system for a horizontal antenna that is connected to the coax, but not at the feed point, literally 20 or 30 feet or more up the feed line from said feed point.

I can go on and on here but I think this is a good place to stop.  This post is already longer than I wanted it to be...

So yea, the word "counterpoise" can literally mean virtually anything and will have different meanings and uses to different people.  The one take away I have for this is every use of this word has a more accurate and descriptive word or phrase to describe what is going on.


The DB

SangueG wrote:

There is more than one definition of counterpoise. In short it's something for the antenna to work against. If you have 10 mins, David Casler describes better than I could..

The Ask Dave YouTube videos are excellent on a wide variety of subjects for radio.

Interesting one well for Victor anyway.
2 pictures below one with auto tuner on and one with it off.
Changed my 49:1 unun for a 5:1 unun and tested it out on top band 160m.
Antenna is 67ft with a 110uH coil for the 80m band.
All comments welcome as i am scratching my head while smiling at the same time lol.
Top right you see the red transmit icon.
Tuner off

Tuner on.

Playing again.
Just made another 49:1 balun.
This one is slightly different in that i didn't twist the first 2 winding much at all and went on to add some extra turns 7 in fact.
Read about doing it this way so i thought i would give it a go.
With resistors attached and the RigExpert attached it shows 1.05 up to 1.19.
Plugged it into the vna after only need one picture of that lol.
What do you think.