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Without a balun you throw the entire system out of whack by connecting the unbalanced coaxto the balanced ladderline. More losses from the required balun
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Without a balun you throw the entire system out of whack by connecting the unbalanced coaxto the balanced ladderline. More losses from the required balun
Really? So what does that cause? Are you saying that connecting 50 ohm coax with a choke to the 50 ohm point on a stub won't transfer RF?
What would you expect it will do?
This is a balun:
It is an impedance transformer
This is an RF choke:
It is just supposed to be "ugly" and choke out CMC's . . . lol . . .
It is an impedance transformer
This is an RF choke:
It is just supposed to be "ugly" and choke out CMC's . . . lol . . .
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ok,........ are we gonna change the lenght of the ladder line to adjust the SWRS too?
This is a balun:
It is an impedance transformer
This is an RF choke:
It is just supposed to be "ugly" and choke out CMC's . . . lol . . .
The first image is not a balun. Why do you think it is? Just because it uses a torroid core?
It is a simple choke as well. Same thing as winding a power cord around a torroid. That is if i see coax cable on that torroid. I am on my phone and the image is a bit small.smallish
Right, that's what I'm asking. How much efficiency is it going to lose, and why, by forcing current into and out of the balanced feedline using a cmc at each end in the unbalanced line instead of a balun? Please elaborate.
ok,........ are we gonna change the lenght of the ladder line to adjust the SWRS too?
I believe the tapping point and distance from the shorted stub is what determines the impedance.
If you're comparing cutting unbalanced coax at an electrical 1/2 or 1/4 wave multiple, to cutting shunted stub tapped 450 ohm, I don't believe they are the same since balanced line should offer equal but opposite currents, unlike coax.
Here ya go.
Happy now?
Yes, I am happy now. No need to be snide about it Robb.
Hookedon6, it is indeed a transformer as well. It is a 4:1 transformer that happens to convert from an unbalanced feedline (coax) to a balanced antenna.
The problem as I see it are the terms balun, choke, choke balun (a misnomer BTW) and impedance transformer are all used and most folks do not know the difference between them.
A choke will restrict or choke off CMC's whereas a balun will prevent them from occurring in the first place. The term choke balun is a misnomer as it is really just a choke used between a balanced and unbalanced feedline. It does not perform the function of a balun but it does act as a choke. A balun can also be an impedance transformer like a 4:1 balun etc. An impedance transformer may be either balanced or unbalanced. The latter is commonly called an Un-Un which is a term I hate because all it really is is an impedance transformer for unbalanced line. A common impedance transformer for unbalanced lines is a 50 ohm to 75 ohm (1.5:1) transformer for using 75 ohm CATV cable in a 50 ohm system.To me an un-un is a pungent vegetable that makes your eyes water when you peel and cut it. :laugh:
Hard to say exactly how much efficiency will be lost as it depends on several variables. Impedance of the coax, impedance of the balanced line, SWR on each line, RF currents in each line how bad the balance is upset etc. What I am saying is that by unbalancing the line by using common mode chokes on each end rather than baluns is that the now unbalanced ladder line will radiate as part of the antenna system and signal will be lost on TX and the feedline will pick up signals as well as the antenna.
The balanced line will have equal and opposite currents as long as it stays balanced. throw an unbalanced condition into it and those currents are no longer equal or opposite.
Why would it unbalance the 450 ohm if there were a cmc choke employed at each end preventing >95% of the current from feed line radiating? Remember, according to the cmc chart, 5T @ 4"F provides about 5K ohms impedance, or 100 times a 50 ohm impedance.
An imperfect scenario perhaps, but to what degree?
Considering the loss in using a balun on each end plus the cost in purchasing a set, or the cost in time to learn to correctly make an efficient set, or comparing the loss and cost of 200' of LMR400, I would think this imperfect scenario just might be the least expensive way to get at least equal, if not superior performance resulting in a net savings in cost and a possible net increase in performance.
A common mode choke only keeps the portion of the feedline, coax cable,between the choke and the transmitter from radiating. That is why they are used at antenna feedpoints. Once the balance of a balanced line is upset it will radiate regardless of the presence of another CMC on the other end. It is a good example of two wrongs not making a right.