• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

300 ohm ladder line on 11 meters ?

Needle Bender

...he thinks it's funny that I stepped in it
May 15, 2010
1,403
319
93
.A balun and a coxial choke are two different things. Chokes will still upset the balance.

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? :confused:
What would you expect it will do?
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,883
11,101
823
59
Nova Scotia,Canada
Where did I say it would not transfer RF? A wet string will transfer RF but I would not use it for a transmission line. You should read a bit more about balanced and unbalanced antenna systems. Transferring RF and doing so efficiently are two different things.
 
  • Like
Reactions: 3 people

Robb

Yup
Dec 18, 2008
11,433
3,569
323
Silicon Valley CA, Storm Lake IA
This is a balun:

220px-Homemade_balun.jpg


It is an impedance transformer

This is an RF choke:

G4APLBALUN2A.JPG


It is just supposed to be "ugly" and choke out CMC's . . . lol . . .
 
Last edited:

hookedon6

W9WDX Amateur Radio Club Member
Jun 21, 2008
1,484
243
73
What about just shorting the ends of the 300 ohm and tapping it back a bit at the 50 ohm point for the 50 ohm coax to attach, like a stub match?


ok,........ are we gonna change the lenght of the ladder line to adjust the SWRS too?:whistle:
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,883
11,101
823
59
Nova Scotia,Canada
This is a balun:

220px-Homemade_balun.jpg


It is an impedance transformer

This is an RF choke:

G4APLBALUN2A.JPG


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
 
  • Like
Reactions: NZ8N

Needle Bender

...he thinks it's funny that I stepped in it
May 15, 2010
1,403
319
93
Where did I say it would not transfer RF? A wet string will transfer RF but I would not use it for a transmission line. You should read a bit more about balanced and unbalanced antenna systems. Transferring RF and doing so efficiently are two different things.

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?:whistle:

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.
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,883
11,101
823
59
Nova Scotia,Canada
Here ya go.
Happy now?

Windom-balun-OH7SV.gif


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:
 
  • Like
Reactions: NZ8N

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,883
11,101
823
59
Nova Scotia,Canada
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.

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.



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.


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.
 

Needle Bender

...he thinks it's funny that I stepped in it
May 15, 2010
1,403
319
93
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. ;)
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
16,883
11,101
823
59
Nova Scotia,Canada
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.
 

dxChat
Help Users
  • No one is chatting at the moment.
  • @ BJ radionut:
    LIVE 10:00 AM EDST (y)
  • @ ButtFuzz:
    Of course the 1st day it is nice outside and I go plop the true Rod Of God for 20m on the mobile, All I hear is a couple of yokels talking about bowel movements. What's the 6m calling freq? 50.125?
  • @ ButtFuzz:
    The true Rod of God.