Inverted v balanced line balun question

weccwwe

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Hi all

So I am currently working on creating an inverted v with a total length of 120 feet of insulated, stranded 12 gauge. In the center I would like to use 450 ohm ladder line to the tuner. My intended use is for 80,40,20,10,6

There is approximately 75 feet from the center of the inverted v to the manual tuner (mfj-945e). The tuner has so239 connector.

Where in the v to tuner section should I convert from the 450 ladder to the RG213? Should I use a 4:1 balun at that connection?

Or should I just have the balun at the inverted v center and forget using the 450 all together?

Regards
 
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weccwwe

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Hi All,

Well I have to rephrase my question above. I am over thinking this by a country mile........... And I can't edit the first post.......

What I have:

2 x 60 feet of 12Gauge stranded insulated wire, for an inverted V.
An MFJ-945E Tuner

What I would like to achieve: 80,40,20,10,6

Which Balun do I require for this?

Regards
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
You would generally use a good 1:1 choke balun with the highest isolation or resistive impedance you can find. That will in effect force a balance on the ladder line side by virtue of the high isolation. The reason you would use a 1:1 is because the impedance at the antenna and at the end of the ladder line will be all over the place, could be 5 ohms at one frequency and 2,500 ohms at another, so using a 1:1 will have less IR loss at the really low impedance.

You would only benefit from a 4:1 if you knew for sure the impedance at the balun would always be on the high side like 100 ohms or more at all frequencies or you were using it at both ends of some ladder line going from 50 to 200 ohms and back to 50 again and the 50 ohm sides were matched.

BTW, MyAntennas has the highest isolation choke baluns I've come across. You can easily solder a PL-259 on the ladder line and use their CMC-130-3K or CMC-130S-3K or the BL-8010T-2K has screws on one side for direct connection of the ladder line.

Hi All,

Well I have to rephrase my question above. I am over thinking this by a country mile........... And I can't edit the first post.......

What I have:

2 x 60 feet of 12Gauge stranded insulated wire, for an inverted V.
An MFJ-945E Tuner

What I would like to achieve: 80,40,20,10,6

Which Balun do I require for this?

Regards
 

Ubbe

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Stockholm, Sweden
The website says to use as short coax as possible from their choke balun to the tuner. It's only the mentioned BL type that converts from balanced ladder line to unbalanced coax.

The ladder line are 300 or 450 ohm and won't change much independent of what the antenna does to it, if the ladder line are long enough and 75ft seems to be sufficient enough to isolate most of the antennas impedance to the other end of the ladder line. You should use a 4:1 balun directly at the tuner, or probably from the outher house wall as it is difficult to install a ladder line all the way thru walls and inside rooms without it being too close to other objects that will interfere with it and it will start to radiate and pick up local RF noise.

/Ubbe
 

prcguy

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Different lengths of balanced line like 300 or 450 ohm will act like a transformer and give different impedance readings at the radio end depending on length. A long length of ladder line will not isolate the antenna impedance but it will change it. The resulting impedance you will see at the radio end can still range from very low to very high impedance across a wide frequency range. I would only use a 4:1 if its proven the impedance will always be on the high end for every frequency used, otherwise a 1:1 choke balun is best.

Most 4:1 baluns are voltage type and have little to no choking characteristics, if you do use a 4:1 make sure its a current type and it has a good 30dB or more isolation from input to output.

The website says to use as short coax as possible from their choke balun to the tuner. It's only the mentioned BL type that converts from balanced ladder line to unbalanced coax.

The ladder line are 300 or 450 ohm and won't change much independent of what the antenna does to it, if the ladder line are long enough and 75ft seems to be sufficient enough to isolate most of the antennas impedance to the other end of the ladder line. You should use a 4:1 balun directly at the tuner, or probably from the outher house wall as it is difficult to install a ladder line all the way thru walls and inside rooms without it being too close to other objects that will interfere with it and it will start to radiate and pick up local RF noise.

/Ubbe
 

rja1

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You really want to use 100' of ladder line with this setup. You can zig zag the LL, but don't coil it up, keep it off the ground and away from metal. A 1:1 current balun at the tuner should work.
 

KJ3LR

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Ubbe

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Stockholm, Sweden
Remember that choke baluns are only for coax use and if you have the majority of the transmission line as a ladder line and only a short lenght of coax then you have no use of the choke balun. Ladder line in itself are a balanced transmission line that do not need any choke baluns.
You only need a balun type that converts a balanced 450 ohm ladder line to an unbalanced 50 ohm coax that then connects to your tuner.

Get the proper 450 ohm to 50 ohm balun type.

/Ubbe
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
I'll say again, the impedance presented at the end of the ladder line at the radio end will only be near 450 ohms at a few frequencies, most other frequencies it will be all over the place and can be a few ohms to thousands of ohms. The worst thing you can do for the antenna system where its a few ohms is put a 4:1 balun there, it will introduce more loss and a 1:1 would be much better. The 1:1 will have less problems in general across a wide range of impedance and only if you can prove the lowest impedance across all your frequencies will be on the higher side would you want to use a 4:1 balun.

Any time you go from a balanced antenna to balanced feedline then coax, the antenna system will be unbalanced at the coax junction and you will have RF riding on the ground side of the tuner, radio, mic cord, power supply, etc, because the radio, mic cord and power supply are now a radiating part of the antenna system. Most 4:1 baluns have little to no choking and will not isolate the coax and ladder line "forcing" a balance like a high isolation choke balun will. Any RFI riding on the ground of your electrical system will also be introduced directly to your antenna and will show up as a higher noise floor on your receiver. Using a good 1:1 choke balun, or a 4:1 if you must, and if it has very good common mode rejection will keep the radio free of hot RF and will keep RFI from the house off your coax and ladder line, antenna and your receiver.

You do want to keep the coax run from the tuner to the choke balun as short as possible and use the lowest loss coax you can physically get by with. More coax at this point means higher losses because the coax will be operating under an extreme mismatch condition and the advertised loss of the coax will be many times greater than the 50 ohm matched loss.

Remember that choke baluns are only for coax use and if you have the majority of the transmission line as a ladder line and only a short lenght of coax then you have no use of the choke balun. Ladder line in itself are a balanced transmission line that do not need any choke baluns.
You only need a balun type that converts a balanced 450 ohm ladder line to an unbalanced 50 ohm coax that then connects to your tuner.

Get the proper 450 ohm to 50 ohm balun type.

/Ubbe
 

John_S

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Saratoga Springs, NY
There are lengths of ladderline to avoid...can't remember where I ran into this before though. And the best plan is to use the least amount of coax possible...putting the balun as close as possible to the radio/tuner. Also keep the balun away from ferrous metal objects.
 
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