2:1 match? How?

[HomerBB]

I've noticed that most matching methods for beams seem to bring up the match from say, 25 to 50 ohms, or for dipoles use 4:1 baluns to bring down from 300 to 75 ohms. Is there an easily made, non ferrite cored balun or other system that will match down from 100 to 50 ohms, that is, a 2:1 match?

 

[Robb]

As a guess, It would have to be the way the windings are done inside the balun...

 

[Beetle]

Try Googling "2:1 balun".

 

[W5LZ]

A balun does two things. It 'converts' between a balanced and unbalanced state, and it's an impedance transformer. They can have other desirable characteristics, but those are the only two they are designed/made to do.
Like other transformers, you can design for almost any input/output impedance. Basically a matter of the turns ratio between input/output. So, a 2:1 balun is certainly possible. How do you make one? I've got to be the last one in the world you wanna ask that of! I would recommend 'googling' for "antenna balun" and seeing what you get. You might try this;

ScrewDriver Antenna Balun

There's an interesting torroidal balun for screw driver antennas I'm thinking of trying. I'd keep looking though, there are several interesting ideas in all that 'googling' mess.
- 'Doc

 

[C2]

Don't forget about the non-ferrite core part...

 

[W5LZ]

...rats!
Oh well, already made my first mistake today, now i don't have to worry about making more.
- 'Doc

 

[C2]

This is what happens when you stick big pictures in front of my face...

Now I see that the text below describes a 75 ohm coaxial matching stub.

I think I wanna build that balun too though, so you back on top now Doc.

 

[HomerBB]

Thanks, guys.

The non-ferrite core thing is because I don't have any laying around, the googling gives me all kinds of solutions for 4:1 baluns. I am ignorant of the differences between one type of ferrite core and the other so I don't know which ferrite core to order. (Google seems to have a schoolboy crush on explaining endlessly the building of 4:1).

I am not yet smart enough to figureit out on my own.

Seems the only solution waving its hand to answer the question is the 1/4 wl 75ohm section at the feedpoint.

 

[W5LZ]

Why the deal about 4:1 baluns? Cuz they're usually 'simpler' to do, sort of, not as many wires to keep track of. Are 2:1's any harder to build? Not really, just takes longer, at least for me (that's a guess cuz I ain't made one in a lotta years). Best bet if you really want to know what you are doing is to do some of that reading, finding the time/book/whatever isn't the easy part. There are several books around that tell more than you'll ever want to know about torroidal and other baluns.
That electrical 1/4 wave 'Q' section probably is the easiest solution. The type coax needed is typically available. The only 'trick' to them is to keep 'things' within their capabilities, as in power put through them, there are limits.
They do work! May not be the 'best' solution in every case, but then, this isn't every case, is it? As long as that impedance transformation is done half way reasonably, that's really all that's necessary.
"Easy does it.', in almost every sense of the phrase...
- 'Doc

(all puns, innuendos, whatever, are intended... even the ones I didn't see.)

 

[Robb]

With a short QSO w/Ham Radio Outlet, I discovered that you can a 'unun' kit that gives you the parts to tune a transformer to your own specs. 'Hi-Sierra' also makes a 2:1 balun that runs about $90 - ouch! They also said that Palomar makes a kit as well.
Check with your local HRO distributor for details...

 

[HomerBB]

Thanks, again.

I don't have any power to put through anything other than the radio. No problem there. My quest is for the best antenna setup I can afford, and to build it in the process. I've been a carpenter for years and assembly brings me little to no satisfaction compared to actually crafting a thing.

I'll do what I have to in the long run, however, since the first foal is a good antenna before upping power levels.

 

[jazzsinger]

Thanks, again.

I don't have any power to put through anything other than the radio. No problem there. My quest is for the best antenna setup I can afford, and to build it in the process. I've been a carpenter for years and assembly brings me little to no satisfaction compared to actually crafting a thing.

I'll do what I have to in the long run, however, since the first foal is a good antenna before upping power levels.

try a 6ft length of rg11/u or rg59/u or any other solid dielectric cable with a velocity factor of .66 and a characteristic impedance of 75 ohms.

or 7ft 2inches of rg6 or any other foam dielectric coax with .78-.80 velocity factor with 75 ohm characteristic impedance.

both these will make a 1/4 wave 2:1 transformer and transform your 100 ohms down to around 50 ohms.

formula is Rin=Zo^2/Rout
Rin=75^2/100
Rin=5625/100
Rin=56.25ohms

56.25ohms is near enough to 50 ohms for a decent match.swr would be around 1.1:1

This type of transformer is narrowbanded but should be ok for the US 40ch cb band.its exactly what is used on each side of a cophase harness for dual mobiles or dual base antennas as both of those antennas are stepped up too 100 ohms so that when they are paralleled they give 50 ohms.

technically you could run any odd 1/4 wave multiple of 75 ohm coax right back into your shack to avoid having to join it to a 1/2 wave repeating 50 ohm line and the losses that would incur through the coax plugs and double female joiner necessary to connect the two sections.

as an odd multiple of a 1/4 wave gives the same impedance transformation as a single 1/4 wave.

the further you go above or below 27.185 the more reactance will play a part and the more ineffective this type of transformer will be.

 

[RickC.]

If you can insulate the driven element (I'm assuming that's what you're doing since you're asking about baluns), an inductive match is pretty easy to make- HyGain called them Beta matches, and the name stuck. I've done several of them over the years. Check out W4RNL's articles on them. It was his favorite way to match homebrew yagis, and he has some good info on them.

If you're trying to match a 25 ohm load to a 50 ohm source, the 75ohm Q section won't do it. Now you -can- put two of them in parallel, but that's a PITA.


Rick

 

[jazzsinger]

If you're trying to match a 25 ohm load to a 50 ohm source, the 75ohm Q section won't do it. Now you -can- put two of them in parallel, but that's a PITA.


Rick

you didn't read the originally post properly,he is looking for a way to match 100 ohms to 50 ohms in which case a 75 ohm q section is ideal as long as he ain't wanting it for a huge bandwidth.

 

[RickC.]

you didn't read the originally post properly,he is looking for a way to match 100 ohms to 50 ohms in which case a 75 ohm q section is ideal as long as he ain't wanting it for a huge bandwidth.

You're right, my bad. I've used Q sections several times with quads and delta loops with good results.

Whatcha buildin', Homer?

Rick