2 element Yagi with a Hairpin match

[Crawdad]

Makes no difference which way it is pointed. this is my hairpin match aka Beta match on my home made six element 6m yagi. The reflector is to the left and the directors to the right. Grounding the middle still preserves the balance and also grounds the antenna which would otherwise not be. View attachment 58205

I've modeled the Hairpin facing both ways on a 3-element Yagi. The difference is only a very small change in Inductive Reactance, but did require an adjustment in Hairpin length to get the dip on the desired frequency.

Facing Reflector:


Facing Director:


Facing Reflector:


Facing Director:

 

[Captain Kilowatt]

In other words, you can measure it, but you cannot see it.

 

[Crawdad]

In other words, you can measure it, but you cannot see it.

Exactly. Tiny difference. So I'm gonna have the open end towards the Director. Makes the feedpoint design I have in mind easier to install.

 

[Shadetree Mechanic]

Makes no difference which way it is pointed. this is my hairpin match aka Beta match on my home made six element 6m yagi. The reflector is to the left and the directors to the right. Grounding the middle still preserves the balance and also grounds the antenna which would otherwise not be. View attachment 58205

Just reading back through this, I noticed the three coax connectors. How are they used? Do you use all three?

 

[Crawdad]

Just reading back through this, I noticed the three coax connectors.

Wondered the same thing............

 

[Captain Kilowatt]

Just reading back through this, I noticed the three coax connectors. How are they used? Do you use all three?

Wondered the same thing............

A picture is worth a thousand words but I can't find my pictures of the complete feedpoint. They are on my old laptop that died. The middle connector is for the direct connection of the coax cable that goes to the shack. The two others on either side are for the 1/2 wave coaxial balun. Remember this antenna has a split driver element that is isolated from the boom so it is a balanced antenna. My configuration also has a low driver impedance in the order of 12 ohms. Using a 1/2 wave coaxial balun preserves the balance as well as converts that 12 ohms to near 48-50 ohms. The balun is simply a 1/2 wavelength of good quality coax rolled up and taped to the boom. One side of the element gets connected directly to one end of the balun while the other side has the RF travel thru the 1/2 wave of cable to the other side. This is all I could find at the moment but it shows the connections well. Note that the image shows 75 ohm cable. That is because the antenna in the image is a folded dipole with an impedance of around 300 ohms thus 4:1 means the 75 ohms is transformed to 300 ohms. Use ALL 50 ohm cable for use with a 50 ohms system.

 

[Crawdad]

A picture is worth a thousand words but I can't find my pictures of the complete feedpoint. They are on my old laptop that died. The middle connector is for the direct connection of the coax cable that goes to the shack. The two others on either side are for the 1/2 wave coaxial balun. Remember this antenna has a split driver element that is isolated from the boom so it is a balanced antenna. My configuration also has a low driver impedance in the order of 12 ohms. Using a 1/2 wave coaxial balun preserves the balance as well as converts that 12 ohms to near 48-50 ohms. The balun is simply a 1/2 wavelength of good quality coax rolled up and taped to the boom. One side of the element gets connected directly to one end of the balun while the other side has the RF travel thru the 1/2 wave of cable to the other side. This is all I could find at the moment but it shows the connections well. Note that the image shows 75 ohm cable. That is because the antenna in the image is a folded dipole with an impedance of around 300 ohms thus 4:1 means the 75 ohms is transformed to 300 ohms. Use ALL 50 ohm cable for use with a 50 ohms system.


View attachment 71715

Color me slow-witted CK, but why would it need the Voltage Balun AND the Beta Match as seen in your photo in post #2?

7 3

 

[Captain Kilowatt]

Color me slow-witted CK, but why would it need the Voltage Balun AND the Beta Match as seen in your photo in post #2?

7 3

The beta match cancels out the reactance basically. It also makes the entire antenna DC grounded for lightning protection, otherwise the driver element would be isolated from ground because it is insulated from the boom. Since the driver impedance is so low, in the order of 12 ohms or so, the 4:1 converts that up to the required 50 ohms. The beta match cannot handle the huge transformation from 12 to 50 ohms. It also preserves the balanced condition of the antenna. If the antenna driver impedance was a lot closer to 50 ohms.......say 35-40 ohms......the 4:1 may not be needed if you can reduce the SWR by adjusting the beta match and manipulating the element lengths and spacings, but you would still need a 1:1 to PROPERLY feed the antenna. My configuration yielded a low impedance such that a 4:1 was perfect for it.

I found my old Imageshack pictures, Here is the feedpoint with the balun. Coax to shack connects to the middle connector.

 

[Crawdad]

The beta match cancels out the reactance basically. It also makes the entire antenna DC grounded for lightning protection, otherwise the driver element would be isolated from ground because it is insulated from the boom. Since the driver impedance is so low, in the order of 12 ohms or so, the 4:1 converts that up to the required 50 ohms. The beta match cannot handle the huge transformation from 12 to 50 ohms. It also preserves the balanced condition of the antenna. If the antenna driver impedance was a lot closer to 50 ohms.......say 35-40 ohms......the 4:1 may not be needed if you can reduce the SWR by adjusting the beta match and manipulating the element lengths and spacings, but you would still need a 1:1 to PROPERLY feed the antenna. My configuration yielded a low impedance such that a 4:1 was perfect for it.

I found my old Imageshack pictures, Here is the feedpoint with the balun. Coax to shack connects to the middle connector.

View attachment 71717

Thanks CK, now I get it.

According to EZNEC the Beta match had no issue raising the impedance of a 3-element Yagi from 25 ohms to 50 at design freq. Since we all know everything works on paper and computer screens, does that seem like viable info from EZNEC?? I'm about to build this antenna, my first Yagi build.

Thanks and 7 3

 

[Captain Kilowatt]

Thanks CK, now I get it.

According to EZNEC the Beta match had no issue raising the impedance of a 3-element Yagi from 25 ohms to 50 at design freq. Since we all know everything works on paper and computer screens, does that seem like viable info from EZNEC?? I'm about to build this antenna, my first Yagi build.

Thanks and 7 3

I have never really used EZNEC, but I have no reason to dispute it. A beta match can only be used with a feedpoint less that 50 ohms and you have that. You SHOULD use a balun to preserve the balance of the antenna. A simple 1:1 will work for you. Since mine was near 12 ohms I opted for a 4:1 to simplify things. It just works and works well. IIRC my final match was 50 ohms and 4 ohms of reactance. Good luck with the build.

 

[Crawdad]

Thanks for the advice CK

This will be on it:

I put chokes on everything. Too easy to do.

7 3

 

[BJ radionut]

I think he needs to build a FOUR instead of a three L... model that and see the diff?

 

[Crawdad]

I think he needs to build a FOUR instead of a three L... model that and see the diff?

If he is me Gary, I have modeled 4el and the added gain (.6dB) is not enough to justify the extra weight. I know, I know, but it is what it is. The 3el gain will have to be enough. I'll just be a slightly larger little dog...............

3el


4el

 

[Crawdad]

Here's my version of the Beta/Hairpin for my homebrew 3 element Yagi for 6m.

I'm glad I made the Hairpin adjustable, it makes for quick and easy tuning with an analyzer.

This antenna was a lot of fun to model and build. Cost was ~$80-$100.

Just need 6 meters to open up.......

7 3

 

[HomerBB]

Here's my version of the Beta/Hairpin for my homebrew 3 element Yagi for 6m.
View attachment 72037View attachment 72038
I'm glad I made the Hairpin adjustable, it makes for quick and easy tuning with an analyzer.
View attachment 72039View attachment 72040View attachment 72041
This antenna was a lot of fun to model and build. Cost was ~$80-$100.
View attachment 72042
Just need 6 meters to open up.......

7 3

It looks great!