Impedance Matching Hairpin/Coil?

[QRP 725]

I'm making a 5/8 wave vertical antenna. I understand that inductance matching with a coil lowers the impedance of a 5/8 wave that I believe is about 250 Ohms. Is the coil design using its magnetic field to create inductance as its main purpose? Or is the coil just using its length to electrically lengthen the antenna to 3/4 wave that is closer to 50 Ohms? Maybe its both. I know it is not that the actual physical length of the coil making up the physical difference between a 5/8 and 3/4. But using a coil does shorten it physically as well as a bonus?

Now to the hairpin (beta match) method. A Mako 5/8 vertical uses a tuning ring. It seems to be more like a hairpin design. I thought hairpin matching was for low impedance antennas (less than 50 ohms) using 50 ohm line? More of an adding capacitance technique to bring impedance up.

I thought all the 5/8 antennas where about 200 ohms. So why do some antennas use one method over the other? Is it that some antenna manufactures make different length 5/8 wave verticals? I know the hoop or ring has some inductance even uncoiled. Is this method actually using its physical length to make up the difference between 3/4 and 5/8 electrically and not so much as adding/subtracting impedance? Maybe the real physical length is the difference of a 5/8 and 3/4.

One method lowers inductance and the other raises the inductance, I do not get it? I prefer the look of the ring.

Is the coil actually a hairpin with the added coil magnetic field helping create inductance, with the bonus of shortening the antenna?

 

[The DB]

First things first, I wouldn't get hung up on the magnetism of the loading coil. It is a thing, but not something we are typically concerned about. A step in the right direction would be their inductance, but that is really only half way there. What we are really concerned about is the reactance the device adds to the system, and how it is attached to said system. More on this later.

Also, long post, sorry about that for those that don't like long posts, it isn't the easiest topic to try and explain to someone at his level.

Is the coil design using its magnetic field to create inductance as its main purpose? Or is the coil just using its length to electrically lengthen the antenna to 3/4 wave that is closer to 50 Ohms? Maybe its both.

These are two different ways of looking at essentially the same thing. The loading coil adds inductance, or more specifically inductive reactance. The coil is designed to, along with the reactance of the antenna itself, give a resonant load at the feed point. For a 5/8 wavelength antenna this should be pretty close to 50 ohms at resonance (if I remember correctly, I could be mistaken, its been a while), making it easy to feed with a typical coax.

In the case of the 5/8 wavelength antenna, this is one method that keeps the antenna under a specific physical length, which going beyond tends to negatively affect the radiation pattern of the antenna.

Now to the hairpin (beta match) method. A Mako 5/8 vertical uses a tuning ring. It seems to be more like a hairpin design. I thought hairpin matching was for low impedance antennas (less than 50 ohms) using 50 ohm line? More of an adding capacitance technique to bring impedance up.

Continuing from above (before the first quote), technically speaking, the hairpin match is an inductive device, but it differs from the loading coil mentioned above based on how it is attached to the antenna. Look up series and parallel circuits for more information. Long story short, in many ways it acts similar to adding capacitance, but not every way. If you ever get into designing matching circuits that are more than just a single loading coil, this is a concept that you must understand first.

The Maco V 5/8 and V 5000 is more of a taped coil, where one end of the coil is at 0 ohms (neutral, or many would mistakenly call it ground), the other end is the the impedance of the antenna, and it is tapped at the 50 ohm point. For a more common visual think j-pole. While not exactly the same, you tap the stub at the impedance of the feed line that is being run to it, so if you are using 50 ohm feed line you will tap it at a different place than if you were running, say, 300 ohm twinlead, or 450 ohm window line. Essentially the same thing is happening with the Maco antennas, just a different design.

A good example of a 5/8 with an an actual hairpin match is the Super Penetrator. Someone asked about this once years ago and I modeled a generic hairpin match on a 5/8 wavelength antenna, and was surprised at how close it came to giving a 50 ohm match on my first try, I think it was at 60 or 65 ohms at resonance on my first model where I just threw it in there. I didn't try and fine tune it as I was busy at the time, but I concluded that if you change the layout of said hairpin match it shouldn't be to difficult to get a resonant match at 50 ohms. I'm pretty sure Marconi has modeled the Super Penetrator directly and gotten a match?

That being said, I am also aware they they are typically used on yagi type antennas to bring up the impedance while matching. I haven't really thought about it. At first glance, the one I modeled that got a near match on the 5/8 wavelength antenna was much longer compared to its wavelength than the ones I played with on the 2 meter yagi antennas I made, so I wonder if this had anything to do with it. A lot of times a big enough change in length compared to a wavelength is enough to change how some parts of antennas function. Stub matching is a prime example of this, you can add any given amount of inductance or capacitance by simply changing the length of the stub in question, or how far down the feed line from the antenna it is attached.

An added point to think about, when it comes to antenna matching and the 5/8 wavelength (and really any) antenna, all matching circuits do is change the phase from what appears at one end (aka the base of the antenna) to what is desirable at the other end (aka the end of the coax). This is true if you are using a loading coil, a hair pin, an L network, a Pi or T network, a stub match, or whatever. Some of them are easier to design and or build, some are "more efficient", some provide more SWR bandwidth and I'm sure some of them are designed to simply look cool or impressive, but in the end they all serve the same function.


The DB

 

[QRP 725]

First things first, I wouldn't get hung up on the magnetism of the loading coil. It is a thing, but not something we are typically concerned about. A step in the right direction would be their inductance, but that is really only half way there. What we are really concerned about is the reactance the device adds to the system, and how it is attached to said system. More on this later.

Also, long post, sorry about that for those that don't like long posts, it isn't the easiest topic to try and explain to someone at his level.



These are two different ways of looking at essentially the same thing. The loading coil adds inductance, or more specifically inductive reactance. The coil is designed to, along with the reactance of the antenna itself, give a resonant load at the feed point. For a 5/8 wavelength antenna this should be pretty close to 50 ohms at resonance (if I remember correctly, I could be mistaken, its been a while), making it easy to feed with a typical coax.

In the case of the 5/8 wavelength antenna, this is one method that keeps the antenna under a specific physical length, which going beyond tends to negatively affect the radiation pattern of the antenna.



Continuing from above (before the first quote), technically speaking, the hairpin match is an inductive device, but it differs from the loading coil mentioned above based on how it is attached to the antenna. Look up series and parallel circuits for more information. Long story short, in many ways it acts similar to adding capacitance, but not every way. If you ever get into designing matching circuits that are more than just a single loading coil, this is a concept that you must understand first.

The Maco V 5/8 and V 5000 is more of a taped coil, where one end of the coil is at 0 ohms (neutral, or many would mistakenly call it ground), the other end is the the impedance of the antenna, and it is tapped at the 50 ohm point. For a more common visual think j-pole. While not exactly the same, you tap the stub at the impedance of the feed line that is being run to it, so if you are using 50 ohm feed line you will tap it at a different place than if you were running, say, 300 ohm twinlead, or 450 ohm window line. Essentially the same thing is happening with the Maco antennas, just a different design.

A good example of a 5/8 with an an actual hairpin match is the Super Penetrator. Someone asked about this once years ago and I modeled a generic hairpin match on a 5/8 wavelength antenna, and was surprised at how close it came to giving a 50 ohm match on my first try, I think it was at 60 or 65 ohms at resonance on my first model where I just threw it in there. I didn't try and fine tune it as I was busy at the time, but I concluded that if you change the layout of said hairpin match it shouldn't be to difficult to get a resonant match at 50 ohms. I'm pretty sure Marconi has modeled the Super Penetrator directly and gotten a match?

That being said, I am also aware they they are typically used on yagi type antennas to bring up the impedance while matching. I haven't really thought about it. At first glance, the one I modeled that got a near match on the 5/8 wavelength antenna was much longer compared to its wavelength than the ones I played with on the 2 meter yagi antennas I made, so I wonder if this had anything to do with it. A lot of times a big enough change in length compared to a wavelength is enough to change how some parts of antennas function. Stub matching is a prime example of this, you can add any given amount of inductance or capacitance by simply changing the length of the stub in question, or how far down the feed line from the antenna it is attached.

An added point to think about, when it comes to antenna matching and the 5/8 wavelength (and really any) antenna, all matching circuits do is change the phase from what appears at one end (aka the base of the antenna) to what is desirable at the other end (aka the end of the coax). This is true if you are using a loading coil, a hair pin, an L network, a Pi or T network, a stub match, or whatever. Some of them are easier to design and or build, some are "more efficient", some provide more SWR bandwidth and I'm sure some of them are designed to simply look cool or impressive, but in the end they all serve the same function.


The DB

Thank you for taking the time to help me. I've had made quads, delta loops, EFHW, yagis, moxons using gamma, hairpin (beta), baluns and ununs with great success. I do think the coil design has more to do with the magnetic field as the main differance. I highly recommend a RigExpert antenna analyzer for people into making antennas. Mimana antenna modelling software is useful too.

I think it was Doc that wrote several years ago not to get to hung up about the 5/8 wave vertical. I do think a 1/2 wave has lobes more beneficial for all around long and short dx. I want to make a 5/8 for fun.

I'm still going to make a 5/8 but with wire radials and vertical element for portable use. It could be used for just hanging in a tree permanetly. I think I will go with the coil because of its smaller size. I have never made a 5/8 wave of any sort, so this will be interesting.

Just a side note Of all the antennas I have made a Moxon is the best! easy to make, 50 ohms feed point, small, and best of all it works great at low heights.

DB you really know your antenna theory stuff! Thanks again.

 

[QRP 725]

Thank you for taking the time to help me. I've had made quads, delta loops, EFHW, yagis, moxons using gamma, hairpin (beta), baluns and ununs with great success. I do think the coil design has more to do with the magnetic field as the main differance. I highly recommend a RigExpert antenna analyzer for people into making antennas. Mimana antenna modelling software is useful too.

I think it was Doc that wrote several years ago not to get to hung up about the 5/8 wave vertical. I do think a 1/2 wave has lobes more beneficial for all around long and short dx. I want to make a 5/8 to fun.

I'm still going to make a 5/8 but with wire radials and vertical element for portable use. It could be used for just hanging in a tree permanetly. I think I will go with the coil because of its smaller size. I have never made a 5/8 wave of any sort, so this will be interesting.

Just a side note Of all the antennas I have made a Moxon is the best! easy to make, 50 ohms feed point, small, and best of all it works great at low heights.

DB you really know your antenna theory stuff! Thanks again.

I forgot to mention I'm will be using a wire lead to tap onto the coil. Like a mobile HAM multi band antenna uses for adjusting for different bands.

Just to experiment, I will make my coil and also use the exact length to make a second unraveled tuning part in a u or circle shape. I will interchange using the same antenna and will tap at the exact same spot and compare. I think the second unraveled parts inductive reactance will change.

I think the coils magnetic field creates the needed inductance. Less turns of wire means that the coil will generate a lesser amount of a magnetic field and vice versa.

 

[BJ radionut]

I forgot to mention I'm will be using a wire lead to tap onto the coil. Like a mobile HAM multi band antenna uses for adjusting for different bands.

Texas Bug Catcher

 

[Ranch55]

Texas Bug Catcher

Can't get those new anymore...... I have tried extensively.......
Maybe find a good used one.......