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Simple portable antenna

Help with installing an Antenna, or just choosing the right antenna to go with your radio, or your mobile.

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Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 8:33 AM

This antenna has over 9db of gain
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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 9:54 AM

Radiation pattern
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Re: Simple portable antenna

Post by 295 antenna » Saturday, 19 August 2017, 11:41 AM

do you need a tuner with this or is it already resonant ?
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Re: Simple portable antenna

Post by The DB » Saturday, 19 August 2017, 13:53 PM

A few notes... To start with, the question that was asked...
295 antenna wrote:
Saturday, 19 August 2017, 11:41 AM
do you need a tuner with this or is it already resonant ?
This isn't resonant, and if you adjust the balanced feed line to make it so this antenna is resonant, the impedance is over 150 ohms. This antenna, by itself, will not safely plug directly into your 50 ohm radio.

I'm sorry to say, the modeling results presented above are over reporting gain.

When it comes to the radiation patterns presented above, I modeled this antenna myself, and initially got similar results. However, this was before running something called AGT, which stands for "Average Gain Test". Essentially, AGT is used to check models for accuracy. When I correct the model to correct for this failed test, I get the following patterns. (Click on them if you can't read the gain listed in the lower right corner.)

Image
Image

On my model the antenna was 36 feet above ground. If you mount the antenna below that, or even a little higher than that, you won't see the claimed 10 dBi in gain that the original models predict, it just isn't going to happen. A word of advice, when someone posts a model as part of a claim about an antenna, ask about it. Get a second opinion. See if someone else can get consistent results while checking for known but often overlooked problems with the model that can drastically affect its accuracy, in this case a change of 2 dB.


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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 16:40 PM

3D radiation pattern
I will give the feed point impedance and the impedance transformation at the send end of
300 ohm line.


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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 18:14 PM

DB good catch the 300 ohm feed line length so be 11.81 Feet in length LOL. At a Antenna height of 30 feet.
From 27- 27.4 MHZ at the send of the 300 ohm line the Max SWR= 1.21:1, min is 1.10:1
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Re: Simple portable antenna

Post by The DB » Saturday, 19 August 2017, 18:20 PM

How long and what type of coax was used between the radio and the twin lead?


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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 21:17 PM

DB lMR400
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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 22:00 PM

DB Here the antenna feed point impedance and the far end of the 300 ohm line (send end) impedance vs frequency

FREQ (MHZ) ANTENNA FEED POINT (Z) SEND END (Z) 300 ohm line (SWR) SEND END 300 ohm line, 50 ohm input

27.0 194.1 +j 497.5 48.28 -j11.32 1.21:1
27.1 201.1 +j 517.1 47.22 -j5.88 1.15:1
27.2 208.4 +j 538.6 46.02 -j1.14 1.10:1
27.3 216.0 +j 556.6 44.81 +j2.97 1.13:1
27.4 224.1 +j 576.6 44.07 +j6.61 1.21:1

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Re: Simple portable antenna

Post by KOA4705 » Saturday, 19 August 2017, 22:08 PM

Portable antenna 3D radiation pattern. The antenna wire runs parallel with the Y axis

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Re: Simple portable antenna

Post by MDYoungblood » Sunday, 20 August 2017, 10:42 AM

What modelling programs are you using? I'm interested because I want to build a large horizontal loop in my yard, it will be about 20ft off the ground average and about 200ft long, 4 segments at 50ft each. Creating it on the computer first will give me an idea of if it will work or not.

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Re: Simple portable antenna

Post by The DB » Sunday, 20 August 2017, 15:04 PM

MDYoungblood wrote:
Sunday, 20 August 2017, 10:42 AM
What modelling programs are you using? I'm interested because I want to build a large horizontal loop in my yard, it will be about 20ft off the ground average and about 200ft long, 4 segments at 50ft each. Creating it on the computer first will give me an idea of if it will work or not.

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KOA4705 is using EZNec. From personal experience, I didn't really like using that program. It just wasn't intuitive, or easy for me. On another note, he seems rather new with using it.

I use 4Nec2. It was far easier for me to pick up, and far more intuitive as well. It can also do things that only the very expensive EZNec Pro can do, and its free.

Having used both in the past, even if all of the EZNec versions were free, I would recommend using 4Nec2. Also, having used both in the past, the results from the two programs for identical models are extremely close, the testing I did puts them at less than 0.1 dB difference when it comes to patterns.

If you go the 4Nec2 route and have questions I will be happy to answer them for you.

With your loop, are you planning on feeding the center of one side or one of the corners?


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Re: Simple portable antenna

Post by MDYoungblood » Sunday, 20 August 2017, 16:08 PM

Cool, I was checking both of those out and will probably download both, anything now a days is better than the old trial and error method. On my loop it will be fed at one corner, I'm thinking of using 450Ω ladderline as a matcher to a balun with 50Ω into the house. The 200ft is the max I can lay out, shorter can be done just as easy. Looking at working as much of the HF bands as possible with it.
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Re: Simple portable antenna

Post by KOA4705 » Monday, 21 August 2017, 9:03 AM

This isn't resonant, and if you adjust the balanced feed line to make it so this antenna is resonant, the impedance is over 150 ohms. This antenna, by itself, will not safely plug directly into your 50 ohm radio.


The DB
[/quote]

The antenna 300 ohm feed line can be adjusted to a length 11.81 feet for a SWR of less than 1.22:1 across the band. The antenna can be plug directly into your 50 ohm radio. How did you come up with a real part of over 150 ohms?
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Re: Simple portable antenna

Post by The DB » Monday, 21 August 2017, 12:59 PM

KOA4705 wrote:
Monday, 21 August 2017, 9:03 AM
The antenna 300 ohm feed line can be adjusted to a length 11.81 feet for a SWR of less than 1.22:1 across the band. The antenna can be plug directly into your 50 ohm radio. How did you come up with a real part of over 150 ohms?
Joe
At the time, I didn't know you were using 300 ohm feed line. I modeled wires that don't resemble 300 ohm feed line in the model I made, they actually had a higher impedance, which would throw off the resulting numbers.

I can confirm that if you get the numbers you said you are getting it is possible to get a match that is very close to 50 ohms with some length of 300 ohm coax. My calculations show a bit longer than you are using, however, I did not factor in a velocity factor, that will be present with a 300 ohm twin lead feed line matching transformer like you plan to use. It is hard to say based on the specific twin lead you are using, but I'm guessing a velocity factor of 80% to 85% (most sources use these numbers for generic 300 ohm twin lead), which puts the results in the ballpark of the numbers you are posting.

The two things that has me concerned is, 1) your model seems to be over reporting gain, I still suggest running AGT and seeing what the result of that test is, and 2a) I'm not sure if you are using the default "perfect conductor" or have changed the conductors in the model to copper (or whatever metal you used), which can make a difference when it comes to how long it needs to be when tuning, and 2b) I don't know if you are using bare wire, or wire with a PVC or other covering, and if you are using wire with such a covering was that included in the model? Both 2a and 2b will add a velocity factor to the antenna which will need to be accounted for if you haven't already. A friend on another forum tried to make an antenna from a model, failed to take into account 2a and 2b I mentioned above, and ended up with a wire that was almost 50% of the length the model said he should use...

Hey MDYoungblood, in the next few days, if I get a chance, I plan on making a video for you about modeling such an antenna. It will include what I do at various points in the process and why. The intent will be to show you things to look out for that someone new to modeling won't know to consider. It is also intended to show some good habits, and perhaps point to a bad habit or two to avoid. While the video is intended to be aimed at you and your project specifically, it would also be useful to anyone who might have an interest in modeling. I will also give some advice based on years of working with such software that I had to learn the hard way... That is coming when I have time.


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Re: Simple portable antenna

Post by Bobcat » Tuesday, 22 August 2017, 7:37 AM

The DB, I jumped in here to thank you for that! I had no idea that such even existed. Playing with antennas is one of my favorite aspects of hobby radio and this looks like a handy thing to have! Thanks!

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The DB wrote:
Sunday, 20 August 2017, 15:04 PM

KOA4705 is using EZNec. From personal experience, I didn't really like using that program. It just wasn't intuitive, or easy for me. On another note, he seems rather new with using it.

I use 4Nec2. It was far easier for me to pick up, and far more intuitive as well. It can also do things that only the very expensive EZNec Pro can do, and its free.

Having used both in the past, even if all of the EZNec versions were free, I would recommend using 4Nec2. Also, having used both in the past, the results from the two programs for identical models are extremely close, the testing I did puts them at less than 0.1 dB difference when it comes to patterns.

If you go the 4Nec2 route and have questions I will be happy to answer them for you.

With your loop, are you planning on feeding the center of one side or one of the corners?


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Re: Simple portable antenna

Post by KOA4705 » Tuesday, 22 August 2017, 22:08 PM

The DB wrote:
Monday, 21 August 2017, 12:59 PM
KOA4705 wrote:
Monday, 21 August 2017, 9:03 AM
The antenna 300 ohm feed line can be adjusted to a length 11.81 feet for a SWR of less than 1.22:1 across the band. The antenna can be plug directly into your 50 ohm radio. How did you come up with a real part of over 150 ohms?
Joe
At the time, I didn't know you were using 300 ohm feed line. I modeled wires that don't resemble 300 ohm feed line in the model I made, they actually had a higher impedance, which would throw off the resulting numbers.

I can confirm that if you get the numbers you said you are getting it is possible to get a match that is very close to 50 ohms with some length of 300 ohm coax. My calculations show a bit longer than you are using, however, I did not factor in a velocity factor, that will be present with a 300 ohm twin lead feed line matching transformer like you plan to use. It is hard to say based on the specific twin lead you are using, but I'm guessing a velocity factor of 80% to 85% (most sources use these numbers for generic 300 ohm twin lead), which puts the results in the ballpark of the numbers you are posting.
The two things that has me concerned is, 1) your model seems to be over reporting gain, I still suggest running AGT and seeing what the result of that test is, and 2a) I'm not sure if you are using the default "perfect conductor" or have changed the conductors in the model to copper (or whatever metal you used), which can make a difference when it comes to how long it needs to be when tuning, and 2b) I don't know if you are using bare wire, or wire with a PVC or other covering, and if you are using wire with such a covering was that included in the model? Both 2a and 2b will add a velocity factor to the antenna which will need to be accounted for if you haven't already. A friend on another forum tried to make an antenna from a model, failed to take into account 2a and 2b I mentioned above, and ended up with a wire that was almost 50% of the length the model said he should use...
Hey MDYoungblood, in the next few days, if I get a chance, I plan on making a video for you about modeling such an antenna. It will include what I do at various points in the process and why. The intent will be to show you things to look out for that someone new to modeling won't know to consider. It is also intended to show some good habits, and perhaps point to a bad habit or two to avoid. While the video is intended to be aimed at you and your project specifically, it would also be useful to anyone who might have an interest in modeling. I will also give some advice based on years of working with such software that I had to learn the hard way... That is coming when I have time.


The DB
Good to meet you both! We all have a common interest antenna systems modeling and transmission line theory. Most people are bored out of there minds if you talk to them about this stuff. Your as only as good as your tools. I got tired and frustrated using a noise bridge, antenna analyzer and a General Radio RF bridge for impedance measurements. Due to limited range of impedance that can be measured and or the inaccuracies. I broke down and bought a Vector Network Analyzer which solves all these problem. No more guessing with active and passive devices including common mode chokes, antenna systems, transmission lines, filters, group delay, S parameters, attenuators, directional couplers/ samplers, transistors, dummy loads etc. I could never afford one back in the day the cost was prohibitive. But due to new technology the prices have dropped dramatically.
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Re: Simple portable antenna

Post by The DB » Wednesday, 23 August 2017, 6:18 AM

An old HP network analyzer? Those are neat, I would have one if I had several thousand dollars burning a hole in my pocket. I don't need one, but I kind of collect older RF test equipment so it would be nice to have and play with...

I use something a little more modern, and AIM 4170c VNA. Here are some results from a friends mobile 2/6 meter ham radio antenna. They are to big to put directly in the message so I'll just link them...

http://hittman.us/pictures/3-29-14/3.jpg
http://hittman.us/pictures/3-29-14/4.jpg


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Re: Simple portable antenna

Post by The DB » Wednesday, 23 August 2017, 19:15 PM

MDYoungblood here is that video I mentioned. If you have any questions feel free to ask.

https://www.youtube.com/watch?v=I2glvVKZo2U


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Re: Simple portable antenna

Post by MDYoungblood » Thursday, 24 August 2017, 4:43 AM

The DB wrote:
Wednesday, 23 August 2017, 19:15 PM
MDYoungblood here is that video I mentioned. If you have any questions feel free to ask.

https://www.youtube.com/watch?v=I2glvVKZo2U


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Thanks DB

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Re: Simple portable antenna

Post by KOA4705 » Friday, 25 August 2017, 18:14 PM

The DB wrote:
Wednesday, 23 August 2017, 6:18 AM
An old HP network analyzer? Those are neat, I would have one if I had several thousand dollars burning a hole in my pocket. I don't need one, but I kind of collect older RF test equipment so it would be nice to have and play with...

I use something a little more modern, and AIM 4170c VNA. Here are some results from a friends mobile 2/6 meter ham radio antenna. They are to big to put directly in the message so I'll just link them...

http://hittman.us/pictures/3-29-14/3.jpg
http://hittman.us/pictures/3-29-14/4.jpg


The DB
Hi DB that's a amazing single port VNA at a incredable
price.
Did it come with a calibration kit too? Looking at the
reviews ratings are excellent. The display covers
all pertinent data with S11 inclusive. I also read
that you can also can display a Smith chart plot.

I got a calibration kit from ebay that's good
to 3 Ghz from Israel for $100. HP cal kits are still $1000
on ebay. Like you most all of my test equipment is old HP,Tek,
fluke, Wavetek etc it heavy and big but labratory quality.This
is the same stuff I used through out my career but could never afford
it back in the day. I remember in the 70's a HP141T spectrum analyzer with
a 8555A RF section and a YIG filter cost more that a house.
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Re: Simple portable antenna

Post by The DB » Friday, 25 August 2017, 19:11 PM

KOA4705 wrote:
Friday, 25 August 2017, 18:14 PM
Hi DB that's a amazing single port VNA at a incredable
price.
Did it come with a calibration kit too? Looking at the
reviews ratings are excellent. The display covers
all pertinent data with S11 inclusive. I also read
that you can also can display a Smith chart plot.

I got a calibration kit from ebay that's good
to 3 Ghz from Israel for $100. HP cal kits are still $1000
on ebay. Like you most all of my test equipment is old HP,Tek,
fluke, Wavetek etc it heavy and big but labratory quality.This
is the same stuff I used through out my career but could never afford
it back in the day. I remember in the 70's a HP141T spectrum analyzer with
a 8555A RF section and a YIG filter cost more that a house.
Joe
It works very well, definitely worth the price, at least for those who can understand what that type of device is capable of.

It comes with the calibration loads. It also has a smith chart output, and can do far more than what is shown on that screen.

It can't cover anything near the frequency range of your HP equipment, but it is ok for my needs.

I see they now have a 4300 that covers a wider range of frequencies, and it is a lower price than I paid, $500 for that kind of device? Wish it was that cheap when I got mine...


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Re: Simple portable antenna

Post by KOA4705 » Saturday, 26 August 2017, 9:26 AM

The DB wrote:
Wednesday, 23 August 2017, 19:15 PM
MDYoungblood here is that video I mentioned. If you have any questions feel free to ask.

https://www.youtube.com/watch?v=I2glvVKZo2U


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DB what is the feed point impedance vs frequency? :think:
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Re: Simple portable antenna

Post by KOA4705 » Saturday, 26 August 2017, 20:24 PM

KOA4705 wrote:
Saturday, 26 August 2017, 19:44 PM
KOA4705 wrote:
Saturday, 26 August 2017, 16:43 PM
KOA4705 wrote:
Saturday, 26 August 2017, 9:26 AM
The DB wrote:
Wednesday, 23 August 2017, 19:15 PM
MDYoungblood here is that video I mentioned. If you have any questions feel free to ask.

https://www.youtube.com/watch?v=I2glvVKZo2U


The DB

DB what is the feed point impedance vs frequency? :think: Why didn't you just transpose the antenna feed point to a 50 ohms system elegantly. Instead of first using close to a 1/4 wavelength 450 Zo OWL then a 1/4 wavelength of 75 Zo coax to get to a 50 ohms system :?:
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Re: Simple portable antenna

Post by The DB » Sunday, 27 August 2017, 6:13 AM

He said he wanted to match the system with 450 ohm line, so I used 450 ohm line to see what I would get. Is it bad that I followed his instructions to the letter?

He doesn't want to go any longer than that length of antenna, and shortening it some actually pushes the impedance match after the 450 ohm ladder line transformer further away. That being said, if he learned what he needed, and played with it some he may have found a better solution on his own, or I could have helped him in that direction. My goal was to give him a starting point and help him work towards that goal. In any case, their are longer and shorter antenna lengths that will tune much better when using 450 ohm feed line.

If he used a different impedance feed line, 300 ohm feed line would get him to 45 + j0, which is a near direct conversion for that antenna length. But that isn't what he wanted, so that isn't what I did.

Finally, I was trying to give him the basics on trying to eventually be able to figure this out on his own, again, which is what he wanted. Their is a big difference in doing something for some one and helping them learn to do it themselves. He posts in the antenna section on this forum a *lot*. Helping him gain additional knowledge will only help this forum in the long run.


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Re: Simple portable antenna

Post by KOA4705 » Sunday, 27 August 2017, 10:00 AM

The DB wrote:
Sunday, 27 August 2017, 6:13 AM
He said he wanted to match the system with 450 ohm line, so I used 450 ohm line to see what I would get. Is it bad that I followed his instructions to the letter?

He doesn't want to go any longer than that length of antenna, and shortening it some actually pushes the impedance match after the 450 ohm ladder line transformer further away. That being said, if he learned what he needed, and played with it some he may have found a better solution on his own, or I could have helped him in that direction. My goal was to give him a starting point and help him work towards that goal. In any case, their are longer and shorter antenna lengths that will tune much better when using 450 ohm feed line.

If he used a different impedance feed line, 300 ohm feed line would get him to 45 + j0, which is a near direct conversion for that antenna length. But that isn't what he wanted, so that isn't what I did.

Finally, I was trying to give him the basics on trying to eventually be able to figure this out on his own, again, which is what he wanted. Their is a big difference in doing something for some one and helping them learn to do it themselves. He posts in the antenna section on this forum a *lot*. Helping him gain additional knowledge will only help this forum in the long run.


The DB
OK DB as you demonstrated there are many solutions to a particular transmission matching problem. Transmission line equations are a Hyperbolic function along with complex numbers. To visualize the result by looking at the equations is not obvious. I've have used Matlab to show the transfer functions graphically 3D which is interesting seeing the cause and effect. Thanks for the informative educational video in using NEC 2 antenna modeling program. I saw that long post on this forum about the difference of VSWR with and without a amplifier in line. That was very entertaining to say the least :lol:

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Re: Simple portable antenna

Post by KOA4705 » Sunday, 27 August 2017, 11:52 AM

The DB wrote:
Sunday, 27 August 2017, 6:13 AM
He said he wanted to match the system with 450 ohm line, so I used 450 ohm line to see what I would get. Is it bad that I followed his instructions to the letter?

He doesn't want to go any longer than that length of antenna, and shortening it some actually pushes the impedance match after the 450 ohm ladder line transformer further away. That being said, if he learned what he needed, and played with it some he may have found a better solution on his own, or I could have helped him in that direction. My goal was to give him a starting point and help him work towards that goal. In any case, their are longer and shorter antenna lengths that will tune much better when using 450 ohm feed line.

The DB
DB I'll give you a hint......... You can leave everything the same except the length of the 450 line and one other element to match the system to 50 ohms It's should be intuitive but your thinking way too deep. And no you don't need this equation for the send end impedance.
Zin(l)= Zo(( ZL+Zo tanh(yl)/Zo tanh(yl))
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Re: Simple portable antenna

Post by MDYoungblood » Sunday, 27 August 2017, 12:59 PM

The DB wrote:
Sunday, 27 August 2017, 6:13 AM
He said he wanted to match the system with 450 ohm line, so I used 450 ohm line to see what I would get. Is it bad that I followed his instructions to the letter?

He doesn't want to go any longer than that length of antenna, and shortening it some actually pushes the impedance match after the 450 ohm ladder line transformer further away. That being said, if he learned what he needed, and played with it some he may have found a better solution on his own, or I could have helped him in that direction. My goal was to give him a starting point and help him work towards that goal. In any case, their are longer and shorter antenna lengths that will tune much better when using 450 ohm feed line.

If he used a different impedance feed line, 300 ohm feed line would get him to 45 + j0, which is a near direct conversion for that antenna length. But that isn't what he wanted, so that isn't what I did.

Finally, I was trying to give him the basics on trying to eventually be able to figure this out on his own, again, which is what he wanted. Their is a big difference in doing something for some one and helping them learn to do it themselves. He posts in the antenna section on this forum a *lot*. Helping him gain additional knowledge will only help this forum in the long run.


The DB
Thanks again DB, I have 450Ω ladderline but if 300Ω is a better match than I will get that. I'm downloading the programs today and will play with them on the bad weather days ahead. Yes I am interested in learning since I've gotten into ham radio and will be thankful for any help when I get started on the project.

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Re: Simple portable antenna

Post by The DB » Sunday, 27 August 2017, 14:46 PM

KOA4705 wrote:
Sunday, 27 August 2017, 11:52 AM
DB I'll give you a hint......... You can leave everything the same except the length of the 450 line and one other element to match the system to 50 ohms It's should be intuitive but your thinking way too deep. And no you don't need this equation for the send end impedance.
Zin(l)= Zo(( ZL+Zo tanh(yl)/Zo tanh(yl))
Joe
Look, I know you are trying to be helpful to me, and I appreciate it, but I don't need this help. I'm trying to keep what I am talking about in a range that I know MDYoungblood will understand, or has the potential to reasonably build up to fairly quickly based on his current and previous posts. If you want to talk about some high level aspects of antenna tuning, that is fine, I may need to refresh my memory on several things that go beyond what we normally talk about in a forum environment like this, but their is little that I haven't done at one time or another. Instead of helping me, perhaps you can try and help MDYyoungblood, who is the person that is currently asking questions here.

Speaking of which...
MDYoungblood wrote:
Sunday, 27 August 2017, 12:59 PM
Thanks again DB, I have 450Ω ladderline but if 300Ω is a better match than I will get that. I'm downloading the programs today and will play with them on the bad weather days ahead. Yes I am interested in learning since I've gotten into ham radio and will be thankful for any help when I get started on the project.

3's

Greg
Ham radio? You should have mentioned that this was for ham radio. That changes things a bit.

So the first question I would ask is, do you plan to use this antenna on multiple ham bands? If the answer is yes, then...

A few changes.

When it comes to modeling, I would use a ham band frequency instead of the CB band frequency I used, unless you also want to use this antenna on the CB band, which is fine to. Their is no law saying you can't use an antenna for both CB and ham radio.

I would make a separate model for each of the bands you plan to use the antenna on. You don't have to start from scratch each time, just make one model, copy and rename it, then open the copied model and change the frequency to another ham band, and adjust its frequency to match. Also, check and update AGT for this model as needed. Rinse/repeat for every ham band you wish to use the antenna on. The main reason for the different files for each band is that AGT may be different, so for accurate gain data you would need different information for each band in play. You can get away with using a single file for this, but it is generally more of a hassle, plus with multiple files for each band, you can pull up the band you want right away. One last note on the modeling side, you may need to make the single segment feed point wire we used larger as you go down in frequency. Using auto segmentation like we did, the individual segments the program uses will get larger with lower frequencies.

Next question, do you have or are you getting an antenna tuner? Such a device will make tuning this antenna for multiple bands over the HF spectrum much easier. One that has a built in 4:1 balun in best. Just run the 450 ohm window line straight to the tuner, and dial in SWR with the tuner. If you have trouble tuning on one or two bands, add or remove a few feet from the window line. It really is that simple, no modeling needed.

As you can see, building this antenna for single band CB use is a bit different compared to building it for multiband ham radio use. For single band applications, it is best to tune to said band directly. However, when it comes to multiband setups their are other options that may or may not be better for you in play.

One little bit of information can sometimes change recommendations pretty drastically, can't it...

What class are you now, and are you planning on upgrading any time soon? I am an extra class myself.


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Re: Simple portable antenna

Post by KOA4705 » Sunday, 27 August 2017, 14:52 PM

MDYoungblood wrote:
Sunday, 27 August 2017, 12:59 PM
The DB wrote:
Sunday, 27 August 2017, 6:13 AM
He said he wanted to match the system with 450 ohm line, so I used 450 ohm line to see what I would get. Is it bad that I followed his instructions to the letter?

He doesn't want to go any longer than that length of antenna, and shortening it some actually pushes the impedance match after the 450 ohm ladder line transformer further away. That being said, if he learned what he needed, and played with it some he may have found a better solution on his own, or I could have helped him in that direction. My goal was to give him a starting point and help him work towards that goal. In any case, their are longer and shorter antenna lengths that will tune much better when using 450 ohm feed line.

If he used a different impedance feed line, 300 ohm feed line would get him to 45 + j0, which is a near direct conversion for that antenna length. But that isn't what he wanted, so that isn't what I did.

Finally, I was trying to give him the basics on trying to eventually be able to figure this out on his own, again, which is what he wanted. Their is a big difference in doing something for some one and helping them learn to do it themselves. He posts in the antenna section on this forum a *lot*. Helping him gain additional knowledge will only help this forum in the long run.


The DB
Thanks again DB, I have 450Ω ladderline but if 300Ω is a better match than I will get that. I'm downloading the programs today and will play with them on the bad weather days ahead. Yes I am interested in learning since I've gotten into ham radio and will be thankful for any help when I get started on the project.

3's

Greg
Greg you can match your loop using your 450Ω ladder line, it's a simple approach. But I will need you and DB's help if you want to do this. Greg how many feet of 450 ohm line do you have ? Also how far is the antenna feed point from the shack? DB what are the antenna feed point impedance's vs frequency for the bandwidth of interest? Need DB to check the solution results.
Joe

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Re: Simple portable antenna

Post by MDYoungblood » Sunday, 27 August 2017, 16:56 PM

I'm sorry DB, thought you knew I was a hammie, I just don't publicize it on the forum much, been an "Extra" since 2013. Thanks for the help also KOA4705.
The bands wanted is as many as I can get out of the antennas design. The main band I want the loop for is 40m, seems to have the most openings all the time, 20m would be nice too.
Right now I have a HyGain AV-6160 (for 40m) and a HyGain AV-14AVQ (10-40m). I've made my share of dipoles, doublets, and bazookas along with several telescoping tube antennas, all were made by trial and error, all but one worked well, just looking for another project to play with and to fill up my 200X50ft yard (city dweller) just to irritate the wife.
KOA4705, you asked about the feedpoint, the distance will be about 60ft including going up the 20ft from the ground to the connection point. I downloaded the demo of EZnec, yes I'm too cheap to pay for the 6.0 version.
DB, the video is cool, I have to watch it a couple of times to get the drift, (bad comprehension in my old age), I'll probably use 4nec2 to design and build the loop and cross check it with EZnec. I even have a CAD program to use in designing it.
Getting materials isn't a problem for me, got spools of wire (16 to 8 awg), PVC pipe, lumber, etc. to use up and if I need something radio I have a HRO an hour and a half away in either direction, the Delaware store is best, no sales tax :biggrin: , Virginia store has the radios I can't afford to play with, plus it gives me an excuse to get out of the house for several hours :biggrin: :biggrin: .

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Re: Simple portable antenna

Post by The DB » Sunday, 27 August 2017, 17:16 PM

I do now recall you saying that you were a ham here in the past. I guess the memory just needed to be jived.

Again, if you want it to work on as many bands as possible with an antenna like that, an antenna tuner is the way to go. Get one with a balun inside and a parallel feed line output.

How do you plan to run the window line, along the ground? This type of feed line likes to be at least twice the width of the conductors are apart away from lossy stuff, like earth, as well as any run along metal. Passing a small amount of both is fine. With this type of feed line, unlike coax, the field that stores and moves said energy to and from the antenna is in the space around the conductors, not contained within a metal shielding, and that needs to be accounted for. On the plus side, it is more efficient than even the almighty LMR-400 that a lot of people seem to swear by, but if you are using an antenna tuner that is a very good thing.


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Re: Simple portable antenna

Post by MDYoungblood » Sunday, 27 August 2017, 17:45 PM

My plan was to use the ladderline down the supporting structure terminate it with a balun to 50 ohm coax into the radio room. I'm currently using a LDG AT-600proII tuner with my radio. I can run the ladderline all the way in keeping it 6 to 8ft off the ground but I would have to change to another tuner.

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Re: Simple portable antenna

Post by KOA4705 » Sunday, 27 August 2017, 18:22 PM

MDYoungblood wrote:
Sunday, 27 August 2017, 16:56 PM
I'm sorry DB, thought you knew I was a hammie, I just don't publicize it on the forum much, been an "Extra" since 2013. Thanks for the help also KOA4705.
The bands wanted is as many as I can get out of the antennas design. The main band I want the loop for is 40m, seems to have the most openings all the time, 20m would be nice too.
Right now I have a HyGain AV-6160 (for 40m) and a HyGain AV-14AVQ (10-40m). I've made my share of dipoles, doublets, and bazookas along with several telescoping tube antennas, all were made by trial and error, all but one worked well, just looking for another project to play with and to fill up my 200X50ft yard (city dweller) just to irritate the wife.
KOA4705, you asked about the feedpoint, the distance will be about 60ft including going up the 20ft from the ground to the connection point. I downloaded the demo of EZnec, yes I'm too cheap to pay for the 6.0 version.
DB, the video is cool, I have to watch it a couple of times to get the drift, (bad comprehension in my old age), I'll probably use 4nec2 to design and build the loop and cross check it with EZnec. I even have a CAD program to use in designing it.
Getting materials isn't a problem for me, got spools of wire (16 to 8 awg), PVC pipe, lumber, etc. to use up and if I need something radio I have a HRO an hour and a half away in either direction, the Delaware store is best, no sales tax :biggrin: , Virginia store has the radios I can't afford to play with, plus it gives me an excuse to get out of the house for several hours :biggrin: :biggrin: .

3's

Greg

Hi Greg that's interesting .... I used a antenna similar to what your proposing. The difference was it was a full wave for 75 meters, 265 feet and 30 feet off the ground. I used 600 ohm open wire line to feed it and a linked coupled network to transpose to 50 ohms. It was a very effective antenna system for HF. The reason for link couple tuner it's designed for balanced transmission line and has very low loss compared to other matching networks. I wouldn't use any transmission line mode transformers in this application because they should be terminated into their designed impedance.
There will be a large range of impedances presented to a balun transformer in this case which can and will cause core saturation and destruction. A example of a link coupled network is a Johnson Match Box .
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Re: Simple portable antenna

Post by KOA4705 » Sunday, 27 August 2017, 20:23 PM

MDYoungblood wrote:
Sunday, 27 August 2017, 17:45 PM
My plan was to use the ladderline down the supporting structure terminate it with a balun to 50 ohm coax into the radio room. I'm currently using a LDG AT-600proII tuner with my radio. I can run the ladderline all the way in keeping it 6 to 8ft off the ground but I would have to change to another tuner.

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Greg

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These are the antennas I presently use: 1. 130 Ft center feed dipole, height is 45 ft at the feed point, ends at 65 ft, fed with 600 ohm ladder line. Used on 75- 10 meters with a link coupled matching network. 2. A yagi tri-bander the reflector length is 27 ft antenna weights 42 lbs at 60 ft on a crank-up tower.
Joe
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Re: Simple portable antenna

Post by The DB » Monday, 28 August 2017, 8:06 AM

KOA4705 wrote:
Sunday, 27 August 2017, 18:22 PM
The reason for link couple tuner it's designed for balanced transmission line and has very low loss compared to other matching networks. I wouldn't use any transmission line mode transformers in this application because they should be terminated into their designed impedance.
There will be a large range of impedances presented to a balun transformer in this case which can and will cause core saturation and destruction. A example of a link coupled network is a Johnson Match Box .
Joe
Before I go on, here is a question that may be part of a deciding factor, does anyone actually make link coupled tuners? Heathkit used to have a kit, but aside from that, all the others I have seen have been completely designed and made from scratch. So, long story short, if MDYoungblood isn't interested in making such a device himself, including the rather large (physically) transformer, then the discussion about them quickly becomes pointless. (I'm not sure if the Johnson Matchbox series is currently in production).

Anyway more information on said tuners and actual comparisons.

A link coupled tuner isn't, in and of itself, more or less efficient than a non-link coupled tuner. There are link coupled tuner designs that are very inefficient, and non link coupled tuner designs that are very efficient, and vice versa. The efficiency of the tuner itself depends more on what components are where and their sizes than anything else. If you want as much efficiency in an antenna tuner as possible, get rid of all inductors as they are the primary source of loss in said antenna tuners... :icon_e_smile: Seriously though, most commercially available antenna tuners have a loss of less than 0.1 dB across most of the HF spectrum, so losses in said devices really aren't a problem that you will notice. Even using 600 ohm ladder line you will generally have exponentially more losses in said ladder line than in the tuner over most of the band.

There is a reason baluns use ferrite cores, and that is because ferrite is more efficient as a core than the same amount of air. Honestly, when it comes to overall size, air flat out sucks as a core for any magnetic device. To make make ferrite be able to handle more power and/or a higher impedance, you simply add more cores of the same type of ferrite. To make air would transformers like you see in link coupled tuners as efficient as a ferrite core transformer, you need to use larger coils, much larger coils, and that is why you don't see these commonly available on the market. That being said, with an air core you don't have to worry about saturation, so it will have that advantage.

I will also say this about said link couple tuners, you bring them to any radio gathering anywhere and it will be a conversation piece... That is something that you won't get with any other antenna tuner out there.


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