Simple portable antenna

[KOA4705]

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

[KOA4705]

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))
Joe

[MDYoungblood]

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

[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))
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...

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.


The DB

[KOA4705]

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

[MDYoungblood]

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 , 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 .

3's

Greg

[The DB]

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.


The DB

[MDYoungblood]

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.

3's

Greg

[ Post made via iPad ]

[KOA4705]

[quote=MDYoungblood post_id=387043 time=1503878195 user_id=13927]
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 , 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 .

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 .
Joe

[KOA4705]

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.

3's

Greg

[ Post made via iPad ]

Greg

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

[The DB]

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... 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.


The DB