mobile antenna to base !

[The DB]

DB, it would have help us understand if you had shown us your model in the beginning. I have not analyzed the dipole doing as you note here, but I will try that and get back.

What I am curious about is when I stated it was a 10 foot long center fed dipole more than once, why/how did you come to thinking that I used a ground plane antenna?

What is the difference between the two models above. They have different frequencies. What is significant about this difference and what did the first model ( the one with only one load on each side) show in the impedance on its main screen?

...

Wait, why is it at 26.28 MHz? I didn't check something apparently...

When I corrected the frequency, the segment length changed as I use auto segmentation and said segment size is based on the frequency that was changed. Because of the change in segment length, the two blue dots on each side is simply saying that the load covers more than one segment whereas the first of the models shows the loads only using one segment. I originally intended for the loads to use two segments each.

All I did between those two models was change the frequency to what I intended to use, and then change the inductance to tune the antenna to resonance. Nothing more was changed on my part.

The original number is the one you were erroneously using a ground plane antenna design to try and duplicate.

Are you telling me that the loads you added here are not using the load feature provided by 4Nec2, and that you created them using math?

They are using the loading feature, but not the matching network feature that you mentioned above. Two different things. I didn't use any math, I simply added an inductance, made the inductance a variable, and used the optimizer to get the system near resonant, and fine tuned it myself.


The DB

 

[Riverman]

All three of the antennas I've made using 4' Firestiks (GP with 2 radials slanted down at 45 degrees, horizontal dipole, inverted V dipole) had great receive and TX good enough for me to make some contacts.

Is there anything I could have done to increase performance enough (other than getting the antennas up higher) that it would be reflected on another operator's S-meter? It's my understanding that a very significant change is needed to result in an increase of 1 S-unit.

Getting a better match by using an analyzer to adjust the angle of the radials on the GP or adding a balun to either of two the dipoles isn't going to make that kind of difference. Right?

 

[M0GVZ]

Longer antennas. You can get significant gains from using those, something that would be seen on the S meter at the other end. Changing to using 7ft firestiks for example would give a noticable difference.

Here is a video I shot with my Tarheel antenna. I started out with the short stock whip roughly about 80cm long that comes with the antenna, changed it to a 1.95 metre whip that I liberated from my Sirio Performer 5000 and changed it again to a 1/4 wave whip for the 11m band - the measured lengths are in the video but I'm near enough doubling the length with each change. Each change resulted in an increase of 6dB and the longest whip which was roughly 10ft long gave a total gain of roughly 12dB over the stock whip meaning it was sending a signal out as well as receiving signals 16/17 times stronger than with the stock whip on the band I was demonstrating on.

 

[Riverman]

Thanks, M0GVZ.
That's a worthy difference. I know a wire half wave dipole would be cheaper and even better but i enjoy using mobile antennas.

You have a lot of great videos on youtube.

Jim

 

[Marconi]

I did see you have a second model with two loaded sides as well, but again, I don't even know how long it is to begin with, much less other details.

DB, my dipole model is 95.5" inches and that is not close to your 50" inches I admit. My model indicates it is 95.5" inches in the title of the model.

I did my helix (load) project as a 1/4 wave ground plan. It was my first effort, but not to copy you. I did it to test the idea of adding a physical load to a shortened radiator and compared it to a similar model with a full length radiator as a bases to start.

I started the model using a 102" radiator with 4 slanted down radials as a ground plane. I shortened the radiator to 40" inches and made a coil above it. I was just by guessing at the dimensions...I had nothing to go by. I made the coil 30" inches long and tested the results. I had some geometry and segment errors I had to fix. I fixed those and in the process I made several coils using different data. Finally I got the model to act right and it showed + reactance, so I started shortening it until it showed a nice - reactance. I added a small vertical tip for tuning and I fine tuned it. The model ended up long. I did several more models and repeated the whole process. At one point I got the end results to show an overall length of 60" inches with almost identical results to the 95.5 model I posted here. In my efforts to do a model not knowing the ins and outs of what I was doing...I over wrote the 60" model by accident. I was tired and in pain so I posted what I had. I told you I did numerous versions, saying they all showed similar results, and none showed me R = 27 ohms...they in fact showed 0 reactance right where I made set the antennas frequency. Even the good results did not satisfy my idea that the model was right...but when I compared it to a full length 1/4 GP with slanted down radials...I felt better I was in the ball park at least.

I then used this GP's radiator and copied it to make two 1/4 wave helix loads into a dipole. I didn't like the model results so much, but it did not show the 27 ohms you got in your model...so I posted what I had believing the model was close to correct. Later found I had an issue in my model, but I didn't want to get in the weeds over this issue. If I can remember what it was later, maybe make a new thread.

I figured the issues we already had with our models and if I was comparing models would all settle out in the dust-up in conversation that would hopefully follow, that is unless you got mad at me and quite talking.

Maybe if I get some time tomorrow I'll make a video showing what I am talking about, that might help you see what I did... Unfortunately that is a maybe, if I have time...

Your last video was very understandable to me even though I could not read the details you were making on my monitor, your words were good. I still don't know the steps in the process for making a 4Nec2 model, but maybe one day.............

My computer is acting up, so I will have to continue with my responses to your other comments later. I have to go to the hospital and have some test tomorrow morning early though. DB, I hope I was clear in this posts...I have a prescription drug issue with a blood thinner going on at present and I don't feel well.

Below is my model of the 95.5" dipole...not real short, but it is shorter than my full length 1/2 wave yagi dipole which I modeled after I tested my idea for a physically wound helix on a shortened 1/4 wave radiator...using a slanted down GP that I already had and knew worked well with a full length 1/4 wave radiator to show a good match and nice pattern. The 1/4 wave GP model was not to compare to your idea...it was to have a base line for my idea for a shortened radiator with a helix wound load.

Thanks for bearing with me here, OK?

 

[Riverman]

For a 1/4 wave ground plane, will an antenna made from insulated copper wire work as well as one made from 102" steel whips if the dimensions are the same?

 

[Marconi]

For a 1/4 wave ground plane, will an antenna made from insulated copper wire work as well as one made from 102" steel whips if the dimensions are the same?

71, the insulation does have some effect that is different than using bare wire, but I suspect the difference is negligible. The Eznec manual tell us that the loss of normal insulation coatings will have virtually no effect on antenna performance.

If you find anything in your real world work on this antenna different or unexpected, when using bare wire vs. normal insulated wire, then look for a little difference in resonance between the two if you can.

The wires I used in the models below are short compared to the wavelength, so the effect is less. The long and short is, I wouldn't worry about it unless you see a notable difference in SWR.

Wire with insulation 3.5 Dielectric Constant - Thickness .005" inch.



No insulation on the wire.


I see very little difference in my Eznec models.

 

[M0GVZ]

71, the insulation does have some effect that is different than using bare wire, but I suspect the difference is negligible..

The difference is in the electrical length that X feet of wire is seen as by RF.

Rule of thumb is that insulated wire appears around 4% longer electrically than uninsulated wire when using it for antennas. It isn't 100% theoretically correct as you know because of the different dielectric constants of insulation types but has certainly been my experience that this rule of thumb bears out in practice sufficiently enough that you can build antennas to it.

One of the last antennas I built was a Moxon rectangle for the 10m band for use as a single band entry antenna in the CQ-WPX contest. I got the dimensions using Moxgen and set it to use a centre frequency of 28.500Mhz as it was for 10m. Antenna built I checked the SWR and it was way off. Sticking it on my antenna analyser it was actually tuned for just below 27MHz. Double checked all the measurements, ran it through another Moxon calculator and got similar dimensions and was scratching my head until it finally hit me I'd built it using insulated speaker cable and the Moxon calculators assumed bare wire. I reduced all the wires by 5%, retested and it was just below 28.500MHz.

 

[Riverman]

71, the insulation does have some effect that is different than using bare wire, but I suspect the difference is negligible. The Eznec manual tell us that the loss of normal insulation coatings will have virtually no effect on antenna performance.

Marconi,
In your examples, the insulated wire model has the word "PVC" immediately following 36'. The bare wire model has "mast" immediately following 36'. Why are these terms different?

 

[Riverman]

The difference is in the electrical length that X feet of wire is seen as by RF.

Rule of thumb is that insulated wire appears around 4% longer electrically than uninsulated wire when using it for antennas.

M0GVZ,

Very interesting.

That means the length of a half wave 11 meter dipole could vary as much as 8 inches (4" per leg) between bare and insulated models.

I don't think I've heard that mentioned before. Thanks.

 

[The DB]

What does it matter? Standard procedure for making such an antenna is to make it long and cut it to length anyway, it is not? Or is what you are looking for more informational?


The DB

 

[Marconi]

Marconi,
In your examples, the insulated wire model has the word "PVC" immediately following 36'. The bare wire model has "mast" immediately following 36'. Why are these terms different?

Simple 71, Eznec will only allow a limited number of characters including space in the title name of a model. In this case I took out the word mast and replaced it with PVC and this created two models, one with insulation and one without.

I try and be descriptive in the titles of my models, but due to the character length limitations...I have to be very brief. Sometimes I can't remember what the name really means either...so I'm not surprised at your very appropriate question. It is good to know somebody is watching closely.

Thanks,

 

[Marconi]

I started to elaborate more on this issue, but 71, was referring to a 1/4 wave radiator, and I did not wish to confuse the matter over a length of wire to wavelength ratio discussion. I just told him what I thought he should look for, because I knew tuning was all he had to do to fix it...just like DB suggested in his post.

Connor, I found the same noticeable frequency differences as you did, when I model some Moxon two element parasitic arrays that were balanced at the feed point, and using long physical wires that were all in phase in the antenna. After that I wondered why and how this issue manifested itself in modeling...and I could only come to one conclusion...the total overall length of radiating wire had a big impact and shorter antenna wires did not so much.

The radiator for his GP is short, and the radials appear to me to self cancel and I don't think they add much effect to the model, except maybe for the match and a return currents pathway...among maybe some others.

IMO and if this is true, the radiator for this 1/4 wave GP does not have as much wire to be effected between using insulated wire and bare wire compared to two shortened 1/2 wave radiators that are in phase.

That is just my guess though and this is why I decided not to elaborate.

However, the manual reads as follows in the PDF file below. See the comment in the small highlighted area in the right hand margin.

 

[Riverman]

What does it matter? Standard procedure for making such an antenna is to make it long and cut it to length anyway, it is not? Or is what you are looking for more informational?


The DB

Purely informational, DB. I just find it interesting.

 

[Riverman]

Simple 71, Eznec will only allow a limited number of characters including space in the title name of a model. In this case I took out the word mast and replaced it with PVC and this created two models, one with insulation and one without.

I try and be descriptive in the titles of my models, but due to the character length limitations...I have to be very brief. Sometimes I can't remember what the name really means either...so I'm not surprised at your very appropriate question. It is good to know somebody is watching closely.

Thanks,

I understand. Thanks for clearing that up!