Question for the guru's

[JCH]

I can't get into the technical aspects of a radio or antenna but I do own a TOYOTA TACOMA and they may have done a much better job making a bed liner fit and have boxes built in and etc. but is the floor and sides only plastic or is there steel behind it? seems like there would be. Mine is a 99 TRD with a traditional bed liner and I know you are talking about a much later year just by the bed liner you are talking about. I have a Gull-Wing type tool box that mounts immediately behind the rear window and has four bolts holding it in place and also making a ground for the antenna, if I had no box I would be using a very small diameter box steel several feet just enough to clear the cab and bolting to the top rail and through the bottom inserting threads toward the rear of truck to keep the gap between cab and bed open and positioning it directly in the middle of the rear window but that would be for a coil wound antenna

The design changed in 2005, your truck has a metal bed. The bed on the 2005 and newer (at least to 2007) trucks is of a composite fiberglass-like material. The rear quarter panels are bolted to this composite bed. There are vertical steel supports at the rear of the bed where the tail gate connects.

I'll post up a pic of my antenna setup here after while.

Removing the sprayed-on primer from my antenna seems to have helped with Rx sensitivity issue. fyi.

Edit: With this setup, the SWR was a little high, 2.1-ish prior to bonding the rear quarter panels to the frame, the cab to the frame, the hood to the frame. Now 1.3 after bonding.

Question: Is my poor recieve issue due to the antenna's close proximity to the cab, the plastic bed, all of the above?

thanks guys

 

[Captain Kilowatt]

Marconi.....if you are loking for PROOF that a resonant 1/4 wave antenna ON A MOBILE INSTALLATION is ALWAYS 35 ohms you will not find it. It does not exist. The 35 ohms impedance is over perfect ground. A mobile installation, no matter how good it is, will never be that perfect ground. There are far too many variables in the size and shape of the vehicle as well as total surface area and bonding. All these variables affect ground losses which in turn affect the end resulting impedance. You may get close to that figure with a near perfect installation but I doubt you will get the exact proof you are looking for.

 

[Robb]

Well . . . Unless the car is shaped like a pyramid with the antenna on the top - it might have a chance to show 50 ohms . . . lol!

 

[Marconi]

Marconi.....if you are loking for PROOF that a resonant 1/4 wave antenna ON A MOBILE INSTALLATION is ALWAYS 35 ohms you will not find it. It does not exist. The 35 ohms impedance is over perfect ground. A mobile installation, no matter how good it is, will never be that perfect ground. There are far too many variables in the size and shape of the vehicle as well as total surface area and bonding. All these variables affect ground losses which in turn affect the end resulting impedance. You may get close to that figure with a near perfect installation but I doubt you will get the exact proof you are looking for.

CK, thank you, thank you very much.

I wasn't looking for proof, I posted my proof, and here is what I really said.

I don't know if these models apply to the topic of this thread, but I see some guys claiming a 1/4 radiator has a 35 ohm impedance, but I seldom see that happen.


My real world testing of the 1/4 wave base antenna a few years ago didn't reveal this claim to be true as stated either, and again later, when I learned to model using Eznec, it too didn't prove that the 1/4 always shows a 35 ohm impedance.

I use to think the impedance at the end of a 1/4 wave radiator was always 35 ohms too. The argument that a 1/2 wave dipole showed about 73 ohms at resonance made a very convincing argument for the 1/4 showing about half of what a dipole did.


Since then, very few ever talked about feed point height, among other factors, that can effect the feed point impedance, so I did the following models to show how the feed point impedance for a 1/4 wave varies.

I'm not even getting into how the 1/4 wave radiator act on a mobile, because it is near to impossible to predict how that shape and size effects the ground plan that the 1/4 wave radiator needs to work predictably.


This fact probably helps explain why we hear so many stories about the success and failure for 102" SS whip installs on mobiles.


The models:

#1, is a resonant 1/4 wave whip with 1 suitable horizontal 1/4 wave radiator in the common L configuration at 32' feet. It shows a near perfect match at resonance, but a terrible pattern with a maximum vertical angle above 60* degrees. I think 'Doc is suggesting this weak design for a 1/4 wave with a very good match that doesn't talk worth a flip. Some autos might emulate such a pattern very well depending on install and how the ground plan works, yet it shows a super match which are often serious bragging rights for some owner/operators.


#2, model is a 1/4 wave with 4 x 1/4 wave horizontal radials. Again we see resonance, but the match is a bit high. The pattern is acceptable and workable, and we see the antenna dimensions get longer in order to produce resonance with a very low resistance part for the match. Again this match is still no where near 35 ohms, unless I set the model at a height of 17.75' feet above real Earth. Do you think this is where the idea for a 1/4 wave having an end impedance of 35 ohms came from?


#3, model is a 1/4 wave with 4 x 1/4 wave slanted down at 45* degrees radials that requires the antenna to become considerably shorter in radiator and radial lengths. Here we see a little better pattern, with a little improvement in gain, and again we see a near perfect match. However the maximum angle of radiation as actually gone up a bit, and this is contrary to many others who claims that slanted down radials on a 1/4 wave actually lowers the maximum angle. Not true again.


#4, model is similar to the original Starduster with slanted down radials at about 17* degrees. This configuration still has shorter elements than model
#3, showing a bit better pattern with an improved maximum gain, but the angle is the same in the lower lobe and a bit lower in the upper lobe. So, in this sense only is the angle lowered as a result of slanting the radials down.

Here you can see the results and not just read some words.


In order for me to tweak these models to show no reactance I had to tune using very small increments, maybe less that a .64 of an inch as I got close to Zero reactance. So when you get very close to perfect your adjustments are likely to be extremely small and maybe you didn't know that either. Here you could see the small differences if I posted the wires definitions...but that is just fodder that most don't understand and nobody has ever asked me one question on how to understand the data entry form for this software.


Now I ask you...did you see one 1/4 wave model here that showed a 35 ohm impedance? If I showed you a 1/2 wave resonant dipole, I would bet you would see an impedance near 70-73 ohms however. Go figure.


View attachment 11029


If you don't understand a little about what these models are revealing here...then just ignore my post. Believe me when I say: "...before I learned to model with Eznec I didn't always know how to consider or what to believe about antennas either. Sometimes I found my ideas were confirmed however, but I could not really say in words anything that was really convincing to prove my point. I saw things happen in my real world testing too...that I could not put into words.

Sometimes modeling reveals things in a way that I could understand, and then I present my models with a hope to pass on some that understanding, but in the end it is probably all in vain...me thinks.


However, I hope this helps someone, it looks really clear and revealing to me.

Just in case you missed what I really said on your first go around.

 

[Marconi]

DB, thanks for the info, but I missed a couple of key words in this presentation, words that have been suggested to be essential if we'll see 35 ohms at the feed point for a resonant 1/4 wave.

I don't mean to be rude here, but on your post #28, you suggested the idea using a perfect ground plane with no losses. I did just that, without knowing what to expect, and I posted those results...and we saw no change. That idea went down without a whimper, simply because it did not fit the group thinking.

I can't explain anything else in that regard, but I hear you guys that are positive with your ideas, ideas that you can't or won't support until you are almost challenged.

I'm just giving my opinion here, and if I'm wrong...so be it. Is the truth of a matter not important anymore? I think pride is the ruler around here and if I am convinced by any of you guys arguments...then I benefit.

You also confirmed the idea that a perfect ground plane was essential in order for a 1/4 wave to show a 35 ohms feed point impedance when resonant. My point is that I don't test over a perfect ground plane, and I claim here and now...that no body else does either. So if the idea has to be tested over a perfect ground plane, how in this world would we ever see 35 ohms in this case.

I can't count how many times I've received complaints about producing Free Space models as having some value...and what I hear in return is Free Space models are not real and don't mean nothing. You guys are claiming a perfect ground plane idea here, and to me this is the same O, same O and maybe even worse...since all you guys should know better.

I see what you believe to be true, and for years I believed that too, just like it was cast in granite. However, when I tested my 102" whips with several 102" whips as a suitable ground plane...I didn't see the 35 ohms of resistance I was promised. I mostly saw on my VA1 analyzer less than 35 ohms unless I slanted the radials down some.

I ask you, Ron, and CK, did you guys miss that when you tested 1/4 wave radiators with a suitable ground plane, or did you stop because you didn't have a perfect ground plane available?

What I saw was a lot of values that varied widely some times, but hardly ever was 35 ohms. If I had seen that I would have stopped what I was doing...because for years I was told that is where you stop with a 1/4 radiator.

Did any of you read my link I posted last night where Cebik answered in support of what I've claimed here? I didn't read it all, but I don't recall Cebik making any comments about doing his test over a perfect ground plane. It looked to me like he was doing some regular impedance work with an analyzer, but I could be wrong.

Go to Cebik's table #7, at this link: The 5/8-Wavelength Mystique and you will see his 146 mhz data for the impedance of a 1/4 wave, and it is clear the impedance is 26 ohms with very little reactance, and I don't think we'll read this testing was done over a perfect ground. But, if I'm wrong on that score...I will apologize to everyone here.

 

[Marconi]

Well . . . Unless the car is shaped like a pyramid with the antenna on the top - it might have a chance to show 50 ohms . . . lol!

Rob, you may have been kidding as you tried to find something to support your idea regarding 1/4 waves, but here I'm playing by the rules and getting back on track, but I doubt many will understand these mobile models I've posted at all.

I just ask the ones that have the understanding, to check out the Average Gain values noted, the source data for these two models of a Pick Up truck suggesting the feed point match, the patterns generated, and the impedance and the resulting SWR.

You suggest in you image above that the slant may have something to do with our success or failure to get a good match in a mobile. You are probably more correct than you imagined, because all vertical conductors near the feed point are flush with currents, as well as the elements note on the mobile that are near the ground and are plump with currents. Just check the red lines note and that will tell you a lot about how these currents might flow on the truck body.

View attachment PU models.pdf

This may surprise you.

 

[W5LZ]

" Originally Posted by Marconi View Post
I don't know if these models apply to the topic of this thread, but I see some guys claiming a 1/4 radiator has a 35 ohm impedance, but I seldom see that happen.


My real world testing of the 1/4 wave base antenna a few years ago didn't reveal this claim to be true as stated either, and again later, when I learned to model using Eznec, it too didn't prove that the 1/4 always shows a 35 ohm impedance."

I honestly can't say that I ever claimed a 1/4 wave antenna would -always- show an input impedance of 35 ohms. I have said that an input impedance for them averaged between something like 20 and 40 ohms. You have to admit that 35 ohms falls in that range. Can anyone predict what a typical 1/4 wave mobile antenna's input impedance will be? No, not me or you or that other guy over there. We can all be pretty sure that it will fall in that range of impedance though (20 - 40 ohms).
So, I'm going to take your advice and ignore your posts. You may have learned to operate EZNEC, but I don't think you understand what it's telling you yet.
- 'Doc

 

[Marconi]

An important PM needs you prompt attention

'Doc you've got mail from the man.

You're :bdh:

 

[The DB]

DB, thanks for the info, but I missed a couple of key words in this presentation, words that have been suggested to be essential if we'll see 35 ohms at the feed point for a resonant 1/4 wave.

I don't mean to be rude here, but on your post #28, you suggested the idea using a perfect ground plane with no losses. I did just that, without knowing what to expect, and I posted those results...and we saw no change. That idea went down without a whimper, simply because it did not fit the group thinking.

I simply scanned and quoted the information from said book that you requested. Until recently I have not to my memory been exposed to anything short of a random person in random forums occasionally stating different on the subject. This thread is the first time I remember you mentioning that yourself, and doc saying something similar. I personally try and stick with published information (by published I am referring to books, not web pages) as there is a lot of mis-information around and this is my way of sifting through that information. One thing that has frustrated me on this specifically is charts that are listed as "calculated" yet I have yet to find any mathematical equation that can be used to confirm the calculation.

I can't explain anything else in that regard, but I hear you guys that are positive with your ideas, ideas that you can't or won't support until you are almost challenged.

I'm just giving my opinion here, and if I'm wrong...so be it. Is the truth of a matter not important anymore? I think pride is the ruler around here and if I am convinced by any of you guys arguments...then I benefit.

Because of the evidence that you have shown with your modeling data I have changed my understanding of that bit of information from fact to assumed fact, at least for the time being. Yea, its not much, but its something. Part of my problem here is I personally don't have a complete understanding of modeling, a fatal flaw I know, but I intend to change that lack of knowledge some day. There are benefits, but the results can and have been manipulated on occasion, sometimes unintentionally. You yourself have found errors in your work in the past and corrected them, which I think says a lot about you persoanlly. When I encounter something that I don't expect in modeling (or any claim in this field for that matter) I view it with skepticism until I can verify the information. Sometimes I even learn something in the process.

I'm wondering if there is something that we are missing somewhere that explains both sides of this. It could be something as simple the width of the antenna, or how much separation is between it and that "perfect" ground plane below it, or perhaps even how modeling programs model the feedline connection in this instance (even if you factor out feedline losses and such)...


The DB

 

[Marconi]

Thanks for the info DB. I don't have that year for the ARRL, but I found several links that suggest the 1/4 wave shows a 35 ohm resistance when resonant.

I might try and get my Marconi 5x out and check this idea again.

 

[Road Squawker]

...So, I'm going to take your advice and ignore your posts. You may have learned to operate EZNEC, but I don't think you understand what it's telling you yet.
- 'Doc

Ding, Ding, DING,.... we have a winnah.

 

[Captain Kilowatt]

35 ohms is what you get over a perfect groundplane. It is usually more than that due to ground losses which add to the nominal 35 ohm impedance for a 1/4 wave GP.

That is what I was thinking, however Marconi's modeling software came up with a different figure.

The DB

And yet there are countless examples all over the internet on countless sites that agree with what I said. Gee ....go figure.

 

[The DB]

I think we are a bit off topic at this point but...

And yet there are countless examples all over the internet on countless sites that agree with what I said. Gee ....go figure.

Odd, from less than page of posts after I posted:

...I personally try and stick with published information (by published I am referring to books, not web pages) as there is a lot of mis-information around and this is my way of sifting through that information...

All this over a line that we weren't in disagreement with in the first place... All of my sources agree with all of your sources. The question that led up to this post was asked with another purpose in mind. It led to a response that I did not expect from Marconi, who the question was asked, and that disagrees with both of our sources. Because of this I am wondering why his models are disagreeing with our sources. Is he doing something wrong and if so what?

So CK I ask you this, is there a way other than losses, such as width of the radiator or the distance between the base of the radiator and the theoretical "perfect" groundplane that can change the theoretical "lossless" impedance to something other than 35-37 ohm impedance? Something that can possibly explain Marconi's 25 ohm impedance at resonance?


The DB

 

[Captain Kilowatt]

Good question. Length to diameter ratio can affect it some. Not only is the resonant length shorter for a fat conductor the impedance will be effected a bit too due to the difference in ohmic losses. I suspect this may be part of the reason why we see a certain value for a 10m antenna and yet a different value for a 2m antenna with the same size material used. There is a difference in terms of wavelength and unless even wire size is scaled the outcome would be different. The material used will affect the outcome as well. Copper, aluminum, and stainless steel all have different electrical properties so that will make a bit of a difference as well. How far the feedpoint is from the groundplane will make a difference too as the ground lead has to be factored in. Something I don't think is being taken into account either is that that figure of 35 ohms, and that is a "nominal" 35 ohms not a hard and fast definite value, (sort of like 50 ohms coax being somewhat near 50 ohms but not exactly) not only assumes a perfect groundplane but if memory serves me correctly it also assumes that perfect groundplane is in free space which eliminates any coupling effects to anything other than the groundplane. Antenna installations are so varied that it is impossible to say something will be X value all the time everywhere in all cases. IMHO worrying about whether it is truly 35 ohms or 27 ohms or 41 ohms is simply a waste of time. The fact remains that it must be matched to 50 ohms for most applications and using the nominal value of 35 ohms is as good a starting point as any.

Just as a real example, back in 1986 I moved an AM transmitter site to a new location. The old site being encroached upon by developments and had the original 1948 tower which was a short top loaded affair that was unstable electrically with changes in the weather. I had a 160 foot steel tower installed with a 24 inch face at the new location on a piece of prime dyke land with very good conductivity. The frequency was 1450 KHz making the 160 foot tower a ful 1/4 wave. The ground system consisted of 120 radials spaced equally around the base and each radial was a 1/4 wavelength of 10 gauge bare solid wire. The radials were flat with the exception that about 1/4 of them sloped downwards slightly for about half their length due to terrain. Directly at the base of the tower was a 20 foot by 20 foot ground mat made from 6 gauge stranded wire with the wires running in both directions and spaced one foot apart and silver soldered with Silfoss wherever they crossed. This was done to maintain a more stable ground in the immediate area of the tower. When all was said and done and the tower self impedance measured we ended up with 38 ohms R and just a few ohms of reactance.This was before the electrical cables and clearance lights were added as well as the Austin toroidal lighting transformer at the base. I merely present this as a real world example of an installation and what the results were. Nothing more.


BTW when I said "And yet there are countless examples all over the internet on countless sites that agree with what I said. Gee ....go figure." it was not meant to be against anything you said but merely an observation of facts. I believe we are on the same wavelength to use a very bad pun.

 

[Captain Kilowatt]

CK, thank you, thank you very much.

I wasn't looking for proof, I posted my proof, and here is what I really said.



Just in case you missed what I really said on your first go around.

I messed up who said what. It was not you asking if there was a formula around as I thought. It was theDB that asked that and I replied as if it was you that had asked it. My bad. Too much going on in my personal life right now and no sleep and just started nights. No sleep etc.....yeah excuses but they are honest excuses. LOL