Any comments ???

[Sonwatcher]

Any comments on this article about "coil" antennas ?



www.firecommunications.com/antart.txt

God bless you all !



CDX-897

OT-897

WV-897

CM-2368

American Kangaroo-1897</p>

 

[mr2020]

Yeah another looks good on paper no actual been there done that type thing...

Was taught those same things about antenna therory and when it was applied that therory was shot to hell...Plus there is a bunch of double talk in that message..



Only the price has changed upwards ? HMMMMM if the cat looked around he'd see they are down a bit..Its these truck stops, duplicators and rip off artist shops that sell at the high prices...

Sounds like an engineer ( I say that loosely ) or 2 needs to do more field work and read less books




MR2020 in the Back Woods of Ga

Connex 3300

2-32 pill

4-250b's

2 3cx3000's</p>

 

[freecell]

rebuttal........



a post i saw recently in another forum sums it up best........



"A 1/4 wave antenna has no gain, in fact, it has a negative gain"



Incorrect. It has 0.3 dBi, where the "standard" is the "i", and the "i" stands for isotropic. If you treated your antenna as a point inside a sphere, the "i" means equal illumination flux at all points on the inside of the sphere. the "gain" comes from focusing this flux to less than a perfect 3 dimensional sphere. If all the power was radiated perfectly spherically, and all this power were put into half the sphere, the flux density would be double at any point in the half sphere versus what it was for the whole sphere. This is all antenna gain is. If a "d" were used instead of an "i", then we would have a "standard" of a dipole, which would have been set in reference to the "i", where in all considerations the "i" is the true starting point of reference no matter how you were looking at the picture. The diameter of the sphere matters not, as the total flux density would merely be spread out over a greater area. Many people mistake the inverse square law as meaning the signal gets weaker with distance, which is incorrect. The total photon flux never changes, it just gets spread out to where any certain cross sectional area sees a reduced concentration of flux. The only exception to this would be in the case of absorption of energy by something in the path of the EM wave. Since gain is referenced to isotropic, it is in fact wrong to conclude that the 1/4 wave has negative gain, since isotropic implies 0 dB, and the antenna would have to be below zero, which a quarter wave is not.



but the antennas which are the subject of this article do exhibit negative gain figures below 0.0db. when compared to their full-size 1/4 wave counterparts.



and let's not forget the credits........



Posted: Jun 24 2004, 10:48 PM

By: AB7IF, Russell Clift



in addition, since mr2020 is studying something called "antenna therory" that i am unfamiliar with, i'll refrain at this time from any comments except to say that i would appreciate the opportunity to discuss anything he views as "double talk" in the associated article. until any such time that aberrations or inaccuracies are evidenced the article will remain as-is.



contrary to any presumption on his part, the information in this article was obtained through an accumulated effort involving theory, practical experience and constant application, references and notes of those who have gone before and literally thousands of hours of field use and testing. but then it is so typical of most of those in this area to discount someone elses hard work with little more evidence than mere generalizations and tired cliches.



i'm used to it.




</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/7/04 11:25 am

 

[freecell]

UK MUDDUCK,

just one question........



for the most part, do you operate the mobile in ........

an urban environment, a sub-urban environment or a rural environment....?


</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/7/04 12:49 pm

 

[freecell]

UK MUDDUCK,



if that's what you're dealing with in terms of terrain then more than likely it is a 10K world, for you. just taking into account that you spend 2/3rds of your time in urban-suburban environments dictates that a unity or near unity gain antenna would deliver optimum results that part of the time. in wide-open flat land regions though the near-unity gain 10K will fall on its face in favor of almost any antenna or antenna system producing over-unity gain. the question i asked you in the last post is just one of many that need to be answered before the best antenna for the particular application at hand can begin to be determined.



it would appear that given your particular situation you have exactly what you need. however, don't discount the possibility of an over-unity design when you're in the clear working your dx. the trick would be to select an antenna design that will lower the angle enough to improve the skip distance without lowering it so much that the local terrain obstructs the main incident em wave.



Have Fun,








</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/8/04 2:19 pm

 

[Sonwatcher]

No offence here David. I thank you for your input. I feel it touched something that has seemed to be buried in theory and that is the practicle side. To say what kind of terrain I mostly transmit from cannot be put into one area. I am in construction and go through all of them. I have one of your antennas on my vehicle and after replacing my Firestik with it I talked to my wife about 10 miles away and she said I sounded like I was in the driveway.And that is with it mounted with a trunk mount on a Plymouth Neon<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/happy.gif ALT=""> I didn't have those results with the Firestik. I also found that your antenna was easier to tune than was the Firestik in my case. I can't tell you about theory but I can share the real results.



Ron

God bless you all !



CDX-897

OT-897

WV-897

CM-2368

American Kangaroo-1897</p>

 

[Jay in the Mojave]

Hello Freecell:



Ya forget to give the 1/4 wavelength ground plane gain in dBd, its

-1.8 dBd.



So yeah it does have negative gain.



Jay in the Mojave


</p>

 

[Sonwatcher]

Freecell,

<blockquote>Quote:<hr>you can laugh all you want as to the question i posited in the poll regarding terrain and environment <hr></blockquote>



I suspect you were thinking I was laughing at your poll when I wrote "Hee hee". I was responding to the way Mike wrote up his comment. Sorry if you took it the wrong way.



Ron

God bless you all !



CDX-897

OT-897

WV-897

CM-2368

American Kangaroo-1897</p>

 

[freecell]

"Apparently I must have missed that point. I thought the article was about getting ripped off if you bought a coiled antenna. I also understood this article, and a previous post to say people who buy and sell these antennas are stupid and don't know anything about antenna design, theory, or anything else. I'm sorry but that is the way I took it."



then you read the article but didn't comprehend what was being said.



the antennas listed in the article exhibit no gain. they are classified as near-unity or unity gain type antennas. if the application involves a city type environment then they are more effective in terms of coverage and performance in that type of environment due to the excessive amount of high angle (skyward) radiation that they generate in their associated patterns. on the other hand, this high angle radiation is detrimental to long distance ground wave and skywave operation in areas where the *land is wide open and fairly flat in all directions due to the large amounts of radiated energy being wasted at the higher angles in this setting.



in this environment* we require a design that produces gain by compressing the upper portion of the wavefront towards the ground and eliminating large amounts of radiated and wasted energy at the higher angles to extend communications range. antennas that are designed in this fashion are referred to as over-unity gain antennas. these ARE NOT the antennas listed in the article. instead of discounting what you refer to as theory, you should be instead considering the individual application.



the bottom line here is that one antenna design does not fit all applications. and there are more things to consider here than just the local topography. by the same token, you can't offer or manufacture a single design and then claim to all of the consumer buying public that it's the answer to their unique and individual applications, not even a targeted market group such as truck drivers or those involved in keydown competition.



the same thing applies to over-unity gain antennas. the last thing you want to do is recommend this type of antenna to someone who spends most of their time driving locally in a big city environment. a low angle em wave directed at the base of high-rise buildings is not generally conducive to long-range communications. on the other hand, in the wide open plains or flat desert regions this is exactly what you want in a mobile antenna.



the fact that this is the way that different antenna designs behave is not any vague theory. and you can laugh all you want as to the question i posited in the poll regarding terrain and environment because as long as this question is not asked (along with many others) of each and every customer in the market for an antenna on an individual basis the needs of the individual customer are being ignored for what someone wrongly believes to be "the answer" for every one who walks in the door. sadly, this is not the case.



the ultimate goal in any situation is to deliver the bulk of the em wave at the most advantageous angle above ground to facilitate the reception of the strongest signal possible at the receiver end of the circuit and visa versa.. the required radiation angle to accomplish this varies due to a number of factors, local terrain being only one of them. for the time being there is no single antenna capable of this under all conditions.



as to the question of getting ripped off, i never claimed or implied that. in light of the information provided in this thread and in the mentioned article it is easy to see that this could happen unintentionally by the act of omission. on the other hand, anyone advertising that "this is the antenna you need" regardless, in total disregard to the nessesary answers to mostly unasked questions on an individual basis, one might equate that as being ripped off.



if you're thinking at this point, it's easy to realize why over-unity gain antennas subjected to casual testing in less than optimum environments might not show well when compared to their near-unity or unity counterparts.



some of you in here have already seen for yourselves that the use of longer shafts with coil-loaded antennas produced improved results and have established for yourselves that something "beneficial" was happening as a result of elevated loading coil height above the vehicle and/or counterpoise underneath. some of you have seen more favorable vswr readings, closer-to-50 ohm antenna input impedance indications and noticably improved performance. what you weren't able to see (but obvious nonetheless) is that as the loading coil was raised the radiation angle was being lowered placing more of the incident em wave closer to the horizon.



i suspect that some of you are beginning to understand some of the things i have attempted to explain and to those of you who are referred to here i would like to thank you for testing these things for yourself instead of merely discounting them out-of-hand.


</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/9/04 11:58 am

 

[freecell]

UK MUDDUCK,



that would depend on the height limitations you use to define a "ride-around" antenna........but an over-unity gain antenna will not give optimum performance in all surroundings. the best of both worlds can tentatively be had by using two separate antennas.



they could both be mounted on the vehicle (appropriately separated) and used with an antenna switch or simply changed out at the mount in a moments notice. the first option works quite well at vhf/uhf frequencies as even at the spacings that may be provided on a passenger vehicle the antennas can be at several wavelengths apart from each other whereas at 27 mhz. there will be a large amount of interaction between them. one disadvantage of this scheme at the lower frequencies.



i can think of several antennas that might meet your requirements in the range of 4 - 8 feet in length.



pm or email me if you would like further information........


</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/9/04 11:24 am

 

[freecell]

Jay in the Mojave,



when compared to a half-wave dipole....only problem is that figure can vary considerably when compared to the 1/2 wave dipole depending on a number of factors inherent in the construction, feedpoint elevation, ground conductivity, etc.. on the other hand, the standard reference of the "i" isotropic source never changes. (and i'm actually thankful that it can't be built or it would most conceivably change) besides the reasons explained previously, it helps to have a reference that is relaible for comparison in every instance instead of disputing a physical reference that will produce x amount of gain in one application, y amount of gain in another and so forth. this makes gain figures / comparisons unreliable and does not constitute a baseline reference in the true sense of the word.



since this is the case, i prefer to make comparisons to a reference that remains the same.



"Since gain is referenced to isotropic, it is in fact wrong to conclude that the 1/4 wave has negative gain, since isotropic implies 0 dB, and the antenna would have to be below zero, which a quarter wave is not."



the other thing not given consideration here is that there's a noticable difference in the gain produced between a 1/4 wave at vehicle roof height (or any of the other popular vehicle mounting locations) and the same 1/4 wave with the feedpoint elevated to a wavelength above ground.



ground reflection gain doesn't come into play and provides no incident em wave reinforcement in mobile applications.






</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/9/04 11:48 am

 

[freecell]

Sonwatcher,



no fault, Sonwatcher, though i did get the impression that some might have thought that the poll was frivolous possibly because they may have perceived that terrain and environment had little to do with antenna application and/or performance.



i actually have a reason and a purpose for posting the poll and would appreciate it if all would respond. if i can't get at least 100 votes i won't be able to do much with it!



nothing personal here....lol


</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 7/9/04 11:21 am

 

[Kale Cavel]

freecell, just what is your hobby? If it's radios, what frequency do you monitor and talk on and what kind of antenna do you use? Kale


</p>

 

[freecell]

the dipole reference may represent the real world to you and others but i have a lot less of a problem readily imagining *an antenna as a central point inside a sphere providing equal illumination flux at all points on the inside of the sphere* than i do conjuring up the many possible field pattern scenarios represented by a dipole over earth of various soil conductivity, heights above ground, varying near-field terrain and the like.



the isotropic source is to antennas what the number 0 is to the multitude of whole integers both positive and negative in mathematics. they are a central, totally predictable reference point and neither of them ever changes.



and if these points are not justification enough for the "i" isotropic as a real world reference then just consider this one last point. any deviation from the example of the "i" isotropic given above*_* represents the onset or the beginning of any true gain. this happens the moment that the antenna is moved from the environment of space and comes to rest on the face of the earth. at this point what we understand as the bottom or the underside of the wavefront is being compressed upward by the ground underneath it. this is the onset of antenna gain and we have moved beyond any true unity reference, even if only a few tenths of a db. seeing as how even the smallest system inefficiency can and does eliminate or render null this smallest of advantages (.3db.) the designation of near-unity or unity gain antenna still applies when referring to a 1/4 at or near earth ground.










</p>

 

[freecell]

re-read the article for the latest additions.



Who are you going to believe?



Making The Case For Dual Antennas


</p>