Author Topic: Spray On Antenna  (Read 42619 times)

0 Members and 1 Guest are viewing this topic.

Offline Simon

  • Global Moderator
  • *****
  • Posts: 15714
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Spray On Antenna
« Reply #25 on: February 13, 2012, 07:47:50 pm »
that is a very very good pisstake of videos like the one being discussed
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32752
  • Country: au
    • EEVblog
Re: Spray On Antenna
« Reply #26 on: February 13, 2012, 09:44:09 pm »
It looks like RCA, with all their amazing R&D capability, have investigated the concept and decided not to take it to market:

http://www.gadgetsgeek.ly/2011/01/07/ces-2011-hey-rca-how%E2%80%99s-that-airnergy-wifi-charger-coming-along-oh-no-where-to-be-seen-what-a-surprise%E2%80%A6/

What a shock!


Dave.
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 15714
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Spray On Antenna
« Reply #27 on: February 13, 2012, 10:01:24 pm »
40 dollars for a battery with some dangling wire attached ? - ON YOUR BIKE MATE  ;D
 

Offline gregariz

  • Frequent Contributor
  • **
  • Posts: 545
  • Country: us
Re: Spray On Antenna
« Reply #28 on: February 13, 2012, 11:11:18 pm »
I didn't think you could make an antenna out of capacitors, basically they have designed a quick drying metallic/conductive spray - woo hoo, big deal ? I've never heard debates about antenna material, about antenna design yes but not the material, I guess copper is ideal but see a lot of aluminium due to weight, cost and it don't rust.

If you think about that and then listen to that guy he sounds well ignorant, he's either uttering rubbish or needs to change the presentation but if he's go nothing to put in....... I have to say that all the way through all I was thinking was bullshit, bullshit, bullshit, he was using all the hallmarks of a scam.

Looks like nonsense to me, probably a can of nickel paint.

There are antenna's made out of caps. You can make an antenna out of any type of plasma. The idea is that by leveling out the current pattern (with cap phase changes) you can raise the effective efficiency of the structure (ie pattern is directly proportional to current distribution for most common antennas). This works up to a point but assumes that the antenna is relatively electrically small which is innefficient to begin with. I can tell you that this technology has no serious place in current antenna research. There are a number of other similiar ideas out there. One is the EH antenna concept which is a very short monopole like antenna. There was considerable debate about it and the company even had a russian physicist come up with a highly mathematical (and difficult to disprove) alteration to electromagnetic theory. Its pretty well been debunked now however basically because people noticed that the thing's performance was attrocious with a balun on the cable. What was happening was that the actual antenna was the coax that was feeding the antenna. It wouldnt surprise me if that can of nickel paint works quite well under some circumstances when fed by a transmission line which is acting as the antenna.

I take my hat off to them. Sounds like they have a few physicists on staff with the right line of shit. If they can make that pitch to a few clueless investors and suck a few million out of them, I say go for it.
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #29 on: February 14, 2012, 03:03:29 am »
I am sure it is not simply a conductive spray paint, and Chamtech do have very capable RF designers.  I believe that the project came out of a military request for a product that was a conformal spray-on antenna. The conformal requirement probably made it very difficult to use a conductive paint, as any metallic particles on the surface would allow corrosion to get into the coating.

I was thinking some more about what the product actually is. Notice how they were often painting over the tops of existing copper antenna's?

I think it is exactly what Anthony Sutara said it was - a spray containing micro-capacitor particles. It may even be that a conductor is always needed under the spray - he never actually said it replaces the need for a conductor. Or if the paint does have conductive particles, it may be that they settle on the painted surface leaving the suspended capacitive particles and conformal coating over the top of the conductive layer.

What I think this product does is to change the electrical permittivity in the space between the conductor and the air. This is a known method of improving the performance of small antenna's, but it has usually been done by encasing the antenna in a material, instead of a spray or printable ink.

Here is a document talking about using materials with different electrical permittivity and magnetic permeability  in antenna design:

http://www.mitre.org/work/tech_papers/2011/11_0837/11_0837.pdf

We are still left with no quantitative numbers of actual RF performances, but it is technically possible to change antenna performance by providing a high permittivity layer between the conductor and the air. Perhaps this will not change the antenna world, but Chemtech may be the first on the market with a paint with a high permittivity, and obviously that want to push that for all it is worth. I don't think it is a hoax, unless you want to include the stupid reporting of the story by the technical bloggers and news sites. I think they have a real product that could have some potentially interesting uses.

Richard
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #30 on: February 14, 2012, 03:27:11 am »
I am sure it is not simply a conductive spray paint, and Chamtech do have very capable RF designers.  I believe that the project came out of a military request for a product that was a conformal spray-on antenna. The conformal requirement probably made it very difficult to use a conductive paint, as any metallic particles on the surface would allow corrosion to get into the coating.

I was thinking some more about what the product actually is. Notice how they were often painting over the tops of existing copper antenna's?

I think it is exactly what Anthony Sutara said it was - a spray containing micro-capacitor particles. It may even be that a conductor is always needed under the spray - he never actually said it replaces the need for a conductor. Or if the paint does have conductive particles, it may be that they settle on the painted surface leaving the suspended capacitive particles and conformal coating over the top of the conductive layer.

What I think this product does is to change the electrical permittivity in the space between the conductor and the air. This is a known method of improving the performance of small antenna's, but it has usually been done by encasing the antenna in a material, instead of a spray or printable ink.

Here is a document talking about using materials with different electrical permittivity and magnetic permeability  in antenna design:

http://www.mitre.org/work/tech_papers/2011/11_0837/11_0837.pdf

We are still left with no quantitative numbers of actual RF performances, but it is technically possible to change antenna performance by providing a high permittivity layer between the conductor and the air. Perhaps this will not change the antenna world, but Chemtech may be the first on the market with a paint with a high permittivity, and obviously that want to push that for all it is worth. I don't think it is a hoax, unless you want to include the stupid reporting of the story by the technical bloggers and news sites. I think they have a real product that could have some potentially interesting uses.

Richard

No,sorry,Richard,but if it works as you suggest,why don't they tell us that,rather than spout a lot of mumbo-jumbo.
The guy in the video was supposed to work for "Scamtech",err,Chamtech,so the nonsense isn't from bloggers & news sites,it purports to be direct from the company itself.
There are a lot of scammers out there when it comes to antennas,as well as some quite sincere people who are pushing nonsense
antennas because they believe they have found a way to defeat  the laws of physics.
The patter is classic scam-speak.Notice he says "the government"----Not the US Navy,or Air Force,or NASA( I guess he's a Yank!),or even the local Mayor!



 

Offline MarkS

  • Frequent Contributor
  • **
  • Posts: 530
  • Country: us
Re: Spray On Antenna
« Reply #31 on: February 14, 2012, 04:58:20 am »
I've heard very similar pitches from the free energy folks. They offer just enough data to reel you in, but not enough to make an informed decision. All of the data that is given supports their conclusions with any other data conspicuously missing. They often will make claims that they welcome others to test their device and sometimes ask for partners, but then fail to deliver.

If this is so revolutionary, why no actual reviews? I did a Google search, but all I can find are references to the video in the original post. No one has actually tried the spray and posted anything about it. Anywhere. I really did intend to buy a can and test it or send it to someone better set up to test it, but I then found that you can only buy it directly from Chamtech and to top it off, you have to call for a quote. To quote Admiral Ackbar... It's a trap! Either someone wanting to buy a small quantity for testing wont get past the person answering the phone, or the price will be so ridiculously high that it is unaffordable. I also suspect that a NDA will be required prior to purchase.
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #32 on: February 14, 2012, 05:01:34 am »
I have no knowledge that Chamtech has a military contract, but I do know that DARPA (The US Defense Advanced Resaerch Projects Agency) have been looking for a working spray-on antenna for military use, and I believe that this was the motivation for Chamtech's work. Rett Spencer of Chamtech has reportedly said that the spray-on antenna was conceived when "Chamtech was contacted by the US Military to help them create a conforming antenna for special ops since traditional antenna systems were bulky and hard to hide from the enemy". A year ago, they had a conductive spray. This year, they have the capacitive particle spray.  Are you saying that all of this is totally a lie?

If you read my previous posts, I have criticized Anthony's presentation for the lack in essential details. I am not suggesting that this spray will suddenly increase all antenna's by 20dB.

But that does not mean that this is could be an interesting product that could have some useful applications. I have heard people from companies like Microsoft come out with total rubbish, but I have never accused Microsoft of being a scam, just because of one employee's comment. No way will I claim that Chamtech is a scamming company, until I see some proof that it is. I am not going to condemn a company just because one marketing guy puts the best possible spin on a not-quite released product.

Now, how can you say that the nonsense isn't from the bloggers. Looks at some of the blogger's headlines:

Spray-on Antenna to revolutionize the mobile industry (Was originally "Spray-on Antenna could revolutionize the mobile industry" but some bloggers decided "to" was better")
Spray on Antenna can get rid of ugly cell tower
Spray On Antenna Kit for Signal Anywhere
Magical Spray Makes Everything an Antenna
Spray-on Antenna - Wireless in a Can


When I looked before, I was reading in one blog how the Spray-on Antenna means there will be no more mobile black spots thanks to this spray! To take the results of a single test, like the iPhone test, and to amplify that as a general finding is complete irresponsible reporting. You seem to be blaming the fingers of these bloggers on Chamtech as if the bloggers had no brains and couldn't control what they typed.

I don't like Anthony's presentation, but it was at Google's Solve for X which I gather is a place for broad ideas and rather then details. It is not a place that you present specification sheets which is what we want to see. I do not know what the spray can do. I do not know its permittivity, its dissipation factor vs frequency.

I am much more interested in looking for ideas that could be interesting, then totally dumping ideas outright just because they may be useless. If Chamtech are scammers, please give me some information to show that they do not have a spray containing capacitor particles. If they do have such a spray, I want some more information, as it could be unique and useful.

Richard.

 

Offline MarkS

  • Frequent Contributor
  • **
  • Posts: 530
  • Country: us
Re: Spray On Antenna
« Reply #33 on: February 14, 2012, 05:07:46 am »
I agree with you here, which is why I will at least entertain the free energy folks:

I am much more interested in looking for ideas that could be interesting, then totally dumping ideas outright just because they may be useless.

But I disagree with you here:

If Chamtech are scammers, please give me some information to show that they do not have a spray containing capacitor particles. If they do have such a spray, I want some more information, as it could be unique and useful.

It is up to the person making the claims to provide evidence that they are correct. It isn't for those of us who watched that crappy video to provide proof. Apart from that video, Chamtech has been silent. No info anywhere. Absolute silence. They should be handing this stuff out to independent reviewers freely, and yet, nothing. It raises red flags.
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #34 on: February 14, 2012, 05:34:29 am »
It is up to the person making the claims to provide evidence that they are correct. It isn't for those of us who watched that crappy video to provide proof. Apart from that video, Chamtech has been silent. No info anywhere. Absolute silence. They should be handing this stuff out to independent reviewers freely, and yet, nothing. It raises red flags.

That is why I have just emailed them to see if they can give some more information. I will post anything they send.

If they do nothing, well, so be it. Their funeral.
 

Offline gregariz

  • Frequent Contributor
  • **
  • Posts: 545
  • Country: us
Re: Spray On Antenna
« Reply #35 on: February 14, 2012, 06:13:37 am »
I am sure it is not simply a conductive spray paint, and Chamtech do have very capable RF designers.  I believe that the project came out of a military request for a product that was a conformal spray-on antenna. T

According to http://www.neowin.net/news/the-amazing-spray-on-antenna

According to Chamtech's co-founder Anthony Sutera, he and his team came up with it in his living room two years ago. It works by manipulating magnetic and radio signals through mysterious organic materials, and you can spray it on any virtually any surface and hook into it with a flexible circuit cable.

That must of been between training snipers

http://www.ksl.com/?nid=148&sid=12009441

and between developing sexy pink travel cases

http://raffonedesign.com/home.html
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #36 on: February 14, 2012, 08:13:50 am »
Another interesting URL:-   http://investorshub.advfn.com/boards/read_msg.aspx?message_id=23274062

Maybe not the same  Anthony Sutera?

 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 15714
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Spray On Antenna
« Reply #37 on: February 14, 2012, 10:22:56 pm »
I think this may have started as a method of making a quick make shift antenna, like for the military, no need to carry antenna just have a can of spray and spray it on the nearest tree and whack a nail on the end of the wire into the tree: fine.

His claims of beating current antenna technology performance are piffle !!!, my guess is maybe the military inquired about a potential product and either it did not meet their requirements or they changed their minds, and then some bright spark in the sales department decided to flog it off as something else and some poor sod who looks like a bumbling young version of Kevin Costner gets sent out to make presentations with a written / memorized script but does not even know what he is talking about.

considering that RF radiation goes down to 25% every time you double your distance from the source and he is talking of orders of magnitude increased in power/sensitivity (he never specified) and an order of magnitude is something big not like doubling it he frankly has no idea of the sheer bullshit he is coming out with and is clearly just going off a script.
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #38 on: February 15, 2012, 01:25:32 am »
The thing is,he is supposed to be high up in Management,& involved with the design.
If you look at my link,you will find an Anthony Sutera as President of a company purporting to have made breakthroughs in Aviation.
Yet another Anthony Sutera was involved in some scheme to give people Combat training.
Either the Sutera clan are extremely fruitful,or it just might be the same bloke!
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #39 on: February 15, 2012, 01:59:58 am »
The thing is,he is supposed to be high up in Management,& involved with the design.
If you look at my link,you will find an Anthony Sutera as President of a company purporting to have made breakthroughs in Aviation.
Yet another Anthony Sutera was involved in some scheme to give people Combat training.
Either the Sutera clan are extremely fruitful,or it just might be the same bloke!

It is the same guy. Yes he is a very busy young man. He does hold patents in turbine design, secure near filed communication, headset design. Either he is pretty bright, or has the knack of finding other people who are pretty bright to work with. Definitely an entrepreneur.

I have been trying to locate any of the patents that supposedly exist for the spray on paint, and no luck. Of course they could have done the patents under a new company name that I do not know about. no reply yet to my email yesterday to Chamtech for more information, but my email wouldn't be high on their priority list.

By the way, I looked into that claim from Anthony Sutera about the police antenna heating up. It may not be that far fetched at all. It looks like the police radios can be over 100W RF output, and the frequency bands can be very broad, so they cannot used a highly tuned antenna. A 95% efficient antenna is pretty good, and that could still be dissipating over 5W of heat. The police radios operate on several bands - an example is 136-174MHz on some Motorola police radios. They won't use the whole band themselves, but they may want the ability to talk to other services in the range, like fire, ambulance, civil defense, military, etc.

I am not an antenna designer, but to design a compact broadband antenna that maintained the VSWR at a comfortable level for the transmitter over the whole band, couldn't efficiency drop to under 90% - that could mean 10W of heat in the antenna? That would be a pretty hot antenna. It doesn't make Anthony's argument any more valid, as 10% efficiency losses is only a 0.5dB loss - hardly noticeable.

Richard
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #40 on: February 15, 2012, 04:00:55 am »
"It is the same guy. Yes he is a very busy young man. He does hold patents in turbine design, secure near filed communication, headset design. Either he is pretty bright, or has the knack of finding other people who are pretty bright to work with. Definitely an entrepreneur"

Haven't you entertained the third possibility,that he is a Con Man?
The site I linked to was highly suspicious of his associate's claims of academic achievements.
OK,that doesn't mean that Anthony is guilty by association,but someone who claims amazing improvements in various fields,but doesn't provide any sensible data is surely subject to some doubt!

You are definitely "nice guys" other forums have not been as kind.(QRZ.com,for instance)

Re the police radios,they really only use small segments of the potential frequency range provided by the Radio in any one service,& antennas are optimised for that segment.
The cop radios have a low duty cycle--the police officers aren't talking all the time,so any heating would be dissipated fairly fast.

 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #41 on: February 15, 2012, 05:14:42 am »
"It is the same guy. Yes he is a very busy young man. He does hold patents in turbine design, secure near filed communication, headset design. Either he is pretty bright, or has the knack of finding other people who are pretty bright to work with. Definitely an entrepreneur"

Haven't you entertained the third possibility,that he is a Con Man?
Is is possible. Doesn't mean he is not bright.
Quote
The site I linked to was highly suspicious of his associate's claims of academic achievements.
That was one person he started a company with back in 2001, wasn't it? I am not going to condemn someone because he was associated with a guy who 11 years ago gave a misleading resume.
Quote
OK,that doesn't mean that Anthony is guilty by association,but someone who claims amazing improvements in various fields,but doesn't provide any sensible data is surely subject to some doubt!

You are definitely "nice guys" other forums have not been as kind.(QRZ.com,for instance)
I have been in startup tech companies. It is a tightrope walk to survive. I probably would be shocked if I heard what some of our sales people were promising in order to sell our products at the time. I am not going to try and damage a company based on suspicions, and some over-enthusiastic claims in what was obviously a sales presentation.

Also, as I remember, at the start, you give as little as possible of any real confidential secrets unless someone is offering real money and a signed contract. Anthony sure didn't give much away in terms of facts.
 
If I am going to start publicly label someone as a fake, I am going to do it with real evidence. Up till them, I am very happy to see if there are any useful ideas, and I think in this case, that any company who hands over lots of money without consulting their own designers and engineers would be unbelievably stupid. Assuming Chamtech are genuinely making their spray available, it would not be that hard to do some tests.
Quote
Re the police radios,they really only use small segments of the potential frequency range provided by the Radio in any one service,& antennas are optimized for that segment.
The cop radios have a low duty cycle--the police officers aren't talking all the time,so any heating would be dissipated fairly fast.
That's why Anthony said the antennas were hot if you touched them straight after transmitting.  What he said about the antenna getting hot was bagged in this forum as nonsense, but it could easily be totally true.

What is not true is that the heat demonstrates that conventional antennas are badly inefficient, and he did seem to be implying that his material suffers from close to no dielectric losses in a strong RF field, which sounds impossible. If a conventional antenna is getting a poor 75% of the RF energy into the air, and Chamtech could achieve 100%, it would still be a hardly noticeable improvement.

Richard.
« Last Edit: February 15, 2012, 06:54:35 am by amspire »
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 15714
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Spray On Antenna
« Reply #42 on: February 15, 2012, 06:50:58 am »
no one is disputing that police antennas get hot and it is because a lot of power is shoved into them for a brief period of time and it can gtake that thermal load and will dissipate it in time for the next transmission. But this guy is trying to say that the antennas are crap (not that they are effectively being abused and still work well) and that his are better.
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #43 on: February 15, 2012, 07:59:34 am »

Sarge!,Unc! where are you!
I'm tired of being the heavy on this thread! ;D
 


Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #45 on: February 16, 2012, 12:31:29 am »
I think the National Socialist party may be able to claim prior use of a very similar pattern to that in the first patent.to say nothing of the Ancient Indians! ;D
 

Offline gregariz

  • Frequent Contributor
  • **
  • Posts: 545
  • Country: us
Re: Spray On Antenna
« Reply #46 on: February 16, 2012, 12:47:43 am »
Mr Yagi might also have something to say about the first one.

With regard to that TTR-HP company that he used to run in the link above... just as a general interest it appears they all ended up in court;

http://www.legalmetric.com/cases/patent/utd/utd_204cv00677.html

More recently it was shut down for failing to file returns and is being sued by Nascar

http://investorshub.advfn.com/boards/board.aspx?board_id=3656
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #47 on: February 16, 2012, 03:00:49 am »
http://www.legalmetric.com/cases/patent/utd/utd_204cv00677.html
What is this meant to be? A court case prosecuted by different company that Anthony co-founded involving an injunction against a failed company that was dismissed by the judge simply because a similar case had been filed in the State court?

Wow!  ::)

The TTR HD/Aero Performance company seemed to be a genuine company that made a good product. Seems it was good enough for NASCAR to want to use it. The company failed in 2009. That proves what?

 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 5836
  • Country: au
Re: Spray On Antenna
« Reply #48 on: February 16, 2012, 08:45:37 am »
Going back to the "antennas heating up".
I thought a bit about it.

I am not an antenna guru,but I think I have pretty much covered the situation in the following
If you think I'm talking crap,please consult one of the standard texts on antennas! ;D

Antennas which are operating off resonance look reactive----- Capacitive for short antennas,& Inductive for long ones.

An antenna thus may be R -jX for the first instance,& R+jX for the second.

The value R in the above will be made up of R(losses) + R (radiation).
Where:-
R (losses) is normal resistance,& will remain the same over a large range of frequencies--it is normally for a vertical,earth resistance.
The resistance of the antenna itself for a metal antenna is so small as to be negliglble.(It may not be so in a paint antenna)

R (radiation) is the imaginary resistance which accounts for the"loss" which makes up the radiation.
Although it is not a "real" resistance,it meets all the other requirements of resistance.

When antennas are operated off resonance,the value of R(radiation) changes from the resonant value,so as well as X changing,so does R,BUT the loss part of R does not change!

An antenna which is not matched will reflect part of the RF drive to the Transmitter.
The reflected voltage & current waves are not in phase with each other,or with the incident wave at the load end of the feeder,but each combines with the incident waves at various points along the feeder,either adding or subtracting ,so that current or voltage maxima & minima appear along the feeder.
The voltage ones are better known to the general public--the famous VSWR!

Where current maxima appear,I^2 R losses occur due to the series resistance of the feeder,& when voltage maxima occur, losses
due to insulation leakage occur.--- The feeder gets warm,not the antenna.

If the Transmitter really is 50 ohms output impedance.the reflected  signal is ultimately terminated,so there is no total loss of power,apart from the feeder losses already incurred.

But wait,there's more!----Modern solid state transmitters are equipped with a circuit which reduces the power output when confronted with a high SWR,so if the antenna is that badly off tune,the 100watt? will be reduced to a lower level.
Even if the antenna  could become hot from being off resonance,there would be less power available to make it hot.

For quite a few years,I worked at a medium frequency AM Broadcast station which used a "Dual Mast".
This device was a top loaded vertical radiator,around 150m high,made of painted,galvanised steel,resting at the base on a very large insulator (about the size of a 200l drum).
The antenna was fed with a 55kW ,& a 10kW Transmitter,on different MW frequencies,via a combining unit.
Somebody noticed that the insulator had some kind of "scunge" on various parts of its surface & we were sent after closedown to scrub the insulator.
The thing had been running for around 19 hours straight,but by the time we got set up to do the job--say  3/4 of an hour,the metal of the mast was cold.
In fact,everything was bloody cold!
If you want  a reason to reassess your career path,lying on your back under tons of metal on a cold night,scrubbing an insulator with "Bon Ami" & distilled water will do it! ;D


 
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: Spray On Antenna
« Reply #49 on: February 16, 2012, 11:37:29 am »
Found an Amateur talking about mobile VHF antenna's.

http://www.k0bg.com/options.html

Quote
Most of the import antennas are rated from 75 to 200 watts. Where these power ratings come from is a mystery. The aforementioned V8000 with 75 watts out will burn up the average import antenna in due time, so you need to take their power ratings with a grain of salt. Even the venerable Larsen NMO2/70 will get warm during long transmissions at these power levels. I used to run 160+ watts out mobile to a Larsen NMO150. Due to the high power heating the whip, it was necessary to change the whip about every 6 to 8 months. Don't kid yourself; high output power levels require a lot of special considerations (more on this later on).

So 75 watts is enough to burn out many antenna's, and the police radios can easily be 110W at 13.8V - more at the maximum battery voltage over 14 volts..

I think the difference between fixed solid metal antenna's and flexible antennas made form helical copper wire or straight wire running inside a fiberglass cover, and various loading coils, is that the copper wire gauge is often thin enough to heat up. In the example mentioned in the article above, the antenna used about #24 wire - that is 0.02" thick. Add skin effect and that is not much copper at all. I took a quick look at the Larsen range and most of the VHF antenna's were 51" long which is very big. I would imagine to reduce that to, say, a more practical 20 inches, you probably do need helical windings and coils.

So it can get hot, particularly if cheap antenna's are used.

Richard.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf