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#1
October 24th 03, 04:48 PM
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In , "(Scott Unit 69)"
wrote: snip But what about what Frank said? You know Tnom's test was a sham. I just don't like to see people get cheated. The X-terminator's coils work out to 1.27 uH for the 9 turn coil and 0.60 for the 5 turn coil. The values of the coils and their positions on the shaft are consistent with the design of a center-loaded vertical. For those that don't already know, a loading coil is used to shorten an antenna while still keeping it's electrical length at 1/4 wavelength. But the antenna is necessarily less efficient because the coil radiates part of the power, and that power is lost. Why is it lost? Using the X-terminator picture as an example, you will see that the wire in the coil is oriented perpendicular to the antenna, so any radiation from the coil is going to be horizontally polarized, while the radiation from the antenna is vertically polarized. Some people might think that's a plus because some people have horizontal antennas, but it's really useless because it is radiated from 14 different wires (9 turns + 5 turns), and none of them are in phase with each other. Since there is no receiver publically available that can receive all those signals, put them back in phase with each other and add them to the horizontal signal, the power radiated by the coil is wasted. Nor can a receiver pick out just one signal from the fourteen. Even worse, the coil concentrates the magnetic flux (just like any other coil) and directs it right at the roof of the vehicle, which results in more lost power due to eddy currents induced into the sheet metal. Any loaded antenna is a trade-off between antenna height and efficiency. The only difference between the X-terminator and any other center-loaded vertical is that the former is built for kilowatts (and not very well at that, as the conductors are chrome plated, so it's RF resistance due to skin effect is higher than stainless steel, and much higher than bare copper or silver). There is no way that this antenna will outperform the unloaded 102" stainless-steel whip. Tnom's test may or may not have been a sham -- he may have actually gotten those numbers, but for reasons other than what he presented. Personally, I think the only thing he tested was his imagination. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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#2
October 24th 03, 06:57 PM
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On Fri, 24 Oct 2003 08:48:53 -0700, Frank Gilliland
wrote: In , "(Scott Unit 69)" wrote: snip But what about what Frank said? You know Tnom's test was a sham. I just don't like to see people get cheated. The X-terminator's coils work out to 1.27 uH for the 9 turn coil and 0.60 for the 5 turn coil. The values of the coils and their positions on the shaft are consistent with the design of a center-loaded vertical. For those that don't already know, a loading coil is used to shorten an antenna while still keeping it's electrical length at 1/4 wavelength. But the antenna is necessarily less efficient because the coil radiates part of the power, and that power is lost. Why is it lost? Using the X-terminator picture as an example, you will see that the wire in the coil is oriented perpendicular to the antenna, so any radiation from the coil is going to be horizontally polarized, while the radiation from the antenna is vertically polarized. Some people might think that's a plus because some people have horizontal antennas, but it's really useless because it is radiated from 14 different wires (9 turns + 5 turns), and none of them are in phase with each other. Since there is no receiver publically available that can receive all those signals, put them back in phase with each other and add them to the horizontal signal, the power radiated by the coil is wasted. Nor can a receiver pick out just one signal from the fourteen. Even worse, the coil concentrates the magnetic flux (just like any other coil) and directs it right at the roof of the vehicle, which results in more lost power due to eddy currents induced into the sheet metal. Any loaded antenna is a trade-off between antenna height and efficiency. The only difference between the X-terminator and any other center-loaded vertical is that the former is built for kilowatts (and not very well at that, as the conductors are chrome plated, so it's RF resistance due to skin effect is higher than stainless steel, and much higher than bare copper or silver). There is no way that this antenna will outperform the unloaded 102" stainless-steel whip. Tnom's test may or may not have been a sham -- he may have actually gotten those numbers, but for reasons other than what he presented. Personally, I think the only thing he tested was his imagination. The X-terminator has its main lobe at bit higher angle than the whip does. That may account for some of the differences. Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. |
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#3
October 24th 03, 09:11 PM
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snip
The X-terminator has its main lobe at bit higher angle than the whip does. That may account for some of the differences. Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. I'll have to go through the archives to find the numbers but chrome is a better conductor than Stainless |
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#4
October 24th 03, 09:19 PM
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#5
October 24th 03, 11:40 PM
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In , lancer wrote:
snip Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. I'm not sure, I'll check it and get back on that. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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#6
October 25th 03, 06:23 AM
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In , lancer wrote:
snip Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. For a conductor 102" long with a diameter of 0.625", the following metals have the following AC resistance at 27 MHz: Chromium .0194 ohms Copper .00711 ohms S. Steel .0451 ohms -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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#7
October 25th 03, 06:59 AM
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On Fri, 24 Oct 2003 22:23:48 -0700, Frank Gilliland
wrote: In , lancer wrote: snip Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. For a conductor 102" long with a diameter of 0.625", the following metals have the following AC resistance at 27 MHz: Chromium .0194 ohms Copper .00711 ohms S. Steel .0451 ohms ************************************************** ********** Chromium .0194 ohms ? Copper .00711 ohms ? With these figures Chrome has 36% the conductivity of copper ************************************************** ************ Stainless steel is definitely more resistive than you stated. According to your figure SS has 16% the conductivity of copper. This is not even close. Standard carbon steel has10% the conductivity. Stainless is less. 18-8 is 2.5%, 13-cr is 3.5%, and 18-cr is 3% The conductivity of the above figures on steel and stainless steel come from the "Metals" properties table, page 40, Ugly's electrical reference. George V. Hart |
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#8
October 25th 03, 07:21 AM
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On Fri, 24 Oct 2003 22:23:48 -0700, Frank Gilliland
wrote: In , lancer wrote: snip Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. For a conductor 102" long with a diameter of 0.625", the following metals have the following AC resistance at 27 MHz: Chromium .0194 ohms Copper .00711 ohms S. Steel .0451 ohms http://www.amm.com/index2.htm?/ref/conduct.HTM Chrome has 55% the conductivity of copper Steel (all types ) 3% - 15% |
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#10
October 25th 03, 06:40 PM
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In , Frank Gilliland
wrote: In , lancer wrote: snip Chrome has about the same conductivity that Stainless does, or at least from the info I found. 3-15% for Stainless, 19% for chrome, relative to copper. For a conductor 102" long with a diameter of 0.625", the following metals have the following AC resistance at 27 MHz: Chromium .0194 ohms Copper .00711 ohms S. Steel .0451 ohms By golly, I made -another- mistake in my math, which is not such a suprise. But when I was double-checking my work this time I ran across something that everyone should find VERY significant. So from the beginning..... S = Skin depth in meters = sqrt(2/(2*pi*f*u*q)), where q = conductivity of conductor (mhos/m), and u = 4piE07 * relative permeability of medium This is what's interesting. Stainless steel comes in many varieties. Some of them aren't even steel but use the term because they are used for the same applications. Regardless, some stainless steel is ferromagnetic and some is not. The nonferromagnetic steel will have a relative permeability close to that of copper, or 1 for all practical purposes. OTOH, ferromagnetic steel will have a relative permeability much higher, and the value of 500 was used in the calculations below. AC resistance in ohms = l / (q * S * 2 * pi * r), where l = length of conductor (in meters) r = radius of conductor (in meters) Note that there are two different listings for the conductivity of chromium. The first value is based on the information that it is 55% of the conductivity of copper, and the second value (as well as the values for copper and stainless steel) is based upon CRC's HC&P: Cu Cr #1 Cr #2 S.S. S.S. (ferro) Conductivity: 5.80E07 3.19E07 .769E07 .166E07 .166E07 Skin depth: 12.7E-06 17.1E-06 34.9E-06 75.2E-06 3.36E-06 AC resistance: .0705 ohms .0952 ohms .194 ohms .161 ohms 9.31 ohms!!! Notice that the differences in the resistance are all insignificant except for the ferromagnetic stainless steel. This is because of it's high relative permeability. Now when I realized this issue I put a magnet to my whip it doesn't stick. So I went to the shop this morning and checked a number of SS whips of different lengths. Some were magnetic and some were not. The magnetic whips are now all in a pile for other uses. So even old farts like me can learn something new. From now on I'll recommend to everyone to check an antenna with a magnet before buying it, because that's what I intend to do myself. Now, back to the X-terminator. Comparing the difference in radiation efficiency with regards to length and polarization, the 102" whip has 102" that are vertical. Everything is sent vertically polarized. Nothing is wasted in horizontal polarization. OTOH, the X-terminator has 9.5" vertical, followed by 74" of coil, then 3.75" vertical, 41.23" of coil, 5.5" vertical, and 32" of (gasp!) stainless steel. So you have a total of 166" of conductor, with 50.75" of it radiating the desired vertically polarized radiation, but 115" of it dumping horizontal hash. Let's disregard for the moment that 32" (or 63%) of the vertical total is made of that infamous stainless steel, and forget the extra overall resistance due to the additional length of conductor needed to wind the coils. Let's concentrate instead on the fact that the coils consume 69% of the total 'wire' in this antenna. Now if the current distribution was even throughout the length of the antenna, that would mean the coils are radiating 69% of the power as multi-phasic mush. But that's not the case, as the coils are positioned near the base of the antenna, where the antenna's current distribution is the greatest. That means the coils are radiating -more- than if the current was evenly distributed, and therefore -more- than 69%! And that means the efficiency of the X-terminator is less than 31%!!! And if that isn't bad enough, let's take a look at an el-cheapo 102" stainless steel whip of -magnetic- persuasion. If the whip has an AC resistance of 9.31 ohms, and the input impedance is an ideal 50 ohms, that translates into a loss of only 19%. If the input impedance is 36.5 ohms, the wire diameter is 0.25", and accounting for power reflected back to the radio due to mismatch, loss is still well below 30%. Both scenarios are a -hell- of a lot better than the 69% waste caused by the X-terminator's loading coils, and we didn't even go into absorbtion, reflection, hysteresis and eddy current losses caused from the vehicle roof right below those coils!!! So yes, stainless steel -is- more resistive than chromium. But the difference is not significant. So I'll say it again -- there is no way that this antenna will outperform an unloaded 102" whip whether it's made of fiberglass, stainless steel OR ferromagnetic steel! -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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