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On Fri, 24 Oct 2003 17:48:23 GMT, lancer wrote:
On Thu, 23 Oct 2003 16:22:18 -0400, wrote: Actually it's 62"..........If you can wait a second I'll give you the entire dimensions. Maybe Mmana wants to know? Tnom; I plugged in the values that you posted. By simulation, the Stainless whip has just about a 1 dB edge. The S/S whip has its main lobe at 27.9 degrees, the X-terminator at 31.2 degrees. I posted a current plot for it in: alt.binaries.pictures.radio I played with the parameters for the coils, and one coil works just as well as the 2. Guess it just doesn't look as cool? Did you use the proper conductivity values. Stainless = 3% of copper Chrome = 74.3% of copper |
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! =----- |
In , "(Scott Unit 69)"
wrote: (Twistedhed) wrote: wrote: But what about what Frank said? Irrelevant. _ You know Tnom's test was a sham. _ Countered by.....Frank's claims? THAT is your claim that Tnom's presentation is a sham? I just don't like to see people get cheated. _ It's way beyond that on this group,,,,this is about one who prefers Chevy, one prefers Ford, and yet another prefers Dodge. The margin of difference when applied to the average cber will not be noticeable between the the antennas. The actual "cheating" taking place, if indeed such a thing is to be found among a discussion forum, are the posts of malicious and angry origin, unprovokingly attacking one's character by name, contacting their work, and intentional libelous content of posts. Of course, we can always add the scumbags that post under different nics and play both sides of the fence...... I am not trying to play both sides of the fence Twist, you know me and my CB background. But when it comes to the truth about a product there should be no "fence" that divides us, only the truth. And truth is Twisty's friend!!! -----= 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! =----- |
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! =----- |
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 |
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% |
On Sat, 25 Oct 2003 02:21:12 -0400, wrote:
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% 17-7 ph stainless steel is used for most stainless antennas Its resistivity compared to the standard (copper) can be found here http://www.hpmetals.com/elec_resist.asp Copper = 1.71 microohm-cm 17-7 ph = 83 microohm-cm In other words stainless antenna stock has 2% the conductivity of copper. |
http://www.amm.com/index2.htm?/ref/conduct.HTM Chrome has 55% the conductivity of copper Steel (all types ) 3% - 15% 17-7 ph stainless steel is used for most stainless antennas Its resistivity compared to the standard (copper) can be found here http://www.hpmetals.com/elec_resist.asp Copper = 1.71 microohm-cm 17-7 ph = 83 microohm-cm In other words stainless antenna stock has 2% the conductivity of copper. What type of material is the whip of the exterminator? SS right, the few inches of copper or chrome material of that antenna will make little or no difference what so ever, you guys are nit picking about something that in this application is un noticeable. Yes the whip is SS, but unlike your imagined explanation the antennas others attributes must be making a difference. It does "make a little difference". That was you quote by the way. If it "makes a little difference" and does it at five feet instead of nine then I would say it makes quit a difference. |
On Sat, 25 Oct 2003 07:09:10 -0500, Neil Down
wrote: wrote in : On Sat, 25 Oct 2003 02:21:12 -0400, wrote: 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% 17-7 ph stainless steel is used for most stainless antennas Its resistivity compared to the standard (copper) can be found here http://www.hpmetals.com/elec_resist.asp Copper = 1.71 microohm-cm 17-7 ph = 83 microohm-cm In other words stainless antenna stock has 2% the conductivity of copper. What type of material is the whip of the exterminator? SS right, the few inches of copper or chrome material of that antenna will make little or no difference what so ever, you guys are nit picking about something that in this application is un noticeable. The top section of that antenna is made from stainless steel. The top section also has very little current flowing in it. The bottom section has a majority of the current flow and does most of the radiation. It maybe nit picking, but in theory the difference can be seen. If you would see it in the real world is another question. |
On Fri, 24 Oct 2003 15:49:41 -0500, Neil Down
wrote: lancer wrote in : On Thu, 23 Oct 2003 17:23:26 -0500, Neil Down wrote: "(Scott Unit 69)" wrote in : I wish someone who knew what they were talking about would tell the truth about this antenna.There is enough BS on this group as it is without more myths being spread. The funniest part this antenna is made by workman it is junk, the coils are low Q. No way on gods green earth it beats a full 1/4 wave. No, the coils aren't low Q Yes they are compared to a high q coil. What do you consider high Q? Q (Quality factor) is equal to the inductive reactance/the resistance or loss Capacitive coupling between the turns is part of the loss. The coils for that antenna are large diameter tubing, less resistance. They are spaced from eath other by at least a diameter, less capacitive coupling. They are "air wound", less loss due to the coil form. The coils on that antenna have a Q of 100-300 In a typical tank circuit of a transmitter, smaller wire wound closer together on a ceramic form, a Q of 20 is considered very good. You make think that those coils look like they do for show, there is a proven reason why large diameter, large gauge material is used for the coils. And its not just for the power handling capability. |
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! =----- |
Very nice job Frank............................................. .....
Now, go buy a 7 foot SkipShooter and out talk the 102". Train LOL "Frank Gilliland" wrote in message ... 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! =----- |
On Sat, 25 Oct 2003 21:33:07 GMT, "Train" wrote:
Very nice job Frank............................................. ..... Now, go buy a 7 foot SkipShooter and out talk the 102". Train LOL Frank really gets into his work. Now if he could just transfer that energy to an actual test. The paper work is interesting but does nothing to show how a 102" SS marginally fails to beat some shorter antennas. Theory and formulas are fine but they will never include all the variables. When the results are to close to call you have to go to the end all. The actual test. |
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Yup, the same AOL addy that feels rejected because of their ego being
handed to them on daily basis... |
You are wrong. "Landshark" wrote: Forge "(Scott Unit 69)" wrote in message ... (Twistedhed) wrote: wrote: But what about what Frank said? Irrelevant. _ You know Tnom's test was a sham. _ Countered by.....Frank's claims? THAT is your claim that Tnom's presentation is a sham? I just don't like to see people get cheated. _ It's way beyond that on this group,,,,this is about one who prefers Chevy, one prefers Ford, and yet another prefers Dodge. The margin of difference when applied to the average cber will not be noticeable between the the antennas. The actual "cheating" taking place, if indeed such a thing is to be found among a discussion forum, are the posts of malicious and angry origin, unprovokingly attacking one's character by name, contacting their work, and intentional libelous content of posts. Of course, we can always add the scumbags that post under different nics and play both sides of the fence...... I am not trying to play both sides of the fence Twist, you know me and my CB background. But when it comes to the truth about a product there should be no "fence" that divides us, only the truth. |
Steveo wrote:
wrote: On 24 Oct 2003 02:52:14 GMT, Steveo wrote: wrote: Ok Tnom, You've peaked my interest. URL? I think bills two way sells them? Who makes it? Workman? Is this one ok ? $36.95 SP-5000 X-Terminator V, 1000 Watt Single Open air coil, 1/8" square Copper wire, 70 inch overall length. So anyway Tnom, is the above version ok or do have a recommendation? |
Steveo wrote: Steveo wrote: wrote: On 24 Oct 2003 02:52:14 GMT, Steveo wrote: wrote: Ok Tnom, You've peaked my interest. URL? I think bills two way sells them? Who makes it? Workman? Is this one ok ? $36.95 SP-5000 X-Terminator V, 1000 Watt Single Open air coil, 1/8" square Copper wire, 70 inch overall length. So anyway Tnom, is the above version ok or do have a recommendation? Don't buy it, Steve. |
"(Scott Unit 69)" wrote:
Steveo wrote: $36.95 SP-5000 X-Terminator V, 1000 Watt Single Open air coil, 1/8" square Copper wire, 70 inch overall length. So anyway Tnom, is the above version ok or do have a recommendation? Don't buy it, Steve. Why not? |
snip - Tnom used a radio modified for 'swang' and modulated it with a tone. snip Just a example of how you are making these statements up now. That's why you are an oxyMORON like I said earlier. |
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snip
- Tnom did two tests. The first test used two receivers. If the variables of the test were constant, the readings should have been identical if not proportional. They were neither. In his second test he eliminated the second receiver because it was "not needed". In fact, they -are- needed because it's an empirical method of double-checking your work. snip Frank you are not only a oxyMORON but now you are a liar also. |
snip
- Field strength was not measured from a field strength meter, but from a commercial receiver, almost all of which incorporate some variation of AGC (Automatic Gain Control). IOW, the receiver's gain changes according to the strength of the signal. So for that reason alone the readings are not accurate. snip S-meters are not accurate and I never stated they were. The are very accurate in giving relative readings. |
- Different antenna types and lengths will give different contours when mounted on the same vehicle; so while you might find a little gain in one direction, the other 359 degrees suck. Same deal with radiation angle, which will directly affect the range of the ground wave. Now I might ignore this issue if he had tested the antennas from the top of a flying saucer.... And in my setup the X-Terminator outperformed the 102"SS I never said it would outperform in any other setup because I never ran any other setup. - Probably the biggest problem with Tnom's "test" was that there was no impedance matching from the coax to the antenna. Loaded antennas usually have a lower feedpoint impedance, resulting in a larger mismatch (higher SWR). The problem here is that if the radio and antenna are not properly grounded (and a mag-mount is -not- a proper ground), the SWR meter isn't going to show that mismatch unless the meter is connected at the antenna feedpoint, which was not the case (and wouldn't have mattered anyway because the antenna was not properly grounded). He might have caught the problem had he measured and compared the forward power of all the antennas, but he didn't because he felt is was "not needed". And my setup was typical for a magnet mount. I never said it was anything different. Being a typical setup you would expect typical results. A typical result is the most accurate result for a typical setup. |
- The antenna is ugly. Congrats.......You got something right. |
$36.95 SP-5000 X-Terminator V, 1000 Watt Single Open air coil, 1/8" square Copper wire, 70 inch overall length. So anyway Tnom, is the above version ok or do have a recommendation? http://www.wep4hams.com/mobile_cb_antennas.htm http://www.geocities.com/mgo171/moviles.htm http://www6.mailordercentral.com/hye...ts.asp?dept=41 http://www.bills2way.com/equip/antennas.html I don't know if the 5000 is a performer or not. |
wrote:
$36.95 SP-5000 X-Terminator V, 1000 Watt Single Open air coil, 1/8" square Copper wire, 70 inch overall length. So anyway Tnom, is the above version ok or do have a recommendation? http://www.wep4hams.com/mobile_cb_antennas.htm http://www.geocities.com/mgo171/moviles.htm http://www6.mailordercentral.com/hye...ts.asp?dept=41 http://www.bills2way.com/equip/antennas.html I don't know if the 5000 is a performer or not. Thanks. |
"(Scott Unit 69)" wrote in message ... You are wrong. "Landshark" wrote: Forge "(Scott Unit 69)" wrote in message ... Nope, you're not Scott. Try all you want, but you are forging his name, posting from AOL through put, using Ghostsearchers website. Landshark -- Hard things are put in our way, not to stop us, but to call out our courage and strength. |
Because the reports about this antenna, and antennas like these, are classic examples of the 'miracle miniature' syndrome that plagues antenna manufacturers in their fierce competition. Unlike other industries, they don't have to back up their claims of gain figures, which is why you see ads for rubber duckies with +126 dB gain. Entirely reasonable, provided they tell you what the reference is. A claim of "5 dB gain" is meaningless. In ham circles, when I see this, I automatically assume they mean dBi, but given the level of snake oil in CB circles, I think in terms of dBdummyload. An interesting test would be to measure two of the same antenna, against each other, on the same vehicle, then measure the first one again. Of course the readings should be identical, but differences would indicate problems in mounting most likely, or variations in local conditions, like reflected signal from vehicles and people moving around. It would give a good idea of the size of the inherent error in the measurements made. In order to truly show what's going on, you also need to pattern the antenna, measuring the signal at regular points around the compass. While an onmi antenna mounted on a vehicle may show gain in one direction, there will be a corresponding notch somewhere else. The pattern, when mounted on a vehicle, can be surprisingly "lumpy". In order to do a reasonably accurate test, you'll need a nice RF quiet area to test in, and a whole lot of open space. Ideally, you'd put the vehicle on a turntable, but that's normally not practical. I'd settle for very slowly driving in as tight a circle as possible, to minimize effects from the antenna waving around. - Probably the biggest problem with Tnom's "test" was that there was no impedance matching from the coax to the antenna. Loaded antennas usually have a lower feedpoint impedance, resulting in a larger mismatch (higher SWR). Another variable to consider, is wether they were tuned at all, and if so, were they tuned for resonance, or lowest SWR. I tune for resonance, and match for SWR. The problem here is that if the radio and antenna are not properly grounded (and a mag-mount is -not- a proper ground), the SWR meter isn't going to show that mismatch unless the meter is connected at the antenna feedpoint, which was not the case (and wouldn't have mattered anyway because the antenna was not properly grounded). He might have caught the problem had he measured and compared the forward power of all the antennas, but he didn't because he felt is was "not needed". A 1 wavelength feedline, of something reasonably efficient like FSJ1-50 would suffice. The reactive component will be roated back around to the same point, and it's way more convenient than measuring at the base of the antenna. - Bandwidth was never measured. The coils on that antenna should have a very high Q, which means a very narrow bandwidth. If the test showed that the antenna actually has a wide bandwidth, then there is some power being dumped somewhere as heat and not RF, probably from a resistor hidden somewhere in the shaft, and most likely the shaft inside the coil, shunting the coil and lowering it's Q. Important, and easy to do. Impedance measurements at Ch1 and CH40 would tell the story. - The concept of center-loading an antenna has been around for a very long time. If it were at all possible to shorten a 1/4 wave vertical and get better performance, the design would have been implemented into AM broadcast towers decades ago. Drive around and look at some of the towers in your area. How many of them look like the X-terminator? None. To be fair, fabricating the coils for such an antenna would be an interesting challenge. I run a cobra 6000, which seems a reasonable design. It's mounted in the center of the roof of my Expedition, and just slightly taller than the Diamond SG-7900 in front of it. Overall height is somewhat of a concern. It tunes to resonance nicely, and ends up at a 2/1 SWR, which isn't far enough off to bother matching.. If I had a 2-1 un-un handy, I'd probably use it. I'm not too surprised at the high impedance (100 ohms) at resonance, I think they are designed to be used in a co-phased arraingement on trucks. There's another typical sight, a pair of antennas, often not the same type, running "co-phased" on a very small car, placed much too close together, like 2' separation. The resulting pattern is rather amusing. I run into the same BS on the other end of the spectrum. I recently had to look into antennas for a bluetooth transciever, and was rather dissapointed to find the equivalent of "rubber ducks" at 2.4 GHz, selling for $12. (in production quantities!) These are so called "chip antennas" that are roughly the size of this letter "W" on your screen, being marketed as "high gain" antennas. When I finally was able to get a plot out of them, it turned out that the highest gain was -10dBi, and as low as -20dBi... High gain compared to a 50 ohm resistor the same size, I suppose. We ended up using a simple monopole, just a track on the PCB. Cost, essentially zero. Gain, roughly 1-2dBi. I didn't bother patterning, simple emperical tests show it's overkill for our intended application. It's giving measurably less operating distance than a reference dipole, but the dipole is inconveniently large. Now if you still want to buy the antenna, it's your money to waste. But who knows... it might have some collector value in a hundred years or so, just like all those quack medical devices. My favorite CB gimmick was the "zing ring". You were supposed to clamp this little halo around the bottom of your antenna to improve the ground. The thing had a radius of about 6 inches or so. It wouldn't even have had that effect up on VHF, where it's dimensions become a significant fraction of a wavelength. Lately the Zing Ring is gone, replaced with three little stubby wound whips that connect to the base of the antenna electrically.. The new version looks better anyway.. I'm sure it's just as effective as the old one. You have to laugh at the concept of a "15,000 Watt" antenna, on a mag-mount, fed with cheap RG-58 sized coax. These antenna gimmicks are all 100% effective in meeting their design goals. They look good enough to separate suckers and their money. Any benefit to your radiation efficiency or pattern is totally coincidental. |
In , "Dave VanHorn"
wrote: Because the reports about this antenna, and antennas like these, are classic examples of the 'miracle miniature' syndrome that plagues antenna manufacturers in their fierce competition. Unlike other industries, they don't have to back up their claims of gain figures, which is why you see ads for rubber duckies with +126 dB gain. Entirely reasonable, provided they tell you what the reference is. A claim of "5 dB gain" is meaningless. In ham circles, when I see this, I automatically assume they mean dBi, but given the level of snake oil in CB circles, I think in terms of dBdummyload. .....or dB over the transmission line. An interesting test would be to measure two of the same antenna, against each other, on the same vehicle, then measure the first one again. Of course the readings should be identical, but differences would indicate problems in mounting most likely, or variations in local conditions, like reflected signal from vehicles and people moving around. It would give a good idea of the size of the inherent error in the measurements made. I agree. In order to exclude such confounds the control or reference antenna should be measured several times and any variation noted, even any variation during a single transmission. In order to truly show what's going on, you also need to pattern the antenna, measuring the signal at regular points around the compass. While an onmi antenna mounted on a vehicle may show gain in one direction, there will be a corresponding notch somewhere else. The pattern, when mounted on a vehicle, can be surprisingly "lumpy". That's called "mapping the contour". It's not difficult to do, and is a basic procedure for any antenna testing. In fact, it's a procedure that is required before any broadcast station can get it's license, as the map is used to calculate the ERP of the transmitter. In order to do a reasonably accurate test, you'll need a nice RF quiet area to test in, and a whole lot of open space. Ideally, you'd put the vehicle on a turntable, but that's normally not practical. I'd settle for very slowly driving in as tight a circle as possible, to minimize effects from the antenna waving around. The salt flats in Utah come to mind, but we have some pretty flat desert areas just west of here. - Probably the biggest problem with Tnom's "test" was that there was no impedance matching from the coax to the antenna. Loaded antennas usually have a lower feedpoint impedance, resulting in a larger mismatch (higher SWR). Another variable to consider, is wether they were tuned at all, and if so, were they tuned for resonance, or lowest SWR. I tune for resonance, and match for SWR. That's fine and practical for one antenna, but when comparing several where different input impedances will be encountered, the method of tuning should be independant of input Z. About the only way to do that is with an FSM. After all, a 50 ohm dummy load will show a 1:1 SWR..... The problem here is that if the radio and antenna are not properly grounded (and a mag-mount is -not- a proper ground), the SWR meter isn't going to show that mismatch unless the meter is connected at the antenna feedpoint, which was not the case (and wouldn't have mattered anyway because the antenna was not properly grounded). He might have caught the problem had he measured and compared the forward power of all the antennas, but he didn't because he felt is was "not needed". A 1 wavelength feedline, of something reasonably efficient like FSJ1-50 would suffice. The reactive component will be roated back around to the same point, and it's way more convenient than measuring at the base of the antenna. The problem there is that the feedline may be radiating when there is a mismatch at the antenna. Regardless, he never indicated the length of the coax -or- if the coax was tested for RF on the shield. - Bandwidth was never measured. The coils on that antenna should have a very high Q, which means a very narrow bandwidth. If the test showed that the antenna actually has a wide bandwidth, then there is some power being dumped somewhere as heat and not RF, probably from a resistor hidden somewhere in the shaft, and most likely the shaft inside the coil, shunting the coil and lowering it's Q. Important, and easy to do. Impedance measurements at Ch1 and CH40 would tell the story. Three points (freqs) would be better, as it will verify that the frequency response is curved and not flat (resistive). - The concept of center-loading an antenna has been around for a very long time. If it were at all possible to shorten a 1/4 wave vertical and get better performance, the design would have been implemented into AM broadcast towers decades ago. Drive around and look at some of the towers in your area. How many of them look like the X-terminator? None. To be fair, fabricating the coils for such an antenna would be an interesting challenge. True. But in broadcasting, efficiency is everything. If that antenna design worked better than the basic tower, the justification would be the long-term power savings to the station. And with all the stations that are operating these days, don't you think at least one station would have built such an antenna? I run a cobra 6000, which seems a reasonable design. It's mounted in the center of the roof of my Expedition, and just slightly taller than the Diamond SG-7900 in front of it. Overall height is somewhat of a concern. It tunes to resonance nicely, and ends up at a 2/1 SWR, which isn't far enough off to bother matching.. If I had a 2-1 un-un handy, I'd probably use it. I'm not too surprised at the high impedance (100 ohms) at resonance, I think they are designed to be used in a co-phased arraingement on trucks. You may be getting reflection from the other antenna. Try tuning without the other stick. There's another typical sight, a pair of antennas, often not the same type, running "co-phased" on a very small car, placed much too close together, like 2' separation. The resulting pattern is rather amusing. I saw a Penetrator on a Geo once..... I run into the same BS on the other end of the spectrum. I recently had to look into antennas for a bluetooth transciever, and was rather dissapointed to find the equivalent of "rubber ducks" at 2.4 GHz, selling for $12. (in production quantities!) These are so called "chip antennas" that are roughly the size of this letter "W" on your screen, being marketed as "high gain" antennas. When I finally was able to get a plot out of them, it turned out that the highest gain was -10dBi, and as low as -20dBi... High gain compared to a 50 ohm resistor the same size, I suppose. Didn't someone come out with some sort of quack antenna for cell phones? I thought I saw that on a TV commercial or something.... We ended up using a simple monopole, just a track on the PCB. Cost, essentially zero. Gain, roughly 1-2dBi. I didn't bother patterning, simple emperical tests show it's overkill for our intended application. It's giving measurably less operating distance than a reference dipole, but the dipole is inconveniently large. Now if you still want to buy the antenna, it's your money to waste. But who knows... it might have some collector value in a hundred years or so, just like all those quack medical devices. My favorite CB gimmick was the "zing ring". You were supposed to clamp this little halo around the bottom of your antenna to improve the ground. The thing had a radius of about 6 inches or so. It wouldn't even have had that effect up on VHF, where it's dimensions become a significant fraction of a wavelength. Lately the Zing Ring is gone, replaced with three little stubby wound whips that connect to the base of the antenna electrically.. The new version looks better anyway.. I'm sure it's just as effective as the old one. Sounds like these "tuning rings" on some current antennas. You have to laugh at the concept of a "15,000 Watt" antenna, on a mag-mount, fed with cheap RG-58 sized coax. These antenna gimmicks are all 100% effective in meeting their design goals. They look good enough to separate suckers and their money. Any benefit to your radiation efficiency or pattern is totally coincidental. The thought of 15 KW on a vehicle makes me shudder -- knowing that the vehicle itself is carrying the same voltage and current as the antenna, but terminated with a gas tank!!!! -----= 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! =----- |
Entirely reasonable, provided they tell you what the reference is. A claim of "5 dB gain" is meaningless. In ham circles, when I see this, I automatically assume they mean dBi, but given the level of snake oil in CB circles, I think in terms of dBdummyload. ....or dB over the transmission line. dBradiax? :) The problem there is that the feedline may be radiating when there is a mismatch at the antenna. Regardless, he never indicated the length of the coax -or- if the coax was tested for RF on the shield. This is why I pay $2000/Day to my FCC testing guys. It's not as simple as it looks! You may be getting reflection from the other antenna. Try tuning without the other stick. That's my primary radio. I use the CB for road conditions, but if one of them has to compromise.. Didn't someone come out with some sort of quack antenna for cell phones? I thought I saw that on a TV commercial or something.... Yeah, the "patch" to get your yangtenna up. I got one free in a parts order once. It's worth at least twice what I paid for it. I did give it a fair trial. No noticable effect one way or the other. Sounds like these "tuning rings" on some current antennas. The tuning ring on an Astron 99 or similar at least does something. I use one of those as my HF vertical. The zing ring was the "cell phone antenna sticker" of it's day. The thought of 15 KW on a vehicle makes me shudder Figuring a generous 60% efficiency at the amp, that's 1800A from your battery, more or less. You know, I've always known that power dosen't count for much on these bands, and as I was driving back from Georgia again this weekend, I remarked to the wife that listening to the truckers fade in and out going the other direction, I can't tell much difference between the guy that claims he's running the 150W or 500W amplifier, and the ones that claim not to be.. I certainly don't hear them 20-50 miles away.. -- knowing that the vehicle itself is carrying the same voltage and current as the antenna, but terminated with a gas tank!!!! Back an August, I was sitting at a gas station fueling up the Expedition, which does take a while.. I was sitting there, with my 50W aprs transmitter running periodically (on the glassmount antenna right above the gas tank), the other two VHF transcievers were shut down. I was making a call on my cell phone, when I noticed that the truck parked in the next bay was idling, and dripping something that was spattering on the concrete... The truck was labeled "liquid oxygen", and "no smoking within 50 feet".. As the cold liquid oxygen vapor mixed with the gasoline vapor hugging the ground, I was thinking "and they are worried about my cell phone?" |
You make valid points on testing antennas, It would be great to have actual tests that were run with all variables being accounted for. Looking at the way he did his tests, is more real world. That is, the way a typical person would do when the purchased an antenna and put it on their vehicle. His tests show which one worked best for the testing he was doing. Which would probably have different results on someone elses installation. The trick is to get a feel for the magnitude of the variables that are hard to control, and take that into account when evaluating any measured or perceived differences. The audiophile guys are buying $7500 AC line cords because they think that it makes a difference in how the sound comes out. (ignoring the same old 50' of crappy 12 ga wire in the wall back to the box, and the rest of how the power gets to the house) |
"Landshark" wrote: "(Scott Unit 69)" wrote in message ... You are wrong. "Landshark" wrote: Forge "(Scott Unit 69)" wrote in message ... Nope, you're not Scott. Try all you want, but you are forging his name, posting from AOL through put, using Ghostsearchers website. Landshark Well I am sorry but you are wrong. Since I got my ham license I use Ghostsearchers on Usenet so I don't crap up my regular ISP with spam and trash from rrcb. |
I think the only thing proven with his experiment is that a good antenna can work just as crappy as a crappy antenna -- the only difference is in the installation. Radio requires attention to several factors, such as knowing the difference between an RF ground and a DC ground, how SWR and field-strength meters really work and how to use them, using the right equipment for the right job, location of the antenna on the vehicle, etc, etc. And BTW, these are things that should be learned and put into practice by anyone serious about the hobby. You wouldn't believe (maybe you would, at that) how many hams I know, that think a 6' wire to a ground stake is an RF ground for their VHF/UHF station.. |
On Tue, 28 Oct 2003 15:40:01 -0500, "Dave VanHorn"
wrote: I think the only thing proven with his experiment is that a good antenna can work just as crappy as a crappy antenna -- the only difference is in the installation. Radio requires attention to several factors, such as knowing the difference between an RF ground and a DC ground, how SWR and field-strength meters really work and how to use them, using the right equipment for the right job, location of the antenna on the vehicle, etc, etc. And BTW, these are things that should be learned and put into practice by anyone serious about the hobby. You wouldn't believe (maybe you would, at that) how many hams I know, that think a 6' wire to a ground stake is an RF ground for their VHF/UHF station.. I believe quite a few would believe that on HF, but VHF/UHF. What do you think would make a good RF ground for VHF/UHF? |
I believe quite a few would believe that on HF, but VHF/UHF. What do you think would make a good RF ground for VHF/UHF? A tub of mercury? :) Nothing really. I ground my antennas to a stake, but only for lightning protection. |
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