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#1
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#2
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Coax length is unimportant. However much you need to get from the
antenna to your radio is plenty. If you're matching SWR with coax length, there's something wrong with your antenna. -SSB Guntier C. wrote: I received and old wilson 1000 mag. mount and want to put it on my quad (4 magnet) mount. I hear that I need a 18 ft. piece of coax for a counterpoise. Is that true? Any info appreciated. Thanks, G.C. |
#3
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Thanks Sir, I did not think that was correct. This person said it was
needed because it was mag. mount. Kind of through it was a bunch of bull. Thanks, G.C. sideband wrote: Coax length is unimportant. However much you need to get from the antenna to your radio is plenty. If you're matching SWR with coax length, there's something wrong with your antenna. -SSB Guntier C. wrote: I received and old wilson 1000 mag. mount and want to put it on my quad (4 magnet) mount. I hear that I need a 18 ft. piece of coax for a counterpoise. Is that true? Any info appreciated. Thanks, G.C. |
#4
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![]() "Guntier C." wrote in message ... Thanks Sir, I did not think that was correct. This person said it was needed because it was mag. mount. Kind of through it was a bunch of bull. Thanks, G.C. That person did not know the difference between RF ground and electrical ground. A solid electrical connection makes a decent RF ground in vehicles most of the time but it does not work backwards. Even though the base is insulated there is still an RF ground. Fuggedaboudit and enjoy your antenna!!! Chad |
#5
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On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C."
wrote: I received and old wilson 1000 mag. mount and want to put it on my quad (4 magnet) mount. I hear that I need a 18 ft. piece of coax for a counterpoise. Is that true? Any info appreciated. Thanks, G.C. I'll get slammed for posting the correct answer but what else is new. Manufacturers of Magnetic mount antennas recommend keeping the original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.). Why do they do that? The answer is simple. They realize that there is no such thing as a perfect or exact scenario for an antenna installation. They know that in a typical installation of their antenna the coax length will most likely come into play and can be beneficial. It can be beneficial in that typically the radio will see a better load with the manufacturers recommended coax length. It's not that these antennas can't work with any length of coax. It's just that in most cases you'll get better results with the recommended length. |
#6
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Chad Wahls wrote:
"Guntier C." wrote in message ... Thanks Sir, I did not think that was correct. This person said it was needed because it was mag. mount. Kind of through it was a bunch of bull. Thanks, G.C. That person did not know the difference between RF ground and electrical ground. A solid electrical connection makes a decent RF ground in vehicles most of the time but it does not work backwards. Even though the base is insulated there is still an RF ground. Fuggedaboudit and enjoy your antenna!!! Chad Yep, sounds about right Chad.... Thanks, G.C. |
#7
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![]() wrote in message ... On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C." wrote: I received and old wilson 1000 mag. mount and want to put it on my quad (4 magnet) mount. I hear that I need a 18 ft. piece of coax for a counterpoise. Is that true? Any info appreciated. Thanks, G.C. I'll get slammed for posting the correct answer but what else is new. Manufacturers of Magnetic mount antennas recommend keeping the original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.). Why do they do that? The answer is simple. They realize that there is no such thing as a perfect or exact scenario for an antenna installation. They know that in a typical installation of their antenna the coax length will most likely come into play and can be beneficial. It can be beneficial in that typically the radio will see a better load with the manufacturers recommended coax length. It's not that these antennas can't work with any length of coax. It's just that in most cases you'll get better results with the recommended length. Agreed with tnon. As soon as someone mentions about using a certain length of coax with the CB antenna someone always asssumes it is to adjust SWR. It will not do this. It will change the impedance the radio sees which is not the same as changing the SWR. For example if the impedance of the antenna is 25 ohms 18ft of coax will make the antenna appear as 100 ohms at the radio. SWR will be 2:1 reguardless of the length of the cable. AS most radios are antennas are installed plug and go without benifit of tuning and most all CB antenas represent an impedance lower than 50 ohms antenna manufactures typically reccomend the 18ft coax for best results under these conditions. Most radios work better if they are mismatched above 50 than below 50. This really becomes noticable if SWR is around 3:1. Not uncommon on a typical plug and go installation. Otherwise length does not matter much on a well tuned and properly installed radio and antenna. |
#8
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Jimmie:
SWR is a direct measurement of impedance mismatch. If you change the coax length, thereby changing the angle the coax is conducting, and the SWR changes, then there is something wrong with the antenna itself that needs to be fixed. Physics dictates this. There's no way around it. Coax Length DOES NOT MATTER for a single antenna setup. Period. -SSB Jimmie wrote: wrote in message ... On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C." wrote: I received and old wilson 1000 mag. mount and want to put it on my quad (4 magnet) mount. I hear that I need a 18 ft. piece of coax for a counterpoise. Is that true? Any info appreciated. Thanks, G.C. I'll get slammed for posting the correct answer but what else is new. Manufacturers of Magnetic mount antennas recommend keeping the original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.). Why do they do that? The answer is simple. They realize that there is no such thing as a perfect or exact scenario for an antenna installation. They know that in a typical installation of their antenna the coax length will most likely come into play and can be beneficial. It can be beneficial in that typically the radio will see a better load with the manufacturers recommended coax length. It's not that these antennas can't work with any length of coax. It's just that in most cases you'll get better results with the recommended length. Agreed with tnon. As soon as someone mentions about using a certain length of coax with the CB antenna someone always asssumes it is to adjust SWR. It will not do this. It will change the impedance the radio sees which is not the same as changing the SWR. For example if the impedance of the antenna is 25 ohms 18ft of coax will make the antenna appear as 100 ohms at the radio. SWR will be 2:1 reguardless of the length of the cable. AS most radios are antennas are installed plug and go without benifit of tuning and most all CB antenas represent an impedance lower than 50 ohms antenna manufactures typically reccomend the 18ft coax for best results under these conditions. Most radios work better if they are mismatched above 50 than below 50. This really becomes noticable if SWR is around 3:1. Not uncommon on a typical plug and go installation. Otherwise length does not matter much on a well tuned and properly installed radio and antenna. |
#9
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On Thu, 04 Nov 2004 19:33:08 GMT, sideband wrote:
Jimmie: SWR is a direct measurement of impedance mismatch. If you change the coax length, thereby changing the angle the coax is conducting, and the SWR changes, then there is something wrong with the antenna itself that needs to be fixed. Physics dictates this. There's no way around it. Coax Length DOES NOT MATTER for a single antenna setup. Period. -SSB I'd only agree if the antenna perfectly decoupled and was a perfect load for the radio. In other words if everything operated perfectly in a perfect world. As far as mag mounts and using a automobiles as a counterpoise ? ? ? That scenario is not even close to a perfect world. I often wonder why there is so much criticism when one suggests using the manufacturers recommended length. This criticism seems to be followed by the statement that "any length will do". They believe that 10 feet, 11 feet, 13.5 feet,ect. ect. are fine. Just don't pick 18 feet !!!!!! How hypocritical is that? Isn't 18' also a length contained within the statement "any length will do"? |
#10
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tnom:
Explain this, then... CB radio in my Peterbilt, with a mirror mounted Hustler HQ-27 on the driver's side.. 6 feet of coax shows a 1:1 on 19, 1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same readings... 18 feet of coax shows.. guess what? the SAME RESULTS. IT IS possible to get near "perfect world" results with a little work, and attention to detail. By the way, I've gotten similar results on two meters with a magnet mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the coax because I was sick of the bundle of it in the cab... no change in SWR over a four MHz bandwidth... There goes the "magmount theory" as well.. If changing the length of the coax changes the SWR, then there is something wrong with the antenna. -SSB wrote: I'd only agree if the antenna perfectly decoupled and was a perfect load for the radio. In other words if everything operated perfectly in a perfect world. As far as mag mounts and using a automobiles as a counterpoise ? ? ? That scenario is not even close to a perfect world. I often wonder why there is so much criticism when one suggests using the manufacturers recommended length. This criticism seems to be followed by the statement that "any length will do". They believe that 10 feet, 11 feet, 13.5 feet,ect. ect. are fine. Just don't pick 18 feet !!!!!! How hypocritical is that? Isn't 18' also a length contained within the statement "any length will do"? |
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