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On Fri, 5 Nov 2004 19:27:06 -0500, "M-Tech"
wrote in : snip Yeah, check-check. I'm with ya. I was just trying to ask(albeit, sarcastically) who the hell would loop coax through their vehicle instead of looking for a ground problem!!! I'm also assuming that if the above case was true, you'd NEVER get enough of a ground to get a decent(say 2:1)swr unless you have a few hundred feet in the trunk!! More than you might think: http://tinyurl.com/5z49m I just always was told that if you have a swr problem, it won't be fixed by changing coax lengths. Also, why do people have negative comments about mag mounts? Mine works fantastic. Maybe the paint on my Passat is thin:-) I don't know if you have ever run anything else, but I have and the difference is significant. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Hence, length of coax(within reason, obviously)on a wilson 1000 mag mount means diddly squat. I'm I right, or wrong:-) Don 313 I'd bet you're wrong for many installations.The only way to find out is to take the brand new Wilson 1000 mag mount that you'll purchase to make your point and cut the coax.. If you are so positive that your theory is absolute then you should not have any problem cutting the 18' length to the shortest length possible before you ever key up |
Agreed on the not-enough ground.. that's why counterpoise kits were
available for the W1000's... I had one that worked tits. -SSB Frank Gilliland wrote: On Fri, 05 Nov 2004 22:22:03 GMT, sideband wrote in : Jay: Thanks for your input.. A couple of things, though.. If the coax is being used as a counterpoise, it's not part of a capacitive grounding system. The capacitive ground comes from the metallic base/magnet mount to the vehicle body, not from the coax. That was an issue when I did the mag-mount tests a few months ago. As it turns out, the coax can provide plenty of capacitive coupling to the vehicle, even more than the mag-mount under certain conditions. But neither of them provide much coupling, not nearly as much as would be needed to compare with a properly mounted base. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Hello Sideband:
Really! What counterpoise kits?!?!?!?!?!??!!??!?!?!? Who sold them, what, when, where? Jay in the Mojave Kreedentials: Rock n Roll Fan Owner 1967 Ford F250, 4x4, with worlds loudest PA System Took Electronics in 8th grade, way more better than that ackademic crap that schools now teach kids now a days, ancient European history, liberal arts, and in incoming paper clips, in place of industrial arts. Paid Member of Mojave Desert Radio Club, 9 dollars now. (Big party coming up soon) Radio enthusiast type of guy sideband wrote: Agreed on the not-enough ground.. that's why counterpoise kits were available for the W1000's... I had one that worked tits. -SSB |
On Fri, 05 Nov 2004 17:37:31 GMT, "Jimmie"
wrote: . "sideband" wrote in message . com... 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. Nobody said it would be any different ,go back and read my post. I was very clear on why manufactureers say to use 18 ft and why you do not have to. UNLESS SOMETHING IS FUBAR CHANGING COAX LENGTH DOES NOT CHANGE SWR. JUST THE IMPEDANCE THE RADIO SEES.SWR IS DETERMINED SOLEY BY THE IMPEDANCE OF THE ANTENNA AND THE IMPEDANCE OF THE TRANSMISSION LINE. YOUR STATEMENT PROVES NOTHING. The only FUBAR is your satements. If you have a matched antenna, and use a 1/2 wave of coax, you can use any coax impedance you want. Take a 50 ohm antenna, feed it with a 1/2 wave of 500 ohm coax, the radio will still see a 50 ohm antenna. |
On Fri, 05 Nov 2004 19:09:51 GMT, "Jimmie"
wrote: "Jimmie" wrote in message . com... "Lancer" wrote in message ews.com... On Thu, 04 Nov 2004 21:59:02 GMT, sideband wrote: 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 SSB; I know this was addressed to Tnom, hope you don't mind my 2-cents worth. Very few mag mounts have an adequate "RF" ground, at least on 11 meters or lower. There isn't enough capacitive coupling to the vehicle body. In some cases the length of the coax can matter, not from a matching point of view, but as a counterpoise for the antenna. I have seen mag mount installations where you could see the SWR change just by moving the coax around. This is true but is totally beside the point of why manufacturers reccomend 18ft of coax. If you have the problem you mentioned fix the ground dont play with the coax length. A good test for a CB antenna is to temporarily splice in 6 ft of coax . If your SWR changes your ground is probably bad.Poorly made SWR meters will cause this too. The 18ft rule is also there for "just in case" . As you change the lenght of the coax the impedance seen by the radio will also change. Assuming the antenna is at resonance you will see a pure resistance at the radio for only 2 lengths, an odd 1/4wl(16ft) and an even 1/4wl. Nope, 18 feet is not an electrical 1/2 wave at 27 Mhz. If the antenna is properly matched and set up, (not just at resonance) any length of coax should work. (setup means, good rf grounds etc) At all other length unless the SWR is a perfect 1:1 match the impedances seen at the radio end will be complex. Like a mag mount with an imperfect coupling to ground? This is not always a bad thing. However there are some complex impedances that the radio may not like. It may dislike it so much the finals fry, the modulation becomes mushy or rx is nearly dead or it may be no problem at all for any length on your radio. There are a lot of different radios out there so the manufacturer usually recommends something safe they figure will work with all radios. 18 ft is a length that will normally allow enough cable to reach just about anywhere on the vehicle and provide a radio friendly impedance at the other end of the cable. Does it really need to be 18ft, probably not.. If you find the rare case where it does you can chase your tail till hell freezes over. |
On Fri, 5 Nov 2004 19:33:30 -0500, "M-Tech"
wrote: wrote in message .. . Very few mag mounts have an adequate "RF" ground, at least on 11 meters or lower. There isn't enough capacitive coupling to the vehicle body. In some cases the length of the coax can matter, not from a matching point of view, but as a counterpoise for the antenna. I have seen mag mount installations where you could see the SWR change just by moving the coax around. Please explain how a poor "RF ground" can be corrected by increasing coax length?? Don He never said that a poor RF ground could be corrected by coax length. He said in effect that the side effects of a poor RF ground could be reduced by a specific length of coax. He sure did. He said mag mounts have a poor ground. He said the length of the coax can help by being "part of the ground plane"(counterpoise). I'm simply saying you'd need a TON of coax to do that...and get a decent swr(point of post). Hence, length of coax(within reason, obviously)on a wilson 1000 mag mount means diddly squat. I'm I right, or wrong:-) Don 313 Don; No I never said that increasing the coax length of the coax will fix the problem. I said most mag mounts mounts don't have enough capacitive coupling to ground to act as adequate ground on their own, which is true, at least at 27 mhz. The length of coax can be a large part of the total antenna system. |
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It was a snazzy little "8-pointed star" contraption that scewed onto
the magmount base, then the antenna coil screwed onto it.. Cost about $15.. and they were worth their weight in gold, let me tell you. I got mine in So.Cal. when I was stationed on Pandelton. BTW, if you get down there, pop on ch 13 and tell Master Blaster that Crazy 1 said howdy. Wish I could remember the name of the manufacturer, but I can't ... sorry. -SSB Jay in the Mojave wrote: Hello Sideband: Really! What counterpoise kits?!?!?!?!?!??!!??!?!?!? Who sold them, what, when, where? Jay in the Mojave Kreedentials: Rock n Roll Fan Owner 1967 Ford F250, 4x4, with worlds loudest PA System Took Electronics in 8th grade, way more better than that ackademic crap that schools now teach kids now a days, ancient European history, liberal arts, and in incoming paper clips, in place of industrial arts. Paid Member of Mojave Desert Radio Club, 9 dollars now. (Big party coming up soon) Radio enthusiast type of guy sideband wrote: Agreed on the not-enough ground.. that's why counterpoise kits were available for the W1000's... I had one that worked tits. -SSB |
The coax on my 1000 is already only 6' long. I can't make it any shorter
:-) Don 313 wrote in message ... Hence, length of coax(within reason, obviously)on a wilson 1000 mag mount means diddly squat. I'm I right, or wrong:-) Don 313 I'd bet you're wrong for many installations.The only way to find out is to take the brand new Wilson 1000 mag mount that you'll purchase to make your point and cut the coax.. If you are so positive that your theory is absolute then you should not have any problem cutting the 18' length to the shortest length possible before you ever key up |
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