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Delta Sloper Question
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna? Right at the 529 connection at the connection end of the antenna the resistance is infinite. But at the bottom of 25ft of coax feeder the resistance is about 5meg ohms. Does that sound right? Also, if I measure the coax at the antenna (not connected to the antenna (just going 25ft to radio) it measures infinite. Don't understand it. Does it have anything to do with my ground maybe? |
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna? Near zero. As I understand a Delta, or Delta Loop antenna, the DC resistance should be zero ohms. The Delta is a closed loop. Down at the end of your coax the DC resistance will be zero from center conductor to shield. Probably need to disconnect the the coax from the antenna and check them seperately to insure the coax is not shorted, and the antenna reads a short. Right at the 529 connection at the connection end of the antenna the resistance is infinite. Not sure about a 529 connection, but if you take the ohm readings with the antenna disconnected from the coax, you should find the problem. 73 Gary N4AST |
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Tainted wrote:
Anyone know how many ohms I should be measuring at the end of a 25ft coax cable connected to a 60ft Delta antenna? DC? or RF? -----= 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 Wed, 07 Jul 2004 22:45:26 -0500, Cecil Moore
wrote: Tainted wrote: Anyone know how many ohms I should be measuring at the end of a 25ft coax cable connected to a 60ft Delta antenna? DC? or RF? -----= 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! =----- DC |
Tainted wrote:
Cecil Moore wrote: Tainted wrote: Anyone know how many ohms I should be measuring at the end of a 25ft coax cable connected to a 60ft Delta antenna? DC? or RF? DC You will be reading the leakage resistance. What kind of coax? -- 73, Cecil http://www.qsl.net/w5dxp -----= 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! =----- |
Cecil Moore wrote: Tainted wrote: Cecil Moore wrote: Tainted wrote: Anyone know how many ohms I should be measuring at the end of a 25ft coax cable connected to a 60ft Delta antenna? DC? or RF? DC You will be reading the leakage resistance. What kind of coax? Isn't he talking about a loop antenna?? jk |
Appreciate the help but it's not a closed loop. At least I don't
think so. There are two antenna lines - ones 60ft and the other 16ft. They are connected to the 529 center post. The ground lead (30ft) is connected to the outer part of the 529. I'm pretty sure it's right that there is infinite ohms there because they are not physically touching in any way. I'm confused because simply adding 25ft of coax causes a 2.5meg ohm reading. In essence I'm still across the 529 just 25ft further away. So nothing should change. You might (as someone else suggested) be reading some leakage resistance from your coax. 2.5 megs seems a low reading for coax in good condition... if it's the coax, you might have gotten some water or other contamination into the connectors, or into the coax itself. Depending on how you're holding your meter probes when you do the measurement, you might be reading your skin resistance by accident. Make sure your skin isn't touching the metal parts of either probe. Depending on the meter you are using, you might not be reading just the resistance. Since you're doing a measurement on a coax and antenna, the antenna is likely to be picking up some amount of RF from nearby transmitters. There would probably be some differential-mode RF within the coax (from in-band reception by the antenna), and likely some common-mode coming down the outside of the coax. Your meter's circuitry might be acting as a pathway to complete the RF circuit - this would allow some amount of RF current to flow through the metering circuitry (in addition to the DC current which results from the resistance-measuring voltage the meter is presenting), and the meter's reading might be the result of this small RF current flow. As an experiment, try bypassing the bottom end of the coax... create an RF short circuit across the PL-259 with a .1 uF capacitor. See if this makes the apparent resistance at this point go up... if so, the resistance reading was probably due to stray RF getting into the meter. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Jim Kelley wrote:
Cecil Moore wrote: You will be reading the leakage resistance. What kind of coax? Isn't he talking about a loop antenna?? Here's a quote by the author from a few postings ago. Appreciate the help but it's not a closed loop. So it must be an open loop. -- 73, Cecil http://www.qsl.net/w5dxp -----= 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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