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Antenna Coax Connections

Help with installing an Antenna, or just choosing the right antenna to go with your radio, or your mobile.

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De_Wildfire
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Antenna Coax Connections

Post by De_Wildfire » Tuesday, 16 January 2018, 15:59 PM

My PL259 connector was replaced on my IMAX 2000 vertical antenna because of a bad connection off and on right behind the radio. It broke off from switching radios over the years and it is LMR400 hard line not flex. I rectified the problem it by correcting the bends and running straight to the other radios. After the connector was replaced, the radio is working great and talking around the country. The SWR's are 1.1 on 27.255 and tested with the analyzer. Now my buddy tested for continuity on his meter and it was beeping a steady tone and indicated there was a problem. When we switched over to the G5RV and inverted L antennas, his meter did not beep meaning the other antennas are working. He said there is a problem with my antenna on the other end and the signal is going to ground and said watch the finals on the radio. Even running 1.5 kw through it on 10 meters, there were no spikes and everything running normal. After the connector was replaced, everything seems to be running normal again. If the continuity is off, then I have been running like this for years. Has anyone had a similar experience.




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MDYoungblood
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Re: Antenna Coax Connections

Post by MDYoungblood » Tuesday, 16 January 2018, 20:31 PM

I believe the Imax is a shunted antenna which will make it read shorted when checking continuity.

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The DB
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Re: Antenna Coax Connections

Post by The DB » Tuesday, 16 January 2018, 23:07 PM

The Imax as well as many other base antennas, as well as a few mobile antennas, will show continunity. This is because at DC their is a direct short between those conductors. For those unfamiliar with how antennas work this sounds bad, however depending on the antenna, this is actually normal.

When we are transmitting and receiving, we are not using DC, like the multimeter uses when testing continuity. We are actually using AC, much like our wall power except at a much higher frequency. How AC and DC work are very different. For example, an inductor, which is used for part of matching networks, will show a direct short circuit at DC 100% of the time, yet at AC it may do something else entirely. Depending on the inductor and the frequency you are using, it can show anything from an direct short, like DC, to an open circuit, which is the exact opposite of a direct short, and in that case the AC signal is blocked. An inductor that blocks AC while allowing DC to pass is called a choke, and is a circuit used in many different devices.

Long story short, continuity on an Imax is not a sign that their is a problem. If you are making contacts and get an ok SWR I would leave it be.


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De_Wildfire
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Antenna: Imax, G5RV, Invtd L

Re: Antenna Coax Connections

Post by De_Wildfire » Wednesday, 17 January 2018, 10:52 AM

Thanks for the feedback. Even after a few posts, I am working good short band openings on 11 meters with 12 watts and a 1.1 SWR. You guys probably saved me some money, I would have gone out and replaced the coax and the same thing happen again. That antenna analyzer really comes in handy to double check and it's nice to check with others on here. This forum has always been a great source of help no matter how much experience we have. Thanks!




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