Possible Short (Sirio 4000)

General Mobile CB antenna advice and troubleshooting

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Nugsport
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Sat Jul 19, 2008 12:34 am

was wondering if someone can just clarify that this isn't what should be happening. I think my Sirio Megawatt 4000 is shorting out, even though i have a 1:1 SWR :? , at first i thought it was the roof mount the DV pin was shorting to earth, when i removed the antenna the mount was fine no short, so i decided to check the sirio's coil and the centre pin and the threaded part at the bottom of the coil are making continuity, and it's the same with the whip.. the threaded part on the bottom of coil will make continuity with the Whip part of the antenna... i really don't have any luck with CB equipment :( it's out to get me im sure of it :roll:

Thanks

Steve.
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Steve
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Homebase - Magnum S-9 Nitro Export > Sirio 827
Mobile - Midland Alan 78 Plus Multi > Sirio Megwatt 4000
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stampman
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Sat Jul 19, 2008 9:05 am

it is the design of the antenna if you dont get a short with the ml145 sirio 3000,4000 or the wilson 1000 , 5000 the the antenna is goosed



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Nugsport
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Sat Jul 19, 2008 9:10 am

:mrgreen: Thanks Stampman i do appreciate the help on here honest :lol: , is the short there to help with the SWR of the antenna? or is it just a RTX Performance thing just wondering if thats why they are designed that way. :)
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Steve
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Homebase - Magnum S-9 Nitro Export > Sirio 827
Mobile - Midland Alan 78 Plus Multi > Sirio Megwatt 4000
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andy@thunderpole.co.uk
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Wed Jul 23, 2008 1:55 pm

Nerdy Answer;

The coil will only measure short circuit at 0Hz i.e. DC, which is what your meter reads. At 27 Mhz which is the frequency of your CB the antenna wont appear as a short atall, it is to do with the laws of impedance but we wont go into that right now! #-o

As Stampman says it is simply the design of the antenna and nothing to worry about.

Andy :wink:

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Nugsport
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Wed Jul 23, 2008 6:03 pm

Thanks mate was just curiuos :)
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Steve
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Homebase - Magnum S-9 Nitro Export > Sirio 827
Mobile - Midland Alan 78 Plus Multi > Sirio Megwatt 4000
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bobthetank
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Tue Sep 05, 2017 12:42 am

The short you are seeing is for matching the antenna correctly and static reduction,yes its DC shorted,but not at RF sees it.

Chance are is the mount,cable or plug are are at fault.
Easy way to prove that put a PL type 50 ohm dummy load into SO-239 mount on antenna base,key up radio with VSWR meter inline and wiggle cables etc,if swr jumps high ,its cable,bad PL plug or something not right with antenna mount or poor grounding.
I would be very surprised if antenna faulty,pretty good antennas.

If antenna mounted on a sirio mag mount,check the coax internally those mag mounts are know for cable faults inside the center plastic piece,mine went like this center of coax broke of pin on SO-239,its a common issue.

Best of Luck

Rob

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