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Coax Cable and Connectors - For general discussion of all things pertaining to coax cable, wave guide or any other medium for passing RF energy. This includes connectors, weather proofing and grounding.

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Old 01-06-2018, 1:18 PM
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Question coax too close?

Hi guy's, in a nut shell, here it is.. I have 4 active antenna's on my roof, and 2 of them are using LMR 400.
Now, they are all tied together on their way across the roof.
Qusetion:
Should they be sepparated or are they fine tied together?
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Old 01-06-2018, 1:27 PM
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As long as they are all receive only, you are fine. If you were transmitting with high power, then RF could bleed from the TX coax to its neighbors.
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Old 01-06-2018, 1:39 PM
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In that case you would have way more pickup from the actual antennas than through the coax. At frequencies above 1Ghz and with higher signal levels like encountered in satellite downlinks you can have some noticeable cross talk in long runs of tightly bundled coax. The distance the cables are running together also has an effect with longer runs having more cross talk.

I would not worry about cable cross talk for scanner antenna stuff.
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Originally Posted by jonwienke View Post
As long as they are all receive only, you are fine. If you were transmitting with high power, then RF could bleed from the TX coax to its neighbors.
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Old 01-06-2018, 1:44 PM
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I'd be more concerned with your antenna separation than your coax separation.

LMR400 is 100% shielded so those are fine, what are the other 2 runs?

As the previous responder said this is only an issue if you are transmitting, for receiving the energy levels are too low for this to be a concern.
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Old 01-06-2018, 1:45 PM
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Roger that gentlemen. I am only recieving.
Thank you very much..
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Old 01-06-2018, 2:06 PM
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The shielding provides at least 80db attenuation so two cables tied together would reduce a transmitted signal by 160db so it's a non issue
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