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Author Topic: RFI & SWR ?  (Read 1896 times)
KE5OKQ
Member

Posts: 203




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« on: December 15, 2007, 08:03:03 PM »

Whenever I experience a lengthy, heavy rainfall, my SWR goes from a 1.1:1 to 3:1 until everything drys out after a day or so. The antenna is a HyGain AV14AVQ vertical, mounted 10 inches off the ground with a dozen #12 radials. I attribute the temporay SWR increase to water in the traps or soil conductivity or both. I have an LDG AT 200Pro autotuner that brings the SWR back down.

I just had a heavy rain this morning and of course the SWR is back up to 3:1. What is different is that I am experiencing RFI in my Sennheiser wireless headophones when transmitting. I can hear myself pretty clearly. Can the SWR increase have something to do with it or is it something else?
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NW5Y
Member

Posts: 25




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« Reply #1 on: January 23, 2008, 11:26:04 AM »

I really think you have an issue with a ground loop in the shack, coax connectors, or cracked transmission line issues. Likely its related to the coax/connections. The issue is probably always there yet it is enhanced and becomes detectable when an entrance for moisture exist which in turn creates a path for an RF "leak". I dont think it would be related to the traps. SWR can fluctuate during heavy rain or icing because the effective electrical  length of an element, usually expressed in wavelengths can be impacted. The electrical length is in general different from the physical length. By the addition of an appropriate reactive element (capacitive or inductive)the electrical length can change.
You state that the issue arises after the rain so I would say it is likely RF on the coax coming back into the shack. Look at the connection at the antenna and any in the transmission line run. Just because a connector looks good doesn't mean it is or that the interface between the connector and coax is sound. Make sure you dont have any ground loops between your equipment going to your ground. Seal external coax connections.
   
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