[RFI] 2.4 GHz and 5 GHz RFI (maybe)

Tom Cox tomcox at iquest.net
Tue May 13 09:31:40 EDT 2003


Now, that is useful information. I hadn't thought about ducting, but the
problems with the 5GHz links didn't start til two weeks ago, about the time
we would expect to see some ducting in this area. Hmm. I also need to check
the FCC database; hadn't thought about that one, either. I'll do that today.

Thanks for the good leads -- 
Tom, KT9OM

At 08:15 AM 5/13/03 , you wrote:
>This information does change the picture a bit.  Assuming that you have
>already performed some sort of functional testing to rule out an equipment
>problem in your own system, there are three suggestions that come to mind:
>1.  Check the FCC data base to see if there are licensed systems operating
>in or near your area in adjacent portions of the spectrum.  You could have
>some other system that has developed spurious outputs and is causing a
>2.  Consider either renting a spectrum analyzer, with appropriate antennas,
>and taking readings during periods of system malfunction, or hiring an EMI
>test house to send someone out with equipment to do the work.  The
>combination of portable horn (or dish) antennas and a spectrum analyzer
>should allow you to DF the interfering source.
>3.  Have these problems just begun, or have they existed for awhile?  The
>reason I ask is because we are now into the time of year in which tropo
>ducting becomes common.  Being an avid VHF/UHF op, I can tell you that some
>real surprises can happen.  Your antennas are up high, and that is why I
>raise the question.  Years ago, I worked microwave for the "original" Ma
>Bell. I recall being at some field sites in mid-summer and just watching
>signals go up and down, disappear, re-appear, and cause all sorts of
>trasnmission problems when the ducts and/or thermals over the corn fields
>set in.  This action occured at both 6 GHz and 10 GHz.
>Best luck.
>73, Dale
>                      Tom Cox
>                      <tomcox at iquest.ne        To:       David Jordan
<wa3gin at erols.com>                                               
>                      t>                       cc:
rfi at contesting.com                                                            
>                      Sent by:                 Subject:  Re: [RFI] 2.4 GHz
and 5 GHz RFI (maybe)                                       
>                      rfi-bounces at conte
>                      sting.com
>                      05/12/2003 02:39
>                      PM
>As I should have mentioned, this is a point-to-point system of wireless
>bridges, not a point-to-multipoint system as is commonly thought of in
>digital wireless applications. These links are on rooftop or tower mounts,
>from several feet above a building roof to over a hundred feet up a tower,
>connected with high-gain, narrow-beam antennas. The 2.4 GHz links connect
>smaller buildings to one, central "hubsite" in the area, which uplinks the
>smaller buildings to a backbone at 5 GHz. What I need is a way to discover
>and locate RFI at 2.4 and 5 GHz that is (or might be) interfering with the
>system. I hope this makes my situation a little clearer. Sorry about the
>incomplete description.
>Tom, KT9OM
>At 02:10 PM 5/12/03 , you wrote:
>>Could be a leaky microwave oven in the kitchen or cordless phones, etc.
>>Might try a booster or relocating  the WAP.
>>Tom Cox wrote:
>>>What is out there for searching the 2.4 GHz and 5 GHz. wireless data
>>>spectra for an interfering signal? We have erratic link drops that are
>>>suggestive of RFI, but no equipment for detecting it. Our school
>>>corporation's wireless WAN is really suffering.
>>>Tom Cox, KT9OM
>>>Anderson (IN) Community Schools
>>>tomcox at iquest.net
>>>RFI mailing list
>>>RFI at contesting.com
>RFI mailing list
>RFI at contesting.com

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