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

dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Tue May 13 09:15:51 EDT 2003


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                                                                                                
                      05/12/2003 02:39                                                                                                 

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
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