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Resolving 2.4 GHz interference



Ray WB3ABN wrote

And what of this suggestion to deliberately create a beacon to fool these devices into moving away from your satellite freq?  Isn't that deliberately causing harmful interference?  

Wayne replies:

I agree with you 100% that a confrontational attitude with neighbors is likely to be counterproductive.

However, I think a 2402 MHz beacon transmitter is very much in the spirit of friendly cooperation and being a good neighbor.  It might resolve cordless phone interference without imposing any behavior change on your neighbor.  Your neighbors wouldn't even have to know that they were causing a problem!  Cordless phones have a lot of frequencies to choose from.  We are stuck with one narrow frequency segment for hearing AO40.


David Schick wrote:

I haven't run the numbers for the average interference scenario, but it seems that using an antenna with high directivity one should be able to avoid most of the local noise.  

Wayne replies:

The noise floor of the AO40 transponder can be as low as -150 dBm, and we need to hear -140 dBm signals for decent intelligibility.  The signals from nearby cordless phones could be higher than -100 dBm.  Our antennas are not likely to have 50 dB of side rejection.  If they did, it wouldn't help because "scatter" signals reflected from surrounding objects would be attenuated by less than 50 dB, and come into the antenna's main beam.  The worst-case, of course, is low-elevation situations where our dish points directly at an interference source.  The only solution is to get the interference source to shut down or change frequency.  The bottom line is that no matter which direction your antenna is pointed, you have a good chance of hearing any cordless phone using 2401 MHz within 500 meters of your antenna.  My strongest cordless phone interference comes from a direction where the nearest house is about 300 meters away.  Even at that distance, the signal is much stronger than AO!
!
40 when I point my dish towards the interference source.  Fortunately, the offending cordless phone doesn't seem to use 2401 MHz all the time, and none of my immediate neighbors have 2400 MHz cordless phones (yet).

Wayne Estes W9AE
Mundelein, IL, USA
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