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868MHz Propagation problem
On Oct 24, 5:14*am, dgleeson422111 wrote:
Hello All We have a propagation issue that is confusing us. We have two 868MHz modules on test, each capable of 500mW transmission. We are testing to find the range of communication. We are testing them as follows. One remains in our office while the other is taken to the street outside. we are communicating charecter strings such as "Im at the lamp post number 1" etc. There is somebody at each end sending text strings in a continuous conversation. There is no protocol, error checking or error recovery. What we have repetadly found is that the radio in the office can receive long after the radio in the street has stopped receiving. (The person with the radio in the street is moving away from the office.) The radios are the same and the power supplies to the radios are the same. Indeed switching the radios gives the same effect. The propagation paths between the two radios are the same in terms of distance. However the radio signal transmitted from the office travels through walls first before then traveling through open space. Its the opposite for the radio in the street, firstly traveling through space and then through the walls in the office. We did think we had identified an interfeering source in one direction (when moving away from the office) so we started moving in the opposite direction. We found exactly the same effect. Are we getting interfeerance from GSM, ISM or Paging? As far as GSM bands go in Europe 890–915 MHz OR 1710–1785 MHz So these shouldnt be our problem. ISM is where we intend to operate and the greatest band occupancy should be 10%. So we should get communication even though we would get some interfeerance. Paging - well this has very much gone out of fashion in Europe. But even if it was the cause then wouldnt it be intermittant communication. We have a constant problem. Can anyone shed light on this phenomonon? Is it an issue of wireless propagation that Im not familiar with or is it Interfeerance? Best regards, and thanks for any input. Denis _____________________http://www.CentronSolutions.com Denis, I agree with some of your previous posts - the outside receiver is likely being desensed by a strong signal, perhaps away from or a harmonic of the frequency you're using. I suggest trying the test away from town and at least 10km from strong transmitting towers. Let us know what you find out - may help those of us who do UHF/VHF mobile/ portable hamming. As a ham I have NOT PROBLEM with the commercial community asking questions on a ham radio group - we can ALL learn from this. Cheers, Dick Post, N7EMW www.repdesign.us |
#2
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868MHz Propagation problem
"Radio_Dick" wrote in message ... On Oct 24, 5:14 am, dgleeson422111 wrote: Hello All We have a propagation issue that is confusing us. We have two 868MHz modules on test, each capable of 500mW transmission. We are testing to find the range of communication. We are testing them as follows. One remains in our office while the other is taken to the street outside. we are communicating charecter strings such as "Im at the lamp post number 1" etc. There is somebody at each end sending text strings in a continuous conversation. There is no protocol, error checking or error recovery. What we have repetadly found is that the radio in the office can receive long after the radio in the street has stopped receiving. (The person with the radio in the street is moving away from the office.) The radios are the same and the power supplies to the radios are the same. Indeed switching the radios gives the same effect. The propagation paths between the two radios are the same in terms of distance. However the radio signal transmitted from the office travels through walls first before then traveling through open space. Its the opposite for the radio in the street, firstly traveling through space and then through the walls in the office. We did think we had identified an interfeering source in one direction (when moving away from the office) so we started moving in the opposite direction. We found exactly the same effect. Are we getting interfeerance from GSM, ISM or Paging? As far as GSM bands go in Europe 890–915 MHz OR 1710–1785 MHz So these shouldnt be our problem. ISM is where we intend to operate and the greatest band occupancy should be 10%. So we should get communication even though we would get some interfeerance. Paging - well this has very much gone out of fashion in Europe. But even if it was the cause then wouldnt it be intermittant communication. We have a constant problem. Can anyone shed light on this phenomonon? Is it an issue of wireless propagation that Im not familiar with or is it Interfeerance? Best regards, and thanks for any input. Denis _____________________http://www.CentronSolutions.com Denis, I agree with some of your previous posts - the outside receiver is likely being desensed by a strong signal, perhaps away from or a harmonic of the frequency you're using. I suggest trying the test away from town and at least 10km from strong transmitting towers. Let us know what you find out - may help those of us who do UHF/VHF mobile/ portable hamming. As a ham I have NOT PROBLEM with the commercial community asking questions on a ham radio group - we can ALL learn from this. Cheers, Dick Post, N7EMW www.repdesign.us ************************************************** * I don't know why I don't get the on your response, but whatever. He can get some feel for what is going on by taking *both* radios outside near his office, and walking around. He should be able to find a particular area that has poor reception. I don't buy the explanations for antenna gain and multipath, they should affect both directions of transmission equally. Tam |
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