| Page 1 of 2 | 1 | 2 |
|
|
868MHz Propagation problem
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 |
868MHz Propagation problem
On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote: Can anyone shed light on this phenomonon? Is it an issue of wireless propagation that Im not familiar with or is it Interfeerance? Nope a question of height |
868MHz Propagation problem
wrote in message ... On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111 wrote: Can anyone shed light on this phenomonon? Is it an issue of wireless propagation that Im not familiar with or is it Interfeerance? Nope a question of height Shouldn't the path be reciprical? |
868MHz Propagation problem
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 You may experience receiver desensitization from a strong out-of-band interferer which is not penetrating well into your office and hence not interferring there. Pere |
868MHz Propagation problem
Hi Guys
Thanks for your input on this. The idea of height being a problem is interesting. The radio in the office is on the 1st floor (i.e above the ground by one floor). If the antenna were at the same height would the problem go away? We will test and see On Oct 24, 11:57*am, oopere wrote: 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 You may experience receiver desensitization from a strong out-of-band interferer which is not penetrating well into your office and hence not interferring there. Pere- Hide quoted text - - Show quoted text - |
868MHz Propagation problem
higher antennas = longer range. Thats your issue.
Also lack of error correction, poor antenna pattern to meet the low power regulations, and a less then robust protocol, ie your probably using some form of on/off modulation where the receiver does not have a continious wave signal to locl on and track. Try sending a preamble character that is 10101010 a few times, assuming your receiver is sophisticated enough to use AGC. This sets the DC level in the discriminator more accurately and reduces errors. your using a radio with intentionally designed in limited range to allow reuse of the frquency. Steve |
868MHz Propagation problem
"dgleeson422111" wrote in message ... 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. Is your office in a concrete building? Or one with any steel reinforcement or steel or aluminum studs? If so, it could well be that there is a standing wave issue, so that a portion of your transmitted signal is being reflected back, and so not making it to the receiver. This would not necessarily affect the reception on the radio in the office from the outside radio. |
868MHz Propagation problem
dgleeson422111 wrote:
\ 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 radio outside is likely being desensitized by some other signal. |
868MHz Propagation problem
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.) I see you have other responses. One test that would establish that is environmental (adjacent signal, receiver desense, etc), if BOTH units could be moved to a relative RF free environment such as a rural setting and then test the range. If this eliminates the problem, then its probably time to break out a spectrum analyzer and take a look at what is around your operating frequency. Andy |
868MHz Propagation problem
It's because the paths are not the same. Think of a silvered mirror. It can
transmit light much easier in one direction than the other. Take both outside and see if it has the same problem. (extremely doubtful because the path's is virtually identical) |
868MHz Propagation problem
On Oct 24, 8:14*am, "Jon Slaughter" wrote:
It's because the paths are not the same. Think of a silvered mirror. It can transmit light much easier in one direction than the other. Take both outside and see if it has the same problem. (extremely doubtful because the path's is virtually identical) Did you design the receive software? Or did buy the receiver "off the shelve"? Perhaps there is a problem with the receivers and how they are receiving the data. |
868MHz Propagation problem
"EE123" wrote in message ... On Oct 24, 8:14 am, "Jon Slaughter" wrote: It's because the paths are not the same. Think of a silvered mirror. It can transmit light much easier in one direction than the other. Take both outside and see if it has the same problem. (extremely doubtful because the path's is virtually identical) Did you design the receive software? Or did buy the receiver "off the shelve"? Perhaps there is a problem with the receivers and how they are receiving the data. um, did you read his message? He said that it was independent of the receiver because they exchanged them and the same problem. i.e., it helps to read the original post. |
868MHz Propagation problem
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. Do you have a license? |
868MHz Propagation problem
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.) You don't say if you are using the same antenna on both ends, but the environment is very different at each end. Consider that Transmitting is about putting signal into an area, while receiving is about capturing the signals in near field of the antenna, then discerning the intellegence. You would have to analyze the output to be sure, but it may be localized reflections, shading or noise at the street level. Because of this it is so difficult to quantify range. There is equipment and software specifically designed to do what you are trying to do but it is expensive. The result is highly detailed signal strength graphic output overlaid on 3d mapping for each fixed site at various frequencies. Most commercial antenna sites have gone to great expense to generate those maps in order to show what their tower does because it is very different for each location. |
868MHz Propagation problem
On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote: 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.) Is the moving station manually portable or is it mounted on a vehicle? If the moving operator is bored and continuously talks on a GSM phone or if the (vehicle) generates some other kind of interference, this would reduce the SNR at the moving station. 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. Does the transmitter have some kind of SWR protection ? If the Tx antenna is close to the wall, it might detune the antenna, increasing the SWR and the SWR protection drops the transmitter power. Paul OH3LWR |
868MHz Propagation problem
"oopere" wrote in message ... 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 You may experience receiver desensitization from a strong out-of-band interferer which is not penetrating well into your office and hence not interferring there. Pere Such as traffic light electronics. Without error correction protocols being employed, you are also at the mercy of multipath interference. You're QRMing your own signal. 8) Ed, NM2K |
868MHz Propagation problem
On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote: 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.) Polarization could be a factor. Reflections change the polarization appr. 90 degrees. Rotate the antennas left & right to find out. (you did not mention your type of antennas) w. |
868MHz Propagation problem
On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote: 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.) This is typical for groundplane antennas. They radiate upwards. Polarization could be a factor. Reflections change the polarization appr. 90 degrees. Rotate the antennas left & right to find out. (you did not mention your type of antennas) w. |
868MHz Propagation problem
On Oct 24, 2:00*pm, "Paul Hovnanian P.E." wrote:
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 Have you tried relocating the office transceiver? There might be something about the office environment that is interfering with its transmission. -- Paul Hovnanian * * ------------------------------------------------------------------ A mathematician is a machine for converting coffee into theorems.- Hide quoted text - - Show quoted text - wow so many of these replies are wrong.. in almost all cases, RF path losses are RECIPROCAL. (even a 1/2 silvered mirror is reciprocal to light) As some have said, the cause of your issue is probably interference to the outside receiver. Or maybe something about the indoor setup is causing the indoor Tx to operate at lower power. It is very unusual for RF path loss to be non-reciprocal. Mark |
868MHz Propagation problem
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 Have you tried relocating the office transceiver? There might be something about the office environment that is interfering with its transmission. -- Paul Hovnanian ------------------------------------------------------------------ A mathematician is a machine for converting coffee into theorems. |
868MHz Propagation problem
dgleeson422111 wrote:
Hi Guys Thanks for your input on this. The idea of height being a problem is interesting. The radio in the office is on the 1st floor (i.e above the ground by one floor). If the antenna were at the same height would the problem go away? We will test and see If I remember my antenna/propagation theory correctly, such a change should affect both the transmit and receive gains equally. That is to say, if moving the office antenna lower will reduce its transmit range, it will also reduce its receive range. What you are looking for is something that is reducing the office end transmit power while leaving its receive sensitivity intact. Someone else suggested an SWR problem due to near field interference with the antenna. -- Paul Hovnanian ------------------------------------------------------------------ Don't anthropomorphize computers. They hate that. |
868MHz Propagation problem
Dave wrote:
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. Do you have a license? Not required in EU for 868 MHz -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P |
868MHz Propagation problem
Anthony Fremont wrote:
dgleeson422111 wrote: \ 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 radio outside is likely being desensitized by some other signal. Most likely scenario. Also make sure that in your design you are powering down the transmitter fully in the receive mode. In some radios there can be a residual carrier from the PLL causing self interference ar interference to other nearby nodes. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P |
868MHz Propagation problem
Mark wrote:
On Oct 24, 2:00 pm, "Paul Hovnanian P.E." wrote: wow so many of these replies are wrong.. This is normal when antenna "theory" comes up. in almost all cases, RF path losses are RECIPROCAL. I agree, including the antenna gains (meaning that the antennas at each end don't have to match). (even a 1/2 silvered mirror is reciprocal to light) Well that guy is usually on a differet page. As some have said, the cause of your issue is probably interference to the outside receiver. That's what I think is the most likely cause. The guy outside probably has his Nextel phone with him. ;-) Or maybe something about the indoor setup is causing the indoor Tx to operate at lower power. I suppose that's possible too. The OP should make sure the power supplies are equivalent (meaning that the output power would suffer more than the receiver gain with a drooping supply). So check the indoor supply. It is very unusual for RF path loss to be non-reciprocal. |
868MHz Propagation problem
On Oct 24, 2:26*pm, "Anthony Fremont" wrote:
Mark wrote: On Oct 24, 2:00 pm, "Paul Hovnanian P.E." wrote: wow so many of these replies are wrong.. This is normal when antenna "theory" comes up. in almost all cases, *RF path losses are RECIPROCAL. I agree, including the antenna gains (meaning that the antennas at each end don't have to match). (even a 1/2 silvered mirror is reciprocal to light) Well that guy is usually on a differet page. As some have said, the cause of your issue is probably interference to the outside receiver. That's what I think is the most likely cause. *The guy outside probably has his Nextel phone with him. *;-) Or maybe something about the indoor setup is causing the indoor Tx to operate at lower power. I suppose that's possible too. *The OP should make sure the power supplies are equivalent (meaning that the output power would suffer more than the receiver gain with a drooping supply). *So check the indoor supply. It is very unusual for RF path loss to be non-reciprocal.- Hide quoted text - - Show quoted text - It is assumed that the path to and from the office should be inferior to the line of sight path out on the street. This may or may not be true. The building may actually be offering gain in certain directions. I would start by seeing if the same condition existed at many more locations. If it does then other ideas need to be examined, I would start by examining the RF environment outside the building. Jimmie |
868MHz Propagation problem
On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), 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. Hi Denis, That is a lot of power for a problem of losing contact in the space of blocks. 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. A very good description of the symptoms and relations. 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. A good test for reducing variables. If you identified an interference, I would presume you could do that again in the other direction. Are we getting interfeerance from GSM, ISM or Paging? Only if the remote set was nearer to an undiscovered interferer. You seemed to have resolved that once, and you should be able to detect the similar occurrence again. As far as GSM bands go in Europe 890–915 MHz OR 1710–1785 MHz So these shouldnt be our problem. This is a flaw in the logic. Your frequency of operation is very close to these bands - unless your sets have been designed with elaborate front end tuning (which seems unlikely). Can anyone shed light on this phenomonon? Is it an issue of wireless propagation that Im not familiar with or is it Interfeerance? One component not discussed is the remote set's proximity to the operator. The operator could disturb the local field (aka shield). Going beyond is the effect of a Fresnel Zone, but your descriptions describe a complete black-out. To test this requires you to go further away to see if you pick up the signal again. This is a long shot, however, as the effect would be distinct within the space of a meter or so. For mobile operation, the Fresnel Zone creates what is called "Picket Fencing" as the signal comes and goes quickly with distance traveled. Perhaps it is the proximity of a Pub, and your operator stopped in for a Guinness. 73's Richard Clark, KB7QHC |
868MHz Propagation problem
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. I'll second Pere and Anthony. Strong out-of-band signals is what I found mostly in situations where path losses seemed strangely non-reciprocal. Post a schematic. One possibility is that your receive input filter is wide open like a barn door and GSM swamps the receiver. Another option if you have a spectrum analyzer: Hang a large near-field probe into a long cable, tape it to a broomstick and hold that out the window for a while. See what pops up on the screen. If this is in a city be prepared for some commotion among the pedestrians down there :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |
868MHz Propagation problem
Hey:
My crystal balls are saying: Multipath where a reflected signal from the source is being cancelled out in the zone sort of like standing waves. It's like waves in a bath tub they bounce of the sides and produce more inter- ference waves, and so on. Or FM broadcast stations signal in the big city with tall buildings, all of a sudden the signal just goes puff while you're driving along down- town. I'd say gits your antenna near a window or put up an outdoor antenna. 73 OM n8zu |
868MHz Propagation problem
"Mark" wrote in message news:89e3cfad-c877-4be6-8eca- wow so many of these replies are wrong.. in almost all cases, RF path losses are RECIPROCAL. ( It is very unusual for RF path loss to be non-reciprocal. Mark I agree. But, one thing that should be proven is that both modules are working as intended. The one being used for the remote application *could* be defective. Swap modules and see if the receiving problem also switches locations, or remains the same. Pete |
868MHz Propagation problem
Hello,
There should be a reciprocal relationship between the modules regardless of height, antennas etc. as long as TX power and RX sensitivity of the modules are the same (which they appear to be). The modules are unlikely to have very good input filters at 868MHz, so any adjacent channel interference (GSM etc.) is likely to cause the out of balance behaviour. Try heading in a different direction outside, or go somewhere else with your experiment. For your real world application, are you likely to have any site close to adjacent channel transmitters (cell or broadcast) ? If so, think about a decant front end filters. This could be costly, but might save you... Regards, Mark On Oct 25, 9:25*am, wrote: On Oct 24, 2:26*pm, "Anthony Fremont" wrote: Mark wrote: On Oct 24, 2:00 pm, "Paul Hovnanian P.E." wrote: wow so many of these replies are wrong.. This is normal when antenna "theory" comes up. in almost all cases, *RF path losses are RECIPROCAL. I agree, including the antenna gains (meaning that the antennas at each end don't have to match). (even a 1/2 silvered mirror is reciprocal to light) Well that guy is usually on a differet page. As some have said, the cause of your issue is probably interference to the outside receiver. That's what I think is the most likely cause. *The guy outside probably has his Nextel phone with him. *;-) Or maybe something about the indoor setup is causing the indoor Tx to operate at lower power. I suppose that's possible too. *The OP should make sure the power supplies are equivalent (meaning that the output power would suffer more than the receiver gain with a drooping supply). *So check the indoor supply. It is very unusual for RF path loss to be non-reciprocal.- Hide quoted text - - Show quoted text - It is assumed that the path to and from the office should be inferior to the line of sight path out on the street. This may or may not be true. The building may actually be offering gain in certain directions. I would start by seeing if the same condition existed at many more locations. If it does then other ideas need to be examined, I would start by examining the RF environment outside the building. Jimmie- Hide quoted text - - Show quoted text - |
868MHz Propagation problem
"dgleeson422111" wrote in message ... 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 its interesting that a commercial company would bring a problem such as this to a bunch of amateur radio operators... true some of the amateurs may be professional engineers, but the remainder are not! I guess that in today's market place we try to gain information on the dirt and cheap way. |
868MHz Propagation problem
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 What is the modulation type and data rate? Could be a delay spread issue. Maybe the outside unit is receiving a reflected signal from the surface of a nearby structure and is experiencing inter-symbol interference that by chance the base unit is shielded from. This would occur only if a high symbol rate was being used. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P |
868MHz Propagation problem
W3CQH wrote:
[...] its interesting that a commercial company would bring a problem such as this to a bunch of amateur radio operators... true some of the amateurs may be professional engineers, but the remainder are not! I guess that in today's market place we try to gain information on the dirt and cheap way. Nah, that's ok. Every one of us occasionally runs into an unusual situation. Then one can either stew on it for days without getting to the ground of it, or ask. IMHO it is a sign of maturity if somebody has the guts to say "Hey, guys, this problem here really has us puzzled". That is especially true for EMI cases and this sure looks like one. Sometimes a brief hint by someone who has been in the trenches for decades can get things going again. And most older ham radio operators had that exposure, fixing the neighbor's electronics because their manufacturers messed up. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |
868MHz Propagation problem
Tio Pedro wrote:
I agree. But, one thing that should be proven is that both modules are working as intended. The one being used for the remote application *could* be defective. Swap modules and see if the receiving problem also switches locations, or remains the same. The OP said that he did that, and the problem remained. It's certainly a desensing problem due to local interference at one end. That's the only possible cause. |
868MHz Propagation problem
In article m,
RFI-EMI-GUY wrote: 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 What is the modulation type and data rate? Could be a delay spread issue. Maybe the outside unit is receiving a reflected signal from the surface of a nearby structure and is experiencing inter-symbol interference that by chance the base unit is shielded from. This would occur only if a high symbol rate was being used. what type of amateur radio application is this for? Or is it a commercial application posted in this amateur radio group? just wondering |
868MHz Propagation problem
what type of amateur radio application is this for? Or is it a commercial application posted in this amateur radio group? just wondering What amateur band covers 868 MHz? Did we get a new one? I'll have to order another transverter, I guess ;) Well, to get this post be on topic, does anyone know of a good source for some SPDT coaxial relays good at 902 MHz and good for 350 Watts at 902? Scott N0EDV |
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 |
868MHz Propagation problem
What is the modulation type and data rate? Could be a delay spread issue. Maybe the outside unit is receiving a reflected signal from the surface of a nearby structure and is experiencing inter-symbol interference that by chance the base unit is shielded from. This would occur only if a high symbol rate was being used. i was thinking about that...but no.... all the multi-path paths are reciprocal as well,,, so whatever the delay spread is one way should be the same the other way. Mark |
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 |
868MHz Propagation problem
dgleeson422111 wrote:
... Best regards, and thanks for any input. Denis _____________________ http://www.CentronSolutions.com Since most of the posts, in their "EXPERT OPINIONS", relate to your receiver being "de-sensed", do you have a way of negating/affirming this? Begin there, and we can get down to "real problems!" :-) i.e., a wide-band field strength meter, freq counter, etc. will either make all this "right" or "wrong." Regards, JS |
| All times are GMT +1. The time now is 11:01 PM. |
|
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com