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how to scan for AP signal with spectrum analyzer |
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Written by GTOV8
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Thursday, 25 January 2007 |
"1. If I put a spectrum analyzer in the same room as a MT with a 5.8GHz sr5 should I see a constant signal at the frequency of the radio when the radio is in AP Bridge mode?
2. How about when it is in alignment mode?
If I can't get any blips at all on the set frequency, should I assume the radio is bad?
Can the router board affect the radio and stop it from working even if I can access the radio and change settings from winbox?
Is the frequency always centered on the selected channel or does it frequency hop? I'm inside an enclosed room and I'm seeing -40db signals all over the place. nothing else is in the room except my laptop (wireless card is turned off) and the MT. we are not near anything that would be putting out this many signals between 5750 and 5850.
Peaks are hopping all over at -40db but none are appearing on the 5805 of the MT."
viperm:
Well if you walk outside the room does it getter stronger or weaker? IS there a Cellualr carrior or any other ISP in the same colocation room as you?
I have not seen a true frequency hopping 5.8 setup only 2.4 You should see the center point as a peak of the freq they are set on and then see weaker signals tapper off to each side of center. It also depends on the width of the freq as to how far on each side from center I.E. if they are using 20mhz channels then you will see the center point and 10mhz to each side usually.
Sounds like there is someone else running 5.7 equipment in your room.
In alignment mode the system is just listening and not actively broadcasting such as in AP bridge mode.
I have not seen a router board that has failed allowing the radio to not work, I am not saying it cant happen I just have not seen it yet. What radio card is it? are you sure you have it set to the correct ant? Is the reading you are getting on the spectrum the channel you are on or is it completely different?
What happens if you unplug or turn off the mikrotik completely does the spectrum go blank or do you still see the signal? If you still see it then I would guess like I said above someone else is in the same room using 5.7.. If this is a true tower site the tower owner should know everyone who is located in that room, what frequencies they are running etc.
cmaenginsb:
My take on your questions:
1. If you do not put the SA in a peak hold mode the signal will appear to hop around in a 20 mhz area grouped on the center frequency. (ie 10 mhz above and below). If you use peak hold it will fill in an area 10 mhz above and below the center frequency. This assumes you're using a 20mhz wide channel.
2. This will be the same as #1
If you don't get a signal than the radio is most likely bad. I haven't seen a routerboard stop a radio from working, but the only way to tell for sure is to try a different radio card in it.
The 5 ghz 802.11a based equipment is direct sequency spread spectrum so it doesn't hop. The only 5 ghz hopper I know of is an older Alvarion unit.
I also agree you need to take a reading with nothing of yours on to determine if it's the Mikrotik or something else giving you the varying readings.
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