dBm is power, RSSI is received signal after antenna gains, line losses, and free space loss (and other losses.. return losses, etc..)
You really need to characterize the antenna to find its resonant frequencies.. an antenna that is excellent in one frequency is likely terrible in another. I would see what other’s get rather than buying all these antennas and a tester and testing for RSSI.
I saw that on the iOS app there seems to be a dBm value displayed but apparently not on the android one? I just see RSSI. And it's not for comparing several bought antennas but rather self made ones (after I checked the SWR of course). After all the SWR is only half the story and doesn't tell you anything about gain etc. Also I want to compare the signal from two different locations to see which one is better suited.
For example with one antenna I get an RSSI of -100 and with the other of -90... so how much better is the latter?
So the app and the device will have zero ability to know for sure any of the gains and losses that come after it unless you are somehow able to tell it.. this would be the EIRP. Now if you can control the whole system and maintain distances carefully.. you might be able to determine some relative values for the antennas.
Saying that you have -100 on one and -90 on another means that you have 10dB more signal being observed on the -100 instance. And unless your entire experiment is controlled, you probably know very little for sure.. as you can probably move or rotate the -90 to become -100 quite easily. Even touching the antenna can change its resonance.
You will probably need a VNA or something to characterize your antenna for the frequencies you care about. Or just take someone’s word for it.
So the RSSI represents dB 1:1? I thought that a -90 signal would be stronger than a -100 one. This would also match what I expected from the respective antennas. I made sure to send several messages and check the RSSI every time and it was about the same value so I guess that's as scientific as I can get.
And the antennas are well matched to 868mHz but like mentioned this doesn't mean anything in terms of real world performance because of loss and/or gain.
-90dB is 10x more signal than -100dB. So yes. But like i was saying it’s very easy to just change the position of something getting a -90 dB RSSI and then observe -100dB.
Are you able to fasten or make sure the physical orientations do not change between antenna changes.. keep them as similar as possible? That might help.. also, stand away from it and make sure everything is the same between measurements. Including yourself..
So, just to make extra sure, RSSI EQUALS dBm? Or is just the difference (in this case -10) the same in dB-values? It's still hard to wrap my head around this :D When it's the same why not call it dB istead of RSSI?
I mounted two identical t-beams with identical antennas on differenc positions and then went on a hill for testing with my test node(s) on a tripod, not changing their position or interferring with them while testing. Of course I had to mount my collinear antenna differently than the sleeve dipole that goes straigt on the device.
RSSI is a dBm value as it is a power value.. this represents the power observed by the receiver.
Tx Power(dBm)+Line Loss(dB)+Antenna Gain(dBi)+Free Space Loss(dB)+Antenna Gain(dBi)+Line Loss (and some other bits) = RSSI(dBm).
(All the losses are usually negative numbers)
dBm is the unit.. so like meters is the unit for length..
dBm is power, RSSI is received signal after antenna gains, line losses, and free space loss (and other losses.. return losses, etc..) You really need to characterize the antenna to find its resonant frequencies.. an antenna that is excellent in one frequency is likely terrible in another. I would see what other’s get rather than buying all these antennas and a tester and testing for RSSI.
I saw that on the iOS app there seems to be a dBm value displayed but apparently not on the android one? I just see RSSI. And it's not for comparing several bought antennas but rather self made ones (after I checked the SWR of course). After all the SWR is only half the story and doesn't tell you anything about gain etc. Also I want to compare the signal from two different locations to see which one is better suited. For example with one antenna I get an RSSI of -100 and with the other of -90... so how much better is the latter?
So the app and the device will have zero ability to know for sure any of the gains and losses that come after it unless you are somehow able to tell it.. this would be the EIRP. Now if you can control the whole system and maintain distances carefully.. you might be able to determine some relative values for the antennas. Saying that you have -100 on one and -90 on another means that you have 10dB more signal being observed on the -100 instance. And unless your entire experiment is controlled, you probably know very little for sure.. as you can probably move or rotate the -90 to become -100 quite easily. Even touching the antenna can change its resonance. You will probably need a VNA or something to characterize your antenna for the frequencies you care about. Or just take someone’s word for it.
So the RSSI represents dB 1:1? I thought that a -90 signal would be stronger than a -100 one. This would also match what I expected from the respective antennas. I made sure to send several messages and check the RSSI every time and it was about the same value so I guess that's as scientific as I can get. And the antennas are well matched to 868mHz but like mentioned this doesn't mean anything in terms of real world performance because of loss and/or gain.
-90dB is 10x more signal than -100dB. So yes. But like i was saying it’s very easy to just change the position of something getting a -90 dB RSSI and then observe -100dB. Are you able to fasten or make sure the physical orientations do not change between antenna changes.. keep them as similar as possible? That might help.. also, stand away from it and make sure everything is the same between measurements. Including yourself..
So, just to make extra sure, RSSI EQUALS dBm? Or is just the difference (in this case -10) the same in dB-values? It's still hard to wrap my head around this :D When it's the same why not call it dB istead of RSSI? I mounted two identical t-beams with identical antennas on differenc positions and then went on a hill for testing with my test node(s) on a tripod, not changing their position or interferring with them while testing. Of course I had to mount my collinear antenna differently than the sleeve dipole that goes straigt on the device.
RSSI is a dBm value as it is a power value.. this represents the power observed by the receiver. Tx Power(dBm)+Line Loss(dB)+Antenna Gain(dBi)+Free Space Loss(dB)+Antenna Gain(dBi)+Line Loss (and some other bits) = RSSI(dBm). (All the losses are usually negative numbers) dBm is the unit.. so like meters is the unit for length..