Over powered SM

I’m having some trouble setting the power level of a connectorized 900 SM. The dBm is around -49 and I need to get this up to about -65 range. I believe that -49 is too powerful. The antenna is a 7dBd Maxrad flat panel. I’ve tried changing the dBm in the SM configuration but it seems to not influence the RSSI levels at all. The possible installation location is .56mi from a tower I have and I don’t have any smaller antennas at this time yet I’d like to get this installed ASAP. Is there another method for lowering the power of the connectorized SM?

Thanks,

Rich

rjk wrote:
I'm having some trouble setting the power level of a connectorized 900 SM. The dBm is around -49 and I need to get this up to about -65 range. I believe that -49 is too powerful. The antenna is a 7dBd Maxrad flat panel. I've tried changing the dBm in the SM configuration but it seems to not influence the RSSI levels at all. The possible installation location is .56mi from a tower I have and I don't have any smaller antennas at this time yet I'd like to get this installed ASAP. Is there another method for lowering the power of the connectorized SM?

Thanks,

Rich


On the SM configuration page turn the power level down until you get the SM power level within 10db of all the other SM's registered on the AP. Use the AP sessions page to determine the power level of all the SM's registered to the AP.

There is a power level setting, for a connectorized unit it is usually set between 24 and 26db by default, generally you can go no lower than 4db, but on one or two SMs I have I've been able to go down to 3db (assuming 900mhz system).

rjk,

What the longest link you have from the AP?
We now know that the link in question is 0.54 miles, but is that the only one?
What is the average distance for all the other SM, from BASE or AP?

I’ve got the dBm level set to 8 right now on the SM and I’m seeing no difference in RSSI/dBm. Still hovering around -49dBm.

The longest link I have is 7.77miles out at this point. On this AP, this is the only client at this point.

The average distance is 4 miles for the SMs. I try to keep their dBm around -75dBm 4 miles out and the closer units at -65 at least.

Is this not a recommended way? I’m trying to avoid de-sensing and other issues by keeping the power levels of the closer SMs a little lower than the SMs further out. Makes sense to me anyway.

Thanks,

Rich

rjk wrote:
I've got the dBm level set to 8 right now on the SM and I'm seeing no difference in RSSI/dBm. Still hovering around -49dBm.

The longest link I have is 7.77miles out at this point. On this AP, this is the only client at this point.

The average distance is 4 miles for the SMs. I try to keep their dBm around -75dBm 4 miles out and the closer units at -65 at least.

Is this not a recommended way? I'm trying to avoid de-sensing and other issues by keeping the power levels of the closer SMs a little lower than the SMs further out. Makes sense to me anyway.

Thanks,

Rich



Are you looking at the power level from the SM side, or the AP side? If you are looking at the power level on the SM you won't see much if any change, you need to look at the power level from the AP's perspective. On the AP the SM is registered to, look at the sessions page, and locate the SM in the list of registered SM, then look at the power level for that SM.

As mentioned above, make sure that you are using the AP sessions page to look at the dBm level. You’re not going to see much if any difference on the SM side as you decrease its power.

Assuming that the AP side is the one you’re referring to, then yes, you’ll want to try to get the power level down. As a temporary solution, you could turn the antenna 180 degrees to face exactly away and use the back of the antenna. That will reduce your antenna gain by the front to back ratio of the antenna.

For the record, can someone back me up on this assumption: We probably don’t care how hot the signal is at the SM at all. The SM won’t be trying to listen to any other APs, so desensing is not an issue from the SM perspective.

rjk,

You have to much gain on the antenna for the 0.54 Mile SM.
7 dbd is ~9dbi.
What I would recommend is to get another low gain antenna. Something like 0dbd or just a dipole antenna.

I wrote once about this, how to make a dipole antenna for 900MHz.
This is What I would do.
Cut a peace of LMR-400 or any cable that you use, 7 inches long.
Leave 3.1 Inches of the center cable, with out the shield.
Put the N Female connector on the other end of the cable.

This will be your low gain antenna.

Cover it with 3M tape,

It would be nice to show you a picture of what the cable ( Antenna ) looks like.

This way you don’t have to change the power level of the AP and have your 7 Miles link also working.

The power level at the SM is not relevant. We are only concerned with the power level of the SM’s (received power) at the AP in the sessions page.

Ignore the level at the SM session page unless it gets above about -35dB, or below your minimum acceptable level.