Placing two SM900's next to each other? Can it be done?


We are running SM900’s for customer connections. There is a location in which the only way to connect two customers is to place an SM for each of them on the same pole.

My fear is that they will effect each other being so close. Can this be done? If so, how close can the SM’s be from one another?

Thanks in advance.

When we have this situation, we use a single radio and a hub/switch. Each customer gets a router which we supply so we can lock it down.

Cheaper than another SM and will not cause inter-SM interference which may or may not be an issue.

The only real issue is that each customer gets the same BW regardless of the plan they are on unless you do something like use a Linksys WRTGL54 that can run Linux and use one of the 3rd party firmware sets that provide BW limiting/shaping.

We just explain to the customer that the radio can supply far more BW than they are paying for so sharing is not an issue.

as far as the router being cheaper hes 100% correct. I had a few nieghbors that hated eachother and refused to use that solution so i ended up mounting 3 5.2 ghz SM’s right next to eachother…no problems so far

I understand what you mean. I was trying to avoid this situation for that reason, shared bandwidth. I will keep this in mind as a last resort. Thanks,

vince wrote:
as far as the router being cheaper hes 100% correct. I had a few nieghbors that hated eachother and refused to use that solution so i ended up mounting 3 5.2 ghz SM's right next to problems so far

Cool. I think I may do a test to see if its possible.

I dont see an issue. They will both rx at the same time. shouldn’t be a problem their. As far as the transmit cycle when they tell the AP they need to send data, if one needs to send and the other does not the AP will be in RX mode while the one is Transmitting. The other one has nothing to recieve because the AP is in Rx mode so their is nothing to interfere with. Don’t see a problem here either. When both are transmitting and the AP is receiving I guess if the SM’s were transmitting at diffarent power levels the weaker signal could get over powered. Just make sure they transmit at the same power level.

Hay but we all know what A.S.S.U.M.E stands for.

You can put SMs that are registering to the same AP right next to each other.

During the SM-receive portion of each frame they are both listening intently. During most of the SM-transmit portion of each frame they only talk when told to by the AP. Only during the “bandwidth request” contention slots of the SM-transmit frame will they possibly step on each other, same as could happen if they were spread out in the sector.

While the SM only transmits data when scheduled by the AP, all SM’s are transmitting RF carrier all the time. This is why SM RF level balancing is so important.

So, if two SM’s are very close to each other, the bleed over between SM’s may cause issues as the beam width of a 900 at 12dB is > 60deg wide with very large side and rear lobes.

SM’s at higher frequencies with reflectors will be able to operate closer to each other as the beam width is much narrower with very small side and rear lobes. We have put two 5.7’s on the same pole and it worked fine.

If you have issues with the radios, just explain that the system does not support multiple SM’s within 100 yards and if they want service they either need to get the SM’s >100 yards apart.

If they use the same SM, they will each need a router and they will need to share the radio. You can provide router that will use 3rd party firmware to allow BW management per router.

I think i need to upgrade all equipment. I want to try 7.3.6 before going to 8+. ANyone know if i can downgrade back to 7.2.9 with the new CNUT tool?

you can downgrade if needed, but you won’t want to.

We have been running 7.3.6 for the last 8 months with a significant improvement over 7.2.9. We have been running it on all AP’s and BH’s.

Just switched by BH’s to SW and changed to 50% downlink and have had a substantial improvement in throughput and latency.

I am hoping this will be true for the shots in question. Especially since my AP on that sector is running 6.1 (i dont know why). So maybe the radio running 7.2.9 communicates better than the 7.3.6 with this AP for that reason. Hopefully the AP upgrade will show improvements. Like I mentioned before:

Ap =6.1

Jitter= 3,4,5
Link test=95 to 100%

SM’s side by side:

Link test=60%

Thanks for the help.

gviator, tell us how it goes. In general a sector is happiest if all radios are on the same release, due to various changes from release to release.

Well, last night I upgraded the 7.2.9 Radio to 7.3.6. It’s link didnt really change. RSSI=1450 to 1500 and Jitter 3,4,5. I am in the process of upgrading the whole sector to 7.3.6. The problem with this particular shot may be due to an ubstruction for the second radio in its line of sight. I wont know until I’m done upgrading and can try again. Thanks guys.