Back when Cellphones were the size of a refrigerator .. they would bleed into 902-914Mhz part of ISM band. Any scanner or SA with demod would pick up conversations.. it became a past time listening to calls on the road while traveling the roads of America. It did cause issues with WaveLAN links if tower close to our antennas. In a galaxy far far away... On Dec 18, 2015 11:21 AM, "Ken Hohhof" <[email protected]> wrote:
> At this tower with FSK, we knew there was another WISP (let's call them > ABC) with an AP 9 miles away LOS on 915 MHz. And we always got the best > results if we also went on 915 MHz and matched their timing parameters, > rather than trying to avoid them. > > After experimenting with the 450i equipment, I am convinced that another > WISP (let's call them XYZ) is operating 900 FSK APs in our area with AP > Eval Data turned off. I know we have a competitor who thinks it's cute to > do that. I think that's a douchebag thing to do. > > Anyway, I'm also convinced that while ABC and us have our APs pointed at > each other, we may be seeing XYZ's SMs as much as their APs. Coexistence > in 900 MHz is tough because free space loss is low so LOS signal carries a > long distance, plus NLOS signal gets through trees and even scatters off > them, plus even the highest gain antennas don't have narrow beams. You > can't count on SMs using narrow beam antennas pointed only at their own > tower. > > So while smartgrid and RTK are certainly contributors to the noise level, > I think we have XYZ using the bottom and top of the band but in stealth > mode. Probably they see ABC on 915 and avoid them. So we are able to > coordinate timing parameters with ABC and coexist in the traditional manner > on the same channel. > > It is possible that we are seeing SMs on other ABC sectors pointed away > from us, but we are only 135 feet AGL, and I don't think their subs would > be high enough that we would see them 10 miles away, given earth curvature. > > So the next hurdle was setting the timing parameters on the 450i to match > ABC's PMP100. For some reason there are checkboxes for what firmware > revision the PMP100 is running, and whether it uses timing port or power > port sync. We did not previously have to know this much detail, I wonder > why. Anyway, I finally hit on a combination that worked: 5 ms frame, > numbers from the Cambium compatibility tool, and Legacy Framing Mode off. > At this point, I was able to get the SMs to register at 915 MHz and run > MIMO-B in a 7 MHz channel. Actually, I started by putting the FSK timing > parameters into the compatibility tool (75%, 10 miles, 3 slots) and it said > OK without any futzing around. > > Some other observations: > > 1) You can power the AP with power port sync off a CTM-2 in 56V OFDM mode > using an adapter cable with pins 5 and 7 swapped, as described in the > manual for a CMM4. I assume the same is true for a 430 SyncInjector. > > 2) According to the CTM-2, the AP is drawing 10 watts (we are not using > the AUX port to power anything), so don't get scared by the 30 watt number. > > 3) The AP and SM are capable of up to 25 dBm xmt power, but with 12 and > 13 dBi antennas it will be slightly less due to regulatory limits. Check > the AP config to make sure it is set to the max you are allowed, I think > mine started out set to 22 dBm. Many WISPs no doubt are using ~17 dBi > yagis or grids without turning down the EIRP to 36 dBm, if so, a legal 450i > system will be at a disadvantage by comparison although antenna gain > doesn't always help through foliage. > > 4) If you leave all the channels and widths enabled, expect it to take > forever for an SM to register. You need to uncheck some of the boxes. > > 5) If you do an SA when you first install the AP and see -35 at 900 MHz, > it may be your tower guy's cellphone. > > 6) The AP has no internal GPS. > > 7) 16 inch coax jumpers will be a little tight, 18 inches or longer will > be better (assuming LMR240). > > 8) The AP comes with one gland which looks like the LPU grounding gland > but it has a rubber insert which is already slit and you can get a > pre-terminated cable through it. It doesn't come with a second gland for > the AUX port. > > 9) The sector requires lots of different wrench sizes, I think the list > is 10, 12 and 14 mm. > > 10) Cambium has made installing the CPE equipment a piece of cake. > Basically take the pre-assembled antenna out of the box, snap on the SM, > attach the SMA connectors and slide the boots down, the only assembly is > the U-bolts. It's very nice. > >
