The tower guys cell phone?
Ken Hohhof 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.
