There are pseudo square waves on ethernet. Those have an infinite number of
harmonics.
----- Original Message -----
From: Brian Rohrbacher
To: WISPA General List
Sent: Wednesday, January 07, 2009 10:11 PM
Subject: Re: [WISPA] FM radio station site strangeness
I installed a cat5 cable next to a guys police scanner one time and as soon
as I plugged the cable (lan cable from poe to computer) in the police scanner
stayed "keyed up" on 15o or 155 mhz as I remember. Unplugged the cable and the
scanner started scanning again, so I always thought it was 150 some mhz.
Brian
Marlon K. Schafer wrote:
So far all I can find on the internet is that ethernet is at either 12.5 or
31.25mhz. NOT 350, that's gigE, not 10/100.
Also, this tower is a 100' wooden pole. Can't move anywhere really.
marlon
----- Original Message -----
From: "Adam Goodman" <a...@wispring.com>
To: "WISPA General List" <wireless@wispa.org>
Sent: Wednesday, January 07, 2009 9:15 AM
Subject: Re: [WISPA] FM radio station site strangeness
It also sounds like there is a new leak in the waveguide. One more
thing you might try is to move the cable from leg to leg on the tower
so that you variable length sections that do not resonate at 350MHz or
~100MHz (FM transminssion).
On Wed, Jan 7, 2009 at 11:16 AM, Adam Goodman <a...@wispring.com> wrote:
We also colocate with an FM transmitter. Only 1300W though. we also
had interference on our Ethernet lines. We solved it by moving radios
away from the FM antenna (3 feet or so on a 90' tower) We also
installed ferrits which helped (I actually used a conduit pipe).
Grounding the cat5 helped too.
I would think that if you find that you need more shielding. put all
your cat5 cables in a conduit and install abreakout box at the top of
the tower. If your area is prone to electrical storms (where isn't
these days?!) you will at some point be very sorry you didn't grount
(and well!!)
On Wed, Jan 7, 2009 at 10:47 AM, Marlon K. Schafer <o...@odessaoffice.com>
wrote:
Hi All,
I think we finally have this all figured out. Now I just have to figure
out
how to fix it.
We've been up there for over 6 years now. It's certainly been a
problematic
site though. Constant channel changes (we have 3 competitors a mile
away
and pick up hundreds of ap's from in town) are the norm.
This fall (a month or two ago) one of the tenants left the building.
This
cleared out most of the hardware that was in there. A little bit before
that I replaced an Inscape Data and a smartBridges combo with a single
MT
access point, using one of the cables that had been working for one of
the
other two.
About a week ago things started to really act up. Multiple devices were
having trouble. I was able to catch it in the act finally. This time
the
problem wasn't a wireless issue, the devices were constantly
disconnecting
and reconnecting at the switch level.
I pulled the Cisco switch out and dropped in a Netgear unit. That
didn't
fix it. Next I put in a Digital Loggers rack mount reboot device. That
wouldn't connect right either.
I finally had to pull all of the hardware off of the shelf and set most
of
it on the floor (or just let it hang there) to get it working at all
well.
Still not perfect but better.
I had by now hiked up there through sometimes knee deep snow 3 or 4
times.
Next I took a motorbike with studded snow tires up and got permission to
turn down the power to the radio station. That didn't fix the problem
either.
Next I borrowed a snowmobile and hauled some help and my spectrum
analyzer
up. I was unable to see any signals that didn't belong.
Next day, another hike up the hill.
OK, maybe a cat 5 cable went bad and I'm getting backfeed through the
switch. DC current or something. So I started testing the cables that
run
to the most problematic units. Well now, look at that. Bad cable. In
fact
there are three of them. Hmmm, kinda strange though. All three have
the
exact same fault! Oh well, better change them out anyway. I ran three
new
cable runs and just for kicks I tested one of them. What the heck?????
The
new cable has the EXACT same fault as the old one! Even though it
didn't
follow the exact same path as the old cables.
Man, this is sure looking like a problem caused by the radio station. I
was
using indoor cat5 and didn't run lightning protection or ground
anything.
Yeah I know, but remember that this has been there for a very long time
like
this. And as a guy with an electrical background I know that there are
actually two ways to deal with stray electrical. Grounding is one.
Insulating is another!!!! Anyway, I know it wasn't built to specs.
I added some grounding and that didn't help at all.
Yesterday I finally had one of the local wireless companies (Day
Wireless)
that mainly does VHF radios, backhaul etc. They also checked things
with
the spectrum analyzer but couldn't find anything amiss. I was able to
duplicate the wiring fault for them (with my Ideal tester). But
suddenly
everything cleared right up! Stuff was looking good, no cable fault
etc.
Pings were looking good, devices were finally negotiating the
connections
right etc.
I called the radio station to ask if I could try turning the power down
again to see if we see any change on the spectrum analyzer. They said
they
thought that I'd already done that because the showed the power was way
down. Turns out someone in the building had bumped a breaker and shut
down
part of the transmitter! Well, we got all of that figured out and guess
what. All of the problems came right back! I then turned the power
back
down and they cleared up.
Tip for you guys, dropping an 18,000 watt system down by even 60% of
it's
normal output isn't always enough. We had to drop down to 10 to 20% to
get
the problems to clear up. The guys from Day Wireless had some small
ferrite
beads with them so we stuck them onto the cables. Put the beads on and
the
radios would negotiate at 100full. Take them off and they'd drop right
back
to 100 half. Duplicatable all day long.
Soooo, current theory is that the radio station is screwing up my cat5
connections. The fact that the building has less hardware in it and we
have
more snow up there than normal has probably caused some different eddy
currents or multipath. Or some other such strangeness.
I have some shielded cable and connectors on the way. I have permission
to
move my gear from one side of the building to the other side. I've got
more
high end ferrite beads on the way (one that is made for cat 5 and is big
enough for three wraps to go through it). Not the little $.50 ones,
these
are nearly $6.00 each.
I also have a Fluke DTX on the way.
http://www.flukenetworks.com/fnet/en-us/products/DTX+CableAnalyzer+Series/
They rent for $650 per month from http://www.trs-rentelco.com/ List is
over
$7000. If I like it I'll probably get one and add it to my two spectrum
analyzers and my bucket truck. grin
Never ever forget that wireless is 50% science and 62% black magic!
I am quite hopeful that the new cable, beads on bother ends of the cat5,
better grounding, and an equipment move will fix this site up nicely.
If
not, who wants to buy it? lol Seriously, this site and one of the ones
that it feeds cause nearly 80% of my trouble calls. With any luck it
wasn't
wireless trouble that I've been having all along. Shrug.
Here's the really strange part to all of this. The hardware that cost
the
most has the most trouble! grrrr
Also, the Day Wireless guy had some kind of wide band sensor. He could
move
it around and see where overall signal levels were unsafe for people.
Right
beside a 4" or so copper pipe that the radio station used as a wave
guide
was pretty bad. A couple of inches from it was ok. The next highest
readings at the whole site? RIGHT a the BASE of the 100' wooden pole
that
everything is mounted on! And what did I do when I installed all this
new
gear a year ago? Yeah, I put the antennas up top and the radios right
down
at the base of the tower so I could get to them without having to rent a
lift. Dang the luck!
Hope that this helps someone else out.
marlon
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