[lug] Wireless router question (OT)

[Stephen Queen]

>
> These guys deal with twisting cables all the time... www.eoss.org.
> Might look at some of their photos of cable assemblies for ideas.  Some
> of their payloads also get to spinning on the way up and induce
> centrifugal force at the end of the payload string -- meaning that their
> interconnecting cables/wires must be able to withstand quite a bit of
> torture.  Especially on the way down in free-fall after the balloon bursts.

I found this site very interesting. I haven't completely
explored it, but the cables I did find pictures of resemble
our early cables. We did get the cables to the point we were
doing production work, but are operators were still pointing
out that the system was still having loss time do to cable
failure.

> Yeah, but it's not working.  ;-)  (Always the pragmatist in the crowd...)

No where in my post did I say the system didn't work. Have
you ever had a cell phone drop out on you? Did you at that
time say to your self, "cell phones don't work, I'm going
back to only using  wired phones?"

I was replying to a post that had asked " given that all the
consumer 802.11b gear is either so-so or total garbage, are
there pro-quality brands that sell consistently good gear?
If so, how much is the price difference?  Do any of you have
experience with 802.11 gear that doesn't suck?" I was just
stating my experience.
  >
> Seriously, 30m is child's play for 802.11b.  You have some other source
> of interference or you've completely goofed up RF connectors or
> something.  I could do the math, but at 100mW, 30M away even with a
> zero-gain antenna system you should have rediculous amounts of S/N
> margin.  Probably in the range of 60dB or better.
>
> Are the AP's below the helicopter talking just to the AP in the
> helicopter?  If so, small panel (flat) antennas laid horizontally on top
> of your payload (if it's big enough - I haven't seen your payload
> strings) would direct the vast majority of the RF signal in an upward
> direction and also hear better because they wouldn't "see" 802.11b
> stations on the ground nearby.
>
> Are you flying in densely populated city areas or close enough to be
> line of sight to one?  If so - your problem is probably on-channel
> interference from existing AP's.
The Lincsys systems were determined to be suceptable to
multipath interference.

It is illegal for a helicopter to fly over populated
structures with a load on the hook. So we rarely if ever fly
in densely populated areas. We have done experiments at
airports from time to time, but not during the relevant
tests.

> You could probably easily find a young RF engineer with access to a
> spectrum analyzer and a kludged together 2.4 GHz antenna that'd be more
> than happy to go for a helicopter ride, if you want to be scientific
> about it and really get REAL data as to why your AP's aren't working.

Again the AP's are working. When they do drop out, it is
fairly easy to determine the problem. Since it has only
happened during landing, there was no data loss.

> >As far as the economics, the AP's are negligible compared to
> >the cost of helicopter time.
> >
> >
> No kidding!  You might want to "fly" the system from a tall building or
> balloon system a couple of times before the next expensive helicopter
> flight to work the bugs out of it.

Usually, when we do a test flight, we have enough
experiments to perform that it justifies the use of a
helicopter. As stated in my original post, we never bothered
to fly the Linksys AP's. They were made for SOHO use, and
were not up to the task in the enviroment we wanted to use
them in.  Actually, we only purchased them for proof of
concept. I would not want to haul 600 lbs of equipment up to
the top of a building, just to test a radio. A ballon or
building would probably not duplicate the operating
conditions well enough to make the experiments conclusive. I
maybe wrong, but I don't believe a ballon developes the
static charge a helicopter does. ( As a side note, in the
beginning this static charge was a great safety hazard. The
pilot would see some one on the ground reach up and try to
stabilize the payload as he was landing. The static shock
would knock the ground crewman down, causing the pilot to
laugh so hard, that he would barely be able to controll the
aircraft.)


> Oh yeah... one other (duh) thought... if the antenna for the AP on board
> the Llama is inside, just get some quality connectors and coax (cheap
> crap doesn't work at 2.4 GHz when you're doing REAL work with it... look
> at the loss numbers for whatever you use and build accordingly... coax
> in general is bad at GHz frequencies, but hardline is a pain to use in
> mobile applications)... and dangle the antenna out the door so it can
> "see" the payload string.

I will address this by saying we are professionals.

>Something omnidirectional or as close to it
> as you can get would be good so it can "see" no matter what direction
> the wind dangles and twists it.  That or temporarily mount a small yagi
> pointing down at the payload string - but at these close ranges, that
> seems to be HUGE overkill.

The FAA and usually the pilot frown on having something
"dangle" from the helicopter other than from the hook. If it
is attached to the airframe, it must be FAA certified ( most
foriegn countries recognize FAA certification). Each
installation is different, but we usually attach the
antenna on the outside of the helicopter.
> I think you're getting hammered by other signals in the 2.4 GHz range.
> Cordless phones, 802.11b, everyone and their grandmother is there now.
> You might have more luck with 802.11a cards at 5.8 GHz...?

 This usually is not a problem. We fly in remote areas.

If you want to know more about our system, you can down load
a technical paper on it from
http://abstracts.seg.org/ease/techprog/index.jsp?selection=Wednesday&Session=Morning&Sessionselection=MIN+3
Then click on the 9:45 am session _NEWTEM-adventures in thin
air_, and it will open a pdf ( or download it if you like )
where you can see a picture of the system and some of the
processed data.

Steve