Re: [Paparazzi-devel] Long Range Flying Wing

[Eduardo lavratti]

Stephen, the xbee 900 not have the same parameter than xtend 900 so i cannot make the adjusts.

I only changed the RR =0 but the problem continue.

Today i will try with 19k2 bps

> Date: Sat, 7 Jul 2012 09:56:24 +0200
> From: address@hidden
> To: address@hidden
> Subject: Re: [Paparazzi-devel] Long Range Flying Wing
>
> Hi Stephen and Chris
>
> Thanks for your explanations and tips.
>
> Our power settings should be correct. We don't use a video link on our
> current airframe. Our next try will be:
>
> - Polling mode not acknowledged / no retries (RR = 0)
>
> If that doesn't help we might change the antenna configuration on the
> aircraft. Unfortunately on our small airframe with high aerodynamical
> goals we are a bit limited on different configurations.
>
> I will let you know our results.
>
> Regards, Reto
>
> 2012/7/6 Stephen Dwyer <address@hidden>:
> > Hello,
> >
> > Regarding range issues:
> >
> > First thing, is the power setting appropriate on both sides?
> >
> > As Chris mentioned, definitely possibilities of interference from
> > other equipment. This can be very hard to debug. As an example, in the
> > past we had horrible problems with GPS reception. After days of
> > changing things around, we used a spectrum analyzer to debug, which
> > really helped solve the problem. I realize it can be difficult to get
> > access to a spectrum analyzer (turned out to be the 500MHz SBC spewing
> > junk RFI at 1.5GHz ... a nice harmonic, some careful shielding solved
> > the problem).
> >
> > We had serious asymmetrical link issues for a while as well. After
> > some debugging, we discovered that the connector on one of the
> > antennas was in poor condition. Switching to a new antenna solved all
> > of our problems. However, this asymmetry also showed significantly
> > decreased range, even in the better telemetry direction. Again, Chris
> > mentioned this: antenna selection, antenna/cable setup and orientation
> > are rather important.
> >
> > Our modems also run warm, but I think this is to be expected with the
> > high power. We make sure to allow some air flow around the modems
> > (i.e. we don't wrap them in foam).
> >
> > A while ago I wrote a small module to measure the RSSI on the airborne
> > side to help debug range problems. It was quite a while back and I am
> > not sure if it is still alive (a quick compile on master failed). I
> > will try to fix it in the next couple days if I get a chance, and do
> > some proper documentation on the wiki for it. Unfortunately, it is
> > currently for LPC21xx only (we use it on a TWOG). Check
> > conf/modules/xtend_rssi.xml for more info.
> >
> > Hope that helps.
> >
> > Thanks,
> > -Stephen Dwyer
> >
> >
> >
> >
> > On Fri, Jul 6, 2012 at 11:09 AM, Chris <address@hidden> wrote:
> >> Well i have flown to a point where the ground station with its 8db patch
> >> could not receive well
> >> the planes data but i was still able to give a command to the plane and
> >> return it home which indicates
> >> good airborne reception.
> >> I use as stated the polling mode with no confirmation and retries are set to
> >> 0.
> >> I have set the addresses somewhere in the top range, FFF0-FFF1 i think and
> >> changed the channel
> >> to 9 (different hopping frequencies).
> >> One day i had a problem communicating with the plane (the downlink was fine)
> >> and it proved to be the video tx.
> >> Since then i have fitted filters to the video tx (high pass) and the modem
> >> (low pass)
> >> and all problems were solved.
> >> The antenna and the modem have to be in a straight line otherwise SWR will
> >> rise,
> >> RF will flow through the wires all over the airplane causing havoc and the
> >> antenna
> >> radiation pattern will be greatly distorted.
> >> The same goes for the video tx.
> >> Chris
> >>
> >>
> >> Hi Stephen
> >>
> >> We configured our 9XTends according to your recommendation
> >> (Acknowledged Polling Mode):
> >>
> >> http://paparazzi.enac.fr/wiki/Modems#Configuration
> >>
> >> As we are sending lots of telemetry and not using datalink joystick
> >> control we chose the air module as the base. It gets pretty warm in
> >> operation. In the workshop everything works fine.
> >>
> >> On the field we experience a very asymmetrical link: The telemetry
> >> data from the aircraft gets well to the ground station, also at range.
> >> But the commands from the ground station only get to the aircraft at
> >> very close range. At range we don't get any commands from the ground
> >> station to the aircraft anymore.
> >>
> >> Can you explain this behaviour? How do you achieve a symmetrical data link?
> >>
> >> We still have a 90 degree bend between the modem body and the antenna
> >> on the airplane. On the ground station we have them in a straight
> >> line. Could this explain the asymmetrical link?
> >>
> >> Regards, Reto
> >>
> >> 2
> >>
> >>
> >>
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> >>
> >
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