Re: [Paparazzi-devel] Long Range Flying Wing

[Reto Büttner]

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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