[Paparazzi-devel] radio interference (was: downlink only)

[Martin P]

Hello Joe!
 
Thank you for your long answer.
 
The cable I am talking about is the 3-wire cable with the PPM signal from the 
receiver to the autopilot and 5V supply from the autopilot to the receiver.
The receiver is a Yeti Rex, 35MHz, see 
http://paparazzi.enac.fr/wiki/Other_Hardware#JETI_REX_5_plus_.28no_MPD.29_receiver
The onboard modem is a 2G4 / 1mW Zigbee with a Nintendo WLAN antenna.
The autopilot is a Tiny.
You can see the setup here
http://picasaweb.google.com/lh/photo/wDgwmBGefqntD2ac6ElqQA?feat=directlink 
http://picasaweb.google.com/lh/photo/OWSuzgAoyvPwSZ5bp6QvNg?feat=directlink
The 35MHz antenna is taped to the left wing (not seen in the picture).  
 
Initially, I twisted the +5V, ground and PPM wires. For a picture, see 
http://picasaweb.google.com/lh/photo/8m9HAOhXbbx1MPgfyTj5oQ?feat=directlink
 
I noticed radio interference when I did a range check on the field (retracted 
antenna, 45m). I was able to control the servo (at this time, only one servo 
was connected). OK, but I had spontanous servo movements too, even when I was 
only 5m away.
 
Removed the modem, no change.
 
Next I strung the twisted PPM cable (including 5V supply) through a ferrite 
core. This defineitely improved the situation.
 
Next I soldered capacitors to the 5V/gnd on the receiver (in case the 
interference would be caused by the switching power supply). No improvement, 
removed the capacitors.
 
Next was the shielding of the PPM signal. The shield is connected to ground on 
the autopilot side only. The improvement was convincing, as I had found a spot 
in the apartment where the servos moved wildly, and with the shielding it was 
gone completely. Back on the field, I had the random servo movements again 
(transmitter antenna retracted) and I were still able to control the servos 
from across the field (40m).
 
Put in the ferrite core again. Seemed to help a little.
 
So what the hell, up in the air. It's an old, small, slow foamie (Multiplex 
Minimag) and there was nobody around to get in danger, except myself. You know 
that I know that I shouldn't do that. It was windy, too. I was so eager to see 
it fly.
 
For the next steps:
A shielded lead from the fuselage to the actual antenna seems easy to do. 
However, in the foamie, I am not really convinced that it will help. But I'll 
try.
 
Ultrasonic height measurement is something I would like to do too, but in 
future. Your report of a 4m plane automatically taking off and landing is very 
impressive!
 
Thanks and Greetings, Martin
 
 

-------- Original-Nachricht --------
> Datum: Tue, 28 Jul 2009 08:24:51 +0200
> Von: "gisela.noci" <address@hidden>
> An: address@hidden
> Betreff: RE: [Paparazzi-devel] downlink only

> Hi there
>
> First time I am using this forum to comment on peoples comments, so hope I
> get it right.
>
> Cannot really comment on the main content of your problem Martin, but the
> last para bothers me. How did you 'shield' the 'receiver cable'? Which
> cable
> did you shield? Not the antenna cable , I trust. Or do you have an antenna
> (whip or trailing wire) external to the fuselage, and the use a piece of
> coax cable from the RX to the antenna? Are you using 2.4Ghz radio
> equipment
> ( for the radio control system, Spektrum or such like)or is it the 35MHz
> or
> similar stuff. If you are using Spektrum, what other equipment do you have
> on the aircraft, datalink, Video transmitters, etc, and are they in the
> 2.4GHz band as well? This is fraught with problems if so, since the very
> close proximity of these elements WILL cause desensing of the Radio
> control
> RX. There is nothing you can do about that; They ALL share the same 2.4GHz
> to 2.5GHz band. If the RX is in the 35MHz (or 70Mhz, etc) band, it would
> be
> better were is not for the fact the typical RX input selectivity is not
> really that good, and the receiver is also desensed. I have had bad
> experiences with JR 9 channel RX and the 9-Xtreme (900Mhz spread spectrum)
> datalinks. The very broad band signal from the datalink severely
> desensitized the RX, and range was reduced to less than 150meters!
> However,
> removing the RX crappy wire antenna, and and connecting a thin (2mm
> diameter) coax cable internally (shield to RX ground) and then routing the
> Coax to an exit point in the fuselage and then connecting the original
> antenna wire to the exiting coax center wire helped a lot. I easily get
> 600meter range now. 
>
> THE FIRST RULE IS : whatever you are testing, be SURE that you have a safe
> and tested means of taking control of the aircraft. Sure, a component
> failure can still foil you, but I cannot condone taking of, intentionally
> or
> otherwise(!), with your backup system ( manual RCS system) non-functional.
> FIRST fix that!
>
> I design Spread Spectrum systems, RF datalinks, Video link, etc, as well
> as
> antenna systems of all types, for the aviation industry, both military and
> commercial, so if there is any way I can help or advise, I will try. I am
> flying Paparazzi for about 7 months now, but have designed my own ground
> control station, and have extensively changed the autopilot - I fly V
> tails,
> with ONLY rudder/elevator, ie, no ailerons, as well as a 4 meter wingspan
> homebuilt A/C, fitted with ultrasonic height detection. This A/C does
> auto-takeoff and auto-land (beautifully!). But I cannot help with any of
> the
> issues related to the A/C  / GCS communication and control, since I have
> done my own....Found the Paparazzi GCS very emcopassing and complete, but
> far to complex, and impossible to certify , even in part, for use in
> restricted civil airspace.
>
> HAVE FUN, be safe...
>
> Joe
>
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden
> ] On Behalf Of Martin P
> Sent: Monday, July 27, 2009 10:46 PM
> To: address@hidden
> Subject: Re: [Paparazzi-devel] downlink only
>
> Hi,
>
> I do not intend to do any settings via the transmitter.
>
> However, I do not seem to have 2-way-communication via the modems.
> Although
> I saw something with the scope, I am not able to use neither the settings
> tab in the ground station nor the settings dialog from the tools menu. The
> latter shows an empty window.
>
>
> On the field I used a modified flight plan which does not stop at the
> holding point. First of all, uplink seems not to work an secondly, most of
> the time I am alone on the field.
>
> Usually, when ground testing, the throttle reacted to the stick in AUTO1.
> Yesterday I switched to AUTO1 and the plane throtteled up and took off
> before I expected (I use a landing gear). Switched to MANUAL and climbed,
> then back to AUTO1. No throttle. Probably this is because I put the
> vmode="throttle" in the takeoff block to get executed anyway.
>
> I havent't seen any vmode statements other than specifying "throttle".
> What
> are the valid values for vmode?
> Could I automaitcally set the vmode to pitch in AUTO1?
>
> Managed to land manually, in spite severe radio interference. Radio
> interference in spite having changed the receiver cable to a shielded
> wire.
>
> So, I am still struggling and learning. Every help is greatly welcome.
>
> Greetings, Martin
>
> -------- Original-Nachricht --------
> > Datum: Fri, 24 Jul 2009 19:00:32 +0200
> > Von: Pascal Brisset <address@hidden>
> > An: address@hidden
> > Betreff: Re: [Paparazzi-devel] downlink only
>
> > Hi,
> >
> > Martin P wrote:
> > > I was wrong, I do have 2-way communication. Looked at pins 2 and 3
> with
> > the scope. (Could have done that earlier)
> > >
> > > Then I do not know why I was stuck in holding point block (before I
> > commented it out).
> > >
> > > With or without 2-way-communication, I am still interested in flying
> > without GCS interaction. Which means that, for the time being, I can
> only
> > follow a pre-determined track and then (attempt to) land.
> > >  
> >  The code to do a setting from RC channel is still there:
> >
> >
> http://paparazzi.enac.fr/wiki/Telemetry#R.2FC_Transmitter_Data_Uplink_.28Obs
> olete.29
> >
> >  But.
> >  It has not been tested for months (years ?).
> >  We will remove it asap
> >
> > --Pascal
> >
> >
> >
> > > Greetz, Martin
> > > -------- Original-Nachricht --------
> > >  
> > >> Datum: Mon, 20 Jul 2009 23:11:58 +0200
> > >> Von: "Martin P" <address@hidden>
> > >> An: address@hidden
> > >> Betreff: [Paparazzi-devel] downlink only
> > >>    
> > >
> > >  
> > >> Hello,
> > >>
> > >> it seems that I have a common problem: GCS doesn't send to the plane.
> > >> Removing the datalink section didn't help.
> > >>
> > >> Anyway, I am not so much interested in the uplink. When I am alone I
> > >> cannot watch the plane and the computer screen at the same time. I
> know
> > that
> > >> Pascal Brisset strongly advises against removing the holding point
> > block from
> > >> the flight plan, but I might do just that.
> > >>
> > >> My starting procedure would be like this:
> > >> Switch on the transmitter and switch to MANUAL, throttle off.
> > >> Power the plane.
> > >> Wait for GPS and do GeoInit.
> > >> Instantly go to Takeoff (a beep or LED signal would be nice).
> > >> As I am still in MANUAL, the propeller doesn't spin.
> > >>
> > >> I don't know how to go on from this point. When I switched to AUTO2
> > >> (without propeller, for safety) I expected the motor to start, but it
> > didn't.
> > >> Does the autopilot wait for a "launch" command which it doesn't get?
> > Does the
> > >> autopilot wait until I have stared manually?
> > >>
> > >> Can you take off from the lawn (with a landing gear) or do you need
> to
> > >> throw the plane?
> > >>
> > >> Greetings, Martin
> > >>