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Re: [Paparazzi-devel] Maxstream 9Xtend problems

From: address@hidden
Subject: Re: [Paparazzi-devel] Maxstream 9Xtend problems
Date: Mon, 18 Feb 2008 05:49:49 GMT


The IR sensors are extremely sensitive to RFI - I have found no solution but have had some success with shielding the entire sensor with copper tape and using pass-thru RFI filters on all leads.  Note that the thermopile cases are 1.7V, not ground as you may expect, so this makes shielding tricky.  Another thing that helps greatly is to wrap the wires several times through ferrite rings.  Also, the quality of the antenna plays a major role - I found that bad antennas caused more interference along with inferior modem range.  Lastly, even the ground modem will interfere with the sensors if it is at 500mW or higher.

Note that the interference usually results in a static offset in the reading, not just noise.  You should check by connecting the Tiny directly to the PC without any modems running to see the difference.  You can also configure the airborne modem to "loopback" by connecting TX to RX.  Then just send data thru the ground modem and the airborne will send it back.  This way you can watch the IR data (thru a direct serial cable) and then simulate modem activity on demand.  You can use the Maxstream software to send data to the loopback modem and this will also allow you to test modem range and diagnose your lockup problem.


-- Uttam Chandrashekhar <address@hidden> wrote:

Hi guys,

We are having problems with the 9Xtend OEM modules. I have it programmed to 100mw RF power. Here's the problem. There seems to be 3 different problems.

1) The 9Xtend seems to be interfering with the IR sensor readings, at 100mw power, there are jumps from 0, to -7. The problem is that the MAV is small, so I can't have the module far away from the board, it's about 2" from the rest of the setup now. The antenna is a PCB triband antenna:

The antenna has been mounted at the bottom of the MAV, with the PCB traces facing out downwards, longitudinally aligned with the plane. The 9Xtend is inside the MAV, mounted flat, at the bottom. It is not affecting GPS signals, and I get a latch under a minute, with strong signals.

2) There is some interference on the 72mhz too. I use the Berg4, and I get some very rare glitch hits on the RX ( The led counts glitches on the Berg ). Outdoors, with TX antenna collapsed, I get about 30' range.

3) One of our cell phone providers operate on the 900mhz band, and they have an antenna just about 150' from my house. I get occasional "Latch up's", where control is absolutely dead. Then it starts working by itself, all of a sudden. Sometimes it just works properly. So there seems to be some external interference too?

To verify 1, I programmed the OEM modules RF power to 10mw, and the IR readings are now rock steady. The 900mhz is also working now, but prior to changing the TX power level, we took the setup outside, and when I powered up, the GCS was receiving data, but the plane controls were locked up, but it detected the change from Manual to Auto1. The GCS and RM were inside the house, and we were outside, probably about 20' away. Then all of a sudden, controls came back and it started working.

What do I do? Do I try the Radiotronix modems that operate on 868mhz? I received 4 of the modules a few days back, and the 868mhz PCB antenna is expected tomorrow.

Is there a better way to mount the Maxstream 9Xtend, to avoid the RF problem?

All wires and cables are twisted. The IR leads are a bit long (6") to facilitate easy mounting, but its a twisted cable.


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