[Canberrauav] antenna tracker
Chris Gough christopher.d.gough at gmail.com 
Mon Apr 11 14:00:44 EST 2011 

Hi Guys,

I have decided to make a tracking antennas, is anyone else working on this?.

For the OBC, I expect a tracking cluster of antennas on a mast will be
the go, driven by something like chunky Dynamixel servos.

What I'm going to make first is very different. Small, portable, quick
to set up, using standard hobby servos connected to a laptop (via a
Polu USB->PWM board). One candidate is a 2.4 GHz patch antenna because
I have a couple in my shed (circular polarised, from memory <10cm
square). Or it will be a 915-930 MHz waveguide (with shelf for an
XBee) because I think that would usefully improve security, especially
with a mesh topology.

I'm doing this because I have a couple of ideas that I want to try out
in software, but I also want to start collecting practical experience
with tracking antennas. The reason the analog video reciever is a
candidate is because it seems simple enough compare two RSSI voltages
to quantify the relative performance of two antenna/reciever
combinations (and I think the video recievers have a RSSI pin). I
asusme there are ways to do this with XBees too but don't know how to
log signal strength, dropped packets, etc. Any hints? (is there
something like NetStumbler for XBee?).

WiFi would be good for this stuff but to begin with I want a rig that
doesn't need a computer in the plane for testing/development
(obviously this will become less of an issue as we progress).

Chris Gough

[Canberrauav] antenna tracker
tridge at samba.org tridge at samba.org 
Tue Apr 12 10:02:34 EST 2011 

 > I have decided to make a tracking antennas, is anyone else working on this?.

not as far as I know.

 > I asusme there are ways to do this with XBees too but don't know
 > how to log signal strength, dropped packets, etc. Any hints? (is
 > there something like NetStumbler for XBee?).

I'd be inclined to do it with the Xbees we're currently using to talk
to the planes. It seems that Xbees have a RSSI pin encoded as PWM:

  http://log.liminastudio.com/itp/physical-computing/measuring-xbee-signal-strength-from-the-rssi-pin

I wonder if we can just connect that pin to one of the spare servo
input pins on the APM in the plane, and measure signal strength that
way? We could then send that data as a mavlink packet down to the
ground station.

Similarly, on the ground, we could use an arduino to measure the
ground stations signal strength.

Cheers, Tridge

[Canberrauav] antenna tracker
Chris Gough christopher.d.gough at gmail.com 
Tue Apr 12 11:50:31 EST 2011 

Hi Tridge,

>  http://log.liminastudio.com/itp/physical-computing/measuring-xbee-signal-strength-from-the-rssi-pin

Bingo, thank you. Xbee it is then.

> I wonder if we can just connect that pin to one of the spare servo
> input pins on the APM in the plane, and measure signal strength that
> way? We could then send that data as a mavlink packet down to the
> ground station.

nice idea, don't see why it wouldn't work.

> Similarly, on the ground, we could use an arduino to measure the
> ground stations signal strength.

I have a laptop/polu board to hand (and working software, no RSSI) so
will start there. However, if there's going to be another micro in the
mix it might as well replace the polu board, especially if future
versions involve giant non-PWM servos.

Maybe it could eventually even replace the laptop too? it could run
the tracking code and pipe serial from the xbee to a socket using an
ethernet shield. I'll worry about that later.

Chris Gough
-- 
.

[Canberrauav] antenna tracker
Jack Pittar jpittar at bigpond.net.au 
Wed Apr 13 00:46:51 EST 2011 

I can help with a heavy duty servo, other servos, or a gearmotors and drive
electronics.
Jack.

-----Original Message-----
From: canberrauav-bounces at canberrauav.com
[mailto:canberrauav-bounces at canberrauav.com]On Behalf Of Chris Gough
Sent: Tuesday, 12 April 2011 11:51 AM
To: tridge at samba.org
Cc: canberrauav at canberrauav.com
Subject: Re: [Canberrauav] antenna tracker


Hi Tridge,

>
 http://log.liminastudio.com/itp/physical-computing/measuring-xbee-signal-st
rength-from-the-rssi-pin

Bingo, thank you. Xbee it is then.

> I wonder if we can just connect that pin to one of the spare servo
> input pins on the APM in the plane, and measure signal strength that
> way? We could then send that data as a mavlink packet down to the
> ground station.

nice idea, don't see why it wouldn't work.

> Similarly, on the ground, we could use an arduino to measure the
> ground stations signal strength.

I have a laptop/polu board to hand (and working software, no RSSI) so
will start there. However, if there's going to be another micro in the
mix it might as well replace the polu board, especially if future
versions involve giant non-PWM servos.

Maybe it could eventually even replace the laptop too? it could run
the tracking code and pipe serial from the xbee to a socket using an
ethernet shield. I'll worry about that later.

Chris Gough
--
.

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