RF Links

Project to send a balloon into lower space with payload
Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

RF Links

Post by Rris » Fri 03 Dec 03 2010 12:16 am

Thread for discussing RF links.

For video, 2.4ghz 500mw or better. 8dBi circular polarised patch as base of payload pointing downwards.
On receiver side, yagi with LNA (or similar)

Data on 433mhz FHSS and 900mhz FHSS, both with dipoles on the payload, redundant yagi + receivers on the ground.

Everything must be redundant as much as possible.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Mon 06 Dec 06 2010 1:15 pm

Looks like Xbee Pro XSC wont do what we want - it's only rated to about 10km which is nowhere near enough.

XTend 900 mhz units from Maxstream will do, however they are $180 each! Aerocomm don't quite have the 40km range that the xtends do (32km) however are less than half the price.

http://search.digikey.com/scripts/DkSea ... 0-1000M-ND

http://lairdtech.thomasnet.com/item/910 ... c4790-1000?
These are also software selectable into Australian licensed frequencies which is quite nice.

Aerocomm are also the most sensitive on the receive side, with -110dbm vs -100dbm on the xbees.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Mon 06 Dec 06 2010 1:48 pm

i couldnt work out the difference between AC4790 and AC4790LR.

The LR is, as i suspected Long Range. Digikey's website specs are wrong, saying that both are -110dbm.

Range, Line of Site (based on 3dBi gain antenna)
AC4790-1x1: Up to 1 mile
AC4790-200: Up to 4 miles
AC4790LR-200: Up to 8 miles
AC4790-1000: Up to 20 miles
AC4790-1000: Up to 20 miles
AC4790LR-1000: Up to 40 miles

Sensitivity
-100dBm typical @ 76.8kbps RF Data Rate
-110dBm typical @ 76.8kbps RF Data Rate (AC4490LR-200/AC4490LR-1000)


Temperature (Operating) -40°C to 80°C
Temperature (Storage) -50°C to +85°C


additionally, the difference between 4490 and 4790.
AC4490 Series - Server/Client Protocol
AC4790 Series - Peer-to-Peer Protocol




http://search.digikey.com/scripts/DkSea ... D&x=8&y=11 is the mating connector. Value Add on the quantity means it's done on demand - i'm guessing they have a long strip of these they cut down.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Mon 06 Dec 06 2010 3:35 pm

I'm going to get a AC9790 dev kit. It has breakouts for the modules which makes life easy..

peer to peer with aerocomm:

MASTERLESS ARCHITECTURE
The Masterless architecture is a true peer-to-peer architecture, where any module that has data to transmit will initiate a communication Session with a transceiver(s) within its range, transmit data and exit the Session. This architecture eliminates the need for a master which dictates data flow control, hence reducing additional system overhead and greatly improving efficiency.




Interface Connector - 20 pin OEM Interface connector (Molex 87759-0030, mates with Samtec SMM-110-02-S-D
MMCX Jack - Antenna Connector (Johnson Components 135-3711-822)

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Mon 06 Dec 06 2010 6:05 pm

I bought the Aerocomm dev kit from digikey as well as a few sensors to test (temp/humidity) and RF shields for the PCB.

Daniel Wee
Site Admin
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Joined: Wed 25 Feb 25 2009 8:00 pm

Re: RF Links

Post by Daniel Wee » Mon 06 Dec 06 2010 9:57 pm

The stated -110dBm is the receive sensitivity. I think you need to find out the output power.

Daniel

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Tue 07 Dec 07 2010 12:28 am

variable, 5mw to 1000mw

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Fri 17 Dec 17 2010 8:01 pm

Installing the aerocomm software is a PAIN IN THE ARSE on windows 7. This is because the drivers in both the installer on the CD, and the download off the website don't have signed drivers!

Based on my testing (numerous system roll backs) - you need to install the new silicon labs CP210X usb to uart driver for windows 7. This can be downloaded here: http://www.silabs.com/support/pages/sup ... ber=cp2102

Once installed, the USB device then needs to be setup:
* Right click on device that didnt find drivers, properties
* Hardware tab -> Properties
* Update Driver
* Browse My Computer for driver software
* Let me pick from a list of device drivers on my computer
* Show all devices
* Browse to Silicon Laboratories
* Select Silicon Labs CP210x USB to UART bridge (first item)
* On the warning, click Yes - it doesnt think this is the right driver, but it is! Just run with it!

NOW, go to LAIRD's website and download the new installer:
http://www.lairdtech.com/Products/Wirel ... o-Modules/
Under "Downloads" tab:
Software Downloads
- Configuration Utility

When installing, it asks if you want to install the drivers that are not signed, click DONT INSTALL!.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Fri 17 Dec 17 2010 8:23 pm

I now have both my transceivers set to 2400baud, max power 10mw (low power). They appear (without having read the docs) to automatically set their power as required.

Setting one dev board to USB enable and the other to loopback

Writing 32byte packets (same as a GPS + header) as a "timed" test type, with 500 as the time (meaning 500ms) and 0 in timing for tx delay, with 1000 for rx timeout i get 100% of 250 packets sent/received back.

When using Timed mode, the tx delay must be set to 0.

I'm getting approx 1200bps. With my 32byte packets twice a second.


WIth the GPS + Sensor data (54 bytes) every 500ms, i'm only getting about 50% of my data (about 600bps).

However, my 54 bytes also fails with a data timeout when sending every second. Going to a 2000ms rx delay gives me a lot more data back (about 75%). I think this is because of how long the packet takes to send and then get sent back.

It looks like data needs to be split up more. Sending 32 bytes every 333ms (3hz) gives me 100% of data back.
Sending 32bytes at 166ms intervals (6hz) also works fine.

Down at 30ms between packets i get 98.5% which was 2 failed packets out of 132 - both one after another early on. This is still approx 1133.2bps.


I need to range test this at 10mw and then higher powers to see how far along ground i can get. This will be very important for once the balloon has landed (urban terrain should simulate rocky areas in the bush fairly well i guess).

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: RF Links

Post by Rris » Mon 20 Dec 20 2010 8:20 am

Ok so been doing more testing and reading the docs. I was having a lot of problems with reliability at 1W transmit, so i changed some settings and am getting much more reliable data when up close.

Interface timeout = 21
Stop bit delay 0
Baudrate 2400

Broadcasting, not paired.

I'm starting to think their software is a bit shite... it looks like VB6 (and so do the exceptions that constantly get thrown). So i'm going to write up my classes for sending/receiving my protocol format then write my own software to send/receive and see how it goes.

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