RF Radio Modules
Updated Dec. 2004. Don Carveth www.botgoodies.com don@botgoodies.com
Here is a summary of sources of radio modules and some suggestions on models that I found interesting. I have been using the SILRX / TXM radios from from RadioMetrix (purchased from Abacom) for a couple of years. I have only been able to get 4800 baud with these but Abacom swears they will do 9600. Mine could be first generation or maybe I'm doing something wrong.
Of note as of this writing are fully transparent serial RF transceiver modems from Radiotronix, MaxStream and Abacom, that do basically what I have been doing and look just like an RS-232 line to the equipment on both ends, for under $50. Two years back these could only be had for > $150. At this price I would forget programming your own microcontroller to handle all of the packetizing, error correction, etc.
My prototype network consists of a PC base station, the robot and a hand held controller, all of which require xmt and receive capability. I also have a standalone data transmitter and plan to add a couple more. I needed one more transceiver and one transmitter to complete the network. I am also looking at using radio's for direction finding and plan to use the signal strength output (RSSI) for that. This really needs two separate frequencies and would be better at 900 MHz (smaller antenna). I can see the RSSI being useful for general system tuning as well.
What did I settle on? I purchased the Linx TXM/RXM-916-ES series from Digikey. These are good for 56K Baud and cost about $15/$18 each. They are surface mount chips so I had to make up a small board. The pitch is pretty course (0.1" spacing) so this is easy to do (could be easily laid out by hand). I opted to buy the ES series separates instead of the SC series transceivers due to cost (the transceivers are $45), higher baud rate (56K compared to 33K), switching times and uncertainty whether the ES's would work with the SC's, as some of my apps are standalone transmitters. These modules have an RSSI output and can be used for analog.
Also tempting is the ATRT-100-433 transceiver, from Abacom, 100 KBaud, $57 and compatible with SILRX/TXM and other low cost modules.
I decided not to go with the lowest cost AM modules as performance is not as good as the FM modules and I have found in house FM performance to be marginal for my application. The AM modules can be had for less than half the cost of the FM modules. See Abacom and Linx.
Here's some pro's and cons of various modules I looked at:
Abacom - wide range of modules
*** ATRT100-xxx $57 for tranceiver, 100 Kbps, FM
*** RTL-Data-SAW $17 for tranceiver, 4800 bps, AM
*** AM-RT4 / AM-HRR3 xmtr/rcvr $12/$11, 2400 bps, AM
http://www.abacom-tech.com/
RXM-433-A receiver / FM-RTF3-433 transmitter. Compatible with my existing network of 2 transceivers / 1 xmtr. Minimal rework required. Good for 9600 baud only. The receiver has an RSSI output - good for testing performance, or, in my case, for direction seeking. This was my lowest cost option as it would work with my existing modules.
ATRT-100-433 transceiver - this is a good looking unit. I would have purchased these if not for the lack of an RSSI output. Rated up to 100 KBaud. Compatible with my existing SILRX/TRX. Would have needed to buy two to get higher speeds but would work right away at 9600. There is a low cost ($14) transmitter available that is compatible (9600 baud).
Linx - mfr. of radio modules, distributed by Digikey
http://www.linxtechnologies.com/ldocs/f_prod.html
*** Low cost modules look good but are SMD only - $7/$14.
*** The TR-916-SC transceiver looks interesting - 33.6Kbps, $48 ea
TR-916-SC-PA - nice transceiver module, pinned or SMD, can buy with integral coax antenna connector (recommended), $48, RSSI output, good for 33Kbaud.
TXM and RXM-916-ES series. Newest module, 56KBaud, SMD package,
$15/$18, RSSI output, look good.
RadioTronix makes some low cost modules with built in packetizing (so you don't need to go through what I did). http://www.radiotronix.com/
Wi.232DTS transceiver - this looks great, transparent wireless serial interface, 152 KBaud, simple setup. I haven't tested these yet but plan to buy a couple for testing. Carried by Mouser and Future.
MaxStream makes some good looking low cost RF modems - transparent UART - for under $50. Have not tested these yet. Available from Digikey. http://www.MaxStream.net
9XStream series - up to 37KBaud, transceiver and xmtr only version (nice feature)
Lemos International - no pricing on website - geared to OEM
http://www.lemosint.com/
OKW Electronics
*** FMRTF3 / FMRRF1 xmtr/rcvr FM - $12/$25, 9600 bps
http://www.okwelectronics.com/products/radiolist.html
Rentron Electronics
Mounts the Linx LC modules on a small board with pins for $14/$21, 4800 bps
*** Have inexpensive AM 2400 bps $8.50/$8.50 - best bet for low cost link.
http://www.rentron.com/PicBasic/RemoteControl.htm
RadioMetrix makes many of the modules sold by the above distributors and has
some good documentation
http://www.radiometrix.co.uk