Hello, I am trying to build a wireless sensor controller where the sensors are distributed and a central device is able to read the status of every node. My knowledge about wireless networks is novice at best. I was looking into zigbee and then got hold of TI's CC2500 development tool. I ran the demo but the distance from the sensor to the pc was too short for my application. I was able to go less than 15 feet (indoors) before I lost connection. I was practically still in the same room except that there was an end table in the line of sight between the receiver and transmitter. Is this something typical of these devices? I am looking for something in the range of 20-30m indoors.
Checkout Chipcon website. I have used CC1010 for both Rx and Tx. It was good for short distance communication. Check if it can be tweaked to your requirements.
I am planning to design my own but for now I just ran the demo that came with the CC2500 chip. Thats when I ran into the distance/range problem. I was just trying to get a feel to what I can or cannot use. What should I look for when I am design? Any ideas?
On Mon, 25 Feb 2008 09:02:35 -0800 (PST), I said, "Pick a card, any card" and amerdsp instead replied:
That really shouldn't be a problem with the right antenna. An
802.11G network has a practical range of about 30 meters with a stock antenna from the box. Use a high gain, unidirectional antenna and some people have gotten as much as 20km with full duplex.
Go here:
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They have several "how to" projects there; all free. They've been playing around with wireless in a big way for years now. There are both unidirectional and omnidirectional antennae there for you to experiment with. The Bow Tie, bi-quad antenna might suit your needs.
The kit is marketed as a development kit not a demo board. Since this kit is meant to advertise the best in the CC2500 chip, I assumed they would put a decent antenna to stand out from the crowd.
I agree the antenna is very important. What I was asking is that perhaps the CC2500 is not meant to have long range transmission. You can use the best antenna out there, but if you do not have the power to drive it nothing is going to happen.
Yes, indeed. Thats what I am planning to do but not before I know that the hardware I am using is able to get the ranges I want.
As I said, RF is not my strength and I thank you for your input.
On Mon, 25 Feb 2008 20:06:21 -0800 (PST), I said, "Pick a card, any card" and amerdsp instead replied:
Nonsense. It's made to test in lab conditions not in the field. You want field performance, buy a working, off the shelf model of something already designed.
There are high gain antennae available. I gave you links to places where you can actually build your own. A small stub antenna may have a gain of 2db to 5db while a dish or bowtie will exceed 16db. That'll put you into the 100 meter range with just .5mw or less depending on other conditions.
Then get someone who is good with RF to design your weakest link. It's not that hard to learn. In another post, I gave you links to lots of help. Go there and read. Those guys wrote for the amateur.
Why did you come here to ignore the only advice that will help you out? You can ask further questions about antenna design. While most here are digital guys there are a few with more well rounded expertise. No harm in asking unless, like you did here, you choose to dismiss it as too hard.
More power is not the answer. It may even be illegal where you live.
Antennas with "gain" have also directivity so this is mainly usable with stationary nodes in more or less line of sight conditions. In a stationary system, the sensors could use directional antennas, but the master would have to use an nondirectional antenna if the sensors are not in the same general direction (or use switchable directional antennas and switch in the correct antenna, when accessing a specific sensor).
However, if the nodes are stationary, why use wireless connections in the first place, what prevents the use of wires ?
In applications, in which the communication path is through reflections or in which the nodes might be movable or reflecting/absorbing surfaces (such as humans) will move in and out of the communication path, the directional antenna can do more harm. In such situations, antennas with more than 3-6 dBi gain (illuminating less than half of an hemisphere) should be avoided, in order to be able to use the best reflection at a particular moment.
If the evaluation board simply relies that a suitable PCB track may radiate something, but may be quite lossy, with gains in the order of
-6 to -20 dB, so even a simple 1/4 wave external antenna would improve the distance considerably.
It should be noted that when using license free frequency bands, the device may have sufficient range in an interference free test setup, but in the actual world with various kind of interference from various sources, the range could be drastically reduced.
I haven't looked at the CC2500 but I assume it puts out at least 0dBm. If you want more power, you need to add a PA.
If you don't have the expertise and equipment (got a 2.5GHz spectrum analyzer?) it is very difficult - quasi-impossible - to experiment with this stuff and you are really much better served by buying a module with a pre-matched antenna. Bluetooth, maybe.
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