Wireless communications

Started by "Kenneth (K) Macrae" September 8, 2008
Hi

I'm currently looking at two wireless options:

2.4GHz
433MHz
I know the lower frequency allows greater transmission distance. What would
one go for?

Both have USART interfaces and both operate off 3 volts.

Please let me know what your ideas / opinions are

Thanks

Kenneth
It is entirely up to you, the differences in range are minimal.
Generally, the 2.4GHz modules allow much faster data transfer than
the 433MHz ones and some of them have built in encoders and decoders
to improve reliability when the signal is poor.

Also note that you will almost certainly need an antenna of some sort
and they are much shorter (or even built into the module) at 2.4Ghz.

433MHz is a little cheaper but not by much and more prone to
interference from other devices such as wireless doorbells, car
remote locking keyfobs and even indoor/outdoor wireless weather
stations.

Brian.

--- In p..., "Kenneth (K) Macrae"
wrote:
>
> Hi
>
> I'm currently looking at two wireless options:
>
> 2.4GHz
> 433MHz
> I know the lower frequency allows greater transmission distance.
What would
> one go for?
>
> Both have USART interfaces and both operate off 3 volts.
>
> Please let me know what your ideas / opinions are
>
> Thanks
>
> Kenneth
>

Hi Kenneth,

2.4GHz and 433MHz have different characteristics of propagation
particularly where indoor use is concerned. A cheap Zigbee module
will fall over once you move into the next room - that's why you need
lots of them in a mesh network :-) They can be quite time consuming
devices to play with, as they are quite complex compared to a simple
RF encoder/decoder scheme.

If you can tolerate an aerial of a several centimetres, a 433MHz
helical does not really take up much space.

If you are requiring wide bandwidth / high data rates (>160kbps) then
it may be you have to use 2.4GHz. Note that 2.4GHz is also becoming
quite congested in some areas. If you are only sending a few bytes of
data on a low duty cycle (e.g. one analogue sample every 10 minutes)
then your options are far greater. UK has VHF (10mW) and UHF (up to
500mW) allocations for 12.5kHz bandwidth applications. Depending on
aerial and environment, point-to-point communications of several miles
are quite feasible! So really you have asked "how long is a piece of
string"! If you are in UK I would start by looking at:

http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/rlans/short/

If you are elsewhere in Europe you are really looking at 169, 433 and
868MHz (as well as ubiquitous "worldwide" 2.4GHz). There are all
sorts of options available when it comes to the hardware. For
example, take a look at

http://www.radiometrix.co.uk/

Hope this helps you.

Tim
--- In p..., "Kenneth (K) Macrae"
wrote:
>
> Hi
>
> I'm currently looking at two wireless options:
>
> 2.4GHz
> 433MHz
> I know the lower frequency allows greater transmission distance.
What would
> one go for?
>
> Both have USART interfaces and both operate off 3 volts.
>
> Please let me know what your ideas / opinions are
>
> Thanks
>
> Kenneth
>