Hi,

I'm currently designing a wireless weather station/generic sensor system 
(I know it can be bought for a fraction of what the components and time 
will cost me, but I'm doing it because it is fun.). I'm wondering what 
is the best frequency to choose for this application. What I need is 
20-30m of range, and ability to pass 1 or 2 concrete walls. I'll be 
using ready-made modules (not enough knowledge in RF to build my own 
from scratch), which I found for 433MHz, 868MHz and 2.4GHz. Which one 
should I choose considering ability to cross walls and possible 
interference from other systems ?

Issue number two is the antenna, the only design I know is the 1/4 wave 
antenna, is there anything better I could build easily to improve the gain ?

Thanks.

vv.

"vic" <n...@bidouille.org> wrote in message 
news:49579caa$0$18986$4...@news.free.fr...
> Hi,
>
> I'm currently designing a wireless weather station/generic sensor system 
> (I know it can be bought for a fraction of what the components and time 
> will cost me, but I'm doing it because it is fun.). I'm wondering what is 
> the best frequency to choose for this application. What I need is 20-30m 
> of range, and ability to pass 1 or 2 concrete walls. I'll be using 
> ready-made modules (not enough knowledge in RF to build my own from 
> scratch), which I found for 433MHz, 868MHz and 2.4GHz. Which one should I 
> choose considering ability to cross walls and possible interference from 
> other systems ?
>
> Issue number two is the antenna, the only design I know is the 1/4 wave 
> antenna, is there anything better I could build easily to improve the gain 
> ?
>
> Thanks.
>
> vv.

When I used to mess with this stuff I have found the best for going through 
buildings was 144 MHz.
Long waves don't fit through openings and short wave bounce off. (Broadly 
stated, I admit)
As far as your antenna, if you want more gain use a directional antenna. I 
get the impression you only need to transmit to your own stationary 
receiver.

Tom 

vic wrote:

> Hi,
> 
> I'm currently designing a wireless weather station/generic sensor
> system (I know it can be bought for a fraction of what the components
> and time will cost me, but I'm doing it because it is fun.). I'm
> wondering what is the best frequency to choose for this application.
> What I need is 20-30m of range, and ability to pass 1 or 2 concrete
> walls. I'll be using ready-made modules (not enough knowledge in RF to
> build my own from scratch), which I found for 433MHz, 868MHz and
> 2.4GHz. Which one should I choose considering ability to cross walls
> and possible interference from other systems ?

I suspect that the frequency you use is going to be the least of your
problems !  The unlicensed 432/3 Mhz band should give you more than
adequate range within the power constraints for that band, as would the
2.4Ghz band.

The modulation scheme you choose is more likely to be a greater issue.
The receiver is going to have to pass that on to be decoded into
reproducing the data the you want transfer.

> Issue number two is the antenna, the only design I know is the 1/4
> wave antenna, is there anything better I could build easily to improve
> the gain ?

There are many better antenna than a simple 1/4 wave !  But, for
example, do you really need a four or eight element yagi for a 1
milliwatt signal a hundred feet away ? 

> 
> Thanks.
> 
> vv.

-- 
Best Regards:
                     Baron.

Baron wrote:
> I suspect that the frequency you use is going to be the least of your
> problems !  The unlicensed 432/3 Mhz band should give you more than
> adequate range within the power constraints for that band, as would the
> 2.4Ghz band.

What if I am limited to, say, 1mW ? That's the kind of power small 
integrated modules are capable of. I forgot to say that the transmitters 
are solar powered so power consumption in an issue.

> The modulation scheme you choose is more likely to be a greater issue.
> The receiver is going to have to pass that on to be decoded into
> reproducing the data the you want transfer.

Sure thing. Actually the modules I plan to use all include a 
modulation/demodulation circuitry, and some even directly encapsulate 
the data.

> There are many better antenna than a simple 1/4 wave !  But, for
> example, do you really need a four or eight element yagi for a 1
> milliwatt signal a hundred feet away ? 

As I said, I don't know much about antennas. So your choice of answering 
my question by another question is perplexing. I can only say "I don't 
know". Let me rephrase my question : is there a better unidirectionnal 
antenna than the 1/4 wave ?


vv.

Tom Biasi wrote:
> When I used to mess with this stuff I have found the best for going through 
> buildings was 144 MHz.
> Long waves don't fit through openings and short wave bounce off. (Broadly 
> stated, I admit)

OK. I don't think 144MHz is an open frequency here (Europe), but 433 or 
868MHz would do, then ?

> As far as your antenna, if you want more gain use a directional antenna. I 

I'm a bit reluctant to use a directionnal antenna since the sensors will 
be subjected to wind, etc, and may move over time. Is there such a thing 
as an unidirectionnal antenna with better performance than the 1/4 wave, 
or is the 1/4 wave the "perfect" antenna ?

> get the impression you only need to transmit to your own stationary 
> receiver.

That's true. Actually transceivers are quite common, and I figured some 
kind of acknowledge would be a nice feature, but it's not a must.

vv.

"vic" <n...@bidouille.org> wrote in message 
news:4957c6a3$0$1636$4...@news.free.fr...
> Tom Biasi wrote:
>> When I used to mess with this stuff I have found the best for going 
>> through buildings was 144 MHz.
>> Long waves don't fit through openings and short wave bounce off. (Broadly 
>> stated, I admit)
>
> OK. I don't think 144MHz is an open frequency here (Europe), but 433 or 
> 868MHz would do, then ?
>
>> As far as your antenna, if you want more gain use a directional antenna. 
>> I
>
> I'm a bit reluctant to use a directionnal antenna since the sensors will 
> be subjected to wind, etc, and may move over time. Is there such a thing 
> as an unidirectionnal antenna with better performance than the 1/4 wave, 
> or is the 1/4 wave the "perfect" antenna ?
>
>> get the impression you only need to transmit to your own stationary 
>> receiver.
>
> That's true. Actually transceivers are quite common, and I figured some 
> kind of acknowledge would be a nice feature, but it's not a must.
>
> vv.

Your directional won't be that narrow that small movement will be a concern.
At the frequencies that you are considering the antennas would be quite 
small.
Maybe you would consider a dish to dish data link setup.

Tom 

On Sun, 28 Dec 2008 19:28:00 +0100, vic <n...@bidouille.org> wrote:


>As I said, I don't know much about antennas. So your choice of answering 
>my question by another question is perplexing. I can only say "I don't 
>know". Let me rephrase my question : is there a better unidirectionnal 
>antenna than the 1/4 wave ?
>
>
>vv.

A 1/4 wave antenna is generally considered to be an omnidirectional
antenna - it radiates (or receives) equally well in all directions at
right angles to its element.  You can make antennas more "efficient"
by making them more directional. (A unidirectional antenna would
radiate in only one direction - Yagi or beam antennas are considered
unidirectional.)

The radiation pattern of a 1/4 wave antenna is shaped something like a
donut, with the antenna passing through the hole. Stacking two 1/4
wave antennas end-to-end, and feeding them with correctly phased
signals, will flatten the donut pattern, and extend the donut outwards
- more energy will be directed at right angles to the antenna, at the
expense of the vertical spread.

Look for amateur radio publications on VHF antennas to get a good
explanation of antenna performance.


-- 
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

vic wrote:
>> There are many better antenna than a simple 1/4 wave !  But, for
>> example, do you really need a four or eight element yagi for a 1
>> milliwatt signal a hundred feet away ?
> 
> As I said, I don't know much about antennas. So your choice of
> answering my question by another question is perplexing. I can only
> say "I don't know". Let me rephrase my question : is there a better
> unidirectionnal antenna than the 1/4 wave ?
> 
> vv.

Sorry if if that came across badly !  The intimation was that a quarter
wave and a milliwatt should be fine at that close range !  Poor
receiver sensitivity could be the cause of a problem if you needed a
bigger antenna.

-- 
Best Regards:
                     Baron.

vic wrote:
>> As far as your antenna, if you want more gain use a directional
>> antenna. I
> 
> I'm a bit reluctant to use a directionnal antenna since the sensors
> will be subjected to wind, etc, and may move over time. Is there such
> a thing as an unidirectionnal antenna with better performance than the
> 1/4 wave, or is the 1/4 wave the "perfect" antenna ?
> 
> vv.

A "Colinear" antenna can be omnidirectional and can be set up to provide
6 - 8 Db of gain or more !  But you sacrifice simplicity for complexity
in construction.  Also you may be in danger of exceeding the allowed
ERP limits if you use one for transmitting.

-- 
Best Regards:
                     Baron.

Tom Biasi wrote:
> Your directional won't be that narrow that small movement will be a
> concern. At the frequencies that you are considering the antennas
> would be quite small.
> Maybe you would consider a dish to dish data link setup.
> 
> Tom

Hi Tom,
In general I agree with you !  But if Vic is to consider dishes then he
needs to go up a lot more in frequency !  Say to around 5 or 6 GHz or
even 10 GHz.  Once he does that, he is then out of the unlicensed
bands. 

-- 
Best Regards:
                     Baron.