Sonsivri

I have a need to transmit data between micro controllers via a wireless solution.  Normally, I would pick one of the off the shelf products and go on my way with it, but in this case, my needs are more unique.  I need EXTREMELY long-range (appx. 50 MILES), but I can live with VERY slow speeds.. 10bps would be just fine.  The antenna can't be all that large either :)

The devices have to communicate with a base-station which CAN have a very large/tall antenna - but LOS is out of the question.

Any recommendations?  even possible? or am I stuck with using CDMA/GSM modems in these devices.

CDMA/GSM is much reliable for long distance. Or else you have to form network of zigbee or WiFi (repeater like) so that there will be less possibility of missing data

How about storing your data, then once or twice a day have a cellular phone call the base and upload the data at high speed? (Long range = high power+good antenna)

I used to live in a city where remote water flowmeters would sample once or twice a minute, then at night call a computer via cellular and upload all the data. Everything was located underground, accessible by a manhole except for the antenna. 

IFF line of sight is possible, WIFI + a couple of sattellite dishes could possibly move the data.

Ideas available here: 

http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/

If it is not a commercial project, amateur radio packet radio could be applied.
Possibly even a few nodes already in place you could move your traffic through.
TAPR has tons of resources:  http://www.tapr.org/

Phone line and a pair of modems might be most reliable way to go.

Use phone line and a pair of PIC use DTMF to send and receive data. It is possible and low cost. I designed and used in 2000. I don't know if I can find the project because I have been move several times. If I can find it, I will post.

Tom

Hai

Use hf,Vhf,uhf transmission.
Cause the frecuencies mean cost.
With frs/gmrs radio that works in free frecuencies allocation.

Cb also an option in USA(hf).

regards
Jeckson

Thank you all for the replies.  I appreciate your help.

Although the cost is substantial, I have decided to go the GSM/CDMA Modem route.  I've found a provider that gives 1MB per Month for $8 per month per card.  I have to monitor about 50 different locations - meaning roughly $400 per month in access costs.

If anyone is aware of a provider (GSM or CDMA) who gives >250kB per month for less than $8, that info would be helpful.

Thanks!
PPtk

if you are going to continually monitoring the data on CDMA or GSM then you have to communicate with provider to get fix IP so that your work will be more easy otherwise your GPRS connection is going to be very very bad. I face this problem then I had words with provider he given me fix ip range of 10 then my unite start working. Yap this is very personal experience. 

Why would each gprs device need a static IP?  I see no reason why they could not be dynamic and communicate to a fixed IP at my office.  I don't need to poll them - they simply need to be able to send data to me.

PPtk

:)

50 miles is nothing to HF ham radio. This would be using 'ground wave' mode. Home brew transmitters are cheap to build or you can buy a kit. As for data modulation and format, take your pick: RTTY, Morse code, DominoEx, PSK31, DTMF, etc. It's all been done before hundreds of times over.

Why is it the younger generation is so ignorant of the experience of the older generations?

$400/month  ::)

I had a quiet similar needs, i am thinking about web based monitoring via ftp, http, or even email where the remote station send data to web service maintained from the base station - static ip is not required. All is still in concept now, i already bought Simcom SIM548 GSM/GPRS + GPS modem for this purpose.

How will the weight and urgency of the data will be? If it is light then i think RF is still a good choice, $400 is not small amount of money - for me at least. Mine is quiet heavy on data and the price of the GPRS service here is far below yours, 125MB for about $5 per month.

I am still doing research for this thing, that is why i asked for a book: http://www.sonsivri.com/forum/index.php?topic=26345.0 (http://www.sonsivri.com/forum/index.php?topic=26345.0)

-ichan

+1 with the ferret's suggestion on using HAM type radio.
You only got to pay for the setup and there would be no monthly fees afterwards.

Hai
PILOTPTK

First only 10 bps....that's the advantages..

Consider your frecuencies rules at your location....

There's numberous free frecuencies and lot of kits that offered that range..with 300 m or more.
Added more gain antennas for that.
Like 43X-44X Mhz.

If lived at USA.I think that CB=Citizen band(11 meter band) is free.Just register and no Exam(+cost)

Must be aware for frecuencies rules...

Regards
Jeckson

I use this http://www.digi.com/products/wireless/point-multipoint/xbee-pro-868.jsp#overview,with dipole antenna have communication at 60km in cofiguration point-to-multipoint(27 points to measured).

I'm very well aware of the distances that HAM type radio has achieved, and personally, I've used PSK31 to communicate for a darn long way.  My reason for not really considering this is that it is a commercial application, which tends to be frowned upon by the HAM community - and the person technically 'operating' the remote units will A) Not have a AR license and B) be using it for commercial purposes.

Are their HF bands that are both free and available to commercial applications?

What country would the system operate in, PilotPTK?

USA

huh
link very slow...

Use CB.There's numberous kits and circuits
It's just registered.

there's also free like 4XX Mhz but need amplify for 50 miles.

CB is the best..

Regards
Jeckson

a good quality+long range waki-tokies ,along with dtmf + good height antenna  is the best idea to go for ,
and it will be cheapest also.

if you cascade the w-t unit you can create repeater for  desired range .

the idea is practical  to implement

Jeckson,

Can you point me to any of these circuits or kits?  I'm quite interested in your CB idea, but I'm not having much luck finding anything on sonsivri or google.

Thanks!
PPtk

CB:  Amplitude modulation, loaded with interference, legal only for voice communication, typically good to about 3 or 4 miles.  For 27 MHz, antennas are not small.

http://wireless.fcc.gov/services/index.htm?job=service_home&id=cb

Hai

>Jeckson,

>Can you point me to any of these circuits or kits?  I'm quite interested in your CB idea, but I'm >not having much luck finding anything on sonsivri or google.

>Thanks!
>PPtk

Just search at CB frecuencies 27-28-29 MHz kit.If I'm not wrong even old handy talky(used at WW II).

Or also could used R/C frecuencies(50 Mhz) but in USA are illegal for more power?

50-54 MHz is a HAM band, license required.

OK 50-54 MHz is licence...

CB band is the way

Regards
Jeckson

(http://www.forumsforjustice.org/forums/images/smilies/poke.gif)  It seems like you missed a critical detail:  CB is legal only for voice communication.

I suppose one COULD use a synthetic or recorded voice to transmit the data and voice recognition to receive the data, but that would be silly.

Data is one AFSK voice :-)................

Jeckson

No sir, data modulated via Audio Frequency Shift Keying is definitely not something the FCC sees as "voice",
their definition refers to human vocalizations.  The FCC regulations do not allow for silly stipulative definitions.

An additional problem: FSK is frequency modulation, where CB is only allowed to be of amplitude modulation.

I just did a little reading on NVIS.  Very interesting.

Can't wait to hear more about your findings.

PPtk