Hello everyone,
A while ago I saw this video of a man making a 'message in a bottle' with a gps module attached to it. Together with a solar panel and a sim module he could get the coordinates from the bottle via sms. I thought this is a very cool idea and I wanted to make it but there is a little problem.
On the ocean a phone will connect to sattalites to send sms and that will be quite expensive (0,50 euro per sms) so I can only receive a couple of coordinates before the sim runs out of credits. My idea was to replace the sim with a radio transmitter to send the coordinates to me so I can decode it. I have little to no knowledge or RF circuits but my idea was to let it send beeps which I can then decode into a binary output. Since the output power of the transmitter can't be too high (by law and because of power consumption) i'm questioning if I can achieve my idea. The signal will have to travel a couple of hundered kilometers but on the other hand the data conversion may be really slow (no problem if a coordinate of 5 bytes will take 2 hours to transfer). I was thinking of a low frequency RF signal but I don't know if this can all be achieved.

If you guys have any suggestions for me i'll be happy to see them.
Gustav.

 

I don't think the idea is practical. Reliable RF communication is a matter of transmitter power and elevation. The surface of the ocean will never allow for elevation and so we are left with constructing a powerful enough transmitter that will last for months to year(s). The choice then comes down to which choice of frequency will allow for sufficient propagation of the RF signal at an appropriate power level. The problem with low frequency signals is that they require physically LARGE antennas and suffer from extremely high noise levels.

Light aircraft ELT devices operate on a frequency of 121.5 MHz and are designed to operate for maybe up to a week.

http://sarasotaavionics.com/category/elts

They may be digital data devices and they do emit a recognizable tone. It is usually an airplane that is searching for such a device and that is where the elevation comes in.

 

There are a number of activities in this area, with protocol solutions.

http://www.arrl.org/news/radio-amateur-s-sub-9-khz-vlf-signal-detected-across-the-atlantic

https://sites.google.com/site/sub9khz/

Also google "vlf amatuer radio long distance".


Regards, Dana.

 

I don't think the idea is practical. Reliable RF communication is a matter of transmitter power and elevation. The surface of the ocean will never allow for elevation and so we are left with constructing a powerful enough transmitter that will last for months to year(s). The choice then comes down to which choice of frequency will allow for sufficient propagation of the RF signal at an appropriate power level. The problem with low frequency signals is that they require physically LARGE antennas and suffer from extremely high noise levels.

Light aircraft ELT devices operate on a frequency of 121.5 MHz and are designed to operate for maybe up to a week.

http://sarasotaavionics.com/category/elts

They may be digital data devices and they do emit a recognizable tone. It is usually an airplane that is searching for such a device and that is where the elevation comes in.

So RF is basically a no-go. Are there any other options I can go for? Note that power consumtion is not a big problem since I want to use a solar panel with a battery (probably a 1W panel and a 2000mAh battery). If the circuits uses more than 1W I can just turn it on at specific times and charge the battery when it's off.

 

There are a number of activities in this area, with protocol solutions.

http://www.arrl.org/news/radio-amateur-s-sub-9-khz-vlf-signal-detected-across-the-atlantic

https://sites.google.com/site/sub9khz/

Also google "vlf amatuer radio long distance".


Regards, Dana.

Thanks for the links, very interesting. However these systems are made by experienced people and even they only achieve minimal usefull results.. I think RF is not the way to go for me, also because low frequency need really long antennas (like @Papabravo said).

 

because low frequency need really long antennas

Not necessarily -

http://www.stormwise.com/page28-VLF.htm

http://www.vlf.it/cr/differential_ant.htm


VLF (9 KHz) is not considered RF, its AF.


Regards, Dana.

 

So RF is basically a no-go. Are there any other options I can go for? Note that power consumtion is not a big problem since I want to use a solar panel with a battery (probably a 1W panel and a 2000mAh battery). If the circuits uses more than 1W I can just turn it on at specific times and charge the battery when it's off.

Not necessarily, I'm just saying that there are enough challenges to make this an unsuitable project for someone without considerable design experience. On top of that I'm not sure I understand completely your requirements.

 

Article here on 200 mW transmitter.

http://www.thespectrummonitor.com/may2017tsm.pdf


Regards, Dana.