Hi all,
For a project I am building I need to have radio telemetry with 25-30km range, what is the best way to achieve this? I can't seem to find any products for sale with this sort of range, should I be looking to make my own circuit? Is there a product available someone can reccomend?
Regards,
Will
The free radio bands are not suitable for the range specified since the transmitter power must be much higher than allowed. It is not possible to make a general estimate of the power needed since there are many parameters that affect range. Also regulation will differ depending on location.
As i can see there are 2 solutions:
High gain directional antennas are your best bet. Assuming both units are stationary this will be easily achieveable with 100mw on 433MHz
Possibly not legal though.
At 455 mhz the anteennas could be large, probably have to make your own as well.
If it causes interference the radio ham fraternity have people who will df you and report.
If line of sight have you considered a laser modulated beam ?
What band width ?
Can you use a mobile phone solution.?
I used to work with equipment like this but it was all on expensive licenced frequencies.
It will be illegal to make your own transmitter for this sort of range in almost every country. Where are you?
A cb radio is probably your best option. If the antena is well placed, it could work quite well. If you pick an obscure channel (such as those in the 30s) you'd likely have a fairly reliable system. (at least within the UK. CBs channels are not very busy nowadays)
Im not sure that digital modulation on CB bands is legal. One way to circumvent this might be getting a traditional modem and using the uilt in modulation (am or fm)
nilton61:
Im not sure that digital modulation on CB bands is legal. One way to circumvent this might be getting a traditional modem and using the uilt in modulation (am or fm)
AX.25 is legal over cb radio (at least in the uk)
This and a 90cm dish in both ends together with wlan adapter might solve the issue
I doubt it.
Anyway putting a dish on a WLAN adaptor is illegal because it invalidates the type approval and exceeds the permitted ERP of the device.
You need line of sight for distances like this even with UHF CB or Ham radio, or any other relatively cheap option.
Once you have to go further than the radio horizon, the calculations of the path loss become extremely difficult to make, and at best will be unreliable.
GPRS is about the only viable solution.
At frequencies above 400 Mhz , wet trees act like blotting paper, and will absorb just about all your signal.
You need line of sight for distances like this
In radio there are two types of "line of sight".
The first just refers to the distance to the horizon and the second means an actual optical path between the two systems. Optical line of sight only starts being needed at about 1GHz.
Thanks guys, it is around 25km and on the other side of a (low) mountain range. It is for a Buoy, so it is not really stationary, but I could have a directional antennae on the base station. I am willing to get whatever required licenses to get this going. Or will GSM be my best option?
Regards,
Will
GSM is your best option.
I presume the buoy is floating in the water, so zero effective height .
Very hard to make a link with obstruction in the middle work with that type of scenerio.
it is around 25km and on the other side of a (low) mountain range.
That rules out high frequencies.
I am willing to get whatever required licenses to get this going.
You may be willing but they are not handed out like candy. To construct stuff you need to have an inspected and approved researcher and development facility. Or get a radio ham license. That involves you taking exams.
So I would agree go with something commercial like GSM.
Totara:
Thanks guys, it is around 25km and on the other side of a (low) mountain range. It is for a Buoy, so it is not really stationary, but I could have a directional antennae on the base station. I am willing to get whatever required licenses to get this going. Or will GSM be my best option?Regards,
Will
Ugh.
Non starter without a repeater.unless you use low frequencies.
As said licencing is problematic, the testing requirments for equipment cost thousands.
cheaper to buy commercial equipment for the required band and geta licence.
Manufacturers will guide you on what is required.
Scrub that at lf you would need an unfeasibly large antenna to mount on a bouy.
Have a look at the raidio ameteur packet radio network.
If you are lucky there may be suitably located repeaters.
Otherwise you could set up your own.
They use the 2 m band which can give over the horizon performance.
A 1/4 wave antenna should sit comfotably on a bouy.
I would definatly recommend talking to the ameteur community about your requirments , they are a knowlegable bunch generally.
Rasbery pi seems to be the preferred repeater or controller option though.
The software is fairly large, but open scource
how much data is send per transmission?