Ideas for low power radio transmission in terrain

[mike548141]

Hi,

I've been mulling over an idea (you know how it is, just to keep the grey matter ticking) on how to build a device for tracking...well anything... from hunting dogs to humans.

The device would include a GPS (lat, long, altitude, vert & horz accuracy, UTC time) to give bearing over time and location.
Potentially also a digital compass (bearing), barometer (altitude and pressure change), hardware encryption to protect the info transmitted and a accelerometer (orientation and sudden acceleration/deceleration). I've also been considering a GSM chipset to assist with location but it would only be passively listening (due to power concerns).
These would all need to be dynamically powered i.e. shut down the chip unless its required.

I'm imaging the worst of conditions i.e.
- it must be small and light thus little space for a aerial or heavy batteries
- a very low position for a aerial say 1-2 feet above ground
- The transmitter may be on top of a small mountain or in a valley
- regular short bursts of data required (say every 2-10 seconds) signaling things like GPS reference etc... Say 100-200 bytes of info
- similarly the receiver is likely to be handheld... Say a iPad size device (approx 10"). However potentially that could be a controller/renderer and the receiver could have a larger aerial and battery say on a quad bike/car/truck/mountain bike etc...

My question is how to efficiently transmit that data?
I was thinking something in the HF range to give it the "legs" and to attempt to break through bush/hills etc that may interfere. I'm looking more at beating mother nature here than urban jungles.
My goal is to achieve 10-20 KM coverage with line of sight, 5-10 KM non-line of sight. I'm also aiming for 12-72 hrs of battery life to transmit which is obviously a mix of battery/power regeneration and efficient radio transmission engineering but the idea is to max out both.

This is all theoretical so we can ignore the need to license frequencies for now.

Many thanks for any ideas/thoughts.

MC

 

[skeptic2]

The way I understand it a transmitter on a hill would send a signal to all the mobile units which would send back their GPS data. Would they all respond at the same time on the same frequency? The mobile units have conflicting requirements for antennas and frequency.

I don't remember where but I have seen FRS walkie talkies with the feature of sending GPS data along with each transmission. All you would need is a means of activating the transmitter periodically. In most cases they should give you the range you need. Also Icom and probably Kenwood make NXDN portable radios with this feature with up to 5 watts of power but a license is required.

If you're wondering more along the lines of what is possible, I saw a presentation from this company a few years ago. They claim to get a range of 2000 miles with one watt on HF by using skip. http://www.hysky.com/

 

[Nik_2213]

You may need 'frequency hopping' or 'spread spectrum' to get the signal/noise you want from micro-power transmitters...

 

[russ_watters]

How is what you are describing different from an iPhone?

 

[berkeman]

How is what you are describing different from an iPhone?

Dang, your huntin' dog is smart, Russ!

 

[mike548141]

How is what you are describing different from an iPhone?

Many of the components would be similar but there are some important differences
a) It would need to be rated IP68 to survive the potential terrain
b) There would be no need for a UI, so no touchscreen etc
c) It would be one way comms
d) It would be much cheaper
e) A longer battery life
f) Built to operate in areas that there is no cellular or WiFi coverage

MC

 

[mike548141]

The way I understand it a transmitter on a hill would send a signal to all the mobile units which would send back their GPS data.

Not quite the transmitter would be attached to a dog/person/whatever so it would be the mobile unit and transmitting at regular intervals. The render (lets call it the base station) is a person tracking the mobile units who would be listening passively (no transmission required from the base station).

Would they all respond at the same time on the same frequency? The mobile units have conflicting requirements for antennas and frequency.

I was thinking that I would need to assign a unique frequency to each mobile unit to be tracked by the base station

 

[NobodySpecial]

In areas with coverage GSM would work best, cheap, tiny and light GSM modems are readily available and send the data as SMS. Antenna are small and don't need to be directional. In the US you can also use two way 900Mhz pager standard, it gives you better coverage than GSM.

Out in the middle of nowhere you will need satelite (ie Iridium and it's replacements) - expensive, both in hardware and call costs, antennae are larger and need to point at the sky.

If this is a limited area, ie a field trial, you could setup your own antenna network on surrounding hills. Trouble is that lower frequency means larger antennea while higher frequency means shorter range and better line-of-sight.

 

[berkeman]

Not quite the transmitter would be attached to a dog/person/whatever so it would be the mobile unit and transmitting at regular intervals. The render (lets call it the base station) is a person tracking the mobile units who would be listening passively (no transmission required from the base station).



I was thinking that I would need to assign a unique frequency to each mobile unit to be tracked by the base station

(For non-commercial public service purposes) We do this already with HAM Radio APRS systems:

http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System

We use amateur radio bands and GPS tied to our radios to track multiple operators' positions, even in remote areas. The terrain sometimes means that we need to set up a mobile repeater or two, but we can generally track all of the radio operators (even if they are not actively talking) on map overlays.

We use this capability in real disasters, but also in practice events, like long-distance endurance run races and bicycle ride events.

 

[NobodySpecial]

How big would the antennae be for a low power 144MHz Ham radio ?
That's about 2m wavelength

 

[berkeman]

How big would the antennae be for a low power 144MHz Ham radio ?
That's about 2m wavelength

Resonant antennas are 1/4 wave monopoles (like magnetic mount antennas on vehicle roofs) or 1/2 wave dipoles (like Yagi multiple-element beams). 1/4 wave monopoles for 2m wavelengts are about 0.5m.

Our handheld transceivers (HTs, like walkie-talkies) use base- or center-loaded antennas to shorten them to manageble lengts, like a foot or so. Our magmount vehicle roof antennas are usually dual band 2m and 70cm, and are about a meter in length.

 

[berkeman]

Ah, wait, I see your point. No huntin' dog that I've ever run with will tolerate an antenna sticking up off of his/her back. The 1.2GHz antennas are a manageable size, but 1.2GHz is more line of sight than 2m. Still, with well-placed repeaters, you could get good coverage.

That is a trade off in general -- better coverage versus the size of the antenna...