Short range low power radar?

davidaprice

davidaprice

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As I was motoring through the Helsinki archipelago today in thick fog, I got to thinking. Puffin has a chart plotter and AIS, but no radar. The chart plotter shows me the shoreline and AIS shows me the ships, the gap in my capabilities is seeing approaching small boats without AIS. A normal radar unit would be expensive overkill for this task: what I really need is a small, compact, low-power radar unit with a range of a mile or so. Do such things exist? Are they even possible?
 
davidaprice said:
As I was motoring through the Helsinki archipelago today in thick fog, I got to thinking. Puffin has a chart plotter and AIS, but no radar. The chart plotter shows me the shoreline and AIS shows me the ships, the gap in my capabilities is seeing approaching small boats without AIS. A normal radar unit would be expensive overkill for this task: what I really need is a small, compact, low-power radar unit with a range of a mile or so. Do such things exist? Are they even possible?
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It isn't the power of the radar that makes it expensive; it's the rotating antenna and processing electronics, none of which would change for a low power version.
 
What you need is a used Navico 3G or 4G radar.. You get superb coverage of that one mile radius, with the other 29 miles thrown in as a bonus.

The Finnish South coast archipelago is one of the best places in the world to sail. But it's extremely complex waters with often less than ideal visibility -- you really want radar. In whatever form you can find it.
 
davidaprice said:
seeing approaching small boats without AIS
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That was one reason why I changed from an AIS Receiver to a Transceiver, hoping that other boats have a receiver. I didn't think it was fair that I could see boats with a Transceiver but they couldn't see me.
I do have an old generation radar which I use in fog but even after fine tuning a small boat can be missed.
 
AntarcticPilot said:
It isn't the power of the radar that makes it expensive; it's the rotating antenna and processing electronics, none of which would change for a low power version.
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I wonder if a phased array could replace the rotating antenna? Apparently phased array radars are very expensive, but those seem to be long-range military and weather applications, not spotting a boat a mile away. Maybe short range, low-power phased array radars would be cheaper? Apparently smart phone MIMO antennas are phased arrays.
 
MontyMariner said:
That was one reason why I changed from an AIS Receiver to a Transceiver, hoping that other boats have a receiver. I didn't think it was fair that I could see boats with a Transceiver but they couldn't see me.
I do have an old generation radar which I use in fog but even after fine tuning a small boat can be missed.
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I have transmitting AIS too, but the boats I'm worried about mostly don't have receiving AIS, so it doesn't help in this case.
 
davidaprice said:
I have transmitting AIS too, but the boats I'm worried about mostly don't have receiving AIS, so it doesn't help in this case.
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It was a few years back, and I was in thick fog in Poole Bay. My AIS transceiver worked well, as did the radar, but back then under 50% of the boats on radar had AIS transmitting. They might have been receiving, but if a boat isn't transmitting, a receiver on another boat is a waste of time.
I know of quite a few boats that don't transmit AIS but have a receiver.
 
davidaprice said:
I wonder if a phased array could replace the rotating antenna? Apparently phased array radars are very expensive, but those seem to be long-range military and weather applications, not spotting a boat a mile away. Maybe short range, low-power phased array radars would be cheaper? Apparently smart phone MIMO antennas are phased arrays.
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Requires much more elaborate electronics and precise manufacture at metre scale. Mobile phone antennae are small enough for easy fabrication and don't require the ability to be steered.
 
Had a 3g radar on the last boat and had no difficulty picking up mooring buoys at 50 metres or so. It was also low power consumption. However I am unaware of any radar that is noteably smaller and cheaper than any other.
 
The smaller the antenna, the wider the beam and the less angular accuracy you get, unless you start to use a phased array and beam forming - but that would increase the price.
 
st599 said:
The smaller the antenna, the wider the beam and the less angular accuracy you get, unless you start to use a phased array and beam forming - but that would increase the price.
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Indeed. The antennae on most small boat radars are at the lower end of the feasible size range already, with angular resolutions of a few degrees. Smaller antennae would result in worse angular resolution.

Phased arrays can't be substantially smaller; they just don't have to rotate. But the angular resolution is determined by the physical dimensions for any directional antenna.

There's another issue and that is that pulsed radars usually have a minimum range, within which they can't see things. This arises because the receiver is blanked while the pulse is transmitted, otherwise the receiver would be overwhelmed. I don't know how this works for CW radars.
 
Birdseye said:
Had a 3g radar on the last boat and had no difficulty picking up mooring buoys at 50 metres or so. It was also low power consumption. However I am unaware of any radar that is noteably smaller and cheaper than any other.
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That very radar, which hasn't been made in some years, is cheap as chips on EBay. That's an ideal budget solution IMHO.
 
AntarcticPilot said:
Indeed. The antennae on most small boat radars are at the lower end of the feasible size range already, with angular resolutions of a few degrees. Smaller antennae would result in worse angular resolution.

Phased arrays can't be substantially smaller; they just don't have to rotate. But the angular resolution is determined by the physical dimensions for any directional antenna.

There's another issue and that is that pulsed radars usually have a minimum range, within which they can't see things. This arises because the receiver is blanked while the pulse is transmitted, otherwise the receiver would be overwhelmed. I don't know how this works for CW radars.
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CW radar doesn't have any "main bang", the close range area which can't be seen with pulse radar. So the near range is limited mostly by height of the antenna and limitations of vertical beamwidth.
 
AntarcticPilot said:
There's another issue and that is that pulsed radars usually have a minimum range, within which they can't see things. This arises because the receiver is blanked while the pulse is transmitted, otherwise the receiver would be overwhelmed. I don't know how this works for CW radars.
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CW radars sweep in frequency, you measure the frequency offset between TX and RX to calculate the time offset and thence the distance.
 
wonkywinch said:
For anyone interested in radar, I read a very interesting book. The title doesn't sound rivetting but the non fiction book read like a James Bond novel with lots of derring do, sneaking magnetrons across the Atlantic etc - The Invention That Changed the World by Robert Bueri.
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Hülsmeyer's 1903 Telemobiloskop is a fascinating bit of kit. Probably a good thing it was forgotten or history could be very different.
 
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