pcatterall
Well-Known Member
Any vessel over 10 feet would cause me concern in a fog!!
hand-held radar
- Thread starter sarabande
- Start date
Any vessel over 10 feet would cause me concern in a fog!!
AntarcticPilot
Well-Known Member
There's two or three issues that might mitigate against such a device - people more expert in the detail of radar will be able to fill in the gaps, but I'd imagine the problems are:
1) Power. The police radar guns have limited range (a few hundred metres?), so can operate at power levels low enough to be safe. But a radar capable of getting a return at useful distances for maritime use would have to put out just as much power as any other maritime radar. That means a) you have to provide the power and b) holding a device emitting that kind of microwave power isn't likely to increase your life expectancy. How do you prevent someone from pointing it at themselves or another person and frying their eyeballs or brain or whatever? Remember that the advice is that a radome must be above the level of people on deck.
2) Size. Basically, you still need to have some kind of antenna to direct the energy in the right direction, and to receive within the same sector. That means a reasonably large antenna, several tens of cm across to narrow the beam sufficiently to be useful. It wouldn't be a lot narrower than a radome, though it could be a rod shape rather than a dish.
1) Power. The police radar guns have limited range (a few hundred metres?), so can operate at power levels low enough to be safe. But a radar capable of getting a return at useful distances for maritime use would have to put out just as much power as any other maritime radar. That means a) you have to provide the power and b) holding a device emitting that kind of microwave power isn't likely to increase your life expectancy. How do you prevent someone from pointing it at themselves or another person and frying their eyeballs or brain or whatever? Remember that the advice is that a radome must be above the level of people on deck.
2) Size. Basically, you still need to have some kind of antenna to direct the energy in the right direction, and to receive within the same sector. That means a reasonably large antenna, several tens of cm across to narrow the beam sufficiently to be useful. It wouldn't be a lot narrower than a radome, though it could be a rod shape rather than a dish.
Mariner69
Well-Known Member
What the OP is describing is the original radar system used at sea. An aerial coupled to an oscilloscope and the time base started as the pulse departs and the response on the scope used to measure the return. Distance between the two gave the time and using the speed of light the range. Swivel it around and you can read the distance of various objects. The scanner and plan position indicator came in to being with the magnetron to improve the power released.
X band radar has always been considered to be relatively safe due to the combination of frequency and power; it was said that having the head hit by the scanner was a bigger risk than the output, that being said it also warned against looking down the wave guide.
With modern electronics it shouldn't be technically difficult but the market would be limited and the thought of all those emitters out there would not go down too well with Offcom.
X band radar has always been considered to be relatively safe due to the combination of frequency and power; it was said that having the head hit by the scanner was a bigger risk than the output, that being said it also warned against looking down the wave guide.
With modern electronics it shouldn't be technically difficult but the market would be limited and the thought of all those emitters out there would not go down too well with Offcom.
Hoolie
Well-Known Member
The transmitted power of the so-called "broadband" radars is orders of magnitude less than conventional pulse radar. FMCW would undoubtedly be more suitable technology for a hand-held and you might even be able to get the required range at permitted power levels.
lw395
Well-Known Member
The police radars and speed cameras are a red herring. They have an easy job to do, looking for returns at a shifted frequency due to Doppler.
Using a hand held radar, you would need a fairly narrow beam, otherwise the return from sea clutter etc in the beam becomes as big as the target.
I think it comes down to what range you think it needs.
A hundred metres might be OK for groping into a small port in fog, but to avoid ships a few km is probably the minimum worthwhile?
Using a hand held radar, you would need a fairly narrow beam, otherwise the return from sea clutter etc in the beam becomes as big as the target.
I think it comes down to what range you think it needs.
A hundred metres might be OK for groping into a small port in fog, but to avoid ships a few km is probably the minimum worthwhile?
sarabande
Well-Known Member
then what gives range (if you exclude height above SL ? Power or frequency or beam width ?
(This is all triggered by my borrowing a small laser surveying device which can read the distance to an object, by shining a red laser beam. For marine use, bearing is indicated by where it's pointed. Distance is read out on a small screen. Useless in fog, I imagine.)
(This is all triggered by my borrowing a small laser surveying device which can read the distance to an object, by shining a red laser beam. For marine use, bearing is indicated by where it's pointed. Distance is read out on a small screen. Useless in fog, I imagine.)
prv
Well-Known Member
Mostly power, I'd have thought. Probably some effect from frequency at a guess. Can't see why beam width would affect range, except in that it dissipates power over a wider area.
Pete
lw395
Well-Known Member
Beamwidth does affect range in a clutter environment, because if you shine your radar at a larger area of empty sea, you get a larger return from sea clutter, hence a given 'radar cross section' target becomes lost in the clutter sooner.
Also, the wider the beam, the less intense the radar wave at the target, so the weaker the return. And the wave returning to the aerial is received less effectively.
An aerial is a bit like a lens, if you focus it into a narrow beam to transmit, it also magnifies the return.
Power also affects range, it dictates the point at which an echo is above the noise or sensitivity of the receiver.
Frequency (wavelength) affects the beamwidth of the antenna, and also varies the characteristics of the target. And the losses due to atmosphere.
Other things like how short you can make the pulse matter too.
Then there is processing to average the results from a few pulses.
AntarcticPilot
Well-Known Member
Lasers have an extremely narrow frequency range - for practical purposes they can be thought of as being a single frequency. So the receiver has a simple task - look for returns at that frequency and reject anything else. A radar isn't so tightly tuned, so it has to look for returns over a range of frequencies. All this means is that the losses are much higher (I'm sure that someone can explain this better!), so you need more power to start with. Second, the wavelengths are much longer, so to get a narrow beam, you need a correspondingly larger antenna, and practical sized antennae give a much wider beam than a the beam from an optical laser, which benefits both from being monochromatic and being very much shorter wavelengths. Again, that means the power is spread over a wider area, so you need more of it to start off with.
Finally, the short wavelengths of a surveying instrument don't penetrate fog. Even a slight haze that isn't apparent to an observer can block them; I've experienced this myself. Small particles in the air scatter the light so that it gets dispersed and the pwoer returned drops sharpish! The longer the wavelength, the better the penetration of fog - which is why radar has no problems operating in fog.
So, to answer your question, the answer is that range depends on the power that returns to the receiver from the transmitter. Short wavelengths like light or infrared can use less power because the beam is more tightly focussed and have a very narrow range of frequencies, but because of the short wavelength, they don't penetrate fog - even a slight haze that you can see through can block them. Radar wavelengths - a few centimetres and upwards - easily pass through fog, but can't be so tightly focussed because an antenna to focus them so tightly woould be impractically large. They also disperse energy over a wider range of frequencies.
The point about surface scatter is a good one - a radar operating from eye level on a small boat would probably be overwhelmed by surface scatter anyway. Again, it's down to the beam-width - you can't get a narrow enough beam width that the waves aren't in the beam.
Bertramdriver
Well-Known Member
Gentlemen, and Ladies perhaps, thank you for that. Extremely interesting. Hope you find a solution. If you do I doubt whether the military will let you play. What you're describing is an all weather sniping / targeting system.
2copplane
Well-Known Member
I think i have something along these lines stashed somewhere in my garage. Never used it but basically a gun that senses radar, point at at a ship with radar and it lights up.
Zing
Well-Known Member
I think the solution is a simrad/B&G radar. They are not expensive in the small size, turn on in a few seconds and turn off again after your check straight away. Power consumption therefore next to nothing and speed, as fast as you need. Better than a hand held as if there is a problem you need your hands free to deal with it, whilst still monitoring the problem. No need to reinvent the wheel.
srm
Well-Known Member
What the OP describes already exists, or at least used to. It was a proper RADAR set, RAdioDetectionAndRange, that transmitted a pulse and indicated the range of an echo.
Made in the USA in the early 80's and was sold in the UK for a while. I still have one at home and did test it again a few years back. About the size and shape of a brief case. Range quoted as 2 miles, perhaps a little more. Held it in front of you, direction was at 90 degrees to the case's face. Return was monitored by earphones plus an analogue signal meter that indicated range. Low pitch sound at max range increasing in pitch as range decreased. Ran off boats 12v supply. Probably had quite a wide beam width, but effective range was short so practical. Optional extra was a little dome compass mounted on top to monitor target bearings.
Seemed a good idea at the time as fixed radars were prohibitively expensive and power hungry in those days. In practice it had limited use, but did warn if something big was close, or could detect the end of a headland. Mainly used it for reasurance that I was not getting too close to the cliffs when making a DR/RDF landfall in fog. (Long before the advent of GPS)
Can not remember the trade name or give more info at the moment as the set is in Orkney and I am in Canada.
Made in the USA in the early 80's and was sold in the UK for a while. I still have one at home and did test it again a few years back. About the size and shape of a brief case. Range quoted as 2 miles, perhaps a little more. Held it in front of you, direction was at 90 degrees to the case's face. Return was monitored by earphones plus an analogue signal meter that indicated range. Low pitch sound at max range increasing in pitch as range decreased. Ran off boats 12v supply. Probably had quite a wide beam width, but effective range was short so practical. Optional extra was a little dome compass mounted on top to monitor target bearings.
Seemed a good idea at the time as fixed radars were prohibitively expensive and power hungry in those days. In practice it had limited use, but did warn if something big was close, or could detect the end of a headland. Mainly used it for reasurance that I was not getting too close to the cliffs when making a DR/RDF landfall in fog. (Long before the advent of GPS)
Can not remember the trade name or give more info at the moment as the set is in Orkney and I am in Canada.