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      A Few Simple Rules   05/22/2017

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jhiller

Radar and frying your nuts

14 posts in this topic

I'm planning on mounting a radar dome on a pole at the aft end of the cockpit. Old fashioned radars had enough radiation that it was always a concern if you were to close to the beam.

I haven't been able to find much info about the newer solid state low power units. Is the risk of frying your nuts and/or brain less ? Pole is more that 8ft high.....

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I'm planning on mounting a radar dome on a pole at the aft end of the cockpit. Old fashioned radars had enough radiation that it was always a concern if you were to close to the beam.

I haven't been able to find much info about the newer solid state low power units. Is the risk of frying your nuts and/or brain less ? Pole is more that 8ft high.....

 

Not an issue with that high of a mount. The distance and the fact that you will not be at the peak of the beam due to antenna fall-off makes it safe. I did the calculations a few years ago and one met the safety standards just by being a couple of feet away. Your increased distance and the antenna issue mentioned above makes it safe (based on current guidelines), although, it obviously isn't good for you. Solid state means nothing, it's transmitter power, PRF, pulse length, and antenna properties. You will be fine.

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I presume you are referring to the new broadband radars from the Simrad Group. They allege that they are "huggable", but you wouldn't catch me that close.

 

The smaller conventional arrays are not particularly dangerous, especially with the separation you are contemplating. Move up in power and I would start to be more concerned.

 

There was a good discussion on Panbo some time ago: My link. The recently released units may be even less of a concern.

 

Starkindler

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I always thought it odd that power boaters mounted their radar on the forward end of the flybridge right at the Crown Jewel height and ran radar in broad daylight. Could explain the dramatic drop in power boaters on the water. That and high gas prices. LOL.

 

 

 

I'm planning on mounting a radar dome on a pole at the aft end of the cockpit. Old fashioned radars had enough radiation that it was always a concern if you were to close to the beam.

I haven't been able to find much info about the newer solid state low power units. Is the risk of frying your nuts and/or brain less ? Pole is more that 8ft high.....

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4G Broadband Radar is the way to go. Been researching this over the past year. Awesome stuff. And because of the low cost of production/materials, I wouldn't be surprised to see this technology available for half what it is now...in the sub $1000 range in a year or so (the 'old' 3G radar is already under $1000). Even then that's pretty high. Realistically, I'd bet they could sell these things for under $500 and still make a hefty profit, but no way they'd sell 'em that cheap just because it's 'Marine'. There is nothing to these things other than a high-powered cell phone and a motor.

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RYA explanation: RYA Broadband Radar

 

Starkindler

 

They're using pulse compression. For engineers, think Fourier Transforms. It is still the average power that hurts the body so a longer pulse at a lower power vs still is more/less equivalent to a higher power pulse that is shorter. The main reason for pulse compression is that it allows lower peak power transmitters (lower cost) to be used to achieve the same performance.

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My dad is a radar guy. Surprising how long these ideas took to get to the marine market, they've been around since the 60s. 4G my ass. The idea is "pulse compression" using a "chirp," which is what the corresponding audio signal would sound like. More generally, the design of a radar signal to give a narrow "point spread function."

 

No downside other than range, as I see it, with an overwhelming upside in higher resolution and low power consumption.

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RYA explanation: RYA Broadband Radar

 

Starkindler

 

They're using pulse compression. For engineers, think Fourier Transforms. It is still the average power that hurts the body so a longer pulse at a lower power vs still is more/less equivalent to a higher power pulse that is shorter. The main reason for pulse compression is that it allows lower peak power transmitters (lower cost) to be used to achieve the same performance.

Now I'm curious, why should I be thinking Fourier transforms? Is there some benefit to doing the power calculation using the Parseval relation? What is the Fourier transform of a chirp?

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RYA explanation: RYA Broadband Radar

 

Starkindler

 

They're using pulse compression. For engineers, think Fourier Transforms. It is still the average power that hurts the body so a longer pulse at a lower power vs still is more/less equivalent to a higher power pulse that is shorter. The main reason for pulse compression is that it allows lower peak power transmitters (lower cost) to be used to achieve the same performance.

Now I'm curious, why should I be thinking Fourier transforms? Is there some benefit to doing the power calculation using the Parseval relation? What is the Fourier transform of a chirp?

C/2*B Where C is the speed of light and B is the bandwidth of the signal...easily figured from the manufacturer. FYI, I spent years with airborne systems that ranged from 100-2000GHz range bandwidth...do the math. Parseval?

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RYA explanation: RYA Broadband Radar

 

Starkindler

 

They're using pulse compression. For engineers, think Fourier Transforms. It is still the average power that hurts the body so a longer pulse at a lower power vs still is more/less equivalent to a higher power pulse that is shorter. The main reason for pulse compression is that it allows lower peak power transmitters (lower cost) to be used to achieve the same performance.

Now I'm curious, why should I be thinking Fourier transforms? Is there some benefit to doing the power calculation using the Parseval relation? What is the Fourier transform of a chirp?

C/2*B Where C is the speed of light and B is the bandwidth of the signal...easily figured from the manufacturer. FYI, I spent years with airborne systems that ranged from 100-2000GHz range bandwidth...do the math. Parseval?

ok, and bandwidth B is derived from the Fourier transform. Thanks. Parseval relates energy in the time domain to energy in the Fourier domain, follows from the Fourier basis being orthonormal. It's why your formula works, actually, so my instincts weren't bad.

 

I'll end this now.

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My dad is a radar guy. Surprising how long these ideas took to get to the marine market, they've been around since the 60s. 4G my ass. The idea is "pulse compression" using a "chirp," which is what the corresponding audio signal would sound like. More generally, the design of a radar signal to give a narrow "point spread function."

 

No downside other than range, as I see it, with an overwhelming upside in higher resolution and low power consumption.

 

I researched this pretty thoroughly a year ago before settling on the 3G Broadband (B&G). Rationale was (is), a) close-in NavAid and harbor/anchorage details, B) low power consumption, and c) not endangering myself or the kids on deck by radar mounted aft on a radar mast. In theory, this allows the mast to be slightly lower too enabling easier servicing of everything up there (radar is still 12' off the water). Arguably, the only negatives are reduced range and missing certain weather features. But for that I have the Zeus chartplotter and Wx. It's fantastic to finally see stuff in the water at night literally next to the boat. Immediate on/off is nice too. I'm happy with it.

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My dad is a radar guy. Surprising how long these ideas took to get to the marine market, they've been around since the 60s. 4G my ass. The idea is "pulse compression" using a "chirp," which is what the corresponding audio signal would sound like. More generally, the design of a radar signal to give a narrow "point spread function."

 

No downside other than range, as I see it, with an overwhelming upside in higher resolution and low power consumption.

I researched this pretty thoroughly a year ago before settling on the 3G Broadband (B&G). Rationale was (is), a) close-in NavAid and harbor/anchorage details, B) low power consumption, and c) not endangering myself or the kids on deck by radar mounted aft on a radar mast. In theory, this allows the mast to be slightly lower too enabling easier servicing of everything up there (radar is still 12' off the water). Arguably, the only negatives are reduced range and missing certain weather features. But for that I have the Zeus chartplotter and Wx. It's fantastic to finally see stuff in the water at night literally next to the boat. Immediate on/off is nice too. I'm happy with it.

I think of the "pre-broadband" radars as brute force, where the modern chirp radars are the finesse option, using well-known (since the 60s) technology. For me, giving up some ability to track squalls for close-to-boat awareness, low power, instant-on, worthwhile.

 

Does anyone know if the new radomes are lighter than the old-school? That would be good, as putting weight aloft on a carbon stick never seemed good to me.

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I have an ICD (implanted defribulator) and have been told to stay out of the path of any rader, radio transmitter or any other rf device. Never use a handheld VHF or a cell phone on my left side or in my left chest pocket. if you have a crewmember with one of these, it is worth thinking about where you put an antenna

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