Broadband Radar
- Thread starter Bob Poff
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Hello,
I good source for info on radar (and all things marine electronics) is at Panbo.
http://www.panbo.com/
Barry
I good source for info on radar (and all things marine electronics) is at Panbo.
http://www.panbo.com/
Barry
By the overwhelming response in this thread, they must be selling loads of them.
The improvement in resolution makes sense to me.
The elimination of the the Main Bang is elementary.
What I wonder about is the range claims with 100mW of transmitter power.
However, I haven't found what the antenna gain is.
Must have a great receiver.
The improvement in resolution makes sense to me.
The elimination of the the Main Bang is elementary.
What I wonder about is the range claims with 100mW of transmitter power.
However, I haven't found what the antenna gain is.
Must have a great receiver.
Bob, one of the magazines did a report on the broadbands versus the regulars a few months back.. report was favorable, but sometimes it is hard to tell such a "report" from advertising..??
Here is the link:
http://www.cruisingworld.com/gear-a...dband-radar-in-the-real-world-1000077711.html
Here is the link:
http://www.cruisingworld.com/gear-a...dband-radar-in-the-real-world-1000077711.html
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High bandwidth means a lot more power on the target. A matched filter in the receiver causes a long pulse to look like a short pulse when received, which allows for a high degree in resolution in terms of range, in addition to a higher signal-to-noise ratio (more sensitivity). Digital radar processos allow things to be done more cheaply with software rather than hardware. A time-delay program is a hell of a lot cheaper than a time-delay lines.
Would that still apply when the transmitter is operating in CW with the carrier sweeping about 70 Mc as this "broadband radar" does?
Gotta be a heck of an improvement when they claim the same range as a 2.5 KW pulsed radar with the 100 mW this thing runs.
Gotta be a heck of an improvement when they claim the same range as a 2.5 KW pulsed radar with the 100 mW this thing runs.
I think you're a bit confused. The OP Is talking about the new broadband radar from Northstar/Lowrance/Simrad. It doesn't use a high-energy pulse, but rather a modulated continuous low power signal instead.
One issue that seems to be a problem with Broadband radar is the range and interference from other radar band signals. They're supposedly working on this, but this affects the discrimination of the radar at longer ranges. However, in the closer ranges, broadband radar is supposed to be the bomb.
One issue that seems to be a problem with Broadband radar is the range and interference from other radar band signals. They're supposedly working on this, but this affects the discrimination of the radar at longer ranges. However, in the closer ranges, broadband radar is supposed to be the bomb.
A frequency modulated pulse is one way to increase bandwidth. A digital radar is going to have a matched filter that will cause the returns associated with different frequencies (from the same frequency modulated pulse) to stack up so that the return pulse will appear narrower to the receiver. Though the pulse is narrower, it contains the same energy, causing the peak voltage in the detector to be higher (more sensitivity). An analogy would be to compare the RF (radio frequency) energy in the pulse going through a matched filter to the air in a balloon. Squeezing the balloon causes the balloon to bulge out else where (provided it doesn't pop). My remarks are based on general radar theory and is not constrained to just marine radars of a specific brand.
Where I'm getting confused is that this isn't conventional radar.
Not pulsed at all, or so they describe it.
They are presenting it as operating purely in CW.
Here's a link : Simrad FMCW radar
Ahhhhhh.....
Re-reading your last, I think that I getting the picture. (pun intended)
It's not that they have a hot receiver, but much better processing.
If it plays as well as they claim, it would be great. No magnetron to mess with.
Low power consumption, no dead zone from the main bang, great resolution.
I see you're in Alabama.... close to Enterprise by chance?
Not pulsed at all, or so they describe it.
They are presenting it as operating purely in CW.
Here's a link : Simrad FMCW radar
Ahhhhhh.....
Re-reading your last, I think that I getting the picture. (pun intended)
It's not that they have a hot receiver, but much better processing.
If it plays as well as they claim, it would be great. No magnetron to mess with.
Low power consumption, no dead zone from the main bang, great resolution.
I see you're in Alabama.... close to Enterprise by chance?
Yup. Everyone is a radar engineer up here.
I didn't read the link but you said FMCW. I suspect that the purpose of FM--frequency modulation--is to widen the bandwidth. The CW--continuous wave--is a misnomer. Though the transmitter will always be transmitting while the receiver is listening (as opposed to switching the transmitter off when the receiver is switched on to listen), there will be still short burst pulses being transmitted; moreover, the frequency of each pulse will be chirped over its duration. The matched filter in the receiver will cause each return pulse, reflected from a target, to stack up and form a shorter blip with a higher peak causing a higher voltage in the detection circuit. This is slick because the transmitted pulse utilizes low power, allowing the receiver to always be on. It is slick but not innovative. They've been doing this stuff in military radars for 1/2 a century. However, universal computers allow this to now be done very cheaply ;-).
I've been holding off on buying an analog radar for my old morgan until I can find an affordable digital one. The day is getting near.
I didn't read the link but you said FMCW. I suspect that the purpose of FM--frequency modulation--is to widen the bandwidth. The CW--continuous wave--is a misnomer. Though the transmitter will always be transmitting while the receiver is listening (as opposed to switching the transmitter off when the receiver is switched on to listen), there will be still short burst pulses being transmitted; moreover, the frequency of each pulse will be chirped over its duration. The matched filter in the receiver will cause each return pulse, reflected from a target, to stack up and form a shorter blip with a higher peak causing a higher voltage in the detection circuit. This is slick because the transmitted pulse utilizes low power, allowing the receiver to always be on. It is slick but not innovative. They've been doing this stuff in military radars for 1/2 a century. However, universal computers allow this to now be done very cheaply ;-).
I've been holding off on buying an analog radar for my old morgan until I can find an affordable digital one. The day is getting near.
Broadband Radar - Info gleaned to date
A pulsed radar on its 6 mile range with a peak pulse power of 4Kw, a pulse length of 250ns and a pulse repetition frequency (PRF) of 1,000pps puts out and average power of only 1 watt.
Because a broadband or continuous wave (CW) radar floods the targets with microwave energy continuously it does not need to use powers in the orders of kilowatts so magnetrons with their high voltage pulses are not necessary. The CW signals carry similar amounts of energy but it is just spread over a longer time period rather than in one big pulse.
The CW radar technique is to repeatedly sweep the transmitter frequency in a linear? manner through a predetermined band. When the signals are reflected back from targets to the receiver the transmitter is already on a slightly different frequency so the receiver measures the difference in the two frequencies and, with a knowledge of how long it was between the transmitter being on the original frequency and its present one, it can calculate how far these signals have travelled - and thus the range of the target.
This occurs for all target reflections so a picture can be built up in a similar way to the PPI (Plan Position Indicator) displays of pulsed radars.
The actual operating frequencies are in the same waveband as pulse radars so they can use similar scanners - which thus have similar beam widths. So the claimed increase in resolution of CW radars only applies to the range discrimination and not the angular discrimination. Improvements in angular (azimuth) discrimination are only achieved through signal processing which could equally benefit pulse radars too. I believe CW radars will also suffer sea clutter and rain clutter as do pulsed radars.
Other apsects are of interest. A CW radar does not activate, nor can it display a RACON which is a buoy which re-transmits a series of identifying dashes when it is scanned by a pulse radar. These are of great interest to ships but less so to the average leisure sailor.
Of much more importance is that CW radars do not activate or do they 'see' SARTS (Search & Rescue Transponders). So, if you have such devices on board you had better hope the search vessels are not looking for you on their broadband CW radars.
It just happens that the "Authorities" are keen to get rid of pulsed radars because they occupy a large part of the spectrum which they could otherwise sell to mobile telephone companies and the like.
This spectrum they wish to sell does not 'belong' to anyone in particular so I am enraged by the thought of governments wanting to license companies for its use. I see this like trying to sell us the air we breath!
Hitherto the only charges for radio and radar spectrum were just to cover the administration and regulation costs - and were reasonable. Now governments seek to make tremendous profits, (billions of pounds/dollars/euros) from something they do not own. Here in the UK we now have the "Opportunity Pricing" of wavebands and the on cost to telephone companies - and hence the phone users - are extortionate. Here we are engaged in battle with our government to prevent hefty licencing costs being lumped upon sailing club rescue boats and their shoreside radios.
Even our Royal National Lifeboat service, which is a charity, has had to lobby hard to keep its radio and radar frequencies free of Opportunity Pricing charges.
A pulsed radar on its 6 mile range with a peak pulse power of 4Kw, a pulse length of 250ns and a pulse repetition frequency (PRF) of 1,000pps puts out and average power of only 1 watt.
Because a broadband or continuous wave (CW) radar floods the targets with microwave energy continuously it does not need to use powers in the orders of kilowatts so magnetrons with their high voltage pulses are not necessary. The CW signals carry similar amounts of energy but it is just spread over a longer time period rather than in one big pulse.
The CW radar technique is to repeatedly sweep the transmitter frequency in a linear? manner through a predetermined band. When the signals are reflected back from targets to the receiver the transmitter is already on a slightly different frequency so the receiver measures the difference in the two frequencies and, with a knowledge of how long it was between the transmitter being on the original frequency and its present one, it can calculate how far these signals have travelled - and thus the range of the target.
This occurs for all target reflections so a picture can be built up in a similar way to the PPI (Plan Position Indicator) displays of pulsed radars.
The actual operating frequencies are in the same waveband as pulse radars so they can use similar scanners - which thus have similar beam widths. So the claimed increase in resolution of CW radars only applies to the range discrimination and not the angular discrimination. Improvements in angular (azimuth) discrimination are only achieved through signal processing which could equally benefit pulse radars too. I believe CW radars will also suffer sea clutter and rain clutter as do pulsed radars.
Other apsects are of interest. A CW radar does not activate, nor can it display a RACON which is a buoy which re-transmits a series of identifying dashes when it is scanned by a pulse radar. These are of great interest to ships but less so to the average leisure sailor.
Of much more importance is that CW radars do not activate or do they 'see' SARTS (Search & Rescue Transponders). So, if you have such devices on board you had better hope the search vessels are not looking for you on their broadband CW radars.
It just happens that the "Authorities" are keen to get rid of pulsed radars because they occupy a large part of the spectrum which they could otherwise sell to mobile telephone companies and the like.
This spectrum they wish to sell does not 'belong' to anyone in particular so I am enraged by the thought of governments wanting to license companies for its use. I see this like trying to sell us the air we breath!
Hitherto the only charges for radio and radar spectrum were just to cover the administration and regulation costs - and were reasonable. Now governments seek to make tremendous profits, (billions of pounds/dollars/euros) from something they do not own. Here in the UK we now have the "Opportunity Pricing" of wavebands and the on cost to telephone companies - and hence the phone users - are extortionate. Here we are engaged in battle with our government to prevent hefty licencing costs being lumped upon sailing club rescue boats and their shoreside radios.
Even our Royal National Lifeboat service, which is a charity, has had to lobby hard to keep its radio and radar frequencies free of Opportunity Pricing charges.
Here's a dumb question:
Will a new broadband radar connect to an earlier Raymarine C series display?
I've had the display for awhile but never got around to buying an analog radar. Besides, I don't have enough room on my pedestal to mount a wide screen display.
Will a new broadband radar connect to an earlier Raymarine C series display?
I've had the display for awhile but never got around to buying an analog radar. Besides, I don't have enough room on my pedestal to mount a wide screen display.
Interesting. I had never heard of this mode before Simrad starting hawking it.
But then I've never been that interested in radar until recently.
Looks like I'm going to need to do start reading.
Snotter, I had the chance to work with Fred Newsome for a week last summer when he came to upgrade our EEC 250 KW weather radar here at work. Found it fascinating. I've played radio for over 30 years, but nothing with radar. Learned a lot that week.
Certainly enough to tell me that I still know nothing. As you can tell by this thread.
And donalex, thanks for your input. I didn't realize the peak/average ratio was that great.
But then I've never been that interested in radar until recently.
Looks like I'm going to need to do start reading.
Snotter, I had the chance to work with Fred Newsome for a week last summer when he came to upgrade our EEC 250 KW weather radar here at work. Found it fascinating. I've played radio for over 30 years, but nothing with radar. Learned a lot that week.
Certainly enough to tell me that I still know nothing. As you can tell by this thread.
And donalex, thanks for your input. I didn't realize the peak/average ratio was that great.
Other manufacturers
Only one manufacturer makes them at present. In my case, I really really hope Garmin can adopt this technology quickly and produces a radar unit that is compatible with my 3010. Not sure if there are patents preventing that, though.
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