B&G (Simrad) 4G Radar

[Roy M]

I recognize that the absolute range of my 4kw Raymarine exceeds that of the 4G. I also recognize that keeping the RM in standby uses more juice than the 4G in full transmit. That's why I'll be keeping the more powerful unit, AND have the 4G poised above it (or below it) to fulfill the strengths that I've observed it has. It's only a few pounds more, not enough for my boat to suffer from. And I can instantly confirm any traffic or obstructions while sailing along in periods of poor visibility, both long range and close in. Then there's the factor of redundancy for a very valuable navigational tool (and systems).

[colemj]

Originally Posted by Roy M

I also recognize that keeping the RM in standby uses more juice than the 4G in full transmit.

I doubt that, unless your RM is a cathode tube unit - then it is a function of the display and not the radar. As several of us established by actual measurements in use (in another thread), there is very little difference in power draw when both units are transmitting (0.3-0.5A). In stdby, your RM will draw less current than the 4G in operation.

Mark

[twistedtree]

The 4G radar installation guide, available for download from the Simrad web site, answers most if not all of the questions being posed here.

-The vertical beam for the 4G is +/-25 deg above and below the horizon, with 50% of the beam power concentrated in +/-12.5 deg.

- Ideally the unit is mounted such that none of the beam is blocked by the vessel, and you definitely don't want to block the +/-12.5 deg center part.

- If you have blockage forward of the radar, you can offset its location to move the obstruction out of your give-way zone. They give formulas for figuring the distances to offset.

As a reference point, the Simrad Pulse radar has a +/- 10 deg vertical beam, so the 4G is indeed a wider beam by order 2x

[goboatingnow]

I think there is a lot of misinformation about FMCW radar, I mean it has its place, its like all electronics a compromise. So are magnetron based radars.

Im just waiting for a leisure active electronically scanned array (AESA) radar anyway.!!

Tests have shown that the 4G unit doesnt have anything like savings in standby over pulse radar as claimed. Most people get confused over the 4kw tag stuff anyway.

For range and distance precision, high quality 3degree or better open arrays are going to be best no matter what. Approvals for high energy FMCW systems are very hard to do. ( unless you are a DoD) so energy levels will always be low to met the statutory emissions criteria ( which is whats limits SIMRAD etc al)

Good kit is good kit .

PS if you can see cars in the car park , well!!!!! Id say enage astern rapidly

Dave

[goboatingnow]

Originally Posted by twistedtree

The 4G radar installation guide, available for download from the Simrad web site, answers most if not all of the questions being posed here.

-The vertical beam for the 4G is +/-25 deg above and below the horizon, with 50% of the beam power concentrated in +/-12.5 deg.

- Ideally the unit is mounted such that none of the beam is blocked by the vessel, and you definitely don't want to block the +/-12.5 deg center part.

- If you have blockage forward of the radar, you can offset its location to move the obstruction out of your give-way zone. They give formulas for figuring the distances to offset.

As a reference point, the Simrad Pulse radar has a +/- 10 deg vertical beam, so the 4G is indeed a wider beam by order 2x

Err , I think your wrong here

SIMRAD

Antenna Horizontal Beam Width [deg] 5.2°+/-10% (-3dB width) °
Antenna Receiver Noise Figure [dB] 6
Antenna Rotation Speed 24/36 rpm +/- 10% RPMs
Antenna Vertical Beam Width 25°+/-20% (-3dB width) °


its 25 degress

Raymarine RD424D 4Kw HD dome
3.9° horizontal, 25° vertical

Raymarine has the same vertical , and better horizontal !!

dave

[colemj]

And twistedtree's 6' open array should have a horizontal beam width around 1 degree. That's why I think he will not get any better resolution from the 4G. In fact, I think it will be worse.

The Furuno DRS4D 4kW dome: 3.9* horizontal, 25* vertical, 24/36/48 rpm.

Mark

[colemj]

Originally Posted by goboatingnow

Tests have shown that the 4G unit doesnt have anything like savings in standby over pulse radar as claimed. Most people get confused over the 4kw tag stuff anyway.

When in stdby, the 4G uses ~1.3A less than pulse in stdby. When in use, there is very little difference at all. That 1.3A in stdby is for keeping the magnetron warmed.

So there is a significant power savings with 4G if one chooses to never operate their radar.

Mark

[goboatingnow]

Originally Posted by colemj

So there is a significant power savings with 4G if one chooses to never operate their radar.

Mark

LOL

[twistedtree]

Originally Posted by goboatingnow

Err , I think your wrong here

SIMRAD

Antenna Horizontal Beam Width [deg] 5.2°+/-10% (-3dB width) °
Antenna Receiver Noise Figure [dB] 6
Antenna Rotation Speed 24/36 rpm +/- 10% RPMs
Antenna Vertical Beam Width 25°+/-20% (-3dB width) °


its 25 degress
dave

Would the "-3db width" of 25 deg be equivalent to the 50% power within +/- 12 deg that I reported? Do I remember that every 3db is a halving of the power? It looks like they might just be using different terminology in different parts of their manual. I see the spec section that you are quoting and it's in the same book as the stuff I quoted.

Maybe the 4G radars don't have as sharp a cutoff as the pulse radars? In the 4G installation they are concerned about the extra 12 deg of edge beam, where I've never seen discussion of anything other than the +-12 deg beam on a pulse radar.

I'm going on what I read in the manuals. I'm far from a radar expert.

[zboss]

I feel irradiated already!

[goboatingnow]

Maybe the 4G radars don't have as sharp a cutoff as the pulse radars? In the 4G installation they are concerned about the extra 12 deg of edge beam, where I've never seen discussion of anything other than the +-12 deg beam on a pulse radar.

Almost all pulse radars typically have 25 degrees of vertical beam width, this is a function of antenna design and lobe design. They could have more, but power would be wasted.

Large vertical beam widths are useless anyway, all you are doing is wasting energy. ( why you want to see your deck on your radar being a totally different question!!)

The antenna on a FMCW is not a microwave guide and doesnt have to be as precise anyway.

3db is the standard cutoff point for such measurements, so they can be directly compared , ie there is no effective difference in the antennas performance.


FMCW like the 4G gives better close in resolution for several reasons, one is a basic function of FMCW, one is close in pulse discrimination in pulse radars requires fast processing, ( the pulses drowning in their own noise etc).

So to some extent close in FMCW performance is a side effect. Quite why you want to see the boats 30 feet in front is beyond me.

AT sea, its all about ( ' to abuse the saying , theres no substitute for cubic inches") horizontal beam width and pulse power, combined with now good advanced post processing.

( ever seen teh river radars they use on the EUropean rivers, 10-12 open array , now thats a radar under 1 degree beam width!!)

Here the design dynamics of pulse radar, large arrays, etc simply will always beat anything else hands down.( with what is on the market currently)

High power FMCW is a great system, better suited to modern DSP processing and capable of far better performance then standard pulse. BUT, thats not whats in the SIMRAD 4G

Its a good radar the 4G, whether its a 'great ' radar remains to be seen.

dave

[twistedtree]

Originally Posted by colemj

And twistedtree's 6' open array should have a horizontal beam width around 1 degree. That's why I think he will not get any better resolution from the 4G. In fact, I think it will be worse.
Mark

I honestly have no idea how they will compare in real life. My decision logic went as follows:

1) I've got room for an open array, so that's what I selected. The 10KW model gets you a 6' antenna for better resolution, so I picked that over the 6KW. 25KW seemed overkill. Even with 10KW, I think the horizon will be the limiting factor way more than power.

2) I want a second radar for backup, if nothing else. Loss of a radar in a very remote place can be a real problem. The question becomes what to use as a backup. Choices were a) Pulse dome radar, b) 4G dome radar, c) another open array. If figured that the 4G brings something new to the mix rather than just being a backup with no complementary functionality, so that's what I'm doing it. If there are any situations where the 4G does better than the Pulse, then I'm ahead of the game. If it doesn't, then I got an affordable backup which is what I minimally needed. I see little to no down side to the approach.

It will actually be real interesting to try both side by side, and I'll report on what I find, but it will be a long time before I get to try it.

[colemj]

I don't see anything wrong with your reasoning either. Or any downside. I am jealous that you can mount and use a 10kW unit with a 6' open array. I don't think you will find the 4G comparable in any way with that unit, except for possibly power consumption (I am assuming the larger motor and magnetron in the 10kw unit will use more power). Of course, you have never stated how old that unit is - it is possible that its performance is not up to par because of age.

The horizon is the limiting factor, and you won't see much further with the 10kw vs. 4G, but the resolving power and accuracy of the 10kw should outperform the 4G.

When the marketing people talk about the superior resolution of 4G vs. pulse, I don't think they have units like yours in mind. I think they are marketing into the mostly 2kW buyers and stretching by proximity to the 4kw buyers.

Certainly, it is false to make a summary statement that 4G has superior resolution than pulse, because there are lots of commercial and military pulse units that show otherwise.

Mark

[twistedtree]

Originally Posted by colemj

(I am assuming the larger motor and magnetron in the 10kw unit will use more power). Of course, you have never stated how old that unit is - it is possible that its performance is not up to par because of age.
Mark

It's all new gear (or "kit" as my UK friends say) for a boat under construction.

[CAELESTIS]

Two months or so ago, I was in the San Diego West Marine. The salesman was waiting on two US Navy submariners while I waited. They were buying some cables. I struck up a conversation with them and asked what kind of radar they have (Los Angeles class fast attack subs). Simrad 4G, right off the shelf.