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Broadband vs. Pulse Radar


 

Capt Ed Wiser for Coastal Angler Magazine, Sept 2013

 

Technological advances continue to make radar lighter, more efficient, more accurate, easier to use, and more affordable. The stand-alone type with a dedicated monochrome screen has faded away to be replaced by multifunction displays with chartplotter, fishfinder, and radar all on one screen. Broadband radar has revolutionized the market and has significant advantages over conventional pulse radar. Here is a quick overview.

 

Pulse radar is the type we think of when radar is mentioned. It was developed concurrently in the US and UK in the late 1930s and has been continuously refined ever since. Many WWII battles were won or lost because of how radar was used or misused.

 

It contains a magnetron which emits a pulsing signal from the rotating arm on the antenna, called an array. These are of two types, the open array where the arm can be seem, and a closed array commonly called a radome. Other factors being equal, the longer the “arm” the better the resolution. This means that with an open array and a six-foot span, you are more likely to see a boat tied to a buoy as two different objects. With a shorter arm as found in a radome, it is likely the two reflections will merge as one object.

 

As the arm swings it is sending out blasts of microwave energy that is reflected off a solid object.  Yes, wave tops and birds are considered solid for our purposes. The time lapse between the signal transmission and the return echo gives range. The bearing is determined by internal computer that knows what direction the arm was facing when it sent out a given pulse.

 

Pulse radar emits significant, often dangerous amounts of microwave radiation. Generally, you do not want to get within ten feet of the beam of a 4 KW radome. The minimum safe distance is much farther for people with heart problems and a pacemaker. This is just one more reason to mount the unit as high as practical.

 

Pulse technology generally offers greater range than broadband through its ability to transmit more power. This is an important consideration in ocean-going vessels but is rarely a factor in recreational navigation.

 

Broadband radar has been called the “most significant radar breakthrough since 1940.” Hyperbole perhaps, but it is a great leap forward. Broadband sends out a continuous signal at a variable frequency while listening for a change in that frequency. It receives and transmits at the same instant, unlike pulse units which transmit and then go through an internal change to receive. This is how the “sunburst” in the middle of the screen so common to pulse units is eliminated. The unit measures the change in frequency to determine bearing and range.

 

Instead of a 2-3 minute warm-up period, the broadband set turns on and transmits immediately. Power consumption is a fraction of the older units using a magnetron. Simrad’s 3G Broadband unit with 24 nautical mile range needs less than 1.5 amps at 12 volts. This reduction in power means decreased microwave hazards. A broadband array puts out about 1/5th the amount of microwaves as your cell phone and you can literally sit next to it all day without any danger.

 

The primary technical difference between pulse and broadband is the constant transmission of one versus the pulse of the other. Broadband makes it possible to process shorter range targets due to not having to switch between transmit and receive modes. Short range resolution is far superior to pulse units at ranges of less than three miles, while pulse units are better at longer distances. This counts in foggy harbors and marinas where the distance between obstructions can be fifty feet or less. Plus, broadband is improving and this disparity between the two types is going away rapidly.

 

Wiring is sometimes easier than pulse units because there is no need to open the dome or do any tuning. It is still critical to precisely place, angle, and secure the unit to conform to the peculiarities of the vessel and operation so as maximize information and minimize clutter. Wire runs and connections are important as always. So how complex is the installation? Simrad warns repeatedly that only qualified techs should install their systems and they provide an extended warranty and an on-board warranty if a factory certified tech does the installation, as do Garmin and Raymarine.

 

Other factors to consider are how the array will be mounted. Are you using a t-top? If so, is there a sheet of aluminum in place to bolt down the unit or will you have to add one? If mounting to a hardtop, is there adequate access to through-bolt the unit? Do you need a wedge to alter the angle? Do you need a pedestal to get the arm high enough to clear obstructions? Will it block navigation lights or spotlights? Can it be placed at an angle where it will be parallel to the surface of the water when underway at cruising speed? Will your electrical system support the power demand? Will the wires be exposed? How will the information be displayed? If on a chartplotter, avoid mixing manufacturers and check to insure the radome or open array will interface properly.

 

Last, but very important, if using a pulse unit will it project a flow of microwave energy on GPS or XM antennas or you and your passengers? One boat I run on a regular basis has the Furuno radar arm at knee level, on a cabin top about 6 feet forward of the flybridge steering station. Needless to say, I don’t use it often.