Active radar reflector response to broadband radar

[NPCampbell]

Originally Posted by Cyrus Safdari

As I understand it of course once the radar identifies a target then it makes no real distinctions however the selling point of active reflectors is

1- it presents a much better signal than the current passive reflectors
thus making you more likely to be seen
Is this still the case?

2- *Apart from what the ships radar picks up* (or not) the active blip was supposedly more likely to *get the attention of the ships operators* by making you "look like a tanker" due to the much better signal.

Is this still the case?

I don't believe it is the case.

A radar screen contains spatial information so a strong return from a single pulse can really only be indicated by single dot unless you want to skew the spatial information on the screen. Different colors however, are used to represent the strength of the signal. Additionally, there are other means to tell the size of the object (apart from AIS, doppler shift, etc)

For instance, lets say a boat 35 feet long is perpendicular to you, 1 mile out. If your pulse repetition frequency is quick enough, it will paint that boat multiple times as the radar sweeps across it.

For instance, take a CHIRP radar with a rotation rate of 24 RPM with a minimum PRF of 1200Hz. This means that a pulse will be sent out every 24*360/60/1200 = .12 degrees. An arc length of 35 feet (the boat length) at 1 mile forms a .38 degree angle to the radar transmitter. This means the boat will be painted exactly 3-4 times with every pass. Therefore the radar should show 3-4 blips if all of the reflections were detected.

Conversely, a 900 foot tanker running perpendicular to you at 1 mile will get painted 80+ times showing a line 20 times longer.

I am ignoring the fact that modern solid state radars don't use narrow pulses with scalar returns and they routinely have higher PRFs than 1200. They use wide pulses with swept frequencies providing even more resolution information.

[Nicholson58]

Originally Posted by goboatingnow

Sorry 1.5 is plenty distance to avoid another yacht. Ships don’t use echo maxes. Passive reflectors on FMCW radars are even worse anyway.

I’m not sure what your point is. Broadband radars are so good , the yacht with them will see you echomax or no echomax.

Very few people have active radar target enhancers anyway

I have to agree totally with everything he said. What the heck are you driving that need more than a quarter mile to get out of the way? Where is your AIS? In the dark, fog, you will both be aware of the other vessel way before this threshold. Just consider the 1.5 a data point in your knowledge base for the echomax.

You and the other guy are both supposed to be standing visual watch. Your radar will see the other guy at leas ten miles out. Where we sail, Caribbean, anyone with modern radar is highly likely to be running AIS. In daylight, nobody runs radar except commercial vessels.

[capn_billl]

My take on this is.

1. I have a newer chirp style radar, and love it.

2. As ols S band radars break more people will replace them with modern radar, even on the big ships.

That leaves active reflections as an obsolete piece of kit to be chunked alongside the Loran, and syncro radars of a bygone era.

[drdoyle]

Your problem is not whether or not you will be sceen, it is that secondary crew manning the bridge at night will avoid you. The watch standers often don't know how to change coarse. They will come up directly behind you and run you down. Many incidents in the Bahamas in the last couple of years. Two major crashes from behind and many near misses. Don't forget to watch your stern. You might want to get an ais reciever and a radar alert alarm.

[Brian Renwick]

Keep a good lookout.
Visibility is moderate, about 5 miles.
Wind 28 knots, plenty of white horses.
Watchkeeper on bridge of big container ship, motoring at 22 knots, has a look around the horizon and sees the white yacht 3 miles off his stbd bow, but doesn’t realise it is a yacht (it looks similar to a breaking wave on a dull day). He assesses the radar screen, but fails to notice the echo of the yacht as it is buried amidst the sea clutter, which has been inexpertly tuned..
Watchkeeper goes to chart room to brew a hot drink. 2 minutes later he answers a phone call from the captain. By now 3 minutes have lapsed and the yacht is now out of sight (from Mk 1 eyeball, and radar) under the flare of the bow…
Did I mention that for the last 10 minutes the yacht watchkeeper has been distracted by a piece of uncooperative gear, and doesn’t have enough juice in the batteries to run a radar even if he had one? Doesn’t have a working AIS. Returns to the cockpit just in time for the Big Crunch, combined speed of 28 knots. The crew on the box boat don’t notice anything until the pilot embarks a week later and mentions the sail wrapped around the stbd anchor😱…

[RaymondR]

After being missed by about 200 yards by a very large one carrier I scrapped my old radar for dopler unit. My philosophy is that since I have no control over the efficiency of the other ships watch standing crew I want be aware of it in plenty of time to dodge.

[goboatingnow]

Originally Posted by drdoyle

Your problem is not whether or not you will be sceen, it is that secondary crew manning the bridge at night will avoid you. The watch standers often don't know how to change coarse. They will come up directly behind you and run you down. Many incidents in the Bahamas in the last couple of years. Two major crashes from behind and many near misses. Don't forget to watch your stern. You might want to get an ais reciever and a radar alert alarm.

Just get a transmit ais. Watch the commercial ships turn to avoid WAFFIs.

[CarlF]

Why would anyone install an active radar reflector when a good AIS transceiver costs less?

AIS has been the primary collision avoidance system on ships for decades. Why would you not want to be visible on their AIS display?