Two quick radar questions:

[rudewarrior]

Does British radar have a minimum range?

Does U-boat deflection or size (e.g. decks awash) have any effect on radar signal strength. If so, could I get some explanation as to how it works?

Thanx in advance.

[Fish In The Water]

Originally Posted by rudewarrior

Does British radar have a minimum range?

Not in stock, although it is adjustable via the AI_Sensors.dat file.

Does U-boat deflection or size (e.g. decks awash) have any effect on radar signal strength. If so, could I get some explanation as to how it works?

Minimal effect. The stock setting is for a 'surface factor' of 5.0 which is quite low. In addition the 'MinHeight' variable is zero so there is no added advantage in gaining a slight increase in depth.

[rudewarrior]

Ok, some follow ups then:

IRL, is there any data to indicate that the radar used by Allied forces in WWII had a minimum range?

Also, again, IRL, is there any data to conclude that radar was significantly effected by the deflection of the u-boat or its surface radar signature due to the sea state?

There are some mentions to tactics in regards to these conditions in the u-boat KTB's, but considering how the Germans came to the conclusion that the British were picking up on their RWR emissions, I am hesitant to even begin to believe this conclusion.

[Letum]

Originally Posted by rudewarrior

Ok, some follow ups then:

IRL, is there any data to indicate that the radar used by Allied forces in WWII had a minimum range?

Also, again, IRL, is there any data to conclude that radar was significantly effected by the deflection of the u-boat or its surface radar signature due to the sea state?

There are some mentions to tactics in regards to these conditions in the u-boat KTB's, but considering how the Germans came to the conclusion that the British were picking up on their RWR emissions, I am hesitant to even begin to believe this conclusion.

(The following comes from 15mins of goggling and should not be mistaken for actual knowledge or understanding)


There is certainly a theoretical minimum range for all radar.
It's determined by pulse length.

Radar typically sends out a pulse and then goes into a quiet listening mode.
If the target is so close that the start of the pulse is reflected back to the
radar before the radar goes into listening mode, it won't see the target.
In short: the minimum range for any radar set is half pulse length.

If you want to see things a long way from you, it is important to have a
long pulse so you gets lots of echo return, but long pulses have a larger
minimum range, a longer wait before you can repeat the pulse and a poorer
resolution (they can't distinguish between multiple targets less than half a
pulse length apart).

Most 1940s radio sets had a choice of several pulse lengths. I don't know
what the minimum pulse lengths of the allied radars where, but 3-4km would
be a good guess. Of course, if the enemy isn't expecting you to be close
by, he may be using long pulse radar and his minimum range will be much
greater.

Metox and other radar warning systems can be used to tell what pulse
length the enemy is using and, if you know how far away they are, you can
use the pulse length to find out if they can see you on radar. If the enemy
can see you on radar, you can tell when he is getting closer because he will
switch to a shorter pulse length.

Metox might not be able to measure pulse length, but it could concertina
measure pulse frequency and unless the enemy is being very clever, high pulse
frequency will always equate to short pulse length.



How it works in game:
1) You detect radar signals, but don't see the enemy, despite good visibility
Conclusion: The enemy might be too far away to see you on radar, but maybe not.

2) The enemy is close to you and you detect radar
Conclusion: the enemy has seen you on radar

How it worked in reality:
1) You detect short pulse radar signals, but don't see the enemy, despite good visibility
Conclusion: The enemy can't see you on radar. He is exspecting close targets.

2) You detect long pulse radar signals, but don't see the enemy. It's foggy
Conclusion: Maybe the enemy can see you, but if he can see you, he is a long way away. If the pulses get shorter, he can see you and is getting closer.

3) You detect long pulse radar signals and see the enemy close to you
Conclusion: The enemy can not see you on radar. If he switches to short pulse then it means he has likely made visual contact with you.

4) You detect radar signals that switch from long pulse to short pulse constantly
Conclusion: The enemy knows your about somewhere, but has no idea if your close or far away (or perhaps the radar operator is just doing a very thorough job!)

5) You detect pulses that get shorter and shorter rapidly.
Conclusion: Something is approaching you fast! Aircraft? (or the radar is tracking something approaching it fast. Friendly aircraft?)


A question I can't answer is this:
Can more than one ship use radar with out interference?
If not, does that mean that if your on the other side of the convoy from the ship using radar, you can not be seen?
and:
Can Metox and your own radar both be used at the same time?

[rudewarrior]

Originally Posted by Letum

There is certainly a theoretical minimum range for all radar.
It's determined by pulse length.

I looked up some pulse lengths for some radar on aircraft around that time, and they all seem to have pulse lengths no longer than 2.5 us. This works out to a 325 m minimum range.

In the KTB's reports suggest that the escorts have difficulty picking up surfaced u-boats by radar at about 1.5 km. The then suggest that you turn perpendicular to the course of the escort to escape. It seems that this is dangerous and unreliable (but they were having some real problems fighting come Mar '43). To get a 1.5 km minimum range would require a pulse length of 10 us, which seems to be a pretty long time, especially b/c they would probably switch to a shorter pulse length to start dealing with the U-boat as it got closer anyway.

Is there any indicator that there were mechanical issues that would force a minimum range? Say that the apparatus is high up and cannot "see" targets below a certain angle from horizontal, therefore it results in a minimum range?

Also, does anyone know what the destroyer AI would do when it loses contact at ~1.5 km? I am assuming it would head to the last known spot as quickly as possible to look for you. How would visual contact start working at this point?

[Leitender]

Interesting research!

Maybe this is the reason for the reported 1.5km range. The radar antennas were (are) mounted on top of the highest mast (about 15-30m, depending on the ship´s size) to get the widest range. If the target is close, the antenna has to be rotated downwards with the result of watching into the sea, not horizontally parallel to the water surface.

It´s just an asumption, but I read that the outlooks of the japanese Subs had similar problems when looking into the water, not parellel to the surface. Their british counterparts (and the german too) had a quite lower base on which the outlooks stood, so they could recognise the enemy´s silhouette much better. This was obviously the reason, why many japanese Subs were sunk in the indian ocean by british subs.

To get back to the radar, i figure that the radar display is to be disturbed when the antenna looks down into the water. I remember in the 80´s the military aircrafts in Germany exercised flying at very low height (less then 100m/50m, don´t know anymore) not be caught up by russian radar. (I can remember well because in that time many germans protested against those low-level flights).

If not a minimum range, there should be a minimum elevation, below that radar doesn´t work.