Collins weather radar question
 

Hello
Can somebody explain this extract from Collins weather radar Manual (page 3-7)

UPDATE RATES
The total time required to complete one cycle of the MultiScan process
in all modes except windshear is 8 seconds. When in windshear mode,
the total cycle time for both MultiScan and windshear is 11.2 seconds.
Thus, there is no significant change to observed weather during one
cycle of the MultiScan process. What does change is the relationship
of the aircraft to the weather. To compensate for this, MultiScan
translates(figure 3-8) androtates(figure 3-9) the stored digital image
to compensate for aircraft movement.
The result is that the Collins MultiScan updates all radar displays every
four seconds in all modes except windshear, in which case the displays
update every 5.5 seconds. One interesting element of this process is
that the antenna scan is no longer tied to the display sweep. This frees
the antenna to perform multiple functions without interrupting the pilot’s
weather presentation

My question: The paragraph says the total time required to complete one cycle is 8 seconds, what is one cycle, is it the sweep the radar antenna does from right to left ?

The second paragraph says the result is that multi scan updates all radar displays every four seconds. Why does it say 4 seconds now, I thought the 1st paragraph said 8 seconds

What does it mean when it says "One interesting element of this process is
that the antenna scan is no longer tied to the display sweep. This frees
the antenna to perform multiple functions without interrupting the pilot’s
weather presentation" ??

Can somebody please take some time out to answer my question and also please explain what are these 2 paragraphs talking about

Thanks in advance

One cycle is from when & where it starts until it is back in the same position again. That would be, for example starting at the far left position, a sweep to the far right then another sweep back to the far left. Normally if those two sweeps take 8 seconds total then there will be two screen updates - one for each sweep - so every 4 seconds. They seem to be using some memory storage to buffer the antenna signal prior to being written to the display. That would allow the display sweep to be somewhat independent from the antenna sweep.

Your display is updated every 1/2 scan with a new "picture" as opposed to an older generation radar that is updating one small slice on eager another. You don't see the continuous sweep.

Left to right scan it makes a new picture to be presented, then right to left the next.

Depending on how much processing is required the new picture may be presented part way through the next scan.

Clear as mud?

Thank you LASJayHawk and Tinstaafl

I get it now.

But what does it mean when it says "One interesting element of this process is
that the antenna scan is no longer tied to the display sweep. This frees
the antenna to perform multiple functions without interrupting the pilot’s
weather presentation"

Personally i have only seen a sweep on the screen when you change the mode from manual to auto or vice-a-versa. Do they mean the older wx radars when you see a display sweep (on the screen) is when there would be an update? Isn't it the same now
can you please explain it in layman terms

Thanks a lot for helping me with this

Think of the older radar sweep like windshield wipers. That's how they paint the screen. And it is tied to the antenna position

The multiscan makes a whole sweep and makes a complete picture. That picture will stay on the screen until it has finished the next picture and then displays that.

One "sweep" is for both captains and f/o's display settings. Don't forget the selected weather radar transceiver is providing both display computers which can be set to different ranges. The fact that it stores the 'image' allows for the movement of the aircraft relative to the scan ie. if the aircraft is banking.:ok: