beryl george wrote in
:

Can any one give guidance or know of a possible
internet download that might help in the initial
manual settings of tune, pulse width, gain,
sea and rain clutter.

The controls seem so inter-reactory, by their
adjustment to my eye identical echo images are
displayed. Even with tune I cannot really
determine any great changes.

There must be some logical progression to make
these adjustments rather than my constant tweaking,
all guidance greatly received.

Beryl.


Tune - tunes the receiver frequency to the transmitter's frequency. You'll
only see any difference on very weak targets, like a bouy way off in the
distance, but over the horizon. Radar is very widebanded, as is its
receiver. Tuning is very broad because of this. Find a very weak target
that barely makes a dot as far off as you can see anything. Tune it for
maximum return, then leave it alone....tuning done. If it has automatic
tuning, just leave it on. Electronics tunes better without you.

Pulse width determines how long the radar transmitter stays on during its
transmission period. During the transmitting, the receiver is turned off.
The pulse width, how long it keeps transmitting in microseconds, determines
how long the receiver is turned off...on the screen this is measured from
the boat in the center of the display outward. The shorter the pulse
width, the CLOSER the radar can see near the boat....like that bouy we're
about to run over in the fog. The narrower pulse width also is part of how
FAR the radar can "see". A narrow pulse is less likely to get a good
return off a far target thrashing about in the waves than a wide pulse
width, which increases our chances of getting a return the receiver can
detect. So, if we want to see the bouy 100 yards away, we use a very
narrow pulse width. If we want to see a tower 12 miles away, we use a wide
pulse width. Modern radars now adjust their pulse widths, automatically,
when you change ranges on the display to optimize this setting. When the
radar is on the 12 mile range, the narrow pulse width produces so narrow a
"target blip" as to be near unreadable. The wide pulse width makes a
wider, more easily seen target, on such a long range. It shows up in
thickness from the center of the screen to the edge (that's time on the
display).

Gain is how sensitive the receiver is. It's like a video volume control,
what the receiver sees. Modern radars are, again, automatic to produce a
display of the targets, without too much gain, which displays white noise
as false target spots at random. Turn the gain up until you see a bunch of
clutter, then reduce it back until the clutter just disappears and the
targets are all you can see. At night, you can raise the gain a bit as the
thermal noise caused by the sun radiating off everything, including the
antenna parts it heats, drops. You'll have to reduce it again in the
daytime as the thermal noise starts producing clutter, again. Rainstorms
also make lots of clutter, drop the gain to a point where the rain doesn't
wipe out the targets. This is all analog, you know...even if you've a
digital display unit.

Sea and Rain clutter filters are sort of like the treble control on your
stereo. They filter out fast returns caused by the radar bouncing off wave
tops and rain drops, but let the big targets like ships and boats still
show up. If you set them too high, they filter out everything and you run
over that damned bouy we were headed for in the fog. Turn them up just
enough to reduce the clutter to a reasonable level. They're not very
effective. New radars have digital signal processing that only shows you
targets that act like ships/boats/bouys....repetitive echos that appear to
come from still or slow-moving targets. Random returns that don't repeat
all the time are simply not sent to the digital display. Much
improvement...vast improvement. They're also automatic from the smartassed
electronics.

Does this help?

Not to worry....The world is going to help you with AIS....

http://www.nasamarine.com/AIS/AIS.html
http://www.jrcamerica.com/product.as...311&l1=5311&l2
=
http://www.ozsay.com/urun.asp?prod_id=412
http://www.mcga.gov.uk/c4mca/mcga-ml...DE77872207FE9A
http://www.panbo.com/yae/archives/cat_ais.html
http://www.navcen.uscg.gov/enav/ais/default.htm

AIS provides you with, on each target:
• MMSI (Maritime Mobile Service Identity)
• IMO Number (where available)
• Call sign & vessel name
• Length and beam
• Type of ship
• Location of position-fixing antenna on ship
• Ship's position with accuracy indication and integrity status
• UTC
• COG, SOG and Heading
• ROT (Rate of Turn) where available
• Ship's draught
• Navigation status
• Hazardous cargo (type)
• Destination and ETA (at captain's discretion)
• Short safety-related messages and free messages

Wanna watch AIS LIVE! on the net? Europe is online at:
http://aisfree.aislive.com/
really cool...AIS is on VHF and you get a target EVEN AROUND THE BEND!

--
Larry