Hi Jeff;
I don't know if you got your answer yet or not what I learned from
the Navy.
Your radar sends out a fairly directional beam of energy straight
out the front of the antenna, then receives the reflection of the
other ships (usually large and metal) and shows you the blip on the
screen. Ideally that's all you'll see. But radar antennas aren't
perfect and they also transmit a tiny bit of energy off to each side
of the main beam at about 45 degrees relative to the main beam. So the
arc you see starts as the first lobe sweeps the big ship and the
antenna sees that as the beginning of the arc. Then the main beam
sweeps the ship and you get your blip. Then the other lobe sweeps the
ship and that's the arc on the other side of the blip your seeing.
This all happens as the antenna is rotating pass the large metal ship.
Well I hope that helps.
Steve Hicks

As I recall, the spec mentions sidelobe energy at something like -20dB. That seems like a big
reduction, but when I'm passing a large ship at several hundred yards, that's still a lot of energy
bouncing around.
Thanks,
-jeff

"Steve" wrote in message
om...
Hi Jeff;
I don't know if you got your answer yet or not what I learned from
the Navy.
Your radar sends out a fairly directional beam of energy straight
out the front of the antenna, then receives the reflection of the
other ships (usually large and metal) and shows you the blip on the
screen. Ideally that's all you'll see. But radar antennas aren't
perfect and they also transmit a tiny bit of energy off to each side
of the main beam at about 45 degrees relative to the main beam. So the
arc you see starts as the first lobe sweeps the big ship and the
antenna sees that as the beginning of the arc. Then the main beam
sweeps the ship and you get your blip. Then the other lobe sweeps the
ship and that's the arc on the other side of the blip your seeing.
This all happens as the antenna is rotating pass the large metal ship.
Well I hope that helps.
Steve Hicks

On Tue, 23 Dec 2003 06:46:41 -0500, "Jeff Morris"
wrote:

As I recall, the spec mentions sidelobe energy at something like -20dB. That seems like a big
reduction, but when I'm passing a large ship at several hundred yards, that's still a lot of energy
bouncing around.
Thanks,
-jeff

I remember a couple of powerful radars you had to turn off if you were
coming too near a reflective object, like driving by another ship in a
channel. There was so much power reflected back, the stupid things
would blow their OWN receivers!

Navy used to have a huge air search radar, AN/SPS-30, easily
identifyable because of its huge round dish with giant "arm" out in
front to hold up the big waveguide and feed horn. It ran so many
megawatts it would cut seagulls out of the air, cooking them in
flight. We used to point them at the moon and pulse them, manually,
while feeding a signal generator into the test repeater (display) so
it would keep sweeping. That way you could count the number of sweeps
and measure the distance to the moon! You could actually measure the
difference over time in the moon's distance with it. Cool stuff.


Larry W4CSC

NNNN

On Tue, 23 Dec 2003 14:10:14 GMT, (Larry W4CSC) wrote:

On Tue, 23 Dec 2003 06:46:41 -0500, "Jeff Morris"
wrote:

As I recall, the spec mentions sidelobe energy at something like -20dB. That seems like a big
reduction, but when I'm passing a large ship at several hundred yards, that's still a lot of energy
bouncing around.
Thanks,
-jeff

I remember a couple of powerful radars you had to turn off if you were
coming too near a reflective object, like driving by another ship in a
channel. There was so much power reflected back, the stupid things
would blow their OWN receivers!

Navy used to have a huge air search radar, AN/SPS-30, easily
identifyable because of its huge round dish with giant "arm" out in
front to hold up the big waveguide and feed horn. It ran so many
megawatts it would cut seagulls out of the air, cooking them in
flight. We used to point them at the moon and pulse them, manually,
while feeding a signal generator into the test repeater (display) so
it would keep sweeping. That way you could count the number of sweeps
and measure the distance to the moon! You could actually measure the
difference over time in the moon's distance with it. Cool stuff.


Larry W4CSC

NNNN


Oh yah, that must have been a sight. A trail of dead seagulls floating
behind the ship. Or did they just catch on fire and burn up before
they hit the water.

Gary

On Tue, 23 Dec 2003 15:58:07 GMT, Gary Schafer
wrote:


Oh yah, that must have been a sight. A trail of dead seagulls floating
behind the ship. Or did they just catch on fire and burn up before
they hit the water.

Gary

Just dropped. Never knew what hit 'em.

I heard a story back when there was a Soviet Union of a radar picket
ship that trained its SPS-30 onto the bridge of a Soviet warship that
kept threatening to ram our ship. Some guys I knew aboard it said you
could see flourescent tubes exploding on the deck and in the wheel
house....(c;

Of course, it could all be BS, but the physics of it is quite
possible. Noone was allowed outside on the 02 level when the radar
was on the air.


Larry W4CSC

NNNN

On Tue, 23 Dec 2003 15:58:07 GMT, Gary Schafer
wrote:


Oh yah, that must have been a sight. A trail of dead seagulls floating
behind the ship. Or did they just catch on fire and burn up before
they hit the water.

Gary

Just dropped. Never knew what hit 'em.

I heard a story back when there was a Soviet Union of a radar picket
ship that trained its SPS-30 onto the bridge of a Soviet warship that
kept threatening to ram our ship. Some guys I knew aboard it said you
could see flourescent tubes exploding on the deck and in the wheel
house....(c;

Of course, it could all be BS, but the physics of it is quite
possible. Noone was allowed outside on the 02 level when the radar
was on the air.


Larry W4CSC

NNNN

We used to point them at the moon and pulse them, manually,
while feeding a signal generator into the test repeater
(display) so
it would keep sweeping. That way you could count the number of
sweeps
and measure the distance to the moon! You could actually
measure the
difference over time in the moon's distance with it. Cool
stuff.


Larry,
We those pulses a CQ????? :-p

Leanne W1WXS
s/v Fundy

On Tue, 23 Dec 2003 13:30:49 -0500, "Leanne" wrote:



Larry,
We those pulses a CQ????? :-p

Leanne W1WXS
s/v Fundy


Not enough power for SETI.
Larry W4CSC

NNNN

I was thinking of moonbounce. The moon, I believe is -54db
passive reflector and with that power, there should have been a
bit coming back. Old Paul Wilson did it with a lot less on 2
mtrs.

Leanne

"Larry W4CSC" wrote in message
...
On Tue, 23 Dec 2003 13:30:49 -0500, "Leanne"
wrote:



Larry,
We those pulses a CQ????? :-p

Leanne W1WXS
s/v Fundy


Not enough power for SETI.
Larry W4CSC

NNNN

I was thinking of moonbounce. The moon, I believe is -54db
passive reflector and with that power, there should have been a
bit coming back. Old Paul Wilson did it with a lot less on 2
mtrs.

Leanne

"Larry W4CSC" wrote in message
...
On Tue, 23 Dec 2003 13:30:49 -0500, "Leanne"
wrote:



Larry,
We those pulses a CQ????? :-p

Leanne W1WXS
s/v Fundy


Not enough power for SETI.
Larry W4CSC

NNNN