This is more bull**** Jeff. There is nothing wrong with your
magnetron.
The "rings" that you see associated with a strong target are the
result of side lobes on your antenna.

If it were the magnetron "double pulsing" you would see multiple
targets at the same azimuth as the real target. They would be in front
of or behind the real target.
Unless of course you had a bad magnetron and you were right on top of
a large target then you could get rings and multiple targets together.

The radar antenna has a narrow beam that sweeps around in azimuth. The
antenna azimuth is synchronized with the sweep on your display so that
the sweep on your display always points in the same direction as your
antenna.

To picture clearer what is happening, think about what it would be
like if there were no motor turning the antenna. You had to rotate it
by hand. As you point the antenna at a target the transmitter is
transmitting pulses many times per second. Between each of those
pulses your receiver listens for an echo of those pulses being
reflected from a target. Depending on how far away the target is
determines how long it takes for the echo to return to the receiver.

The sweep on your scope is traveling out toward the edge of your
display at the same rate that it takes to send out the radar pulse and
get it back. This also happens many times per second. Exactly in sync
with the radar pulse being transmitted. The center of the screen is at
the time the radar pulse leaves the radar transmitter. Time zero =
zero miles.

As an echo is received the sweep gets intensified at that time.
With out the antenna rotating you would see a bright spot at the range
on the sweep line on your screen. Now as you manually slowly rotate
your antenna in one direction you will continue to see the bright spot
at the same range but the sweep will be at a slightly different
azimuth on your display. The spot will now get stretched out and
appear to be forming a small line or arc still at the same range. This
arc will be visible as long as the target is within the beam width of
your antenna.

The line or arc appears on the screen due to the digital circuitry
holding or remembering the signal. On older radar's without digital
storage this holding of the arc was dependent on the type of
phosphorus used in the display tube. It would slowly fade. You tv tube
works much in the same way but fades much faster.

Anyway, as you continue to manually rotate your antenna, you will
reach an azimuth where the beam width of the antenna is no longer
illuminating the target. The dot on your display sweep will not be
seen any more.
But the small arc will still be visible because of the storage. It
will hold that image or display until the next time the sweep has made
a full 360 degree rotation. Then it will erase that information and
display the new information if there is any to display.

As you continue to rotate the antenna, if one of the side or rear
lobes are strong enough you will again see the dot on the sweep appear
at the same range as you did earlier. But now your antenna may be
pointed 10 or 20 degrees away from the target and your display, being
in sync with your antenna will also be 10 or 20 degrees off the
target. So the dot will look like there is another target at the same
range but a different azimuth to the original target. As you continue
to turn the antenna it will form an arc on the screen as long as that
side lobe is strong enough to give a return signal.

It is not uncommon to be near a large ship and see what looks like the
same ship 180 degrees from the original.

Sometimes when the target is close and very large you can pick it up
in 360 degrees on your radar. Turning down your gain will get rid of
the unwanted responses as your main lobe is always stronger than the
side lobe signals. But be careful if you turn down the gain for this
purpose as it will also eliminate many of the weaker wanted targets
too.

Regards
Gary


On Wed, 3 Dec 2003 15:24:35 -0500, "Jeff Morris"
wrote:

I hope its not age in my case - my radar is less than 4 years old and I believe
I had this effect from the beginning.




"Me" wrote in message
...
In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

Hmmm, sounds like maybe your Magnitron is getting old. Been know to
cause mutiple echo's from a single boat, or rock. If they are infront
of and behind the real target, it is reflections. If it is right or left,
could be what is known as Multiple Pulsing.

Me

I've seen this problem on 3cm, 10cm; big sets, small sets; cheap sets,
expensive sets; new sets,old sets .... I still say, it's generally a
matter of adjusting for the range scale you're using and, generally
you'll get rid of it ....either that, or the target will move out of
range G

I've seen this problem on 3cm, 10cm; big sets, small sets; cheap sets,
expensive sets; new sets,old sets .... I still say, it's generally a
matter of adjusting for the range scale you're using and, generally
you'll get rid of it ....either that, or the target will move out of
range G

On Wed, 03 Dec 2003 19:44:00 GMT, Bruce in Alaska
wrote:

In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

What this seems to be is Magnitron Double-Pulsing. This is where,
as the Magnitron ages, and the Modulator Parts age, they get into
a multiple pulse state, and produce a very ragged and multiple peaked
pulse, that shows up as multiple echos in near vacinity of a REAL Target.
The fix for this is, to replace the Magnitron, and the Pulse Forming
Capacitors in the modulator. Not usually found in Noncommercial Marine
Service, because these units typically die of mechanical age, long
before the electronics age out.

I doubt that. This is the new replacement for an ancient Furuno that
never did it.


Well se what "Me" has to say on the subject.


Bruce in alaska




Rodney Myrvaagnes J36 Gjo/a

"That idiot Leibniz, who wants to teach me about the infinitesimally small! Has he therefore forgotten that I am the wife of Frederick I? How can he imagine that I am unacquainted with my own husband?"

On Wed, 03 Dec 2003 19:44:00 GMT, Bruce in Alaska
wrote:

In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

What this seems to be is Magnitron Double-Pulsing. This is where,
as the Magnitron ages, and the Modulator Parts age, they get into
a multiple pulse state, and produce a very ragged and multiple peaked
pulse, that shows up as multiple echos in near vacinity of a REAL Target.
The fix for this is, to replace the Magnitron, and the Pulse Forming
Capacitors in the modulator. Not usually found in Noncommercial Marine
Service, because these units typically die of mechanical age, long
before the electronics age out.

I doubt that. This is the new replacement for an ancient Furuno that
never did it.


Well se what "Me" has to say on the subject.


Bruce in alaska




Rodney Myrvaagnes J36 Gjo/a

"That idiot Leibniz, who wants to teach me about the infinitesimally small! Has he therefore forgotten that I am the wife of Frederick I? How can he imagine that I am unacquainted with my own husband?"

Finally, this guy got it right!

On Wed, 03 Dec 2003 22:04:51 GMT, Gary Schafer
wrote:

This is more bull**** Jeff. There is nothing wrong with your
magnetron.
The "rings" that you see associated with a strong target are the
result of side lobes on your antenna.

If it were the magnetron "double pulsing" you would see multiple
targets at the same azimuth as the real target. They would be in front
of or behind the real target.
Unless of course you had a bad magnetron and you were right on top of
a large target then you could get rings and multiple targets together.

The radar antenna has a narrow beam that sweeps around in azimuth. The
antenna azimuth is synchronized with the sweep on your display so that
the sweep on your display always points in the same direction as your
antenna.

To picture clearer what is happening, think about what it would be
like if there were no motor turning the antenna. You had to rotate it
by hand. As you point the antenna at a target the transmitter is
transmitting pulses many times per second. Between each of those
pulses your receiver listens for an echo of those pulses being
reflected from a target. Depending on how far away the target is
determines how long it takes for the echo to return to the receiver.

The sweep on your scope is traveling out toward the edge of your
display at the same rate that it takes to send out the radar pulse and
get it back. This also happens many times per second. Exactly in sync
with the radar pulse being transmitted. The center of the screen is at
the time the radar pulse leaves the radar transmitter. Time zero =
zero miles.

As an echo is received the sweep gets intensified at that time.
With out the antenna rotating you would see a bright spot at the range
on the sweep line on your screen. Now as you manually slowly rotate
your antenna in one direction you will continue to see the bright spot
at the same range but the sweep will be at a slightly different
azimuth on your display. The spot will now get stretched out and
appear to be forming a small line or arc still at the same range. This
arc will be visible as long as the target is within the beam width of
your antenna.

The line or arc appears on the screen due to the digital circuitry
holding or remembering the signal. On older radar's without digital
storage this holding of the arc was dependent on the type of
phosphorus used in the display tube. It would slowly fade. You tv tube
works much in the same way but fades much faster.

Anyway, as you continue to manually rotate your antenna, you will
reach an azimuth where the beam width of the antenna is no longer
illuminating the target. The dot on your display sweep will not be
seen any more.
But the small arc will still be visible because of the storage. It
will hold that image or display until the next time the sweep has made
a full 360 degree rotation. Then it will erase that information and
display the new information if there is any to display.

As you continue to rotate the antenna, if one of the side or rear
lobes are strong enough you will again see the dot on the sweep appear
at the same range as you did earlier. But now your antenna may be
pointed 10 or 20 degrees away from the target and your display, being
in sync with your antenna will also be 10 or 20 degrees off the
target. So the dot will look like there is another target at the same
range but a different azimuth to the original target. As you continue
to turn the antenna it will form an arc on the screen as long as that
side lobe is strong enough to give a return signal.

It is not uncommon to be near a large ship and see what looks like the
same ship 180 degrees from the original.

Sometimes when the target is close and very large you can pick it up
in 360 degrees on your radar. Turning down your gain will get rid of
the unwanted responses as your main lobe is always stronger than the
side lobe signals. But be careful if you turn down the gain for this
purpose as it will also eliminate many of the weaker wanted targets
too.

Regards
Gary


On Wed, 3 Dec 2003 15:24:35 -0500, "Jeff Morris"
wrote:

I hope its not age in my case - my radar is less than 4 years old and I believe
I had this effect from the beginning.




"Me" wrote in message
...
In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

Hmmm, sounds like maybe your Magnitron is getting old. Been know to
cause mutiple echo's from a single boat, or rock. If they are infront
of and behind the real target, it is reflections. If it is right or left,
could be what is known as Multiple Pulsing.

Me

Finally, this guy got it right!

On Wed, 03 Dec 2003 22:04:51 GMT, Gary Schafer
wrote:

This is more bull**** Jeff. There is nothing wrong with your
magnetron.
The "rings" that you see associated with a strong target are the
result of side lobes on your antenna.

If it were the magnetron "double pulsing" you would see multiple
targets at the same azimuth as the real target. They would be in front
of or behind the real target.
Unless of course you had a bad magnetron and you were right on top of
a large target then you could get rings and multiple targets together.

The radar antenna has a narrow beam that sweeps around in azimuth. The
antenna azimuth is synchronized with the sweep on your display so that
the sweep on your display always points in the same direction as your
antenna.

To picture clearer what is happening, think about what it would be
like if there were no motor turning the antenna. You had to rotate it
by hand. As you point the antenna at a target the transmitter is
transmitting pulses many times per second. Between each of those
pulses your receiver listens for an echo of those pulses being
reflected from a target. Depending on how far away the target is
determines how long it takes for the echo to return to the receiver.

The sweep on your scope is traveling out toward the edge of your
display at the same rate that it takes to send out the radar pulse and
get it back. This also happens many times per second. Exactly in sync
with the radar pulse being transmitted. The center of the screen is at
the time the radar pulse leaves the radar transmitter. Time zero =
zero miles.

As an echo is received the sweep gets intensified at that time.
With out the antenna rotating you would see a bright spot at the range
on the sweep line on your screen. Now as you manually slowly rotate
your antenna in one direction you will continue to see the bright spot
at the same range but the sweep will be at a slightly different
azimuth on your display. The spot will now get stretched out and
appear to be forming a small line or arc still at the same range. This
arc will be visible as long as the target is within the beam width of
your antenna.

The line or arc appears on the screen due to the digital circuitry
holding or remembering the signal. On older radar's without digital
storage this holding of the arc was dependent on the type of
phosphorus used in the display tube. It would slowly fade. You tv tube
works much in the same way but fades much faster.

Anyway, as you continue to manually rotate your antenna, you will
reach an azimuth where the beam width of the antenna is no longer
illuminating the target. The dot on your display sweep will not be
seen any more.
But the small arc will still be visible because of the storage. It
will hold that image or display until the next time the sweep has made
a full 360 degree rotation. Then it will erase that information and
display the new information if there is any to display.

As you continue to rotate the antenna, if one of the side or rear
lobes are strong enough you will again see the dot on the sweep appear
at the same range as you did earlier. But now your antenna may be
pointed 10 or 20 degrees away from the target and your display, being
in sync with your antenna will also be 10 or 20 degrees off the
target. So the dot will look like there is another target at the same
range but a different azimuth to the original target. As you continue
to turn the antenna it will form an arc on the screen as long as that
side lobe is strong enough to give a return signal.

It is not uncommon to be near a large ship and see what looks like the
same ship 180 degrees from the original.

Sometimes when the target is close and very large you can pick it up
in 360 degrees on your radar. Turning down your gain will get rid of
the unwanted responses as your main lobe is always stronger than the
side lobe signals. But be careful if you turn down the gain for this
purpose as it will also eliminate many of the weaker wanted targets
too.

Regards
Gary


On Wed, 3 Dec 2003 15:24:35 -0500, "Jeff Morris"
wrote:

I hope its not age in my case - my radar is less than 4 years old and I believe
I had this effect from the beginning.




"Me" wrote in message
...
In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

Hmmm, sounds like maybe your Magnitron is getting old. Been know to
cause mutiple echo's from a single boat, or rock. If they are infront
of and behind the real target, it is reflections. If it is right or left,
could be what is known as Multiple Pulsing.

Me

Yes, but a day before this post I said that side lobes seemed like the best explanation.

--
-jeff



"Steve H" wrote in message ...
Finally, this guy got it right!

On Wed, 03 Dec 2003 22:04:51 GMT, Gary Schafer
wrote:

This is more bull**** Jeff. There is nothing wrong with your
magnetron.
The "rings" that you see associated with a strong target are the
result of side lobes on your antenna.

If it were the magnetron "double pulsing" you would see multiple
targets at the same azimuth as the real target. They would be in front
of or behind the real target.
Unless of course you had a bad magnetron and you were right on top of
a large target then you could get rings and multiple targets together.

The radar antenna has a narrow beam that sweeps around in azimuth. The
antenna azimuth is synchronized with the sweep on your display so that
the sweep on your display always points in the same direction as your
antenna.

To picture clearer what is happening, think about what it would be
like if there were no motor turning the antenna. You had to rotate it
by hand. As you point the antenna at a target the transmitter is
transmitting pulses many times per second. Between each of those
pulses your receiver listens for an echo of those pulses being
reflected from a target. Depending on how far away the target is
determines how long it takes for the echo to return to the receiver.

The sweep on your scope is traveling out toward the edge of your
display at the same rate that it takes to send out the radar pulse and
get it back. This also happens many times per second. Exactly in sync
with the radar pulse being transmitted. The center of the screen is at
the time the radar pulse leaves the radar transmitter. Time zero =
zero miles.

As an echo is received the sweep gets intensified at that time.
With out the antenna rotating you would see a bright spot at the range
on the sweep line on your screen. Now as you manually slowly rotate
your antenna in one direction you will continue to see the bright spot
at the same range but the sweep will be at a slightly different
azimuth on your display. The spot will now get stretched out and
appear to be forming a small line or arc still at the same range. This
arc will be visible as long as the target is within the beam width of
your antenna.

The line or arc appears on the screen due to the digital circuitry
holding or remembering the signal. On older radar's without digital
storage this holding of the arc was dependent on the type of
phosphorus used in the display tube. It would slowly fade. You tv tube
works much in the same way but fades much faster.

Anyway, as you continue to manually rotate your antenna, you will
reach an azimuth where the beam width of the antenna is no longer
illuminating the target. The dot on your display sweep will not be
seen any more.
But the small arc will still be visible because of the storage. It
will hold that image or display until the next time the sweep has made
a full 360 degree rotation. Then it will erase that information and
display the new information if there is any to display.

As you continue to rotate the antenna, if one of the side or rear
lobes are strong enough you will again see the dot on the sweep appear
at the same range as you did earlier. But now your antenna may be
pointed 10 or 20 degrees away from the target and your display, being
in sync with your antenna will also be 10 or 20 degrees off the
target. So the dot will look like there is another target at the same
range but a different azimuth to the original target. As you continue
to turn the antenna it will form an arc on the screen as long as that
side lobe is strong enough to give a return signal.

It is not uncommon to be near a large ship and see what looks like the
same ship 180 degrees from the original.

Sometimes when the target is close and very large you can pick it up
in 360 degrees on your radar. Turning down your gain will get rid of
the unwanted responses as your main lobe is always stronger than the
side lobe signals. But be careful if you turn down the gain for this
purpose as it will also eliminate many of the weaker wanted targets
too.

Regards
Gary


On Wed, 3 Dec 2003 15:24:35 -0500, "Jeff Morris"
wrote:

I hope its not age in my case - my radar is less than 4 years old and I believe
I had this effect from the beginning.




"Me" wrote in message
...
In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

Hmmm, sounds like maybe your Magnitron is getting old. Been know to
cause mutiple echo's from a single boat, or rock. If they are infront
of and behind the real target, it is reflections. If it is right or left,
could be what is known as Multiple Pulsing.

Me

Yes, but a day before this post I said that side lobes seemed like the best explanation.

--
-jeff



"Steve H" wrote in message ...
Finally, this guy got it right!

On Wed, 03 Dec 2003 22:04:51 GMT, Gary Schafer
wrote:

This is more bull**** Jeff. There is nothing wrong with your
magnetron.
The "rings" that you see associated with a strong target are the
result of side lobes on your antenna.

If it were the magnetron "double pulsing" you would see multiple
targets at the same azimuth as the real target. They would be in front
of or behind the real target.
Unless of course you had a bad magnetron and you were right on top of
a large target then you could get rings and multiple targets together.

The radar antenna has a narrow beam that sweeps around in azimuth. The
antenna azimuth is synchronized with the sweep on your display so that
the sweep on your display always points in the same direction as your
antenna.

To picture clearer what is happening, think about what it would be
like if there were no motor turning the antenna. You had to rotate it
by hand. As you point the antenna at a target the transmitter is
transmitting pulses many times per second. Between each of those
pulses your receiver listens for an echo of those pulses being
reflected from a target. Depending on how far away the target is
determines how long it takes for the echo to return to the receiver.

The sweep on your scope is traveling out toward the edge of your
display at the same rate that it takes to send out the radar pulse and
get it back. This also happens many times per second. Exactly in sync
with the radar pulse being transmitted. The center of the screen is at
the time the radar pulse leaves the radar transmitter. Time zero =
zero miles.

As an echo is received the sweep gets intensified at that time.
With out the antenna rotating you would see a bright spot at the range
on the sweep line on your screen. Now as you manually slowly rotate
your antenna in one direction you will continue to see the bright spot
at the same range but the sweep will be at a slightly different
azimuth on your display. The spot will now get stretched out and
appear to be forming a small line or arc still at the same range. This
arc will be visible as long as the target is within the beam width of
your antenna.

The line or arc appears on the screen due to the digital circuitry
holding or remembering the signal. On older radar's without digital
storage this holding of the arc was dependent on the type of
phosphorus used in the display tube. It would slowly fade. You tv tube
works much in the same way but fades much faster.

Anyway, as you continue to manually rotate your antenna, you will
reach an azimuth where the beam width of the antenna is no longer
illuminating the target. The dot on your display sweep will not be
seen any more.
But the small arc will still be visible because of the storage. It
will hold that image or display until the next time the sweep has made
a full 360 degree rotation. Then it will erase that information and
display the new information if there is any to display.

As you continue to rotate the antenna, if one of the side or rear
lobes are strong enough you will again see the dot on the sweep appear
at the same range as you did earlier. But now your antenna may be
pointed 10 or 20 degrees away from the target and your display, being
in sync with your antenna will also be 10 or 20 degrees off the
target. So the dot will look like there is another target at the same
range but a different azimuth to the original target. As you continue
to turn the antenna it will form an arc on the screen as long as that
side lobe is strong enough to give a return signal.

It is not uncommon to be near a large ship and see what looks like the
same ship 180 degrees from the original.

Sometimes when the target is close and very large you can pick it up
in 360 degrees on your radar. Turning down your gain will get rid of
the unwanted responses as your main lobe is always stronger than the
side lobe signals. But be careful if you turn down the gain for this
purpose as it will also eliminate many of the weaker wanted targets
too.

Regards
Gary


On Wed, 3 Dec 2003 15:24:35 -0500, "Jeff Morris"
wrote:

I hope its not age in my case - my radar is less than 4 years old and I believe
I had this effect from the beginning.




"Me" wrote in message
...
In article ,
Rodney Myrvaagnes wrote:

I do see what you describe occasionally with a Raytheon SR 70. I never
have seen the other phenomenon, and I never saw this one with the
previous Furuno 1720.

I don't think it indicates an active radar on the target, because I
have had it happen with big rocks. It usually goes away pretty soon.

Hmmm, sounds like maybe your Magnitron is getting old. Been know to
cause mutiple echo's from a single boat, or rock. If they are infront
of and behind the real target, it is reflections. If it is right or left,
could be what is known as Multiple Pulsing.

Me