Radar Mounting Question
 

More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on it;
is it merely the way radar works, or is the radome mounted incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary

wrote:

A cold night's discussion evolved into: if my radar is picking up a
target ... I'll lose it when it gets close enough to where I can
physically see it ...

If that's the case; i.e., losing a radar target when you close on
it; is it merely the way radar works, or is the radome mounted
incorrectly or are there other variables I'm unaware of insofar as
radar and minimum range/tuning?

The simplest explanation is that the height of the transmitter (aka, radome)
enters into the equation.

--
Good luck and good sailing.
s/v Kerry Deare of Barnegat
http://kerrydeare.home.comcast.net/

In article .com,
wrote:

More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on it;
is it merely the way radar works, or is the radome mounted incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary


There are a number of things that make up MRR (Minimum Radar Range)

1. The PRR (Pulse Repition Rate) and PL (Pulse Length) of the
Transmitter, and the RGD (Receiver Gate Delay) of the
Receiver all effect the "Minimum Radar Range". The first
two you have no control over, but the RGD is usually set
when the radar is installed, for the vessels installation.
2. The VB (Vertical Beamwidth) of most Radar Antennas is in
the neighborhood of 25 Degrees. 12.5 above and 12.5 below
the Horizontal center of the antenna. If the antenna is
mounted up HIGH, (Like over 30 meters) like a Large ship
then the 12.5 degree lower Beamwidth will lose the target
much sooner that one mounted at sat 3 meters. So antenna
hight, and antenna VB, need to be taken into consideration
during installation.
3. Antenna Shading can also play a significant roll in MRR.
When a Radar antenna is place at the rear of a vessel,
and must look forward thru all the masts and rigging of
Say, a sailboat, then all that stuff deflects and obscures
the RF Pulse that the radar produces and the return echo
that it needs to show the target. The narrower the HB
(Horozontal Beamwidth) of the antenna, the better it will
decern targets, near or far. This is why Radar Antennas
should be mounted where they have a CLEAR, unobstructed
view, forward.


Hope that helps......


Bruce in alaska
--
add a 2 before @

On Tue, 18 Jan 2005 14:48:17 -0500, "Armond Perretta"
wrote:

If that's the case; i.e., losing a radar target when you close on
it; is it merely the way radar works, or is the radome mounted
incorrectly or are there other variables I'm unaware of insofar as
radar and minimum range/tuning?

The simplest explanation is that the height of the transmitter (aka, radome)
enters into the equation.

================================

Antenna height is part of the issue but there is also a minimum
turnaround time from transmit to receive which enters into it. 25 to
50 yards is about normal in my experience. At that range you should
be able to guage your required offset and steer a straight course to
the proper side of the buoy, picking it up again after you pass it.

Are we talking a big midchannel buoy with strong radar return or a mooring
buoy which is lost in the sea return (if ever seen).
G
wrote in message
oups.com...
More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on it;
is it merely the way radar works, or is the radome mounted incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary

On Tue, 18 Jan 2005 21:29:16 GMT, Bruce in Alaska
wrote:

In article .com,
wrote:

More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on it;
is it merely the way radar works, or is the radome mounted incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary


There are a number of things that make up MRR (Minimum Radar Range)

1. The PRR (Pulse Repition Rate) and PL (Pulse Length) of the
Transmitter, and the RGD (Receiver Gate Delay) of the
Receiver all effect the "Minimum Radar Range". The first
two you have no control over, but the RGD is usually set
when the radar is installed, for the vessels installation.
2. The VB (Vertical Beamwidth) of most Radar Antennas is in
the neighborhood of 25 Degrees. 12.5 above and 12.5 below
the Horizontal center of the antenna. If the antenna is
mounted up HIGH, (Like over 30 meters) like a Large ship
then the 12.5 degree lower Beamwidth will lose the target
much sooner that one mounted at sat 3 meters. So antenna
hight, and antenna VB, need to be taken into consideration
during installation.
3. Antenna Shading can also play a significant roll in MRR.
When a Radar antenna is place at the rear of a vessel,
and must look forward thru all the masts and rigging of
Say, a sailboat, then all that stuff deflects and obscures
the RF Pulse that the radar produces and the return echo
that it needs to show the target. The narrower the HB
(Horozontal Beamwidth) of the antenna, the better it will
decern targets, near or far. This is why Radar Antennas
should be mounted where they have a CLEAR, unobstructed
view, forward.


Hope that helps......


Bruce in alaska


Nice post, Bruce!

Brian W

Bruce in Alaska wrote:
In article .com,
wrote:

More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in
a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you
can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on
it;
is it merely the way radar works, or is the radome mounted
incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary

Bruce,

Jeez ... you oughta teach ...

Recreational boat, height say 12 feet ... would making a change in the
angle of the radome be wise? In other words, would it make sense it to
have a unit that
could be maneuvered up and down (up being level, down being a degree or
two difference from ideal)?

For that matter, would "up" increase range (obviously losing minimum
read)?

Gary


There are a number of things that make up MRR (Minimum Radar Range)

1. The PRR (Pulse Repition Rate) and PL (Pulse Length) of the
Transmitter, and the RGD (Receiver Gate Delay) of the
Receiver all effect the "Minimum Radar Range". The first
two you have no control over, but the RGD is usually set
when the radar is installed, for the vessels installation.
2. The VB (Vertical Beamwidth) of most Radar Antennas is in
the neighborhood of 25 Degrees. 12.5 above and 12.5 below
the Horizontal center of the antenna. If the antenna is
mounted up HIGH, (Like over 30 meters) like a Large ship
then the 12.5 degree lower Beamwidth will lose the target
much sooner that one mounted at sat 3 meters. So antenna
hight, and antenna VB, need to be taken into consideration
during installation.
3. Antenna Shading can also play a significant roll in MRR.
When a Radar antenna is place at the rear of a vessel,
and must look forward thru all the masts and rigging of
Say, a sailboat, then all that stuff deflects and obscures
the RF Pulse that the radar produces and the return echo
that it needs to show the target. The narrower the HB
(Horozontal Beamwidth) of the antenna, the better it will
decern targets, near or far. This is why Radar Antennas
should be mounted where they have a CLEAR, unobstructed
view, forward.


Hope that helps......


Bruce in alaska
--
add a 2 before @

In article .com,
wrote:

Bruce,

Jeez ... you oughta teach ...

Recreational boat, height say 12 feet ... would making a change in the
angle of the radome be wise? In other words, would it make sense it to
have a unit that
could be maneuvered up and down (up being level, down being a degree or
two difference from ideal)?

For that matter, would "up" increase range (obviously losing minimum
read)?

Gary

Gary,
I do teach, and have taught many a budding Marine Electronics Techs,
as well as Commercial Operators and Skippers, for many years.

Changing the Pitch of the Antenna is only slightly effective, in lowering
a radars MRR. This is due to the Vertical Beamwidth being 25 or
so degrees. This beamwidth is expressed at the -3db points (Half Power)
of the Main Lobe of the Antenna Pattern. so moving it just a coule of
degrees isn't going to have a significant effect on MRR.

The Largest Factor, that can be adjusted for, in MRR, is RGD (Receiver
Gate Delay) and this is usually set via an internal control at
installation. If it is set to short, Close in targets will curve in
toward the center of the display on the Shortest Range. If it is set to
long, then close in targets will bow out from the center of the display
on the Shortest Range. It is a very small adjustment of only a few
microseconds, one way or the other.
This adjustment is required because the designer can't know how long the
interconnect cable between the Display and the RF Deck is going to be
in any installation and it must therefor be adjusted AFTER the cable is
installed, and cut for length, if nessesary. Some of the later models
of consumer radars, don't allow for the interconnect cable length to be
changed, and therefor the Factory Setting is good enough, but if the
installation requires ANY change in interconnect cable length, then the
RGD setting must be recalibrated for proper operation, as specified in
most installation and user manuals.

Years ago we installed an Xband Furuno Radar on the ForeMast of 260 Ft
Reseach vessel, that had an AftHouse design. This allowed the new Radar
to have a clear, unobstructed, view forward, so as to allow the best
possible sensitivity for seeing small Research Bouys at the langest
ranges. The interconnect cable was 5 or 6 times as long as what the
designers intended, and we had the Factory help us install a modification
of the RGD system to take that fact into account, during installation.

Bruce in alaska
--
add a 2 before @

In article ,
Wayne.B wrote:

The most
important thing however is to get it above eye level for safety
reasons.

Wayne,

The only reason one would need to worry about Safety, would be
if the consumer or commercial Radar Antenna, had an exposed rotating
antenna, and it could hit someone in the head, while operating.

All the notions about RF Exposure in S and Xband for Marine Radars
is nothing but Oldwives Tales, and outdated equipment, concerns.
The Power Density of 2nd and 3rd Generation Radar Transmitters and
Antenna Systems is not even close to that required for ANY physiological
effects. The Largest of the Commercial Marine Radars today, have a PPP
(Peak Pulse Power) in the 10Kw, and by the time that energy is conducted
thru the rotory Joint and spread out over the 6 Ft, or longer, Slotted
Waveguide Antenna, it is considerable reduced in W/cmSquared. Also
consider that PPP isn't what causes physiological effects, but AvP
(Average Power) and the PL (Pulse Length) and PRR (Pulse Repition Rate)
of the transmitter drop the AvP down to like less than 10 Watts at the
Magnitron output, before it goes to the rotory Joint and Slotted
Waveguide Antenna. This discussion has been covered MANY Times
on various UseNet NewsGroups over the years, and the math hasn't changed
since the last time. Google is your Friend, if you need further
information.
That said, We are talking about CONSUMER, and, or, Commercial Marine
Radars here, and not Military, or First Generation Marine Radars.
Certainly there were a few of the first Generation Decca Radars that
had PPP in the 40Kw and 80Kw ranges that MAYBE could be considered,
possibly, Dangerous, but they have been long gone, for years, in most
cases.


Bruce in alaska
--
add a 2 before @

On Thu, 20 Jan 2005 21:22:22 GMT, Bruce in Alaska
wrote:
The only reason one would need to worry about Safety, would be
if the consumer or commercial Radar Antenna, had an exposed rotating
antenna, and it could hit someone in the head, while operating.

All the notions about RF Exposure in S and Xband for Marine Radars
is nothing but Oldwives Tales, and outdated equipment, concerns.

=========================================

I hope you're right Bruce because my old boat had a 4kw scanner right
in front of the flybridge. Raytheon recommends at least 2 meters
separation and that one was right on the cusp. I never operated it
unless necessary. The jury is still out on the RF exposure medical
studies, and each new one frequently conflicts with the old depending
on who sponsored the research. Meanwhile I'll still try to stay out
of the beam of anything as much as possible.

I gotta go with Wayne on this one. I did a great study on mircrowave
exposure effects...mainly because of a microwave site near neighborhoods.
Depending on what country you choose, the allowable exposure is variable.
No two people will agree on the effects.
The problem is in trying to prove a negative.
Me? I stay as far away from RF as possible....particullarly ionizing radiation.
Eyeballs are really sensitive to RF.
Norm B

On Thu, 20 Jan 2005 20:56:52 -0500, Wayne.B wrote:

On Thu, 20 Jan 2005 21:22:22 GMT, Bruce in Alaska
wrote:
The only reason one would need to worry about Safety, would be
if the consumer or commercial Radar Antenna, had an exposed rotating
antenna, and it could hit someone in the head, while operating.

All the notions about RF Exposure in S and Xband for Marine Radars
is nothing but Oldwives Tales, and outdated equipment, concerns.

=========================================

I hope you're right Bruce because my old boat had a 4kw scanner right
in front of the flybridge. Raytheon recommends at least 2 meters
separation and that one was right on the cusp. I never operated it
unless necessary. The jury is still out on the RF exposure medical
studies, and each new one frequently conflicts with the old depending
on who sponsored the research. Meanwhile I'll still try to stay out
of the beam of anything as much as possible.

On Thu, 20 Jan 2005 19:30:06 -0800, engsol
wrote:

Me? I stay as far away from RF as possible....particullarly ionizing radiation.

================================

RF and ionizing radiation are two entirely different animals. RF is
electromagnetic, ionizing is from sub-atomic particles, at least in my
laymans view of the universe...

On Thu, 20 Jan 2005 23:05:25 -0500, Wayne.B wrote:

On Thu, 20 Jan 2005 19:30:06 -0800, engsol
wrote:

Me? I stay as far away from RF as possible....particullarly ionizing radiation.

================================

RF and ionizing radiation are two entirely different animals. RF is
electromagnetic, ionizing is from sub-atomic particles, at least in my
laymans view of the universe...

There is a frequency above which RF becomes ionizing. To be honest
the work I did in that area was so long ago I just don't remember the
numbers.

In article ,
engsol wrote:

.mainly because of a microwave site near neighborhoods.

Here again if you do the math, and figure the antenna bandwidths,
and RF Paths to and from the site, you will know that there is
insignificant exposer to RF from a microwave communications site,
anywhere on the ground, or in the nearfield of the antennas.


Bruce in alaska
--
add a 2 before @

engsol wrote:
On Thu, 20 Jan 2005 23:05:25 -0500, Wayne.B wrote:


On Thu, 20 Jan 2005 19:30:06 -0800, engsol
wrote:


Me? I stay as far away from RF as possible....particullarly ionizing radiation.

================================

RF and ionizing radiation are two entirely different animals. RF is
electromagnetic, ionizing is from sub-atomic particles, at least in my
laymans view of the universe...


There is a frequency above which RF becomes ionizing. To be honest
the work I did in that area was so long ago I just don't remember the
numbers.

I think EM radiation has to be up the the X Ray part of the spectrum to
be ionizing.

On Fri, 21 Jan 2005 10:07:17 -0800, engsol
wrote:

On Thu, 20 Jan 2005 23:05:25 -0500, Wayne.B wrote:

On Thu, 20 Jan 2005 19:30:06 -0800, engsol
wrote:

Me? I stay as far away from RF as possible....particullarly ionizing radiation.

================================

RF and ionizing radiation are two entirely different animals. RF is
electromagnetic, ionizing is from sub-atomic particles, at least in my
laymans view of the universe...

There is a frequency above which RF becomes ionizing. To be honest
the work I did in that area was so long ago I just don't remember the
numbers.
No common radar band is ionizing. They can be hazardous if they are
powerful enough to cook you, like a microwave oven.



Rodney Myrvaagnes NYC J36 Gjo/a


"Be careful. The toe you stepped on yesterday may be connected to the ass you have to kiss today." --Former mayor Ciancia

On Fri, 21 Jan 2005 19:37:00 GMT, Bruce in Alaska wrote:

In article ,
engsol wrote:

.mainly because of a microwave site near neighborhoods.

Here again if you do the math, and figure the antenna bandwidths,
and RF Paths to and from the site, you will know that there is
insignificant exposer to RF from a microwave communications site,
anywhere on the ground, or in the nearfield of the antennas.


Bruce in alaska

Bruce, you're right as rain. Even considering the near field nulls
and nodes the radiation reaching the ground (at any given range)
from a dish on a tower is less than the radiation from the sun at that
frequency. The reason I brought up the neighborhood microwave site
is because I had to appear before the Portland City Council to defend
our (my company's) desire to establish one. I was the Project Manager
for the MW network, and had to "prove" there was no hazard.
Actually it was a bad post on my part, as .I didn't explain my position
very well.
Norm B

In article ,
engsol wrote:

On Fri, 21 Jan 2005 19:37:00 GMT, Bruce in Alaska wrote:

In article ,
engsol wrote:

.mainly because of a microwave site near neighborhoods.

Here again if you do the math, and figure the antenna bandwidths,
and RF Paths to and from the site, you will know that there is
insignificant exposer to RF from a microwave communications site,
anywhere on the ground, or in the nearfield of the antennas.


Bruce in alaska

Bruce, you're right as rain. Even considering the near field nulls
and nodes the radiation reaching the ground (at any given range)
from a dish on a tower is less than the radiation from the sun at that
frequency. The reason I brought up the neighborhood microwave site
is because I had to appear before the Portland City Council to defend
our (my company's) desire to establish one. I was the Project Manager
for the MW network, and had to "prove" there was no hazard.
Actually it was a bad post on my part, as .I didn't explain my position
very well.
Norm B


Yep, reminds me of when RCA Americom wanted to build an EarthStation
for the Aurora 1 Comms Sat on Vashon Island, Washington, so they could
bring the Alaska Longlines Traffic into the ESS4 Switch in Seattle.
The neighbors went TOTALLY nuts and delayed the project for a couple of
years in the KIng County Planning Commission. Some fool got this group
together and strung it out forever. RCA even went so far as getting
Dr. Renolds from the UW Applied Physics Lab to testify on their behalf,
and that didn't satisfy them. Total foolishness, to the extreme.
They finally built the EarthStation, but had to paint the 10Meter Dish
Brown/Green so it would "Blend into the neighborhood", and that was the
only consession that they were granted in the end.


Bruce in alaska who knows the foolishness of the uneducated......
--
add a 2 before @