Need info about the Open Array 72" verse 48"

"TimJay" wrote in news:wdidnd9mKMdB5y_fRVn-
:

Need info about the Open Array 72" verse 48"




In any radar system, from any manufacturer, you need to think about how far
it is to the horizon from the altitude your antenna is located. Ask
yourself, "Can this system give me good returns from a normal boat at the
horizon?" It cannot see beyond its horizon. Its horizon is dependent on
its altitude. Altitude is also a tradeoff with close-in target acquistion.
If you put the antenna up high to get a longer horizon, you won't be able
to see that damned bouy someone put in your way in the fog you are about to
run over. I'll trade seeing that bouy in really close to the boat for
seeing a boat out 35 miles any day of the week. Of course, having two
radars, one low down to see that bouy and one up high to see those long-
range targets is much nicer. It also gives you redundancy for the
inevitable failures of these cheaply made boat systems.

A 72" array WILL have a narrower beamwidth than the 48". A narrower
beamwidth translates into resolution, not range, of the targets on the
scope. Instead of the two targets out there painting as one wide one, you
MAY be able to see them as two distinct targets, as if that really made any
difference. AS you get closer to the targets, the wider beamwidth antenna
also shows them as separate targets closer in, which I think makes the
point moot. The higher power of the 72" transmitter WILL show small
targets like towers and bouys at larger ranges by painting them with more
brute RF power force, creating a larger return signal above the noise floor
of the receiver. If seeing a bouy 18 miles away instead of 10 miles away
is important to you, the higher the power the better. If under sail, with
limited power resources, higher power eating the batteries soon becomes
more important than seeing the bouy so far away. At 30 gallons per hour,
it matters little.

Hope this makes you think of your particular situation. Everything is a
compromise.

--
Larry

In article ,
Larry W4CSC wrote:

"TimJay" wrote in news:wdidnd9mKMdB5y_fRVn-
:

Need info about the Open Array 72" verse 48"




In any radar system, from any manufacturer, you need to think about how far
it is to the horizon from the altitude your antenna is located. Ask
yourself, "Can this system give me good returns from a normal boat at the
horizon?" It cannot see beyond its horizon. Its horizon is dependent on
its altitude. Altitude is also a tradeoff with close-in target acquistion.
If you put the antenna up high to get a longer horizon, you won't be able
to see that damned bouy someone put in your way in the fog you are about to
run over. I'll trade seeing that bouy in really close to the boat for
seeing a boat out 35 miles any day of the week. Of course, having two
radars, one low down to see that bouy and one up high to see those long-
range targets is much nicer. It also gives you redundancy for the
inevitable failures of these cheaply made boat systems.

A 72" array WILL have a narrower beamwidth than the 48". A narrower
beamwidth translates into resolution, not range, of the targets on the
scope. Instead of the two targets out there painting as one wide one, you
MAY be able to see them as two distinct targets, as if that really made any
difference. AS you get closer to the targets, the wider beamwidth antenna
also shows them as separate targets closer in, which I think makes the
point moot. The higher power of the 72" transmitter WILL show small
targets like towers and bouys at larger ranges by painting them with more
brute RF power force, creating a larger return signal above the noise floor
of the receiver. If seeing a bouy 18 miles away instead of 10 miles away
is important to you, the higher the power the better. If under sail, with
limited power resources, higher power eating the batteries soon becomes
more important than seeing the bouy so far away. At 30 gallons per hour,
it matters little.

Hope this makes you think of your particular situation. Everything is a
compromise.

Open Arrays are really SlotLine Waveguide Antennas, and legnth is
proportional to Antenna Gain, and Transmitted Peak Power. It is also
Inversely proportional to Horozontal Beamwidth. More is better, for
all cases, and less beamwidth is better always. I only have one nit to
pick with Larry's above, and that is Detection Distance for any
particular target is a combination of all the above factors and a few
more, but one of the biggies is Peak Transmitted Power, More power,
equals better targets, at longer ranges. In the old days before Loran,
and GPS, Radar was used for Position Fixing, and mountains were often
used as targets for navigation, at ranges exceeding 72 miles, with the
Decca 3xx, and 4xx series radars that had 20Kw and 40Kw XBand
transmitters with 6 and 7.5 Ft antennas.
Rule of thumb: Bigger is better, longer is better , but all this
"better" costs alot more money. So, eventually money is the limiting
factor.


Bruce in alaska
--
add a 2 before @

On Fri, 17 Jun 2005 21:43:43 GMT, Bruce in Alaska
wrote:

In article ,
Larry W4CSC wrote:

"TimJay" wrote in news:wdidnd9mKMdB5y_fRVn-
:

Need info about the Open Array 72" verse 48"




In any radar system, from any manufacturer, you need to think about how far
it is to the horizon from the altitude your antenna is located. Ask
yourself, "Can this system give me good returns from a normal boat at the
horizon?" It cannot see beyond its horizon. Its horizon is dependent on
its altitude. Altitude is also a tradeoff with close-in target acquistion.
If you put the antenna up high to get a longer horizon, you won't be able
to see that damned bouy someone put in your way in the fog you are about to
run over. I'll trade seeing that bouy in really close to the boat for
seeing a boat out 35 miles any day of the week. Of course, having two
radars, one low down to see that bouy and one up high to see those long-
range targets is much nicer. It also gives you redundancy for the
inevitable failures of these cheaply made boat systems.

A 72" array WILL have a narrower beamwidth than the 48". A narrower
beamwidth translates into resolution, not range, of the targets on the
scope. Instead of the two targets out there painting as one wide one, you
MAY be able to see them as two distinct targets, as if that really made any
difference. AS you get closer to the targets, the wider beamwidth antenna
also shows them as separate targets closer in, which I think makes the
point moot. The higher power of the 72" transmitter WILL show small
targets like towers and bouys at larger ranges by painting them with more
brute RF power force, creating a larger return signal above the noise floor
of the receiver. If seeing a bouy 18 miles away instead of 10 miles away
is important to you, the higher the power the better. If under sail, with
limited power resources, higher power eating the batteries soon becomes
more important than seeing the bouy so far away. At 30 gallons per hour,
it matters little.

Hope this makes you think of your particular situation. Everything is a
compromise.

Open Arrays are really SlotLine Waveguide Antennas, and legnth is
proportional to Antenna Gain, and Transmitted Peak Power. It is also
Inversely proportional to Horozontal Beamwidth. More is better, for
all cases, and less beamwidth is better always. I only have one nit to
pick with Larry's above, and that is Detection Distance for any
particular target is a combination of all the above factors and a few
more, but one of the biggies is Peak Transmitted Power, More power,
equals better targets, at longer ranges. In the old days before Loran,
and GPS, Radar was used for Position Fixing, and mountains were often
used as targets for navigation, at ranges exceeding 72 miles, with the
Decca 3xx, and 4xx series radars that had 20Kw and 40Kw XBand
transmitters with 6 and 7.5 Ft antennas.
Rule of thumb: Bigger is better, longer is better , but all this
"better" costs alot more money. So, eventually money is the limiting
factor.


Bruce in alaska

I agree with Bruce, bigger is always better. The larger array provides
narrower beam width along with higher gain. The narrower beam width
will help with target resolution on all ranges. It can be most
appreciated on the shorter ranges where Larry says it does not matter.
When on a narrow waterway the larger array will allow you to
distinguish a boat from shore objects that can not be done on the
small radar's.
The higher power will let you see small objects like those small buoys
that the small radar's may not even see.

A note on peak power. It is really the amount of average power that
determines how much of a return you get from the radar. The higher the
average power the better return.

The wider the pulse width of the radar pulse the greater the average
power transmitted. But the wider the pulse width the less resolution
in range you have. This is particularly important on short ranges.
This is why most radar's use a wide pulse width for long range (gives
higher average power) and very narrow pulses on short range. The
narrow pulse gives much better range resolution but lowers the average
power of the signal. But at short ranges you can get by with less
average power because signal returns are generally stronger.

The peak power of the transmitter usually remains the same whether
long or short pulses are being used. It is necessary to have a rather
high peak power transmitter in order to achieve enough average power
for decent returns as pulse widths are narrowed.

With a given pulse width, the higher the peak power of the transmitter
the higher the average power will be.

Some radar's have poor range resolution because they are under powered
and have to use wider pulses (to raise the average power) in order to
get strong enough returns on ranges where the pulses being used should
be narrower for better range resolution.

Usually radar's are advertised by how much peak power they have.
Sounds more impressive. Few tell you what the actual average
transmitted power is which is the most important.

Regards
Gary

On Fri, 17 Jun 2005 20:36:15 -0400, Gary Schafer wrote:

On Fri, 17 Jun 2005 21:43:43 GMT, Bruce in Alaska
wrote:

In article ,
Larry W4CSC wrote:

"TimJay" wrote in news:wdidnd9mKMdB5y_fRVn-
:

Need info about the Open Array 72" verse 48"




In any radar system, from any manufacturer, you need to think about how far
it is to the horizon from the altitude your antenna is located. Ask
yourself, "Can this system give me good returns from a normal boat at the
horizon?" It cannot see beyond its horizon. Its horizon is dependent on
its altitude. Altitude is also a tradeoff with close-in target acquistion.
If you put the antenna up high to get a longer horizon, you won't be able
to see that damned bouy someone put in your way in the fog you are about to
run over. I'll trade seeing that bouy in really close to the boat for
seeing a boat out 35 miles any day of the week. Of course, having two
radars, one low down to see that bouy and one up high to see those long-
range targets is much nicer. It also gives you redundancy for the
inevitable failures of these cheaply made boat systems.

A 72" array WILL have a narrower beamwidth than the 48". A narrower
beamwidth translates into resolution, not range, of the targets on the
scope. Instead of the two targets out there painting as one wide one, you
MAY be able to see them as two distinct targets, as if that really made any
difference. AS you get closer to the targets, the wider beamwidth antenna
also shows them as separate targets closer in, which I think makes the
point moot. The higher power of the 72" transmitter WILL show small
targets like towers and bouys at larger ranges by painting them with more
brute RF power force, creating a larger return signal above the noise floor
of the receiver. If seeing a bouy 18 miles away instead of 10 miles away
is important to you, the higher the power the better. If under sail, with
limited power resources, higher power eating the batteries soon becomes
more important than seeing the bouy so far away. At 30 gallons per hour,
it matters little.

Hope this makes you think of your particular situation. Everything is a
compromise.

Open Arrays are really SlotLine Waveguide Antennas, and legnth is
proportional to Antenna Gain, and Transmitted Peak Power. It is also
Inversely proportional to Horozontal Beamwidth. More is better, for
all cases, and less beamwidth is better always. I only have one nit to
pick with Larry's above, and that is Detection Distance for any
particular target is a combination of all the above factors and a few
more, but one of the biggies is Peak Transmitted Power, More power,
equals better targets, at longer ranges. In the old days before Loran,
and GPS, Radar was used for Position Fixing, and mountains were often
used as targets for navigation, at ranges exceeding 72 miles, with the
Decca 3xx, and 4xx series radars that had 20Kw and 40Kw XBand
transmitters with 6 and 7.5 Ft antennas.
Rule of thumb: Bigger is better, longer is better , but all this
"better" costs alot more money. So, eventually money is the limiting
factor.


Bruce in alaska

I agree with Bruce, bigger is always better. The larger array provides
narrower beam width along with higher gain. The narrower beam width
will help with target resolution on all ranges. It can be most
appreciated on the shorter ranges where Larry says it does not matter.
When on a narrow waterway the larger array will allow you to
distinguish a boat from shore objects that can not be done on the
small radar's.
The higher power will let you see small objects like those small buoys
that the small radar's may not even see.

A note on peak power. It is really the amount of average power that
determines how much of a return you get from the radar. The higher the
average power the better return.

The wider the pulse width of the radar pulse the greater the average
power transmitted. But the wider the pulse width the less resolution
in range you have. This is particularly important on short ranges.
This is why most radar's use a wide pulse width for long range (gives
higher average power) and very narrow pulses on short range. The
narrow pulse gives much better range resolution but lowers the average
power of the signal. But at short ranges you can get by with less
average power because signal returns are generally stronger.

The peak power of the transmitter usually remains the same whether
long or short pulses are being used. It is necessary to have a rather
high peak power transmitter in order to achieve enough average power
for decent returns as pulse widths are narrowed.

With a given pulse width, the higher the peak power of the transmitter
the higher the average power will be.

Some radar's have poor range resolution because they are under powered
and have to use wider pulses (to raise the average power) in order to
get strong enough returns on ranges where the pulses being used should
be narrower for better range resolution.

Usually radar's are advertised by how much peak power they have.
Sounds more impressive. Few tell you what the actual average
transmitted power is which is the most important.

Regards
Gary

One thing I see missing as to short range is the TR time...i.e., how quickly
after the tx pulse quits can the rx receive and process the echo.
It's possible to "blind" the rx even if the isolation between tx/rx is 100 dB or better.
Anyone know some numbers?

Norm B (who has never worked on a solid-state radar, but has on
tube type 2 and 5 mega Watt ones)

engsol wrote in
:

One thing I see missing as to short range is the TR time...i.e., how
quickly after the tx pulse quits can the rx receive and process the
echo. It's possible to "blind" the rx even if the isolation between
tx/rx is 100 dB or better. Anyone know some numbers?

The modern ones are really fast. The 2KW Raymarine radome, before it rots
from the condensation in the dome, can see the 3rd boat down the dock.
That's really fast at the speed of light, especially considering its
antenna is simply a printed circuit board array of microstrip dipoles. I
don't have the specs on its pulse width, but from the outward resolution
I'd say it's very short, indeed, which accounts for its very low average
power drain on sailboat batteries.


Norm B (who has never worked on a solid-state radar, but has on
tube type 2 and 5 mega Watt ones)


Navy? AN/SPS-6? SPS-55? SPS-30? SPS-21, the old Raytheon Pathfinder?

Been there, done that, got the T-shirt...(c; Old Navy Fart, here. The 30
could see the moon if you kept keying the repeater with pulses on its
trigger input. It would kill a seagull in its beam out several hundred
yards.


--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.

On Fri, 17 Jun 2005 18:22:09 -0700, engsol
wrote:

On Fri, 17 Jun 2005 20:36:15 -0400, Gary Schafer wrote:

On Fri, 17 Jun 2005 21:43:43 GMT, Bruce in Alaska
wrote:

In article ,
Larry W4CSC wrote:

"TimJay" wrote in news:wdidnd9mKMdB5y_fRVn-
:

Need info about the Open Array 72" verse 48"




In any radar system, from any manufacturer, you need to think about how far
it is to the horizon from the altitude your antenna is located. Ask
yourself, "Can this system give me good returns from a normal boat at the
horizon?" It cannot see beyond its horizon. Its horizon is dependent on
its altitude. Altitude is also a tradeoff with close-in target acquistion.
If you put the antenna up high to get a longer horizon, you won't be able
to see that damned bouy someone put in your way in the fog you are about to
run over. I'll trade seeing that bouy in really close to the boat for
seeing a boat out 35 miles any day of the week. Of course, having two
radars, one low down to see that bouy and one up high to see those long-
range targets is much nicer. It also gives you redundancy for the
inevitable failures of these cheaply made boat systems.

A 72" array WILL have a narrower beamwidth than the 48". A narrower
beamwidth translates into resolution, not range, of the targets on the
scope. Instead of the two targets out there painting as one wide one, you
MAY be able to see them as two distinct targets, as if that really made any
difference. AS you get closer to the targets, the wider beamwidth antenna
also shows them as separate targets closer in, which I think makes the
point moot. The higher power of the 72" transmitter WILL show small
targets like towers and bouys at larger ranges by painting them with more
brute RF power force, creating a larger return signal above the noise floor
of the receiver. If seeing a bouy 18 miles away instead of 10 miles away
is important to you, the higher the power the better. If under sail, with
limited power resources, higher power eating the batteries soon becomes
more important than seeing the bouy so far away. At 30 gallons per hour,
it matters little.

Hope this makes you think of your particular situation. Everything is a
compromise.

Open Arrays are really SlotLine Waveguide Antennas, and legnth is
proportional to Antenna Gain, and Transmitted Peak Power. It is also
Inversely proportional to Horozontal Beamwidth. More is better, for
all cases, and less beamwidth is better always. I only have one nit to
pick with Larry's above, and that is Detection Distance for any
particular target is a combination of all the above factors and a few
more, but one of the biggies is Peak Transmitted Power, More power,
equals better targets, at longer ranges. In the old days before Loran,
and GPS, Radar was used for Position Fixing, and mountains were often
used as targets for navigation, at ranges exceeding 72 miles, with the
Decca 3xx, and 4xx series radars that had 20Kw and 40Kw XBand
transmitters with 6 and 7.5 Ft antennas.
Rule of thumb: Bigger is better, longer is better , but all this
"better" costs alot more money. So, eventually money is the limiting
factor.


Bruce in alaska

I agree with Bruce, bigger is always better. The larger array provides
narrower beam width along with higher gain. The narrower beam width
will help with target resolution on all ranges. It can be most
appreciated on the shorter ranges where Larry says it does not matter.
When on a narrow waterway the larger array will allow you to
distinguish a boat from shore objects that can not be done on the
small radar's.
The higher power will let you see small objects like those small buoys
that the small radar's may not even see.

A note on peak power. It is really the amount of average power that
determines how much of a return you get from the radar. The higher the
average power the better return.

The wider the pulse width of the radar pulse the greater the average
power transmitted. But the wider the pulse width the less resolution
in range you have. This is particularly important on short ranges.
This is why most radar's use a wide pulse width for long range (gives
higher average power) and very narrow pulses on short range. The
narrow pulse gives much better range resolution but lowers the average
power of the signal. But at short ranges you can get by with less
average power because signal returns are generally stronger.

The peak power of the transmitter usually remains the same whether
long or short pulses are being used. It is necessary to have a rather
high peak power transmitter in order to achieve enough average power
for decent returns as pulse widths are narrowed.

With a given pulse width, the higher the peak power of the transmitter
the higher the average power will be.

Some radar's have poor range resolution because they are under powered
and have to use wider pulses (to raise the average power) in order to
get strong enough returns on ranges where the pulses being used should
be narrower for better range resolution.

Usually radar's are advertised by how much peak power they have.
Sounds more impressive. Few tell you what the actual average
transmitted power is which is the most important.

Regards
Gary

One thing I see missing as to short range is the TR time...i.e., how quickly
after the tx pulse quits can the rx receive and process the echo.
It's possible to "blind" the rx even if the isolation between tx/rx is 100 dB or better.
Anyone know some numbers?

Norm B (who has never worked on a solid-state radar, but has on
tube type 2 and 5 mega Watt ones)

A radar mile is 12.36 microseconds. It takes that long for a radar
pulse to make the round trip, out and back, for one nautical mile.
One nautical mile is around 6076 feet, times 2 = 12152 feet for a
round trip.
If you divide that by 12.36 you get about 983 feet for 1 microsecond.
So if the pulse width was 1 microsecond wide and if the receiver
recovered immediately, then the closest you could see would be 983
feet away.

With a .1 microsecond wide pulse the minimum range would be around 98
feet.

But there is some time required for the transmitter to stop
transmitting and for the receiver to recover to be useful and that
adds to the minimum range.

I don't have a manual handy for a small radar, but they usually show
pulse widths used and tell you the minimum range.

Regards
Gary

On Sat, 18 Jun 2005 09:06:01 -0400, Larry W4CSC wrote:

engsol wrote in
:

snip

Norm B (who has never worked on a solid-state radar, but has on
tube type 2 and 5 mega Watt ones)


Navy? AN/SPS-6? SPS-55? SPS-30? SPS-21, the old Raytheon Pathfinder?

Been there, done that, got the T-shirt...(c; Old Navy Fart, here. The 30
could see the moon if you kept keying the repeater with pulses on its
trigger input. It would kill a seagull in its beam out several hundred
yards.

Yep, Navy '55 thru '59....the aviation part, so it was the APS-20 and APS-45.
Later I worked on the FPS-16 at Vandenburg AFB.
The DEWLine had a really old radar,,,FPS-19 as I recall...
it used a klystron rather than a maggie. Strange beast, but reliable.

engsol wrote in
:

it used a klystron rather than a maggie. Strange beast, but reliable.



The really big radars still use klystrons, not magnetrons. FAA's S-band
radars used by centers for enroute traffic uses a magnetron firing into an
amplitron for their power. I visited lots of FAA's radar sites in the 90's
calibrating the site test equipment from a mobile lab.

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.