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Old 13-04-2013, 18:47   #136
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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I'm with you Paul. When the seas pick up my screen gets cluttered as well. It's a great tool, but certainly there are times when its usefulness is marginal (heavy seas, rain).
I recently swapped my 20 year old Raytheon for a Furuno 3D and the difference is remarkable, especially with all the digital noise/clutter suppression and target enhancement. I worked on a bunch of ships radars (professionally) in the mid 80's and this digital Furuno with it's silly little 2' dome antenna outperforms those radars that had 10' open arrays. Of-course today the ships radars have had the same or even better refinements over time; it's just to demonstrate how much they improved over time.

When you use an old Pathfinder, the difference with the modern units will be dazzling
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Old 13-04-2013, 18:56   #137
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I recently swapped my 20 year old Raytheon for a Furuno 3D and the difference is remarkable, especially with all the digital noise/clutter suppression and target enhancement. I worked on a bunch of ships radars (professionally) in the mid 80's and this digital Furuno with it's silly little 2' dome antenna outperforms those radars that had 10' open arrays. Of-course today the ships radars have had the same or even better refinements over time; it's just to demonstrate how much they improved over time.

When you use an old Pathfinder, the difference with the modern units will be dazzling
I made the mistake of getting a 2kw dome that isn't the new "HD" stuff they have out now. Live and learn I guess.
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Old 13-04-2013, 19:57   #138
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Re: Want the Best, Cheapest Easiest AIS solution:-)

Well I used to have a 12-year old Raymarine 4KW unit, but replaced that system a few years ago with the Furuno NN3D gear. The Furuno 4KW HD radar is great, but I still can't see a semi-submerged log in the waves.

Now that I'm up here in the PNW San Juan Islands, I'm going to get lots of practice spotting logs in the (relatively) calmer water. I sailed to Victoria (Vancouver Island) around Christmas, and it was a regular obstacle course. We were sailing in daylight, so the detection was all visual.
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Old 13-04-2013, 22:42   #139
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Relax Paul! You are not loosing your grip. I was using a little bit of flamboyance in my reply to the steel boaters:-) Radar is great, but then so are your eyes, just another tool, to make Sailing easier. Like ais. I am definitely not a Luddite, but definitely not a jump on the "look at mine its bigger and better than yours wagon".
Why do you think I bought steel?

So I can bash logs with impunity!

The finest radar I can buy may or may not see the log I'm bearing down on. That really depends on my own skills at a) tuning the thing, and b) interpreting the various pips and blobs.

There's only so much I can do with that. Eyes and luck and collision bulkheads fill in the gaps.
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Old 13-04-2013, 22:47   #140
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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I made the mistake of getting a 2kw dome that isn't the new "HD" stuff they have out now. Live and learn I guess.

There's still two schools of thought on this. My broad understanding from quizzing fairly intensively the fellows who install these units is that digital/HD/etc. radar is very good at discerning relatively close returns, i.e. getting into a marina in fog at night...every pole and boat is clearly defined.

The older, analog, pulse radars, on the other hand, seem to still have the edge on range (assuming the radome is at the same height) and their ability to spot and define heavy weather.

It was seriously suggested to me that I get a broadband radar for final approach, but to keep an old Koden or Furuno for offshore!

That argues for a revival of the ketch, so you have two masts from which to hang the differing radomes!
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Old 13-04-2013, 23:28   #141
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Re: Want the Best, Cheapest Easiest AIS solution:-)

I bought my boat case it Sails. It was designed as a "fast blue water passage maker" By the time I have tied all the bits on I will be surprised if she still floats:-) I have sailed alot on the North pacific coast over the last 25 years and have rumbled a few logs. It is the dead heads in rough weather that scare me. I have never heard of a plastic boat sinking from a log encounter, bent rudders,shafts etc.

Again Radar like Ais, GPS, DSC, MBH all add up to ways to make our passion ,hobby, get away, alter ego, safer while at the same time making people a very lucrative living.
I am still unsure about what I am going to do. AIS yes just as an extra set of eyes, will I go for the full monty? Not sure, see how things add up. Time is short So May 21 is my personal deadline.
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Old 14-04-2013, 01:48   #142
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Time is short So May 21 is my personal deadline.
Forget about putting things on your boat to make it safer for a moment, what about taking things off, a calendar is one of the single most dangerous items you can have on a boat
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Old 14-04-2013, 02:09   #143
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Re: Want the Best, Cheapest Easiest AIS solution:-)

true.

I Live up a long narrow alley. I can not leave before July, I cant handle another Northern Wintr on the boat.

Bur you are right I need to remember that.
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Old 14-04-2013, 06:11   #144
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Want the Best, Cheapest Easiest AIS solution ...
Unfortunately, you generally only get to select two of those three criteria.
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Old 14-04-2013, 07:00   #145
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Unfortunately, you generally only get to select two of those three criteria.
Spoken like a true engineer.
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Old 14-04-2013, 21:57   #146
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Also, doesn't splitting and amplification each act to decrease sensitivity? It's really about signal to noise ratio, right? The splitting decreases signal no matter how you slice it. And amplifying increases noise.
A common misconception when considering a receivers SNR is that the only noise you must consider is noise presented externally to the receiving system at the antenna. Of course, simply amplifying noise along with the wanted signal will not improve the SNR at the antenna. And Brad is right, no matter which way you slice it, splitting a received signal will result in some signal loss on the down stream paths.

However, a receiver system is not just made up of an antenna and an "ideal noise free black box". Amplifying, mixing, filtering and demodulating on the receive path, along with noise introduced by other system components to support all of this, all contribute to the overall system noise figure. When an RF engineer considers noise figure (NF) and SNR they are considering not just noise at the antenna, but noise right through to the output in the system that results in a demodulated signal that can be digitally processed at a given error rate.

One way to reduce the NF is by adding gain to the front of the system. If the amplifier has a smaller NF than the rest of the system then Friis's formula shows that the total system NF will follow. So it must be a low noise amplifier (LNA) i.e. we cant just amplify and introduce new sources of noise in the process. An LNA is a nice way to compensate for signal loss in a splitter, as if the NF of the LNA is lower than your systems NF, it wont just compensate, it may actually improve your system performance.
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Old 14-04-2013, 22:36   #147
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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Since we are limited to line-of-sight with VHF frequencies, how much signal strength overall is needed to receive line-of-sight targets? (And how much transmit is really needed?)
At 2W transmit power, with an omni directional antenna and 1dB of cable loss in both TX and RX with both antennas 20m above the water line, a theoretically reliable distance of ~12nm could be achieved with -107dBm sensitivity. But in practice using real world antenna systems, I've found it to be about 7-10nm.


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Also, doesn't splitting and amplification each act to decrease sensitivity? It's really about signal to noise ratio, right? The splitting decreases signal no matter how you slice it. And amplifying increases noise.
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Originally Posted by Carl Omundsen View Post
An LNA is a nice way to compensate for signal loss in a splitter, as if the NF of the LNA is lower than your systems NF, it wont just compensate, it may actually improve your system performance.
Our splitter has 12dB of gain with a 1.5dB noise figure. This results in a 6dB gain in sensitivity on our transponders.


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How much signal loss do you get from a 2nd vhf antenna at the top of the mast, inches from the other VHF antenna? Let's say in the worst part of the antenna pattern.
I don't recommend putting two antennas side-by-side in the near field because it can cause RX overload or even damage. If you want to use the masthead for both, then use the splitter. As for losses with a masthead antenna, cable loss is typically the most significant factor.


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Putting the above three thoughts together, a lot of the installation choices depend on what's needed to only hit line-of-sight. I guess I'm looking for a graphic showing the operational envelope from all these parameters. That and some feedback from real-world experiences.
I don't have a graphic for you, but the parameters are antenna system losses (primarily cable loss and antenna matching), height of transmit and receive antennas, power output (2W for Class B) and receive sensitivity (min -107dBm @ 20% PER for Class B).

For a practical example, on my boat using the masthead antenna along with one of our transponders and splitters my receive range is around 10nm for Class B and 20-25nm (often more) for Class A.

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(I'm a big believer in starting with the highest gain omnidirectional antenna that still has a beamwitdh in excess of your typical angle of heel. There's a lot more complexity, money, and effort needed to overcome a sub-optimal antenna. For example, using a higher gain antenna can overcome signal loss from using a splitter. So the best advice could be to both upgrade your masthead antenna and use a splitter.)
It's already been mentioned, but you probably don't want to use a high gain antenna due to angle of heel. Rather, I usually recommend a standard 3dB gain omni-directional. But I think your final advice is spot-on for maximizing range... if your masthead antenna is sub-optimal (eg. old and unknown quality, damaged, water-logged, poorly matched) then upgrade it and use a splitter with a low noise amplifier.

Sorry for the delay on the follow-ups... gotta get out and sail on the weekends
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Old 15-04-2013, 05:08   #148
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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The older, analog, pulse radars, on the other hand, seem to still have the edge on range (assuming the radome is at the same height) and their ability to spot and define heavy weather.

It was seriously suggested to me that I get a broadband radar for final approach, but to keep an old Koden or Furuno for offshore!
I think you might be mixing up HD and broadband radars, HD radars are analogue pulse radars with added DSP.

Dave
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Old 15-04-2013, 07:28   #149
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Re: Want the Best, Cheapest Easiest AIS solution:-)

Greetings and welcome aboard the CF, Carl Omundsen.

Thanks for your expert contribution.
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Old 15-04-2013, 14:31   #150
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Re: Want the Best, Cheapest Easiest AIS solution:-)

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I think you might be mixing up HD and broadband radars, HD radars are analogue pulse radars with added DSP.

Dave
I think you're correct. I mean the difference between analog/magnetron types, which I was told were still superior for distance, and the new digital/broadband/"3D" types that seem to do very well closer (under 10 NM) in.

The advantage to me is that the newer radars seem to draw considerably less power over the older types and require less in the way of "warming up" and tuning. Admittedly, my experience is based on playing around with a 20 year old Koden and a few other antiques.
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