[Amel Yacht Owners] Range of AIS


Mark Erdos
 

Eric,

 

I can’t explain the anomalies. I can just elucidate the theory.

 

Best regards,

 

Mark

 

SM2K #275

www.creampuff.us

 

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of sailormon
Sent: Thursday, March 20, 2014 8:06 PM
To: amelyachtowners@...
Subject: [Amel Yacht Owners] Range of AIS

 

 

Mark,

I have frequently received AIS from ships over 50 miles away.

One time as I was rounding Montauk point I was able to read ships anchored outside Manhattan. Over 100 miles.

I believe this is due to the fact that many of these ships AIS antennas are over 100 feet above the water.

 

With respect to the transmission of class B AIS , I believe it is only 5 watts as the class A is 25 watts. Many times I see ships but they only see me at about 5-6 miles. When I feel rich, I will buy a class A unit.

Fair Winds

Eric

Kimberlite SM 376

 

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of Mark Erdos
Sent: Thursday, March 20, 2014 10:09 AM
To: amelyachtowners@...
Subject: RE: [Amel Yacht Owners] ais antenna

 

 

Mark,

I think you need to check your AIS. If you are showing vessels 50-100nm away, these are most likely ghost images or images where you have not received a transmission for quite some time. The should not be on the screen. The AIS works on a VHF frequency. This is a direct line of sight transmission. Meaning, that both the transmitting antenna and the receiving antenna need to “see” each other. Due to the curvature of the earth this limits the transmission range. The maximum range of a VHF transmission is 25 nm.

The range in nautical miles - that is, how far your radio can 'see' to the horizon is equal to 1.23 times the square root of the height of your antenna in feet.

http://www.frugal-mariner.com/images/Range2.png

So if, for instance your antenna height is 60 feet, the distance it can transmit before it runs into the horizon is ~ 9.5 nautical miles. ( the square root of 60 = 7.74. Multiply that times 1.23 to come up with approximately 9.5.)

Now, keep in mind, the vessel to which you are transmitting also has his antenna above the water. So, let's assume, for example, his antenna is 18 feet above the water. He can transmit about 5.2 miles. You can add your range to his to come up with 14.7 nautical miles.

A land based station is usually much higher. An antenna on a hill on a tower might be very high, but for argument's sake, let's say it's 400 feet. So theoretically, he can transmit 24.6 miles. Add that to your 9.5 miles and you have about 34.1 nautical miles.

This seems to exceed the roughly 25 mile maximum range limit. Well, many other factors come in to play here. The first of which is the rapidly diminishing strength of the transmitted signal with distance. The power density of an electromagnetic wave is proportional to the inverse of the square of the distance from the source. So, for every 4 miles your signal travels, its strength is reduced by a factor of 16. It won't take too long for that 25 watt signal to reduce itself to next to nothing.

Best regards,

Mark

SM2K #275

www.creampuff.us

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of markghayden@...
Sent: Thursday, March 20, 2014 9:56 AM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] ais antenna

Several years ago we installed AIS on Northfork. We initially used the existing AM/FM antenna and a year later had a VHF antenna that was designed for use with AIS professionally installed on the top of the main mast with a new run of coax to our nav station.

The difference was dramatic. The range increased from 10nm (with AM/FM antenna) to 50-100nm (with VHF/AIS antenna).

best, Mark

SM2K #331

On Thu, Mar 20, 2014 at 12:31 PM, <sailw32@...> wrote:

When I bought a Garmin AIS 600 ,I was told by the salesmen at the GPS store as well as a Garmin rep. that I should install a separate antenna . Now that I am ready to install it on top of the mizzen mast and thinking of the difficulty of the install, I am questioning if its worth the effort and the cost of the antenna. Putting a splitter into the vfh would be much easier. My question is for those that have a splitter , do you have a good AIS signal and is there any reason to have a separate antenna ?

  ; Thanks, Pat SM #123

[Non-text portions of this message have been removed]


sailormon <kimberlite@...>
 

Mark,

It shouldn’t work at that range as you stated, but it does—I guess we are using the force !

Fair Winds

Eric

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of Mark Erdos
Sent: Thursday, March 20, 2014 9:14 PM
To: amelyachtowners@...
Subject: RE: [Amel Yacht Owners] Range of AIS

 

 

Eric,

 

I can’t explain the anomalies. I can just elucidate the theory.

 

Best regards,

 

Mark

 

SM2K #275

www.creampuff.us

 

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of sailormon
Sent: Thursday, March 20, 2014 8:06 PM
To: amelyachtowners@...
Subject: [Amel Yacht Owners] Range of AIS

 

 

Mark,

I have frequently received AIS from ships over 50 miles away.

One time as I was rounding Montauk point I was able to read ships anchored outside Manhattan. Over 100 miles.

I believe this is due to the fact that many of these ships AIS antennas are over 100 feet above the water.

 

With respect to the transmission of class B AIS , I believe it is only 5 watts as the class A is 25 watts. Many times I see ships but they only see me at about 5-6 miles. When I feel rich, I will buy a class A unit.

Fair Winds

Eric

Kimberlite SM 376

 

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of Mark Erdos
Sent: Thursday, March 20, 2014 10:09 AM
To: amelyachtowners@...
Subject: RE: [Amel Yacht Owners] ais antenna

 

 

Mark,

I think you need to check your AIS. If you are showing vessels 50-100nm away, these are most likely ghost images or images where you have not received a transmission for quite some time. The should not be on the screen. The AIS works on a VHF frequency. This is a direct line of sight transmission. Meaning, that both the transmitting antenna and the receiving antenna need to “see” each other. Due to the curvature of the earth this limits the transmission range. The maximum range of a VHF transmission is 25 nm.

The range in nautical miles - that is, how far your radio can 'see' to the horizon is equal to 1.23 times the square root of the height of your antenna in feet.

http://www.frugal-mariner.com/images/Range2.png

So if, for instance your antenna height is 60 feet, the distance it can transmit before it runs into the horizon is ~ 9.5 nautical miles. ( the square root of 60 = 7.74. Multiply that times 1.23 to come up with approximately 9.5.)

Now, keep in mind, the vessel to which you are transmitting also has his antenna above the water. So, let's assume, for example, his antenna is 18 feet above the water. He can transmit about 5.2 miles. You can add your range to his to come up with 14.7 nautical miles.

A land based station is usually much higher. An antenna on a hill on a tower might be very high, but for argument's sake, let's say it's 400 feet. So theoretically, he can transmit 24.6 miles. Add that to your 9.5 miles and you have about 34.1 nautical miles.

This seems to exceed the roughly 25 mile maximum range limit. Well, many other factors come in to play here. The first of which is the rapidly diminishing strength of the transmitted signal with distance. The power density of an electromagnetic wave is proportional to the inverse of the square of the distance from the source. So, for every 4 miles your signal travels, its strength is reduced by a factor of 16. It won't take too long for that 25 watt signal to reduce itself to next to nothing.

Best regards,

Mark

SM2K #275

www.creampuff.us

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of markghayden@...
Sent: Thursday, March 20, 2014 9:56 AM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] ais antenna

Several years ago we installed AIS on Northfork. We initially used the existing AM/FM antenna and a year later had a VHF antenna that was designed for use with AIS professionally installed on the top of the main mast with a new run of coax to our nav station.

The difference was dramatic. The range increased from 10nm (with AM/FM antenna) to 50-100nm (with VHF/AIS antenna).

best, Mark

SM2K #331

On Thu, Mar 20, 2014 at 12:31 PM, <sailw32@...> wrote:

When I bought a Garmin AIS 600 ,I was told by the salesmen at the GPS store as well as a Garmin rep. that I should install a separate antenna . Now that I am ready to install it on top of the mizzen mast and thinking of the difficulty of the install, I am questioning if its worth the effort and the cost of the antenna. Putting a splitter into the vfh would be much easier. My question is for those that have a splitter , do you have a good AIS signal and is there any reason to have a separate antenna ?

  ; Thanks, Pat SM #123


svperegrinus <no_reply@...>
 

This does not address the original poster's question of what happens if you use a splitter, but here's some additional data:

1.  VHF radio (with a 4' antenna on top of main mast)
This radio has an AIS built-in.  No antenna splitter, it uses the same antenna used for the voice radio.    Currently the furthest reliable signal is "Dole Chile", steaming at 25.6 miles away.

2.  Dedicated AIS on its on 4' antenna on top of mizzen
This got a fragmentary tx from "Dole Chile", but lost that signal before it could receive the actual name (only got the MMSI), and never got ROT, nor draught, etc., although bearing, SOG and position were picked up.
The furthest reliable signal is "Bimini Superfast", steaming at 23.9 miles away, a signal also picked by the VHF.

Other than antenna height, a factor could be that even though both systems use 4' antennas, the VHF has a "Shakespeare Phase III Marine Cell" (mod. 6410) antenna, whereas the AIS has a "Shakesperare Phase III Marine AIS" (mod. 6396) antenna.   But I doubt the antennas make much difference.

Net/net, mast height makes a difference, as Mark proposes.

There are 144 targets right now.

s.v. Peregrinus
SM2K #350 (2001)


drbobgray@...
 

Hi,
I'm new to this users group and joined to listen and learn all about the Amel's while my family and I search for a well-maintained used SM53 to buy and use in the Great Lakes.

Here's some theoretical numbers that I've calculated which may may be helpful in understanding what happens when using a 2-way splitter and a 3-way splitter:

2-way splitter...your theoretical insertion loss will be -3dB which is a 50% reduction.

3-way splitter...your theoretical insertion loss will be -4.77dB which is a 67% reduction.

best,
Bob


Bill & Judy Rouse <yahoogroups@...>
 

Thanks Bob,

For everyone in the Amel Owner's Group, Robert (Bob) Gray, Ph.D. is at Penn State and is Associate Professor of Electrical Engineering/Electrical Engineering and Electrical Engineering Technology.

I thought I would add that bit of information so that you will place some weight on his calculations. Bob is too modest to have added it.

He could be a great resource for us in some of our electrical challenges.

I hope you find your Super Maramu.

Bill
BeBe 387




On Sat, Mar 22, 2014 at 8:08 PM, <drbobgray@...> wrote:
 

Hi,
I'm new to this users group and joined to listen and learn all about the Amel's while my family and I search for a well-maintained used SM53 to buy and use in the Great Lakes.

Here's some theoretical numbers that I've calculated which may may be helpful in understanding what happens when using a 2-way splitter and a 3-way splitter:

2-way splitter...your theoretical insertion loss will be -3dB which is a 50% reduction.

3-way splitter...your theoretical insertion loss will be -4.77dB which is a 67% reduction.

best,
Bob



Patrick McAneny
 

Bob, That's interesting, I was told there would be a loss by the rep. for Garmin , approx. 2db, which was their argument for a dedicated antenna. I just did not and still don't understand why you have a loss assuming good connections and the antenna only servicing one unit at a time either vhf or ais.  Thanks, Pat

-----Original Message-----
From: drbobgray
To: amelyachtowners
Sent: Sat, Mar 22, 2014 4:08 pm
Subject: RE: [Amel Yacht Owners] Range of AIS

 
Hi,
I'm new to this users group and joined to listen and learn all about the Amel's while my family and I search for a well-maintained used SM53 to buy and use in the Great Lakes.

Here's some theoretical numbers that I've calculated which may may be helpful in understanding what happens when using a 2-way splitter and a 3-way splitter:

2-way splitter...your theoretical insertion loss will be -3dB which is a 50% reduction.

3-way splitter...your theoretical insertion loss will be -4.77dB which is a 67% reduction.

best,
Bob


Herbert Lackner
 

 

Trying to summarize:

 

Receiving mode:

·         General the splitter is splitting the signal to two (or more) receivers.  If the signal - that has been splittet up – is not amplified again you loose 3dB (50% -  because you split it up for two receivers). 

·         Most oft he modern splitters are active splitters that have a built in amplifier, need power, and will amplify the splitted signal so that in the end no signal reduction should be on both (or more) receivers

·         Anyway there will be some signal loss because of additional connectors… that cannot be restored through amplifying

 

Sending Mode:

·         The splitter has to make sure that only one device sends at one time. In general they are designed in such a way, that the VHF signal has priority, that means that the AIS is only allowed to transmit if the VHF is not sending.

 

Splitter or no splitter:

·         When using an active splitter there should be no noteworthy difference between splitter or no splitter in transmitting or receiving

·         From a security point of view it is an additional piece of electronic that can fail.  If so the decision hast o be made if VHF or AIS hast o be used, because only one of them can work. According to murphys law this can occur in a situation where nobody wants to remove the VHF /AIS cover to change the cables…

·         From a „ease of installation“ point it is much easier to install the splitter because its just connecting it, ready

·         Considering the costs it does not make a big difference (splitter is a little bit more expensive).

 

So, in the end, it is just the question if more reliability or additional installation effort is more important.

 

On our Santorin we use a Banten active splitter and a comar AIS class B transponder with one antenna without any receiving problems, but sometimes the AIS is not able to transmit and sends an Alarm. I could not find out if that is due to splitter problems but I will change this installation abyway in this year when we change the running rigging and service the mast and install an additional antenna on the mizzen for the AIS. I will keep the Splitter as a spare part, if fore any reason then one oft he antennas will fail I can still go back to the current situation with AIS and VHF on one antenna.

 

Fair winds

 

Herbert

Kali Mera, SN120

 

 

 

 

 

Von: amelyachtowners@... [mailto:amelyachtowners@...] Im Auftrag von Patrick Mcaneny
Gesendet: Sonntag, 23. März 2014 12:34
An: amelyachtowners@...
Betreff: Re: [Amel Yacht Owners] Range of AIS

 

 

Bob, That's interesting, I was told there would be a loss by the rep. for Garmin , approx. 2db, which was their argument for a dedicated antenna. I just did not and still don't understand why you have a loss assuming good connections and the antenna only servicing one unit at a time either vhf or ais.  Thanks, Pat

-----Original Message-----
From: drbobgray <drbobgray@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Sat, Mar 22, 2014 4:08 pm
Subject: RE: [Amel Yacht Owners] Range of AIS

 

Hi,
I'm new to this users group and joined to listen and learn all about the Amel's while my family and I search for a well-maintained used SM53 to buy and use in the Great Lakes.

Here's some theoretical numbers that I've calculated which may may be helpful in understanding what happens when using a 2-way splitter and a 3-way splitter:

2-way splitter...your theoretical insertion loss will be -3dB which is a 50% reduction.

3-way splitter...your theoretical insertion loss will be -4.77dB which is a 67% reduction.

best,
Bob


Mark Erdos
 

Bob,

 

Also, does this take into consideration the splitter is “powered” as opposed to a non-powered splitter? The specs of the powered unit claim negligible insertion loss. I can’t imagine they could claim this with a  50% loss.

 

 

Best regards,

 

Mark

 

SM2K #275

www.creampuff.us

 

 

 

 

From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of Patrick Mcaneny
Sent: Sunday, March 23, 2014 7:34 AM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] Range of AIS

 

 

Bob, That's interesting, I was told there would be a loss by the rep. for Garmin , approx. 2db, which was their argument for a dedicated antenna. I just did not and still don't understand why you have a loss assuming good connections and the antenna only servicing one unit at a time either vhf or ais.  Thanks, Pat

-----Original Message-----
From: drbobgray <drbobgray@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Sat, Mar 22, 2014 4:08 pm
Subject: RE: [Amel Yacht Owners] Range of AIS

 

Hi,
I'm new to this users group and joined to listen and learn all about the Amel's while my family and I search for a well-maintained used SM53 to buy and use in the Great Lakes.

Here's some theoretical numbers that I've calculated which may may be helpful in understanding what happens when using a 2-way splitter and a 3-way splitter:

2-way splitter...your theoretical insertion loss will be -3dB which is a 50% reduction.

3-way splitter...your theoretical insertion loss will be -4.77dB which is a 67% reduction.

best,
Bob


drbobgray@...
 

Pat,  Good question.  I'll explain why.  There is a (nodal analysis) rule that says the sum of the electric currents entering a node equals the sum of the electric currents leaving a node. 
Think of a 2-way splitter shaped like a "Y"   At the center is the one and only node. At the bottom of the "Y" symbol is the input from the VHF antenna.  At the top of the "Y" are the two output paths; one output path is attached to the AIS radio, the other output path is attached to the VHF radio.  Because electric current is related to power, the same nodal rule holds. 
Let's say the the incoming signal power (in watts) from the antenna into the node is 1 watt.  Then the outgoing signal power from the node will be 1/2 watt each.  1/2 watt goes to the AIS + 1/2 watt goes to the VHF radio.
The theory holds:  1 watt input = 1/2 watt output + 1/2 watt output.
The reason it's a 50-50 equal split between the radios is because everything that's attached to the node are all the same:  they are each 50-ohm loads.
If the AIS and the VHF radio weren't both at 50-ohms, the nodal analysis still works, but each radio would receive a different amount in watts.
Hope this helps.
Bob


drbobgray@...
 

Mark,
Hmmm.  Good question.  I wouldn't know unless I looked at the tech spec sheet.  I couldn't find your spec sheet but I was able to find the tech sheet for a different splitter that another person mentioned (easySplit, Active Antenna Splitter, 3-way antenna splitter, part # A026). 
From what I could tell I think the way it works is that the power supplied to this splitter is used to control two relays that are used to isolate the AIS radio and FM radio antenna inputs when the VHF radio transmits. They probably do this to protect the AIS and FM radios from the VHF transmit output power.  There doesn't seem to be any amplifier used in this device to make up for insertion losses.  In fact, the device states -3dB power divider and says on another page in the tech literature that it's a "passive power divider"  In summary, the active part of this particular splitter seems to be that it switches relays on/off to protect the AIS and FM radios during VHF radio transmissions.  The insertion loss is -3dB with 2 radios attached and they say something about -3.8 dB with three radios attached.  A question I would ask the company that makes it is "what happens if the splitter isn't powered and the VHF radio is transmitted?"  My concern would be the AIS and/or FM radios could be hurt and/or the splitter damaged.
best,
Bob


Richard03801 <richard03801@...>
 

Hi all with a single ant on the main mast with a 1:2 splitter that picks up ships at 30 miles. We have successfully called them at around that range. Net effect in our case with a receive only is very good. 

Regards 
Richard Piller

Cell 603 767 5330

On Mar 23, 2014, at 17:12, <drbobgray@...> wrote:

 

Mark,
Hmmm.  Good question.  I wouldn't know unless I looked at the tech spec sheet.  I couldn't find your spec sheet but I was able to find the tech sheet for a different splitter that another person mentioned (easySplit, Active Antenna Splitter, 3-way antenna splitter, part # A026). 
From what I could tell I think the way it works is that the power supplied to this splitter is used to control two relays that are used to isolate the AIS radio and FM radio antenna inputs when the VHF radio transmits. They probably do this to protect the AIS and FM radios from the VHF transmit output power.  There doesn't seem to be any amplifier used in this device to make up for insertion losses.  In fact, the device states -3dB power divider and says on another page in the tech literature that it's a "passive power divider"  In summary, the active part of this particular splitter seems to be that it switches relays on/off to protect the AIS and FM radios during VHF radio transmissions.  The insertion loss is -3dB with 2 radios attached and they say something about -3.8 dB with three radios attached.  A question I would ask the company that makes it is "what happens if the splitter isn't powered and the VHF radio is transmitted?"  My concern would be the AIS and/or FM radios could be hurt and/or the splitter damaged.
best,
Bob


Patrick McAneny
 

Bob, Thanks for your reply and your attempt to enlighten the dim. I assume you would agree then, that I would receive a better, stronger signal by installing a dedicated AIS antenna. Good luck on your search for a SM and welcome to the group, we can use all the electrical engineers we can get.
                                                                                                                                                                            Thanks Again,
                                                                                                                                                                   Pat  SM Shenanigans

-----Original Message-----
From: drbobgray
To: amelyachtowners
Sent: Sun, Mar 23, 2014 4:38 pm
Subject: RE: [Amel Yacht Owners] Range of AIS

 
Pat,  Good question.  I'll explain why.  There is a (nodal analysis) rule that says the sum of the electric currents entering a node equals the sum of the electric currents leaving a node. 
Think of a 2-way splitter shaped like a "Y"   At the center is the one and only node. At the bottom of the "Y" symbol is the input from the VHF antenna.  At the top of the "Y" are the two output paths; one output path is attached to the AIS radio, the other output path is attached to the VHF radio.  Because electric current is related to power, the same nodal rule holds. 
Let's say the the incoming signal power (in watts) from the antenna into the node is 1 watt.  Then the outgoing signal power from the node will be 1/2 watt each.  1/2 watt goes to the AIS + 1/2 watt goes to the VHF radio.
The theory holds:  1 watt input = 1/2 watt output + 1/2 watt output.
The reason i t's a 50-50 equal split between the radios is because everything that's attached to the node are all the same:  they are each 50-ohm loads.
If the AIS and the VHF radio weren't both at 50-ohms, the nodal analysis still works, but each radio would receive a different amount in watts.
Hope this helps.
Bob


Alan Leslie
 

True if it is really a passive splitter...

The ones with a relay for switching to transmit should have minimal loss, there maybe splitters with amplifiers to compensate for the  losses.....but they need to be powered...


We have a separate VHF antenna on the pushpit rail and it works fine..we see ships 10-12 miles away...and always someone is on watch ......with the CPA and TPCA alarms set...we haven't hit anyone yet !!


Cheers

Alan

SV Elyse SM437


Herbert Lackner
 

Dear all,

 

I invested some time on my AIS and would like to share my findings, maybe that will answer Pat’s question and will add some info to Bob’s mail. (just for info: there are so many things regarding our Amels that I do not know and where I need info and help from the group, this area is finally something that I understand being an electrical engineer and computer scientist J )

 

general information about splitters and how they work:

·         If someone wants to use one antenna for multiple devices a splitter ha to be used.

·         Splitter will split up the received signal to multiple outputs. If the splitter has no amplifier the power for each output will be reduced, Bob did explain it already excellent

·         There are some splitters that – due to their manufacturer – will not make the signal weaker (~0dB). Examples are “Watchey S Splitter” or” Simrad NSPL 400”. I did not check the data sheets but I believe them if they tell it.

·         A splitter uses relais to make sure that, if one device (eg the VHF) is transmitting, the other  device (eg the AIS transponder) is disconnected. This is necessary that the other device will not suffer damage (- it is not good for the AIS if it receives the 25Watt from the VHF…). The relais  also makes sure that only one device is allowed to transmit and not both at the same time. The VHF has priority while transmitting.

·         If the splitter is not powered or if there is a defect  the relais should make sure that only the VHF is connected (at least for sending)

 

Range of AIS:

·         As already mentioned by Mark AIS (VHF) the propagation is moreless optical. Therefore the higher the antenna is the bigger is the distance that can be covered (Mark explained this in detail). More transmitting power may add only some additional  miles

·         Transmission Power for class B AIS is 2 W, for class A 12,5W.  class A transmits every 2-3 seconds, class B every 30 seconds.

 

where to mount the antenna ?

·         Main mast: best choice for VHF antenna, but a splitter has to be used for the AIS because antennas should have a minimum distance from 1 meter from each other, otherwise sending can become difficult.

·         Mizzen: best choice if no splitter will be used

·         Rail:  ok for AIS when distance is not so important. will reduce distance by some miles (~8 miles less), still absolute ok for AIS for most sailors.

·         Cabling: if you use Aircell 7 instead of  RG58 you will have about 2 dB less damping at 20 meter cable length (please think here about the 3dB splitter damping discussion!!)

 

implications on distance:

·         You will receive AIS signals from a bigger distance the higher the antenna is mounted, height here is more important than transmitting power. If the antenna is mounted on the main mast that is  ~3,5 meters higher than the mizzen you will have a bigger range of about  1 mile.   

·         Even if the splitter reduces the VHF signal by 50% for the AIS you will still get an AIS signal not later compared to have a second antenna mounted on the mizzen.

·         If you use an active splitter with low signal reduction (eg “Watchey S Splitter” or” Simrad NSPL 400”) and the antenna is on the main mast you will see other ships earlier compared to an antenna without splitter on the mizzen

 

So, answering Pat’s question if he would get a better, stronger signal with a dedicated antenna the answer is:

·         It depends. The signal will be stronger compared to a not amplified splitted signal (but with minimal effect on distance)

·         The signal will be approx.. the same strength with an amplified signal

·         But: the range is determined by the height , and here is the main mast with the splitter (amplified or not) better.

 

Implications on reliability and security:

·         Using one antenna on the main mast with a splitter is less reliable than using two antennas without a splitter,  one on the main and the other one on the mizzen

·         For me personally reliability is more important than an additional range of one or two miles. I will add an extra antenna at the mizzen for the AIS and change my existing installation.

 

 

I hope I could explain it clear enough and it helps when deciding where and how to mount.

 

Fair winds,

 

Herbert

SN120

 

 

 

Von: amelyachtowners@... [mailto:amelyachtowners@...] Im Auftrag von divanz620@...
Gesendet: Montag, 24. März 2014 12:49
An: amelyachtowners@...
Betreff: Re: [Amel Yacht Owners] Range of AIS

 

 

True if it is really a passive splitter...

The ones with a relay for switching to transmit should have minimal loss, there maybe splitters with amplifiers to compensate for the  losses.....but they need to be powered...

 

We have a separate VHF antenna on the pushpit rail and it works fine..we see ships 10-12 miles away...and always someone is on watch ......with the CPA and TPCA alarms set...we haven't hit anyone yet !!

 

Cheers

Alan

SV Elyse SM437


Patrick McAneny
 

Herbert, Thanks for your excellent  detailed explanation , It echoes what Bob and Mark had to say on this subject . While the splitter would be easier , I will install the dedicated AIS antenna on the Mizzen.  Thanks Again,
                        Pat

-----Original Message-----
From: Herbert Lackner
To: amelyachtowners
Sent: Mon, Mar 24, 2014 11:37 am
Subject: AW: [Amel Yacht Owners] Range of AIS

 
Dear all,
 
I invested some time on my AIS and would like to share my findings, maybe that will answer Pat’s question and will add some info to Bob’s mail. (just for info: there are so many things regarding our Amels that I do not know and where I need info and help from the group, this area is finally something that I understand being an electrical engineer and computer scientist J )
 
general information about splitters and how they work:
·         If someone wants to use one antenna for multiple devices a splitter ha to be used.
·         Splitter will split up the received signal to multiple outputs. If the splitter has no amplifier the power for each output will be reduced, Bob did explain it already excellent
·         There are some splitters that – due to their manufacturer – will not make the signal weaker (~0dB). Examples are “Watchey S Splitter” or” Simrad NSPL 400”. I did not check the data sheets but I believe them if they tell it.
·         A splitter uses relais to make sure that, if one device (eg the VHF) is transmitting, the other  device (eg the AIS transponder) is disconnected. This is necessary that the other device will not suffer damage (- it is not good for the AIS if it receives the 25Watt from the VHF…). The relais  also makes sure that only one device is allowed to transmit and not both at the same time. The VHF has priority while transmitting.
·         If the splitter is not powered or if there is a defect  the relais should make sure that only the VHF is connected (at least for sending)
 
Range of AIS:
·         As already mentioned by Mark AIS (VHF) the propagation is moreless optical. Therefore the higher the antenna is the bigger is the distance that can be covered (Mark explained this in detail). More transmitting power may add only some additional  miles
·         Transmission Power for class B AIS is 2 W, for class A 12,5W.  class A transmits every 2-3 seconds, class B every 30 seconds.
 
where to mount the antenna ?
·         Main mast: best choice for VHF antenna, but a splitter has to be used for the AIS because antennas should have a minimum distance from 1 meter from each other, otherwise sending can become difficult.
·         Mizzen: best choice if no splitter will be used
·         Rail:  ok for AIS when distance is not so important. will reduce distance by some miles (~8 miles less), still absolute ok for AIS for most sailors.
·         Cabling: if you use Aircell 7 instead of  RG58 you will have about 2 dB less damping at 20 meter cable length (please think here about the 3dB splitter damping discussion!!)
 
implications on distance:
·         You will receive AIS signals from a bigger distance the higher the antenna is mounted, height here is more important than transmitting power. If the antenna is mounted on the main mast that is  ~3,5 meters higher than the mizzen you will have a bigger range of about  1 mile.   
·         Even if the splitter reduces the VHF signal by 50% for the AIS you will still get an AIS signal not later compared to have a second antenna mounted on the mizzen.
·         If you use an active splitter with low signal reduction (eg “Watchey S Splitter” or” Simrad NSPL 400”) and the antenna is on the main mast you will see other ships earlier compared to an antenna without splitter on the mizzen
 
So, answering Pat’s question if he would get a better, stronger signal with a dedicated antenna the answer is:
·         It depends. The signal will be stronger compared to a not amplified splitted signal (but with minimal effect on distance)
·         The signal will be approx.. the same strength with an amplified signal
·         But: the range is determined by the height , and here is the main mast with the splitter (amplified or not) better.
 
Implications on reliability and security:
·         Using one antenna on the main mast with a splitter is less reliable than using two antennas without a splitter,  one on the main and the other one on the mizzen
·         For me personally reliability is more important than an additional range of one or two miles. I will add an extra antenna at the mizzen for the AIS and change my existing installation.
 
 
I hope I could explain it clear enough and it helps when deciding where and how to mount.
 
Fair winds,
 
Herbert
SN120
 
 
 
Von: amelyachtowners@... [mailto:amelyachtowners@...] Im Auftrag von divanz620@...
Gesendet: Montag, 24. März 2014 12:49
An: amelyachtowners@...
Betreff: Re: [Amel Yacht Owners] Range of AIS
 
 
True if it is really a passive splitter...
The ones with a relay for switching to transmit should have minimal loss, there maybe splitters with amplifiers to compensate for the  losses.....but they need to be powered...
 
We have a separate VHF antenna on the pushpit rail and it works fine..we see ships 10-12 miles away...and always someone is on watch ......with the CPA and TPCA alarms set...we haven't hit anyone yet !!
 
Cheers
Alan
SV Elyse SM437