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Old 24-07-2015, 14:15   #31
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Re: AIS Antenna on Spreaders

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Originally Posted by Paul L View Post
The first one was Shakespeare, the second Digital Antenna.
Thanks! Now we know that Shakespeare will give BS in writing at times.
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Old 24-07-2015, 15:34   #32
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Re: AIS Antenna on Spreaders

Quote:
Originally Posted by redsky49 View Post
It seems that a successful installation can be achieved with the antenna mounted in various locations. That is good to know. I am leaning toward the use of a splitter or mounting on the pushpit. If stern rail is the ultimate choice, I might install a post with arms for multiple antennas (my antenna farm) as the rail is starting to be rather congested.

I am also starting to consider WiFi/tablet, etc, in addition (or alternative) to a dedicated device such as the Vesper Watchmate 8500 which has previously been my objective.

Appreciate all the various options/opinions!
I've been carrying out some very unscientific research over the last little while.

First bit was simple and has been ongoing... my antenna is on the taffrail/pushpit at about 2 metres..... class B Amec. Constant reception of Class A ships out to 15/20 miles when at sea with the odd stray at 50 or so....
Given that the 'line of sight' range between a 2m ant and a ships 25 metre ( not all that high) ant is about 14 miles that seems to be good.

The second part of my very unscientific research has involved MarineTraffic https://www.marinetraffic.com/en/ais...d4b47e105e02af using the data available from their shore stations. I did this with a variety of shore stations around the world... simply select a class B target, find out what shore station is receiving it ( click on the number down the bottom of the little 'ships info box'). Then scroll down on the right hand side to the polar diagram showing reception ranges. Ideally select a station with a lot of class B traffic. Hover over the red box showing maximum ranges.
Lots of variables in here but receiver details and height of shore station rx ant is shown top left of the page. I checked an assortment of stations globally including the English Channel area where there are lots of class B

Now... we don't know how high the various class B ants are but this does show us how far Class B signals can travel ( 2W compared with 12.5W for class A).
The max at St Heliers as I write this about 25 miles but this may be a bit skewed as HMNZS Wellington ( a bit bigger than your average boat ) is poking around the area and is only fitted with Class B.
What I do think is that it demonstrates that these low power signals can go the distance. The very clever people who designed this stuff would have made sure of that.
I do know that my taffrail class B transmission is being picked up by StHeliers at about 15 miles - it loses me at low tide as I am stuck in the middle of a 1000 boat marina with a seawall and car park between me and the station.

So there you go.
MTBW
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Old 24-07-2015, 17:25   #33
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Re: AIS Antenna on Spreaders

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Originally Posted by svlamorocha View Post
What manufacturer said that "..it 180 degrees out of phase for what you are trying to receive"? That sounds like rubbish to me.

There may be an impact though. If the antenna is design to maximize gain at a "downangle" (a bit below horizontal) then the angle will be inverted. That said, I would expect an antenna designed for a boat (as opposed to an antenna designed for a mountaintop repeater or shore station) to have max gain at exactly horizontal, in which case it would not matter if you inverted it.
Of course you are right. A proper monopole has maximum gain 90 degrees from vertical (0 degrees elevation). Mounting it upside down doesn't change that a whit. The 180 degree nonsense is just stupid. I would ask them for an elevation plot of antenna gain and see what they come back with. I guess it's hard to get good help to answer the phone these days.

Now if one were to mount the antenna to the mast sticking out horizontally that would create loss due to polarization as well as most of the signal would be radiated up/down/fore/aft with very little to port or starboard.
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Old 25-07-2015, 15:40   #34
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Re: AIS Antenna on Spreaders

TIA,
You ask some good questions....and you already got some good answers and info! (such as from yttrill, Wanderlust, colemj, transmitterdan, Paul Elliot, Jeff Robbins, Dockhead, etc.....even if some of their approaches are different/contradictory, etc..)

Before I go any further.....please allow me to point you to a recent thread regarding VHF and AIS Radiowave Propagation and VHF and AIS Radio Range...
VHF and AIS Radiowave Propagation and VHF and AIS Radio Range
And, let me comment (negatively) on this important piece of info...
Quote:
Originally Posted by redsky49 View Post
... if located say 12-15" from mast, will that block enough of the transmissions to be an issue?
This is NO good!!!
12" - 15" is WAY too close!!!
This will significantly effect the antenna's pattern!!
(this will create a "cardioid" pattern in the direction away from the mast, and a significant null in the direction of the mast....AND significant reduction in pattern fore and aft)
So, the answer here is....Yes, this IS an issue...please do NOT do this....
In general you will need to be 2 - 3 times this distance (30" or more) in order for to not have significant pattern distortions...




But, perhaps I can add a few pieces of info (fact) that will help??
{BTW, in addition to my 45 years of cruising experience, and 40+ years of radio communications experience, and 30+ years in the electronics industry....
I installed an AIS receiver (using a masthead antenna) over 9 years ago (in early 2006)....and used this for almost 6 years and > 12,000 miles offshore (including multiple Atlantic crossings), before installing a Class B AIS transponder about 3 years ago....
So, I have both the technical expertise and real-world experience in this matter...}

Please bear with me here, as I go thru this point-by-point, as it will take a bit...but it is the only way to fully answer your questions!!
And, what is so confusing to many layperson sailors (and frustrating to me to explain in brief!), is that almost anything metallic can work as antenna, to some extent, even if mounted in a less than optimal fashion....and with so many, many other variables in the mix, the average layperson sailor has no real "factual" info to base their choices/decisions on...(except for some of my long-winded ramblings!! )



So....here we go!!

Quote:
Originally Posted by redsky49 View Post
Has anyone any experience with such an installation? Decent reception? Any interference with halyards or other lines?
As others have pointed out, it IS do-able....and some have had success with it....(and if using my upper spreader, there would be no issues with genoa, halyards, etc.!)

My main issues were:
a) needed to pull mast and run new cabling!!!
b) needed to place antenna at least 1/2-wavelength away from mast, in order to reduce/eliminate significant antenna pattern skewing...(and even then, there would still be a null in direction of mast, perhaps insignificant, but it would still be there!)...and at approx. 30" away from my mast, this would place the tip of the antenna approx. 4 - 6 inches away from the upper/outer shroud diagonal, and I was planning on securing this with some cable ties and PVC tubing, in order to keep the antenna from whipping around, and possibly contacting the shroud, etc...

All said, I chose:
a) Originally, to use a stern-rail / solar-panel rail mounted antenna, mounted at approx. 9' - 10' off the water, as my AIS transponder antenna / back-up VHF antenna....
b) Then later, to use the Vesper SP-160 AIS/VHF antenna splitter/relay, on my masthead VHF antenna....
{the switch to the Vesper SP-160, was a good choice FOR ME and MY APPLICATION, as I was more concerned about the lower-mounted (stern-rail mounted) antenna being blocked by the waves (especially when heeled over) when sailing in a good sea....understand that with a Class B transponder's 30-second transmission interval, it doesn't take many missed transmissions for a ship to start closing on you...
Understand that a lower-mounted antenna is fine for many AIS users....but some may choose to get the antenna above the average wave height and "in the clear"....
The actual maximum range wasn't an issue for me...}


Maybe mount Wi-Fi antenna on opposite spreader?
An external Wi-Fi bridge (w/ antenna)??
Yes, this is okay....but you need to keep it as far away from the mast as possible....as the 2.4Ghz Wi-Fi signals don't like reflections!!!
If you were going to try to just use a Wi-Fi antenna here, with the Wi-Fi router/bridge below in the cabin, then the cable loss would be too great to be of any benefit!!

How did you mount it and how was the cable routed?
Others have answered this...

Top of the mast is already too busy and I am too old to climb all the way up if the spreaders will do.
Understand that if you did desire to place a separate VHF antenna at the masthead (for use as an AIS antenna), then they would need to be at least 6' apart horizontally, in order for you to not sustain any damage from each others' transmitter, and not cause significant interference to each other....
(3' separation is an ABSOLUTE minimum, and I do NOT recommend anything closer than 6'!!!)


And will RG-8X be adequate for the antenna cable?
Although I prefer a lower loss cable, such as RG-213 (or LMR-240, should you not have the room inside the mast conduit for the larger cable), the fact is that with the antenna at about 30' off the water, you'll probably only be using about 50' of coax, so the loss difference will be slight...

The loss of 50' of various coaxial cables at marine VHF freqs is:
RG-213 = 1.4db
RG-8x = 2.35db
LMR-240uf = 1.4db
LMR-400uf = 0.75db

Will the extra ~ 1db loss of RG-8x (vs. RG-213) be detrimental??
No...
But, it is extra loss in the system, and if have the room for the RG-213, then use this...and it will even last a lot longer than the RG-8x!!!....if you don't have the room for the larger cable, I recommend the LMR-240uf (please note the "uf"!!!! This is VERY important!!!)

Coaxial Cable Attenuation Chart

LMR | Times Microwave
http://www.timesmicrowave.com/docume...LMR-240-UF.pdf
http://www.timesmicrowave.com/docume...LMR-400-UF.pdf

TIA
Quote:
Originally Posted by redsky49 View Post
Utilizing the existing masthead VHF antenna, I have a 3' antenna tuned to 156 mhz, not the 162 mhz for AIS transmissions [I may have those numbers slightly, or grossly, off!!] How much difference that makes I don't know.
In the real world, this will not make much difference...

I use my regular masthead VHF antenna (NOT specifically tuned for the AIS freqs) and also have a stern-rail / solar-panel mounted antenna (tuned for the AIS freqs), and have found no significant difference in SWR readings at the radio end of the cable...(as some of the mis-match is masked by the cable losses...)
And, since the great advantage in height (9' - 10' off the water vs. 65' off the water) far out weighs any additional cable losses due to less than optimal SWR at the antenna end!!

Plus some loss though the splitter.... Except maybe not with the Vesper?
In addition to Vesper actually posting/publishing real factual specs for their units....I also did real-world testing of their SP-160 splitter/relay (using $1000's of dollars worth of my lab equipment), and found excellent results, which are even slightly better than the Vesper published specs...
Please see this detailed info here...
Vesper AIS SP-160 "relay/splitter" test results, lab/real world


On the spreader, I am at 30-35 ft. or so, not the 60+ ft. that the masthead antenna has.
This is plenty of height!!

Plus, if located say 12-15" from mast, will that block enough of the transmissions to be an issue?
This is NO good!!!
12" - 15" is WAY too close!!!
This will significantly effect the antenna's pattern!!
(this will create a "cardioid" pattern in the direction away from the mast, and a significant null in the direction of the mast....AND significant reduction in pattern fore and aft)
So, the answer here is....Yes, this IS an issue...please do NOT do this....
In general you will need to be 2 - 3 times this distance (30" or more) in order for to not have significant pattern distortions...

Does the higher elevation make any substantive difference?
While the height (~ 30' above the water) is good....mounting the AIS antenna that close (12" - 15") to the mast is NOT good!! And no matter how "high" it is, being this close to the mast is not going to work well for you....and I highly recommend against this!!
(you'd be better off with a good stern-rail antenna, about 10' off the water...or even better with the Vesper SP-160 splitter/relay!!)

The splitter sounds the easiest install, but not sure it's the best performing option.
If you read the above referenced threads on both, VHF (and AIS) radiowave propagation / VHF (and AIS) range, and the Vesper SP-160 splitter/relay, I think you'll understand things a bit better....
VHF and AIS Radiowave Propagation and VHF and AIS Radio Range

http://www.cruisersforum.com/forums/f13/vesper-ais-sp-160-relay-splitter-test-results-lab-real-world-130803.html

But, you haven't mentioned YOUR application / type of sailing you do / where / etc....so I cannot make a 100% / absolute recommendation!

I want to locate somewhere other than an antenna at the pushpit is why I am asking.
Have a look at the photos of my stern-rail antennas....and you'll see some options...


I do have concerns about potential damage to a spreader mount, but that might be just theoretical and not true in reality.
While every boat is different...those of us with double-spreader rigs, don't have these issues with using the upper spreader, and most don't have spin halyard issues either....
But, only YOU know your boat and your sailing....so this is up to you!!!
Quote:
Originally Posted by redsky49 View Post
In order to muddy up the question even further -

I have two fixed VHF radios, The nav station has the better Icom with a GPS interface for the DSC, LMR-400 cabling, masthead antenna and serves as the long distance/"this is important" radio of choice. Or when it is just too crappy outside, and this is my excuse to go below for a break
Assuming you're using LMR-400uf (UF), then you have an EXCELLENT low-loss VHF antenna cable....and while I understand your trepidation about adding anything that add loss to this, understand that adding the < 1 db loss (on VHF transmit) of the Vesper SP-160, would still place you well above the average vessel's VHF antenna/cable system performance!!!

But, also....
I'm wondering why not install a remote mic in the cockpit (aka "RAM Mic"), for the main VHF radio (your Icom)???
But, this is really no big deal....I'm just curious...

In the cockpit I have a Standard Horizon with a 5' fiberglass antenna on the stern rail. This I use mostly for line of sight communications as the range seems to top out at 7 or 8 miles most of the time.
I'm wondering why not install a remote mic in the cockpit (aka "RAM Mic"), for the main VHF radio (your Icom)???
But, this is really no big deal....I'm just curious...
BUT...

But, the GOOD news here is:
a) You can add a Vesper SP-160 splitter/relay into your primary/masthead VHF antenna cabling, and use this antenna system with both your primary Icom VHF and your AIS transponder...(I have this!)
b) Continue to use your existing Standard Horizon radio in the cockpit as you do...(my back-up VHF, redundant Icom M-602, is stowed below)
c) Add/install a remote cockpit mic for the primary Icom VHF......(I have this!)
d) Have enough coaxial cable to allow you to swap radios/antennas to either radio or antenna....(I have this!)

These allow you to have a totally redundant system...

For vessel crossing situations I am just as likely to be in the cockpit as at the nav station below. Maybe stepping on the AIS transmission/reception wouldn't be an issue (again, most of the time) if I utilize the cockpit radio whenever possible.

I'm wondering why not install a remote mic in the cockpit (aka "RAM Mic"), for the main VHF radio (your Icom)???
But, this is really no big deal....I'm just curious...
BUT...

But, the GOOD news here is:
a) You can add a Vesper SP-160 splitter/relay into your primary/masthead VHF antenna cabling, and use this antenna system with both your primary Icom VHF and your AIS transponder...(I have this!)
b) Continue to use your existing Standard Horizon radio in the cockpit as you do...(my back-up VHF, redundant Icom M-602, is stowed below)
c) Add/install a remote cockpit mic for the primary Icom VHF......(I have this!)
d) Have enough coaxial cable to allow you to swap radios/antennas to either radio or antenna....(I have this!)

These allow you to have a totally redundant system...


Haven't figured out where I would mount the AIS display either - down below or in the cockpit. Clearly, I haven't thought this through very well.
I have lots of good info / advice here as well...
But, I'm running out of time at the moment...so more later!!!
Quote:
Originally Posted by redsky49 View Post
It seems that a successful installation can be achieved with the antenna mounted in various locations. That is good to know. I am leaning toward the use of a splitter or mounting on the pushpit. If stern rail is the ultimate choice, I might install a post with arms for multiple antennas (my antenna farm) as the rail is starting to be rather congested.
Good ideas/thoughts here!!
Please see photos below, of my "stern-rail antenna farm"...

I am also starting to consider WiFi/tablet, etc, in addition (or alternative) to a dedicated device such as the Vesper Watchmate 8500 which has previously been my objective.

Appreciate all the various options/opinions!
TIA, again I have a LOT more to mention (more facts and more recommendations)....but am running out of time...gotta' go....

BUT...

But, please also let us know WHERE you are sailing/cruising...and what your specific applications are....'cause this will affect our recommendations...













You will also find a great deal of AIS, Antenna, VHF, etc. info and clarifications, here in these threads...

Poor AIS range with Furuno FA50

Antenna recommendation

Pull VHF cable through mast


And, you may wish to read this old article of mine regarding transition from 6 years of using an AIS receiver, to installing an AIS transponder...
AIS Transponder




I hope the above helps...

fair winds..

John
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Old 25-07-2015, 20:05   #35
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Re: AIS Antenna on Spreaders

Quote:
Originally Posted by ka4wja View Post
TIA,
You ask some good questions

Before I go any further.....please allow me to point you to a recent thread regarding VHF and AIS Radiowave Propagation and VHF and AIS Radio Range...
VHF and AIS Radiowave Propagation and VHF and AIS Radio Range
And, let me comment (negatively) on this important piece of info... This is NO good!!!
12" - 15" is WAY too close!!!
This will significantly effect the antenna's pattern!!
(this will create a "cardioid" pattern in the direction away from the mast, and a significant null in the direction of the mast....AND significant reduction in pattern fore and aft)
So, the answer here is....Yes, this IS an issue...please do NOT do this....
In general you will need to be 2 - 3 times this distance (30" or more) in order for to not have significant pattern distortions...

With a single spreader rig, I could maybe find that space for separation, but I am tending to dismiss the spreader option.


But, please also let us know WHERE you are sailing/cruising...and what your specific applications are....'cause this will affect our recommendations...

Near term plans are for back to the Bahamas this fall. Likely will follow the thorny path around to Panama. Will make the decision at that point where to head next. Just the two of us on board and less eager for extended passages as we get older. I like easy sailing




In the cockpit I have a Standard Horizon with a 5' fiberglass antenna on the stern rail. This I use mostly for line of sight communications as the range seems to top out at 7 or 8 miles most of the time.
I'm wondering why not install a remote mic in the cockpit (aka "RAM Mic"), for the main VHF radio (your Icom)???
But, this is really no big deal....I'm just curious...
BUT...


For the sake of redundancy, the cockpit radio is separate power circuit, antenna and cable, and is mounted in aft cabin with a RAM type mic in the cockpit. Standard Horizon "black box" type radio, Phantom series PS1000. We have been struck by lightning before and wanted some chance of maintaining at least minimal communications after major calamity, i.e., losing the mast!


I hope the above helps...

fair winds..

John
I am grateful for all your advice!
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