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Old 27-08-2014, 16:12   #31
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Re: AIS Problems with Antenna

Chuck,
I'm not completely clear on whether the "frame" you refer to is vertical (parallel to the VHF antenna) = not too good.....or horizontal (perpendicular to the VHF antenna) = no problem at all.....or runs at a 45* angle across/past the VHF antenna = okay, but not optimal....
Quote:
Originally Posted by AnchorageGuy View Post
My antenna is mounted on the side of the flybridge and is withing inches of the aluminum frame for the hardtop. A few comments say stay away from metal. This is an 8 foot Shakespeare. Is the aluminum frame going to affect the antenna?
If it is vertical/parallel, then it will effect the antenna overall performance....the longer run of alum tubing against the antenna, the more negative effect it will have....best to keep it 3' away from other long vertical metallic items...
If it is not parallel to the antenna and running along it for a significant distance, I wouldn't worry too much about it...





There are lots of "8' antennas"....not knowing which one you have, I cannot be precise....but..
Quote:
Originally Posted by AnchorageGuy View Post
It's my understanding that the fiberglass antenna is only using the top 19". If that is the case, that is well above the frame.-
But in general, NO the entire antenna is being used....(MOST VHF marine antennas, except for the bottom couple inches, the whole antenna radiates and receives)





Usually what is below the antenna will have little, to no, effect at all...
Quote:
Originally Posted by AnchorageGuy View Post
In a regular installation like the OP talks about, his antenna is mounted on the bimini frame.



I hope this helps...

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Old 27-08-2014, 16:51   #32
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Re: AIS Problems with Antenna

Thanks John. The hardtop frames runs horizontally and intersects with the VHF antenna at about 5 feet from the mount and base leaving about 3 feet extending above the hardtop. This has always been a concern, but it does not seem to have an affect on the VHF or AIS. We are running through an Amec splitter from Miltech marine and the operation of the VHF has been fine. I have not been pleased with the range of the AIS, outside of 5 miles and we don't pick up anything. The antenna is about 17 feet off the water. Both the AIS, Amec Camino Class B, and the splitter, matched for the transponder, have been tested by Miltech and found to be functioning correctly. I am considering installing a separate antenna for the AIS. It would be the same as the VHF antenna except on the opposite side of the boat. Chuck
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Old 27-08-2014, 16:57   #33
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Re: AIS problems with antenna

Quote:
Originally Posted by MarkJ View Post
how the hell would we know if we didnt have it?
Awesome Question!
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Old 27-08-2014, 17:01   #34
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Re: AIS Problems with Antenna

Quote:
Originally Posted by Auspicious View Post
I'll be thrilled if someone has come up with a splitter that changes the game that I'm not yet aware of.

They are called repeater.
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Old 27-08-2014, 17:24   #35
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Re: AIS Problems with Antenna

Signal propagation is reliant on a good ground plane. Just a thought....
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Old 27-08-2014, 17:34   #36
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Re: AIS Problems with Antenna

Jax,
I'm not sure if you're having fun, making jokes....or if you're serious??


If, you're serious about these, I think everyone should be aware that this is total nonsense....
Quote:
Originally Posted by Jaxxiam View Post
They are called repeater.
"Repeaters" have nothing at all to do with this discussion....





RF radiowave propagation / signal propagation is a "mother nature" and "physics" issue....and while having a "good ground plane" is important for "Marconi-type" vertical antennas (typical of MF and HF marine antennas), this is not the case here...
Quote:
Originally Posted by Jaxxiam View Post
Signal propagation is reliant on a good ground plane. Just a thought....


Perhaps, I'm not getting the "joke".....but perhaps you just need to learn a bit more...


Fair winds...

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Old 27-08-2014, 17:45   #37
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Re: AIS Problems with Antenna

Chuck,
This is not a problem...
Quote:
Originally Posted by AnchorageGuy View Post
Thanks John. The hardtop frames runs horizontally and intersects with the VHF antenna at about 5 feet from the mount and base leaving about 3 feet extending above the hardtop. This has always been a concern, but it does not seem to have an affect on the VHF or AIS.




Coax loss and splitter loss, are what may be causing your limited AIS range...(and these are the things that Bill and Dave have been commenting on....and everyone should heed their advice...)
Quote:
Originally Posted by AnchorageGuy View Post
We are running through an Amec splitter from Miltech marine and the operation of the VHF has been fine. I have not been pleased with the range of the AIS, outside of 5 miles and we don't pick up anything. The antenna is about 17 feet off the water. Both the AIS, Amec Camino Class B, and the splitter, matched for the transponder, have been tested by Miltech and found to be functioning correctly. I am considering installing a separate antenna for the AIS. It would be the same as the VHF antenna except on the opposite side of the boat. Chuck
I need to research the Ameco stuff and see what their specs / issue might be....
But, in general, getting rid of the splitter (using a separate antenna) and using lower loss cable, are good ideas....and in your case (where you don't have just one mast to mount a VHF antenna on), it might be the best solution for you....

I gotta' go....more later...

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Old 27-08-2014, 17:52   #38
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Re: AIS Problems with Antenna

Many thanks John, Much appreciated. the splitter is the Amec 160, Alltek Marine ? the AIS Specialists - Producs - Antenna Splitter - CUBO-160 if you want to take a look at it. Chuck
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Old 27-08-2014, 19:08   #39
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Re: AIS Problems with Antenna

Quote:
Originally Posted by AnchorageGuy View Post
Many thanks John, Much appreciated. the splitter is the Amec 160, Alltek Marine ? the AIS Specialists - Producs - Antenna Splitter - CUBO-160 if you want to take a look at it. Chuck
Insertion loss, AIS Receive path Typical 4dB
Insertion loss, VHF Radio Receive path Typical 4dB
Insertion loss, AIS Transmit path Typical 3.5dB
Insertion loss, VHF Radio Transmit path Typical 1.5dB

These are among the worst specifications of any AIS splitter I have seen. There are a lot out there better than this. IMO these specifications are really not very good.
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Old 27-08-2014, 19:21   #40
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Re: AIS Problems with Antenna

Quote:
Originally Posted by ka4wja View Post
Dan,
Are you SURE about this???
The Shakespeare 5215's and 5241's, etc. are NOT DC Ground antennas....
5215-AIS Squatty BodyŽ | Shakespeare Electronic Products Group
I don't have the factory specs for the 4400, but as a base-fed-halfwave-whip, I suspect it is like the other Shakespeare VHF whips, and therefore should NOT show "0" ohms (direct short), but rather "infinite" (open) resistance when measured with a ohm-meter / digital multimeter....

So, again I ask....
Are you SURE about the Shakespeare 4400 being a DC Ground antenna??

And, if as I suspect that the 4400 is not a dc grounded antenna, then we have found the proximate cause of his troubles....the coax and/or the coax/antenna connection...
I may be confusing this with another antenna. Right now I am not at the boat so I can't check it to be sure. So in answer to your question, no, I am not 100% sure about this.

A 3:1 VSWR is 6dB return loss. So if it is a short in the coax it's not a very good one. It could be some small sliver of wire is connecting the inner to the outer.
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Old 27-08-2014, 19:48   #41
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Re: AIS Problems with Antenna

Quote:
Originally Posted by transmitterdan View Post
Insertion loss, AIS Receive path Typical 4dB
Insertion loss, VHF Radio Receive path Typical 4dB
Insertion loss, AIS Transmit path Typical 3.5dB
Insertion loss, VHF Radio Transmit path Typical 1.5dB

These are among the worst specifications of any AIS splitter I have seen. There are a lot out there better than this. IMO these specifications are really not very good.
Thanks, which is why I'm removing it and adding another antenna just for the AIS, and the VHF will be on it's own. Chuck
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Old 27-08-2014, 20:23   #42
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Re: AIS Problems with Antenna

The Digital Yacht splitter also claims 0db insertion loss for both receive and transmit on AIS and VHF. They claim that the fail-safe mode is to VHF on loss of power.

Digital Yacht - SPL2000 VHF-AIS ANTENNA SPLITTER

In fact, the specs are identical to that of the Navico splitter, with the exception of the enclosure size and IP rating. I suspect they may be the same.

Mark
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Old 27-08-2014, 22:26   #43
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Re: AIS Problems with Antenna

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Originally Posted by btrayfors View Post
Well, that's only half right. Or less.
Bill--I am sure you think you are right about this, and you can keep on thinking that. It is fine with me. After 40 years in professsional radio, I have learned that even professionals don't understand antennas and transmission lines very well.
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Old 27-08-2014, 23:01   #44
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Re: AIS Problems with Antenna

Sorry about the error in my upate post. I guess I should not write any replies when I am dead tired.

The ohm meter was showing 0 conductivity (infinite ohms) between core and shield.

New information:

I exchanged the antenna for a new one today. Result: Much better but not great.
Thanks all you guys that recommended to check for any metal object running parallel to the antennay nearby. I had completely missed the man-over-board-pole. Once I removed the pole near the antenna the VSWR was way better.

Picture below shows the antenna and GPS on the starboard side of the bimini. Behind the antenna in the white and red is a MOB-pole only a few inches away.
Click image for larger version

Name:	Bimini <a title=MOB Antenna.jpg Views: 102 Size: 100.0 KB ID: 87199" style="margin: 2px" />

Screen shot below shows antenna connected diectly to AIS temporarly moved into aft cabin, with just the 15' pig tail cable. The MOB-pole is next to the antenna. VSWR is better than with old antenna, but not great.
Click image for larger version

Name:	SWT 2.0 new antenna direct.png
Views:	107
Size:	120.9 KB
ID:	87198

Screen shot below shows AIS moved back to nav station plugged into antenna with my 15' RG8 extension plus the 15' pig tail. MOB-pole is still next to the antenna.
Click image for larger version

Name:	SWR 3.2 Nav Stat with pole.png
Views:	97
Size:	109.2 KB
ID:	87197

Screen shot below shows same conficuration but MOB-pole removed.
Click image for larger version

Name:	SWR 1.2 antenna Nav Stat no pole.png
Views:	97
Size:	117.0 KB
ID:	87196

Now that is much better. Maybe some people can learn from my mistake. For some reason I thought the MOB was pastil, but it is metal.

I guess I will still get the Vesper antenna "splitter", as I still can not see my boat on Marinetraffic.com, which I can when the AIS is conncted to the mast-head VHF. The VHF on the bimini will remain there as a back up.
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Old 28-08-2014, 07:25   #45
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Re: AIS Problems with Antenna

Quote:
Originally Posted by ka4wja View Post

RF radiowave propagation / signal propagation is a "mother nature" and "physics" issue....and while having a "good ground plane" is important for "Marconi-type" vertical antennas (typical of MF and HF marine antennas), this is not the case here...


Perhaps, I'm not getting the "joke".....but perhaps you just need to learn a bit more...


Fair winds...

John
s/v Annie Laurie

There is no doubt that I have things to learn.
Thanks for your comments.

Cheer's
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