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Old 02-10-2011, 09:14   #1
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Icom MXA 5000 AIS

G'Day All,

Considering using an Icom MXA 5000 AIS receiver, newly discounted by Defender. Main reason is ease of installation because of internal antenna splitter. However, their literature mentions an insertion loss of about 3.5 dB.

My question is what does that loss affect?

1. AIS receive
2. VHF transmit
3. VHF receive
4. All of the above.

Anyone know?

Cheers,

Jim
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Old 02-10-2011, 10:44   #2
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Re: Icom MXA 5000 AIS

Not sure of the arithmetic but from a practical point of view our splitter does not appear to effect VHF performance and we get AIS data at 15-17 miles with full details at about 12 miles while the ship is still over the horizon.

The transceiver with a silent option is worth the extra money....

It establishes your boat as a legal entity long before they have you on radar or visual. In fact we have had VHF communications with ships that were within 5 miles and even though the AIS gave our position they could not see us on radar or visually.

We usually contact them at 8-10 miles, establish the fact that they have us on their AIS and we negotiate a safe passing. We usually request that they give us a minimum 1-2 miles separation. In the last 50 interactions we have received nothing but courteous agreement.

This is of course in the open sea situation and not in any situation where the big ship might have difficulty changing course or where they have a legal right of way. However, we still make sure they know where we are and we tell them if we are changing course.

If we cannot contact them we revert to the 'might is right' rule and make sure we stay out of their way.

None of this is done in an arrogant way but is a case of two sets of professionals following the rules.
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Old 03-10-2011, 01:42   #3
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Re: Icom MXA 5000 AIS

3.5dB loss is a lot! It means losing slightly more than half of the received signal strength or half of the transmitted power going out....on top of that you will have to add the losses in the coax going up the mast...usually a thin (cheaper) RG58 coax is installed and tha 156 mHz you will easily lose 1.5- 2.5 dB again....

I think this is more of an issue for your marine VHF than for your AIS reception... seeing a cargo ship at 10 or 12 NM is still more than early enough even if it moves at 15 or 17 knots...
But having 4 till 5 dB loss on my VHF signal at the antenna is not good...

=> I would install a dedicated AIS receiving antenna somewhere at the transom
=> if you have that thinly RG58 coax running up the mast, replace it by a good (expensive!) lowloss coax. Since I did this, I can very often receive AND contact Dover Coast Guard from Zeebrugge (belgian coast) which is about 65 NM away...and it is very common so not a case of occasional signal ducting.

Jan
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Old 03-10-2011, 08:39   #4
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Re: Icom MXA 5000 AIS

Quote:
Originally Posted by Goudurix View Post
3.5dB loss is a lot! It means losing slightly more than half of the received signal strength or half of the transmitted power going out....on top of that you will have to add the losses in the coax going up the mast...usually a thin (cheaper) RG58 coax is installed and tha 156 mHz you will easily lose 1.5- 2.5 dB again....

I think this is more of an issue for your marine VHF than for your AIS reception... seeing a cargo ship at 10 or 12 NM is still more than early enough even if it moves at 15 or 17 knots...
But having 4 till 5 dB loss on my VHF signal at the antenna is not good...

=> I would install a dedicated AIS receiving antenna somewhere at the transom
=> if you have that thinly RG58 coax running up the mast, replace it by a good (expensive!) lowloss coax. Since I did this, I can very often receive AND contact Dover Coast Guard from Zeebrugge (belgian coast) which is about 65 NM away...and it is very common so not a case of occasional signal ducting.

Jan
G'Day Jan,

Yep, I am aware of all of this... that's why I asked the question in the OP: is the insertion loss present in all of the modes, or in just the AIS rx, or the VHF rx or the VHF tx? Makes a difference...

Frankly, I'm not too worried about VHF performance... seldom use it for anything save short range communication. VHF antenna is on the radar arch, not the masthead so the line losses are not so big. Next time I pull the mast I will do a proper installation, but for now there isn't room in the conduit to fish a piece of RG-8 through.

And even with such a poor antenna location we do usually get 15 mile contacts with other yachts when required... and have heard the Tin Can Bay VMR (Queensland Australia) in Noumea, NEw Caledonia at a distance of nearly 1000 miles... clearly ducting, but quite remarkable none the less!

Cheers,

Jim
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Old 03-10-2011, 08:55   #5
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Re: Icom MXA 5000 AIS

Quote:
Originally Posted by Jim Cate View Post
G'Day All,

Considering using an Icom MXA 5000 AIS receiver, newly discounted by Defender. Main reason is ease of installation because of internal antenna splitter. However, their literature mentions an insertion loss of about 3.5 dB.

My question is what does that loss affect?

1. AIS receive
2. VHF transmit
3. VHF receive
4. All of the above.

Anyone know?

Cheers,

Jim
Probably 4 but without seeing the manual or schematic, I really can't say for sure. I may be able to chase one down and if so, I will let you know.

I disagree that 3.5dB is a significant insertion loss but of course it all adds up if one has other losses in the antenna system so it is hard to generalize - this may be an unacceptable loss in one setup, but could be fine in another setup.

Antenna height is more significant unless one has total losses exceeding say 7 or 8 dB IMO.
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Old 03-10-2011, 08:59   #6
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Re: Icom MXA 5000 AIS

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Originally Posted by Wotname View Post
Probably 4 but without seeing the manual or schematic, I really can't say for sure. I may be able to chase one down and if so, I will let you know.

I disagree that 3.5dB is a significant insertion loss but of course it all adds up if one has other losses in the antenna system so it is hard to generalize - this may be an unacceptable loss in one setup, but could be fine in another setup.

Antenna height is more significant unless one has total losses exceeding say 7 or 8 dB IMO.
Thanks, mate!

I await further info with interest... and agree with your estimation of importance.

Cheers

JIm
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Old 03-10-2011, 10:32   #7
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Re: Icom MXA 5000 AIS

I am in the yard and because of the discussion I plan to fit a second mast head antenna today. I will be able to switch from splitter to dedicated and back and I will let you know how performance is affected once the mast is back in in a few days.
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Old 03-10-2011, 13:13   #8
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3.5db insertion usually applies to the VHF Tx signal. In the context of VHF it will have little or no effect on your VHF.

Dave
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Old 03-10-2011, 15:11   #9
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Re: Icom MXA 5000 AIS

Actually, it's just the opposite. The loss on the tx side is usually 1db or less while on the receive side, it is typically 3-4db with the Vesper Marine model claiming 1.5db on receive.

Eric
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Old 03-10-2011, 15:56   #10
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Quote:
Originally Posted by fairbank56
Actually, it's just the opposite. The loss on the tx side is usually 1db or less while on the receive side, it is typically 3-4db with the Vesper Marine model claiming 1.5db on receive.

Eric
You are correct here as I read the mxa 5000 manual which specifically states that. However insertion loss is In general applied to any signal applied to any transmission line.

Btw OP why not get a transponder

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Old 03-10-2011, 16:38   #11
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Re: Icom MXA 5000 AIS

We're not talking about transmission lines, we're talking about active antenna splitters. Icom doesn't really give solid specs for loss like other's do. I checked the specs for several different models to get my information. 1db or less loss on tx and 3-4db for rx is about the norm. There were a couple with less loss than that on rx.

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Old 03-10-2011, 23:33   #12
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Re: Icom MXA 5000 AIS

Quote:
Originally Posted by Jim Cate View Post
G'Day All,

Considering using an Icom MXA 5000 AIS receiver, newly discounted by Defender. Main reason is ease of installation because of internal antenna splitter. However, their literature mentions an insertion loss of about 3.5 dB.

My question is what does that loss affect?

1. AIS receive
2. VHF transmit
3. VHF receive
4. All of the above.

Anyone know?

Cheers,

Jim
OK after reading the MXA 5000 manual I see that 4 was wrong, the correct answer is 3. The radio receive goes via the splitter but the radio transmit bypasses the splitter via relay contacts. However if the AIS receiver is turned off, the splitter is removed from the circuit so if you really need to, you can turn off the AIS and "recover" the 3.5 dB loss back into your radio receiver.

So as others have stated, one could expect a small loss in Tx power due to the connectors, relay contacts etc but it should be typically only 1 dB.

One could argue as that the AIS receiver also goes via the internal splitter, then answer 1 is also correct but as the AIS is designed to always have the splitter in its circuit, IMO it becomes meaningless to suggest that this AIS receiver is so affected.
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Old 03-10-2011, 23:49   #13
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Re: Icom MXA 5000 AIS

Before you close on the Icom check out Standard Horizon GX1250 VHF/AIS combo @ $399.99. My reading of the MXA 5000 was it only matched the M604 VHF! Could be wrong ,I have been before and no doubt will be again!
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Old 04-10-2011, 03:59   #14
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Re: Icom MXA 5000 AIS

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Before you close on the Icom check out Standard Horizon GX1250 VHF/AIS combo @ $399.99. My reading of the MXA 5000 was it only matched the M604 VHF! Could be wrong ,I have been before and no doubt will be again!
Looks like you are right - that is, as stated, you are wrong - but no hard feelings, we can talk it through over a Margaret River red if we ever get the chance!

There is no reason the MXA 5000 won't work with any Marine band VHF, in fact it doesn't need a radio at all to work. Just stick the right antenna in to the antenna port (and perhaps a 50 ohm load on the radio port), connect a display, power it up and away you go.
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Old 04-10-2011, 04:53   #15
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Re: Icom MXA 5000 AIS

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Looks like you are right - that is, as stated, you are wrong - but no hard feelings, we can talk it through over a Margaret River red if we ever get the chance!

There is no reason the MXA 5000 won't work with any Marine band VHF, in fact it doesn't need a radio at all to work. Just stick the right antenna in to the antenna port (and perhaps a 50 ohm load on the radio port), connect a display, power it up and away you go.

I can shout you a Bintang.....I'm in Bali right now!

Correction on the Std /Horizon, it's a GX2150 @ $399.99, I like it anyway and it'll replace my basic Std/horizon Vhf. when I get back over to the boat in 3 weeks time.
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