AIS greatly reduced range

[tanglewood]

I would dump the splitter. I suspect a dedicated antenna, even on a railing, would be better than the mast antenna with a splitter. If nothing else, it would make for a good diagnostic test.

[Jim Cate]

Originally Posted by tanglewood

I would dump the splitter. I suspect a dedicated antenna, even on a railing, would be better than the mast antenna with a splitter. If nothing else, it would make for a good diagnostic test.

He reports that he has connected the AiS directly to the antenna, eliminating the splitter, without improving the range: the splitter is not the faulty bit.

Jim

[CarinaPDX]

Perhaps I missed it, but has the OP checked the antenna with an SWR meter? I would connect the antenna cable that is attached to the AIS to a VHF radio through an SWR meter, then transmit and see the results. I bought a new antenna with the AIS and I confirmed my suspicions of an antenna problem this way. It turned out that a new, quality brand antenna was defective, solved with another antenna.


I much prefer keeping the AIS separate from the communications VHF. I like the inherent duplication, and the simplicity.


Greg

[Montanan]

Reference article regarding use of splitters for AIS and VHF.

https://blog.francis-fustier.fr/en/t...tter-dantenne/

[CarinaPDX]

I assumed that the OP is using a proper "active" splitter designed for this purpose. A simple passive tee would likely damage the AIS output and/or input when the VHF is transmitting. Which is it?


Greg

[tanglewood]

Originally Posted by Jim Cate

He reports that he has connected the AiS directly to the antenna, eliminating the splitter, without improving the range: the splitter is not the faulty bit.

Jim

Thanks. I see that now.

[Reefmagnet]

I just installed a second vhf antenna for an AIS receiver a few days ago and the first thing I noticed was how susceptible a pl259 connected cable is to corrosion should the plug not seal against the socket properly when mounted in an inverted position (as most antenna side connections are). I stuffed mine full of silicon grease as a precaution, but if I were looking for a bad connection this would be one of the first places I'd check.

[CarinaPDX]

Originally Posted by Jim Cate

He reports that he has connected the AiS directly to the antenna, eliminating the splitter, without improving the range: the splitter is not the faulty bit.

My question was whether the splitter was a proper active splitter designed for purpose or just a tee connector. If it was a tee then it wouldn't be damaged, but the AIS certainly would be as a result. I'm just checking the possibilities - anyone doing an AIS install shouldn't make this mistake.


Greg

[double u]

the splitter is a proper, 12VDC powered thing, red leds shoowing "AIS transmit" or "VHF transmit" & all (cost enough!)
I found a badly corroded connection of 2 x PL259 + double-female at the entrypoint of the cables under deck. not having new connectors available here in Porto Bello I'll try soldering the cable ends after cutting off the connectors (no intention of removing the mast in the near future), butb will get new coax for mast & new connectors at nextr stop in Colon/Panama City
BTW: any suggestions as to wwhich coax-type? RG 213 is so fat...

[smac999]

you want the fat cable for the long run

[svmobert]

Originally Posted by double u

the splitter is a proper, 12VDC powered thing, red leds shoowing "AIS transmit" or "VHF transmit" & all (cost enough!)
I found a badly corroded connection of 2 x PL259 + double-female at the entrypoint of the cables under deck. not having new connectors available here in Porto Bello I'll try soldering the cable ends after cutting off the connectors (no intention of removing the mast in the near future), butb will get new coax for mast & new connectors at nextr stop in Colon/Panama City
BTW: any suggestions as to wwhich coax-type? RG 213 is so fat...

RG213 at least. LMR400 is better in several ways but doesn't solve the diameter issue. If space really IS a problem, look at LMR240, it will have a bit higher loss than 213, but smaller diameter.

At 150MHz, 100ft of cable length, signal loss =
LMR-400-UF = 1.5db
RG-213/U = 2.4db
LMR-240-UF = 3.6db

[CarinaPDX]

Originally Posted by Sea-TechSystems

At 150MHz, 100ft of cable length, signal loss =
LMR-400-UF = 1.5db
RG-213/U = 2.4db
LMR-240-UF = 3.6db

IIRC the smaller diameter coax is rated at 6dB loss. For those not familiar with working with decibels, a 3dB loss is a halving of signal, and a 6dB loss leaves just a quarter of the signal. So running 100 ft of coax between the VHF radio and the antenna will reduce the output from 25W to 6.25W with -6dB cable, while the RG-213 will deliver over 14W at -2.4dB. There is a reason RG-213 is the preferred solution: stick with it.


Greg

[Montanan]

Originally Posted by CarinaPDX

IIRC the smaller diameter coax is rated at 6dB loss. For those not familiar with working with decibels, a 3dB loss is a halving of signal, and a 6dB loss leaves just a quarter of the signal. So running 100 ft of coax between the VHF radio and the antenna will reduce the output from 25W to 6.25W with -6dB cable, while the RG-213 will deliver over 14W at -2.4dB. There is a reason RG-213 is the preferred solution: stick with it.


Greg

The physics is similar to communicating with cans, one has to pull the string tighter and / or use bigger cans to be heard better. To pull harder on the string one needs thicker cord. Or shout louder to be able to heard from further distances as there is the inevitable dB loses at greater distances.

[DefinitelyMe]

You can get an idea of whether your antenna/cable might be at fault using a multi-meter. Set it to ‘resistance’ (measured in ohms). Unplug the cable from the splitter and measure the resistance of the cable-antenna assembly between the inside and outside conductors (the central pin and the outside body of the connector). Most (but not all) VHF antennas show zero ohms resistance if they are working properly and all the connections are good. The Shakespeare masthead whip aerials that are the most common in the US fall into this category. Pacific aerials, which are common among New Zealand and Oz boats, don’t (they show an open circuit). Assuming your aerial falls into the former category:

You should, if all is well, see a very low number when you measure the resistance like this. Somewhere between zero and ten ohms max. If you see this then your cable-antenna assembly is probably not the problem.

If you see an open circuit (infinite resistance) then you either have a break in the circuit somewhere or a very damaged antenna.

If you see a number between, say, twenty ohms and several thousand ohms then you have a poor connection somewhere or an antenna that is starting to fail.

This method won’t give a definitive diagnosis of a problem, but it might give you an idea of whether or not a problem is likely to exist and where that problem might be. If you see an unacceptable resistance the next step is to climb the mast, unplug the aerial, stuff a bit of aluminium foil in the connector to short between the conductors and then measure resistance from the other end. That will tell you whether the resistance you are seeing is coming from the cable, the aerial or a combination of the two.

[hoolie]

My Shakespeare V_Tronics antenna has 10k ohms across the connections. I thought this is more common, and useful, with modern antennas than short or open circuit as that could mean some other non-functional condition.