Follow on from my VHF - AIS Splitter thread recently >>

[Refueler]

Recently I asked about use of splitters to combine VHF and AIS to one masthead antenna. On the market there are Passive and Active Splitters. It appeared that most common opinion was that Passive would be AIS receive only AND many seemed to regard as not worth using.

I had already bought a generic Chinese VHF band splitter - which on enquiring of seller - he advised was only for two RECEIVING units to use a single antenna. A waste of 40 quid..... sales page made no mention of that limitation.
Later I was offered a Passive unit for testing - Onwa KA Splitter - which manual and sales pages state actually does accept both VHF and AIS Transmitter / Receiver. Interesting. I made clear that due to my spinal injury - it would be a slow process before actual fitment and test .. which was accepted and I duly rec'd the KA Splitter.

First observation > similar heavy weight as my 'useless' item, but only about 60% the size.
Next > connections clearly labeled VHF .. AIS ... Antenna - indicating specific item in / out design. Promising !

I contacted (with dealer cc on emails) Onwa direct to ask confirmation that it handles 25W VHF as well as my 3W AIS - Transceivers. I duly received reply confirming KA Splitter does. I wanted this confirmation for two reasons : a) to be sure before I connect up, b) if it damages either my AIS plotter or VHF - I have a comeback to Onwa for possible replacements.

First action was to photograph and open up to compare internals, (I did not fully remove boards from the cases - as that requires de-soldering connectors) ...

Two units side by side as received :

Rear panels removed - showing significantly different internals :

Individual ......

'Useless receive only unit' with only a board and a few additions under :

Onwa showing a more elaborate design with a 5W 1000 OhmJ link :

I am checking with an Electronics pal of mine about this link and for his opinion overall. So far he is optimistic about the Onwa unit. I fully accept that being a Passive unit - there will be losses particularly on the low power AIS transmit side ... but given the change from rail to masthead - I think should still give significant range benefit. Price of Onwa unit is a smidgen under 100 quid I think ... less than 1/2 that of competition.... accepted that those would be Active ... and usually with FM provision as well.

I apologise if anyone interested in this matter - but it will be some time before I can actually connect up the Onwa unit - as getting on / off and into cabin of my boat is not so easy on my back ... but I will continue this to final conclusion.

 

[Refueler]

Update :

Onwa later communication made plain that their Splitter would not damage any item and in fact if it did - they would replace any damaged item.

Cannot be fairer than that ....

Onto testing.

Note :
Masthead antenna is approx 8m above ground level.
Rail mounted standard VHF antenna. The boat sits in a channel with a bank of about 2 - 2,5m. This puts the rail antenna only just above ground level. The channel is upriver about 2nm as crow flies from Inner Port area - through housing estates and general town constructions as seen here >

Initially AIS connected to rail antenna : 2 targets received - in the river about 1nm away.

AIS connected direct to masthead antenna : 17 to 21 targets received ... one was even approx 1nm outside port area - fishing boat.

AIS connected to Onwa splitter and Masthead antenna : Initial tests were very poor with only 7 - 9 targets received. Furthest being inner port area. Tests were re-run 2 days later and results were far better - up to 19 targets received with one in the outer breakwater area.

Keying the VHF mic had no adverse effect and unit performed as Onwa stated.

vSWR readings were taken ... but splitter interferes with readings. Therefore the VHF unit Self Test was used. This indicated antenna via Splitter or direct was good.

Note : Target activity is reasonably constant in river / port area - so number comparisons are valid.

Conclusion :

It works - simply put.
The unit relies on having a good masthead antenna setup and will provide an improvement against low mounted antenna.
BUT it does not approach the levels of performance an Active unit would provide.

Would I pay the ~ 100quid price tag ? Debatable as the cheapest Active unit I could find was over 300 quid when including shipping (If I was still living in UK - the tag would be about 250 quid) ......

The unit is still connected and will remain there pending my being able to go to sea - once I'm fully recovered from injuries.

 

[Refueler]

I realise that there are those who will basically disregard such passive unit .. fair enough. But for those with modest means and occasional ventures out of port ... it may be of interest.

I did the tests to see if comments passed previously saying Passive being useless were valid ... conclusion is that the comments are not. That the Passive units do work albeit less than Active.

 

[Bilgediver]

I realise that there are those who will basically disregard such passive unit .. fair enough. But for those with modest means and occasional ventures out of port ... it may be of interest.

I did the tests to see if comments passed previously saying Passive being useless were valid ... conclusion is that the comments are not. That the Passive units do work albeit less than Active.

I think some of the recent discussion was regarding using one of these devices where BOTH the VHF and AIS would transmit.and some devices such as yours may not offer protection in this case. Lets hope yours continues to perform and that you do not Zapp the AIS if a fault develops.

 

[ylop]

I guess what you can't easily test is (if) how much your AIS transmit has improved, or if putting the splitter in has any adverse effect on voice VHF transmission over long distance?

Would you bother with a splitter if you weren't in the river with the obstructions from banks/buildings? Seems that in open sea, rail height will see anything big enough to worry about far in advance and vice versa.

 

[Refueler]

I think some of the recent discussion was regarding using one of these devices where BOTH the VHF and AIS would transmit.and some devices such as yours may not offer protection in this case. Lets hope yours continues to perform and that you do not Zapp the AIS if a fault develops.

That was a concern and why both myself and Dealer pressed Onwa about it in particular. Onwa's reply was blunt and straight ... no damage to either VHF or AIS unit during Transmit of 25W VHF ...

Without dismantling it fully - which I will not do as it would mean unsoldering all PL259 sockets etc. - there's no way of knowing how Onwa have managed to isolate each ... and they won't tell us !! Fair enough - they designed and developed it ...

I am not actively promoting or discouraging use of the unit. I was lucky to have a dealer who was as interested as I in findings. Its take it or leave .. some may use it .. some may not.

 

[Refueler]

I guess what you can't easily test is (if) how much your AIS transmit has improved, or if putting the splitter in has any adverse effect on voice VHF transmission over long distance?

Would you bother with a splitter if you weren't in the river with the obstructions from banks/buildings? Seems that in open sea, rail height will see anything big enough to worry about far in advance and vice versa.

Fair question.

River use is and was not the desired intention. I cruise Baltic ... from Latvia to Gotland to Swedish Archipelago as example. That means crossing shipping lanes.
The matter of river banks / buildings was noted to indicate that testing was being conducted in difficult location and would show significant results between rail and masthead before / after splitter installed.

I am confident that ships AIS antenna height would give good distance for my AIS to receive and mark my display. My wish is to have MY AIS transmission picked up as best as possible and not subject to wave troughs etc.

AIS transmission ? I have various other gear that receives AIS (USB to Computer) - this can be sited suitably to 'hinder 'weak signal' to test .... its actually planned to test later. For VHF - that will comer down to whether I'm heard by VTS etc. as I enter port / harbours ..

Before being given the splitter to test - I was considering mounting an antenna on a spreader ... that would give me more than the 2m separation from masthead VHF antenna.

 

[Stemar]

Related antenna splitter question:

I have a receive only AIS and have managed to break the antenna. I am about to fit an FM radio. Is there any reason why I couldn't use a single antenna for the two? Would I need to use a splitter or other separation device?

 

[Commercial Dave]

Related antenna splitter question:

I have a receive only AIS and have managed to break the antenna. I am about to fit an FM radio. Is there any reason why I couldn't use a single antenna for the two? Would I need to use a splitter or other separation device?

FM radio is 87-108 MHz and AIS is 162 MHz, which is quite a separation. You can probably get an aerial which will do both, but it'll do them badly. Even regular marine VHF radio aerials aren't great for AIS because they're centred on 156 MHz with relatively narrow bandwidth and the AIS frequencies are right on the top edge.

 

[Refueler]

Related antenna splitter question:

I have a receive only AIS and have managed to break the antenna. I am about to fit an FM radio. Is there any reason why I couldn't use a single antenna for the two? Would I need to use a splitter or other separation device?

I cannot see why this could not be possible .... plenty of VHF / AM / FM splitter combiners on eBay / Aliexpress etc.

It may have frequency outside of FM radio - but that Splitter I bought in error - shown in first posts - is matched to VHF / AIS receive only .... while FM will most likely work as well ....