Stupid aerial question ..... Probably

clyst

clyst

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I have a dedicated VHF AIS aerial ? The chart plotter and AIS engine is sited near to a cockpit VHF radio . The aerial of the VHF appears to be b*ggered therefore can use a normal 2way splitter similar to that fo TV etc sold in leccy shops or DIy 'sheds'. ? AIS and VHF needn't be used at the same time .
 
If you mean a mechanical splitter, the type that cost a couple of quid, then the answer is no. When you transmit with VHF you will damage the AIS engine. You need to use a proper powered splitter.

Also, an AIS optimised antenna will be tuned to 162 MHz and its performance on VHF radio at the other end of the range may be compromised. If you're going to split a single antenna over AIS/radio best to use a standard VHF antenna tuned to the middle of the frequency range.

A splitter will cost as much as an additional antenna but it makes for a simpler installation. Downside is no redundancy and a splitter will have a loss of up to 3 dB which is a halving of the signal power.
 
Bit of a stupid question on ariels then...

Do they need to be completely upright? Or can they be at a slight angle?

I ask as I've no idea, and my only reference really is the ones on Baywatch were slanted and looked cool.
In all seriousness though other boats I've seen have had various angles of Ariel.
 
Marine VHF aerials are designed to be used vertically. If you're interested, a bit of Googling will allow you to find radiation plots (both vertical and horizontal) for a typical whip aerial. You'll see that in the horizontal plane it is omnidirectional and in the vertical its maximum radiation is around 90 degrees, with lobes and nulls above and below. This means that if the aerial is raked aft, behind you, you'll be transmitting mostly into the sea and forward, into the sky!

The effects for most of us with masthead mounts on a sailboat is that a lower gain aerial is usually recommended because the vertical lobe is broader and copes better with the rolling and pitching of the boat. It may also account for why , in ver close proximity, you can't raise a neighbour with aerial at a different height!

Rob.
 
Another aspect of VHF antennae is that the radiation is either vertical or horizontal polarisation. Any path that involves an antenna not having the same polarisation at each end will result in a significant loss of signal strength. Hence you may see old VHF TV antennae with some mounted horizontal and some vertical. here in Oz ch 2 VHF is horizontal in the city but 250 miles away a country TV transmitter using ch 2 is vertically polarized to reduce interference one to the other. hence for the country one the rods of the yagi antenna are vertical.
However in practice a little rake on an antenna will not detract much from the long range performance. More so for the longer high gain antennae than the short 1/4 wavelenght whip. good luck olewill
 
Sorry no offence intended, just trying to inform ... it is a very common mistake and regularly occurs in the sailing ( and other ) press , printed books and loads of other places so hardly surprising the error is being absorbed by otherwise very well informed members of this forum. One cannot use a radio with antennae; only aerials or antennas will work with a radio, ie it was not a grammar or spelling issue but was instead the wrong component for the job. It is fundamental to making a transmission system work to use the right components which was the core subject of the thread so I suggest is no less of a correction than suggesting the correct type of splitter. I'll leave it there for fear of setting myself on fire with the flaming I'm inviting.
 
winsbury said:
Antennae are found on butterflies and moths etc., antennas are plural for radio use.
Click to expand...

Nope.

According to OED (my bold):

antenna noun (plural antennae /-niː/)
1 Zoology either of a pair of long, thin sensory appendages on the heads of insects ...
2 (plural also antennas) chiefly North American or technical, another term for aerial. a TV antenna

However, the alternative word is aerial. Not ariel (a character from the Tempest, a washing powder, or the little mermaid), or arial (a Windows font)
 
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