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**Jammer** · 07-08-2018, 07:59

How did you make the tradeoff between the better performance (at the masthead) and the easier maintenance and lack of bridge clearance problems posed with alternative locations?

thomm225 · 07-08-2018, 08:06

To me on a small boat especially, mast head is the only option for the range. (15-17 miles to the automatic Sea Tow Radio Check Channel) Plus, it came that way

My handheld range is really bad.

B23iL23 · 07-08-2018, 08:30

Masthead - 100 foot above the deck. Have a spare on the transom in case we have an 'incident' with it.

SV Bacchus · 07-08-2018, 08:58

Bad thing for us is the masthead is also the location of our AIS antenna. I've read the two side by side isn't good but it seems to work OK for us. Maybe I just don't know how good it could be?

hellosailor · 07-08-2018, 10:45

Bacchus, if your AIS is receive-only, then your only problem might be that the AIS receiver would be overloaded (and go deaf or be damaged) when the VHF was transmitting. If the AIS was transmitting, it might desense or damage the VHF when the AIS transmitted, but that's less likely. Ideally if you can't separate them by at least 1/4 wavelength (about 18"?) then you are better off having one above the other, which would probably put the AIS antenna below the VHF and alongside the mast, reducing range somewhat. But you've got limited options, unless you start getting into custom masthead fixtures. Or installing a mizzenmast.(G)

SV Bacchus · 07-08-2018, 12:28

Good info hello, ours is a transmit AIS and both are presently out of commission due to a lightening strike. I will ask the electronics repair folks about installing the antenna a little lower, that sound like a good idea!

I'm wondering, since both antenna mounts are at the same height, just opposite sides of the mast, could the AIS antenna use its same mount but mount the antenna upside down? Only the base of both antennas would be at the same level that way.

Paul L · 07-08-2018, 13:02

Bacchus
You can mount the antenna pointing down, but you need significant clearance with the mast.

mickt243 · 07-08-2018, 15:40

I don’t have a mast...

Reefmagnet · 07-08-2018, 16:01

Masthead every day of the week. I'm of the opinion that it's best to eek every last inch of range out of VHF. Just like Kev above, an antenna for the AIS receiver is mounted to the radar pole on the stern that can be swapped in no time across to the VHF transceiver in the event of the mast antenna becoming non functional.

Having said that, I most often use my hand held unit because the main VHF is installed down at the nav station.

hellosailor · 07-08-2018, 16:30

What Paul said. However, many antennas or their base loads and connection fittings are designed "this way up" so that water drains "that way down" out from them. You'd need to make sure the base won't be trapping water if it is installed upside down.

**James S** · 08-08-2018, 00:00

Quote:

Originally Posted by B23iL23

Masthead - 100 foot above the deck. Have a spare on the transom in case we have an 'incident' with it.

100ft... wow..
Whats your boat B23iL23?

Telemark43 · 08-08-2018, 10:49

Quote:

Originally Posted by SV Bacchus

Good info hello, ours is a transmit AIS and both are presently out of commission due to a lightening strike. I will ask the electronics repair folks about installing the antenna a little lower, that sound like a good idea!

I'm wondering, since both antenna mounts are at the same height, just opposite sides of the mast, could the AIS antenna use its same mount but mount the antenna upside down? Only the base of both antennas would be at the same level that way.

Consider just one VHF antenna, use by both AIS and VHF with Vesper AIS/VHF/FM Antenna Splitter. Pricey, but works AOK. Mine has been in continuous used for two years, uses minimal power and fail safe is VHF only. Solves problem of two (or three) units using VHF antenna. AIS only broadcasts for a very short time so doesn't really interfere with VHF use.

barnakiel · 08-08-2018, 11:54

We sail offshore only so to us the paramount factor is RANGE.

So at the masttop.

I just wish I knew I wanted the fat cable, not the thin one.

Masttop+thin cable= no real benefit.

Cheers,
b.

SV Bacchus · 08-08-2018, 15:36

Good info all on my VHF AIS situation. I'm going to have a sit down with the electronics installer and discuss options. Hopefully I am now armed with enough info to not be led down "the rosey path"!