VHF vs AIS antenna

[sailjumanji]

Originally Posted by hlev00

We have been very happy with the performance of our Vesper splitter working with our radio and Vesper AIS.

Same here. We had a Vesper XB8000 and SP160 splitter on the last cat, and it worked wonderfully. We went to the same units again when we built the new boat, with same results.

AIS is line of sight, just like VHF. Use a transom antenna, and whether it is "tuned" or not will be miniscule issue compared to the degradation of having it mounted so low. IMO

[Brian.D]

sanibel sailor it depend on who made the antenna and if it is a 5/8 wave or 1/4 wave. It could possibly be a 1/2 wave. But in order to determine the approximate length, we will need to know what type of antenna (in wavelengths) you have.

However, you can take a good guess by measuring the length of the whip. If it's approximately 15"~17" it might be a 1/4 wave. If it is longer than 36" it is probably 5/8 wave. It really all depends on the mount.

So first determine who is the manufacture and see if there is any literature on tuning the antenna. I mentioned some equipment but if you are in the ball park it might work.

As mentioned before, AIS radios will usually give your an SWR reading. Anything between 1.1 ~ 1.5 is very good. 1.6 to 2.0 might cause problems. >2.0 should be avoided.

[doublewide]

Our splitter has worked well, too.

[Simi 60]

I used one of these Glomex AIS antenna with cable for $60
https://www.ebay.com.au/itm/Glomex-A...edirect=mobile

[sanibel sailor]

Thanks for all the replies. Unit is supposed to arrive his week. I will connect it as-i and see how it works. I can fine tune if required.
I have no understanding of how these things work. I am kind of at the tinfoil-on-TV-antenna level of knowledge.
Another question is regarding interference with another antenna.
i have thought about adding a standalone weatherfax which will need an antenna. Since the AIS will be transmitting, will there be interference and how much physical separation is needed?

[Brian.D]

For tuning, do not cut off too much. Maybe 1/4" then retest. You will cut from the bottom of the whip.

For interference, WEFAX is on High Frequency and will not interfere, or be interfered, by the AIS transmissions.

Recommended separation of VHF and AIS antennas should be 6 ft.

Good luck!

[GTom]

I am thinking on the Glomex RA-106, anyone with experience how well it works on AIS and VHF frequencies?

[Riddle]

Glomex VHF antenna's have sometimes bad performance after a few years caused by internal corrosion in the base. Electrically they are ok.
The best are antenna's that are completely sealed inside such as for instance AC Antennas CELmar 0-1.

[GTom]

Originally Posted by Riddle

Glomex VHF antenna's have sometimes bad performance after a few years caused by internal corrosion in the base. Electrically they are ok.
The best are antenna's that are completely sealed inside such as for instance AC Antennas CELmar 0-1.

Thank you! Haven't seen those in Europe. Mostly Shakespeare (found ill-tuned models with VSWR optimized below 156MHz) and Banten I see here, the only Metz partner I know on the continent retired a couple of months ago.

Just realized the RA109 might be a cheaper option with SO-239.

[NorthernMac]

I’d just make sure you have a good and healthy VHF antenna and cable and use a splitter.

[Riddle]

I would stay away from a splitter and use two separate antenna's - if there is space of course.
RG58 coax is getting a bit outdated by now, and there are quite a number of cheap coils on the market here and there. RG213 is old school too. Much better is Belden H155 - same diameter as RG58. If a bigger diameter is not a problem Ecoflex or Aircell are also a good choice. All these have double shielding and lower losses.

[GTom]

Originally Posted by Riddle

I would stay away from a splitter and use two separate antenna's - if there is space of course.
RG58 coax is getting a bit outdated by now, and there are quite a number of cheap coils on the market here and there. RG213 is old school too. Much better is Belden H155 - same diameter as RG58. If a bigger diameter is not a problem Ecoflex or Aircell are also a good choice. All these have double shielding and lower losses.

Splitter will be an emergency measure, in case the separate AIS antenna decides to quit. I have some RG213 collecting dust, will start with that one, a bit reluctant using foam cables on a sailing boat.

[ka4wja]

GTom,
1) Yep, the RA-109 is a better choice for you...or one of the Shakespeare's (that are not mis-tuned)...
See below for the details...

And, yes....RG-213 (if it hasn't been sitting around for many years) is also a good choice!



2) On a side note:
I usually recommend separate VHF and AIS antennas, rather than using a splitter...
But, as you see it's a fairly controversial subject!
And, I don't comment much on this here anymore ('cuz I don't have the time to get into arguments)...
But...

If a decent antenna system is installed, with the antenna about 10' off the water, most find more than adequate range for their AIS system...

The main exception (and the only legit reason to use a "splitter"/relay), is for those that sail offshore in heavy weather, where a low-mounted AIS antenna can be shadowed by waves, etc..(this can be an issue with all Class B AIS transponders, as their position transmit/reports are only done every 30 seconds, and if your stern is down in a wave trough a few times in a row, you may not be seen by some vessels that are quite close in terms of maneuvering)


And, in full disclosure I do have a Vesper SP-160 "splitter"/relay feeding my masthead antenna....and a stern-rail-mounted antenna for my AIS and VHF as needed...

Originally Posted by GTom

Thank you! Haven't seen those in Europe. Mostly Shakespeare (found ill-tuned models with VSWR optimized below 156MHz) and Banten I see here, the only Metz partner I know on the continent retired a couple of months ago.

Just realized the RA109 might be a cheaper option with SO-239.

3) GTom, back to #1...
If you're choosing Glomax, then yes, the RA-109 is the better choice for you...


But, I'd recommend a Shakespeare 5215-AIS...
https://shakespeare-ce.com/marine/pr...-body-antenna/



Whether you choose an end-fed 1/2-wave whip or coaxial-feed-type-"dipole"-vertical, I've been using and recommending Shakespeare for decades, without issue...so, I'm sorry that you found problems with them...FYI, This is the first time I've ever heard of Shakespeare whips having poor VSWR / being tuned below 156mhz?



I have Shakespeare 5215, at 65' off the water on my masthead (fed with low-loss cable), used for my primary VHF and AIS transponder (when offshore), using a Vesper SP-160 splitter/relay...
https://shakespeare-ce.com/marine/pr...-body-antenna/


And a Shakespeare 5215-AIS (although the same as the other 5215 antenna, this one comes from the factory tuned for better VSWR on the AIS freqs, at the higher end of the marine VHF band) at 10' off the water on my stern rail (also fed with low-loss cable), used as my secondary AIS and secondary VHF antenna...
https://shakespeare-ce.com/marine/pr...-body-antenna/




If you look here, you'll see the sweep of my Shakespeare 5215 (the older "standard" model, https://shakespeare-ce.com/marine/pr...-body-antenna/ , not tuned for AIS freqs), which should be more helpful than just the "specs" from the manufacturer...





So, you can see the typical VSWR response across the whole VHF marine band...





I hope this helps?


Fair winds.


John

[GTom]

, thank you John! Ordered the RA109 last night after discovering that it has an SO239 connector. Will see how the coax fares methinks it's around 5 years old, doesn't seem to be corroded.

Depending on the shape of my old antenna (honestly don't know what make it is), I will keep using it for VHF and put the Glomex on the radar pole for AIS/backup VHF.

[ka4wja]

John,
In regards to your WeFax reception antenna....longer is better.
And, no there will be no interference issues between the AIS
/ VHF and your HF WeFax...

It's HF, not VHF....so no need to mount a WeFax antenna on the masthead, etc....and there's no reason to buy/install a commercial HF WeFax antenna, when all you need is a piece of wire (or access to a chain plate / rigging) and a short piece of coax!

Originally Posted by sanibel sailor

I have no understanding of how these things work. I am kind of at the tinfoil-on-TV-antenna level of knowledge.
Another question is regarding interference with another antenna.
i have thought about adding a standalone weatherfax which will need an antenna.
Since the AIS will be transmitting, will there be interference and how much physical separation is needed?

I use a 22' length of rigging (an insulated aft lower shroud), but anything from 20' to 50' long is good, and it's not critical....if you're designing an antenna for just HF WeFax reception (and/or also HF-DSC reception), I recommend something in the 25' to 30'/35' long, as this would be a decently efficient vertical for receiving from 6mhz thru 12mhz, and still be good down to 2mhz/4mhz and up thru 17mhz...
But...

But, if you're looking for a cheap/easy set-up, that can work well (or can pick up some on-board RFI)....you can just attach the center conductor of a piece of coax (such as RG-8x or RG-58) to a chainplate / chainplate bolt / lower end of a piece of your standing rigging....and run this coax to your WeFax receiver....and viola, you have a decent HF WeFax receive antenna, easy-peasy!

Whether your rig / chainplates are all DC grounded / bonded, or not....this does work!



Of course, like all HF receiving on-board, your success is going to almost completely regulated/controlled by two things:
a) Ridding your boat of RFI producing devices....(or at least reducing them and mitigating the RFI)
b) Your knowledge of HF Radiowave propagation....(and learning when / what freqs work best at various times of the day and over various distances)

[I have posted a lot about both of these things, and have made many (free) videos about them....if you do end up deciding on HF WeFax reception, please ask and I'll post some helpful links...]

And, when using the entire rig as an HF receive antenna, in some situations you can have significant receive RFI....(it's very specific to each boat...so, you just have to do it and check....and since it doesn't cost you much in the way of $, it's not a big deal to give it a try...)



Just wanted to pass this on....hope it helps.


Fair winds.


John


P.S.
On a side note regarding "broadbanded-ness" of VHF antennas....it's darn close to impossible to make absolute statements, but fyi....a good rule of thumb is the higher gain antennas (generally bigger/longer) inherently have narrower bandwidths, but are usually designed and "tuned" to allow good operation across the band they are designed for....and while "fiberglass enclosed antennas" can be designed / have their tuning designed to be a broader bandwidth, the same is also true for end-fed whips, where the whip can be tuned as well as the base-matching network....so, you cannot make blanket statements that one is always more broadbanded than the other....


For most sailors, you don't need to worry about all of this....just buy a good antenna from a reputable manufacturer, that has the specs that you require....and you're good-to-go!


But, if you do need to "tune" your VHF antenna to a better match on the AIS freqs (note that 2:1 VSWR is okay), please just trim the bottom of the whip....measure a 1/2" or so, and you can just "score" the whip with a hacksaw, and break it off with a pair of pliers / linesman pliers / vice grips, easy-peasy....(fyi, these SS whips are wicked "hard", and can be a pain to "cut"....but, if you've got a big bolt cutters that you use for cutting rigging wire, that will do fine)