AIS-tuned vs VHF tuned antenna

[GTom]

I was wondering how important is to choose the correctly tuned antenna? VHF channel 16 is 156MHz, AIS is 162MHz, what do I loose if I e.g. buy a VHF-tuned antenna for the AIS, do serve as a best possible backup VHF in case the mast comes down?

[smac999]

some AISs will error on some 156mhz antennas and stop transmitting. more so on the 8' ones though then the 4'.

if it's for AIS transmitting then get the AIS ant.

[GTom]

Originally Posted by smac999

some AISs will error on some 156mhz antennas and stop transmitting. more so on the 8' ones though then the 4'.

if it's for AIS transmitting then get the AIS ant.

Thanks, I think I'll get a broadband one, that's compatible with both. As I understand I am sacrificing very little by accepting a 1.5 SWR value at both end and I have a backup antenna if things go South.

[mlydon]

it doesnt matter as much as people make out.

I have a single metz vhf antenna up the mast, with a vesper splitter. I get reception (and broadcast) at vast distances on the radio, can see AIS targets 10-15 miles out, and I know they can see me.

AIS isn't really important at distance - it's the guy who's going to run you down who's a mile or two out that matters, IMHO. So leave the antenna tuned for best performance on VHF, don't worry about the AIS.

Matt

[stormalong]

The proper length of a 156 MHz 1/4 wave element is 1.5 ft.. At 162 MHz it is 1.445 ft. I don't think you would have a problem with either. I have uses my marine VHF masthead antenna on the 2 meter ham band (144-148 MHz) with good results.

KWARC Dipole Calculator

[mlydon]

The metz manta 6 I use says 34" whip, 1/2 wave. Works great, less filling

Matt

[Brian.D]

AIS is VHF. As mentioned before, Ham, Marine, AIS, all will work with an antenna cut for that frequency range. AIS is within the Marine VHF Frequency pool.

[smac999]

Originally Posted by Brian.D

AIS is VHF. As mentioned before, Ham, Marine, AIS, all will work with an antenna cut for that frequency range. AIS is within the Marine VHF Frequency pool.

actually not. I was testing a shakepeare 5241R from 142-172mhz last week. the low and high of that were off the swr scale. shakespear claims a 7k bandwidth so that is only 153-160 usable.

I'm going to be running 3 different vhf radios with 3 different antennas to get the full vhf range of 142-172 that I need for another project. I just ordered a morad marine ham 144 antenna to cover the lower range. it was the only marine mount ham antenna I found.

as as I said before. the shakespear 8' 5225xt antennas error with a vesper 8000. they are around 3:1 swr. and the vesper stops transmitting. the 4' ones work and are around 2:1swr

[Brian.D]

I just built a 2m Vertical Dipole to see if it is possible emergency VHF antenna for a demasted vessel. The SWR curve is 1.6:1 (137MHz) to 1.9:1 (164MHz). I cut the antenna to use on FM Repeaters (146MHz) in SoCal. Best repeater I hit was 67 miles on Catalina Island. Granted height helped but it was still a successful test.

If one wants to use a ham 2m antenna, one will need to shorten the whip for the marine frequencies. It is do-able.

[StoneCrab]

I've been looking into this recently and was glad to see this forum.

I'd go with multiple antennas but on a sailboat you really only have the masthead to work with. I put an 8 foot marine VHF antenna on the stern rail and it does no better than my handheld, while the masthead antenna works really well.

I want to run two VHF radios and an AIS transponder. I've pretty much decided on the Vesper 8000 with their antenna splitter for the masthead antenna, since the splitter will prevent the AIS from trying to transmit over the VHF and visa versa. This solution still leaves me without a good antenna at the second VHF in the cockpit.

Many of the manufacturer sites tell you in the fine print to be careful with antenna placement since you can overload the other unit when transmitting and blow out the receivers. They recommend a 3 foot minimum separation between antennas. Hard to do on top of the mast....

One upside of the research though was a better understanding of how antennas work and what factors into a low SWR and how to "tune" and antenna. There are several YouTube videos of guys making VHF antennas from RG58 coax by stripping back the outer casing and separating the braiding from the inner core to form two ~ 36" long leads which when spread out form your dipole aerial. If I ever have to Macgyver a radio antenna, that's how I'll role. It might be fun to play with on a passage. The splayed coax could be taped to a halyard and pulled aloft for height.

1/4 wave length is 19.25 inches for each leg. 1/2 wave is twice that. To see two different construction techniques and testing see this video: https://youtu.be/CwOATcwHrBo?t=157
or this one: https://youtu.be/SdEglNHyHB4
All Electronics has the parts at a good price.

If you can borrow an antenna analyzer, you can dial in the SWR by cutting down the wire lengths until you get ideal performance.

There are also some good videos on the effect of a base loading coil or inductor on the antenna length. You can get great performance from a very short antenna with a base load inductor on the antenna. Tuning for that configuration would definitely require a SWR meter.

[svmobert]

FYI, Vesper makes a VHF/AIS Combo antenna which is reasonably priced. The model# is VA159 and it retails for about $75.

[MJH]

Originally Posted by GTom

I was wondering how important is to choose the correctly tuned antenna? VHF channel 16 is 156MHz, AIS is 162MHz, what do I loose if I e.g. buy a VHF-tuned antenna for the AIS, do serve as a best possible backup VHF in case the mast comes down?

I will let the wire-heads discuss the finer points of frequency whatever. I installed a Vespermarne Watchmate 850 and accompanying Vespermarine SP160 VHF splitter and haven't had a single problem with either VHF or AIS locally or on roundtrips to Hawaii and Alaska. I would say avoid the necessity of adding an extra antenna if you can.

~ ~ _/) ~ ~ MJH

[Rapanui]

Personally, I would have a separate antenna for AIS and mount it low down on an arch or pushpit, that should easily give you returns out to 10 miles. Otherwise, you receive just too many long distance AIS returns. Then you have a useable emergency/secondary VHF aerial if you lose the stick or primary VHF aerial.

[Brewgyver]

Rapanui,
I tried doing just that, to avoid using the splitter, due to concerns about degraded VHF voice transmission. I mounted a new VHF antenna on the grab rail on top of the dodger, with it's own very short coax run directly to the Raymarine AIS 250 rx (which has a built-in splitter). I couldn't see any targets past a mile and a half, and this was on a busy part of the coast. I immediately switched to the mast-top coax, with a 1 foot jumper from the splitter to VHF radio, and could see shipping vessels in the 20 mile range. I'm pretty sure it was the low height of the antenna that limited the rx range.

Just checked an on-line range calculator, and with an 11 foot height the range is just over 4 miles. You need to get up to 17 feet to even break 5 miles.

I want a little more warning than that!

[Wotname]

Originally Posted by Brewgyver

...........

Just checked an on-line range calculator, and with an 11 foot height the range is just over 4 miles. You need to get up to 17 feet to even break 5 miles.

I want a little more warning than that!

You need to add the height / range of the distant station (i.e. the other boat / ship) to get the total range.