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Old 07-09-2015, 13:09   #1
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SSB & VHF & AIS & FM Antenna(s)

Dear Friends, I need some advice. I have a Swan 391 and I have recently upgraded all electronics, and most importantly all radios. I have the following:

1. Raymarine AIS
2. FM radio
3. VHF with DSC
4. Icom M802 SSB (with DSC)

At the moment, this is how the antennas are configured:

Mast antenna: VHF and AIS, using the Raymarine automatic splitter
FM separate whip installed on a rail
SSB: HF backstay, no antenna on the ICOM M802 DSC.

What I want to do is:

1. Improve my FM radio reception
2. Connect my ICOM M802 SSB DSC receiver antenna (for redundancy and and also for proper DSC function via the M802)

Thus, I am considering two options:

OPTION 1:

Two mast antennas: Ant #1 for VHF and AIS. ANt #2 for FM receive and ICOM M802 DSC receive). This option requires me to install a second mast antenna.

OPTION 2:

1 mast antenna: VHF Tx/Rx, AIS Tx, FM Rx, ICOM M802 DSC Rx. This would require a 4 way automatic splitter--do these even exist? Is option 2 even feasible?

What is your advice?

Thank you so much,

Mark
USS HUSKA
Swan 391, H#22
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Old 07-09-2015, 15:09   #2
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Re: SSB & VHF & AIS & FM Antenna(s)

Your raymarine splitter already provides an FM output as well as AIS and VHF, all you need is the HF DSC antenna, Metz make a good one, and it doesn't need to be installed on the mast as it's HF.

Regards
Ab


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Old 07-09-2015, 15:22   #3
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Re: SSB & VHF & AIS & FM Antenna(s)

Quote:
Originally Posted by seegem View Post

At the moment, this is how the antennas are configured:

Mast antenna: VHF and AIS, using the Raymarine automatic splitter
FM separate whip installed on a rail
SSB: HF backstay, no antenna on the ICOM M802 DSC.

What I want to do is:

1. Improve my FM radio reception
2. Connect my ICOM M802 SSB DSC receiver antenna (for redundancy and and also for proper DSC function via the M802)

Thus, I am considering two options:

OPTION 1:

Two mast antennas: Ant #1 for VHF and AIS. ANt #2 for FM receive and ICOM M802 DSC receive). This option requires me to install a second mast antenna.
In antenna #2 you are mixing completely different bands (HF for the 802 DSC Rx and VHF for broadcast FM) that require completely different antennas. If you want to move broadcast FM Rx to the masthead then you can use Vesperīs AIS / VHF / FM antenna splitter together with an antenna tuned somewhere between VHF ad AIS bands, which will be good enough for broadcast FM Rx.

It is also a bad idea to have VHF/AIS Tx antenna close to a separate FM Rx antenna because it is possible to push lots of Tx power into the FM receiver. It is much better to either have FM in a separate antenna that is a few wavelengths away, or have it in the same antenna but protected by a splitter that will cut off the FM reception when you are transmitting AIS or VHF.

Quote:
Originally Posted by seegem View Post
OPTION 2:

1 mast antenna: VHF Tx/Rx, AIS Tx, FM Rx, ICOM M802 DSC Rx. This would require a 4 way automatic splitter--do these even exist? Is option 2 even feasible?
I do not think it is possible to find or even make such a 4-way splitter that will work well across HF and VHF.

It would be better to keep the 802 DSC Rx antenna separate and lower (say mount it in the pushpit). By the way, there is no benefit from height for the 802s HF reception.

FM will typically work fine off a masthead antena that is tuned to VHF/AIS and an adequate splitter. If you do not need the height (eg in the Caribbean where the FM Tx antennas are high enough to give you line of sight for dozens of miles) you can just make a simple dipole using duplex wire that is sliced alongside for 1/4 wavelength and stretched apart; all this hidden behind the panel (as in many Beneteaus).

IMHO the two points directly above are slam dunks and the only real question is whether you want to use the same antenna (and coax) for VHF and AIS, which are both critical systems. I am not too fussed about the small difference in frequency (156.8 for Ch 16 and about 162 for AIS) because most antennas have enough bandwidth to cover that range. Another story is that a passive splitter (ie without an amplifier inside and a 12V input to feed it) will hurt your Rx ranges, but the Vesper active splitter will not have that problem.

All that said, you could install VHF or AIS in a separate antenna in a mast spreader (as in some Antares 44i boats) and then have two antennas that are high, separate and identical and could give you redundancy if a coax fails when you cannot replace it.

My base setup would be one masthead antenna for VHF, FM and AIS with a 3-way Vesper splitter and a separate HF DSC Rx antenna mounted in the pushpit or stern arch, etc. A possible tweak would be to save the splitter (cost and power consumption), use a cheap wire dipole for VHF and have AIS and VHF in separate antennas , one in a spreader and the other one in the masthead.

Cheers

C
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Old 08-09-2015, 01:04   #4
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Re: SSB & VHF & AIS & FM Antenna(s)

Forgot to mention, as you have a raymarine AIS have a look at the Pro Ais software, it has a built in VSWR , so you have a rough idea how good your vhf/ais antenna is, I found that the larger the diameter of the coax cable the better the VSWR and reception of the antenna. Not that I am saying the raymarine splitter is the best (they all work I'm sure) but it comes with all the cables to connect to vhf and ais and looks just like the ais650 so it's very neat and tidy to install. I also found that a AIS tuned antenna still works great with the splitter for Vhf, is it better than a normal Vhf antenna, I can't tell.
I have gone down the splitter route as the commissioning yard was provided with vhf coax but I forgot the ais coax and they put in cheap thin white coax which is almost useless, poor reception and pants VSWR.

Regards
Ab


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Old 08-09-2015, 09:15   #5
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Re: SSB & VHF & AIS & FM Antenna(s)

DSC antenna is only used to receive a reply when you send an emergency call. It is receive-only, and if you don't have one, it won't affect your ability to send. It is important to have 2-way communication, though, if you ever have an emergency, so hook something to the antenna input. It could be the Metz, or it could be a length of wire under your headliner or in a locker somewhere near the radio.
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Old 08-09-2015, 10:49   #6
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Re: SSB & VHF & AIS & FM Antenna(s)

Not a radio specialist but I just installed an AIS transponder. Lacking masthead options (one mast so can't install 2 aerials) I used a VHF dipole on the stern arch. Works great with receive ranges well over 50 miles for large ships. Also acts as an emergency VHF if I ever loose the mast
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Old 08-09-2015, 12:02   #7
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Re: SSB & VHF & AIS & FM Antenna(s)

I don't use SSB or SW, but I installed one antenna for the VHF at the top of the mast and one for the AIS transceiver on the stern rail. If I lost the mast, I could use the rail mounted antenna to transmit VHF.
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Old 08-09-2015, 12:25   #8
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Re: SSB & VHF & AIS & FM Antenna(s)

1. Raymarine AIS
2. FM radio
3. VHF with DSC
4. Icom M802 SSB (with DSC)


#1 and #3 can share the same masthead antenna with a splitter, because they are both VHF radios and that works well with a splitter.

#2 is presumably an entertainment radio, ie. 102MHz FM stereo. That needs a physically different antenna. You can find instructions online for using an old extension cord ("zip cord") to make a perfectly good dipole for that, but that's a directional antenna which has to be aimed at stations. If you want a good cheap omnidirectional antenna, buy a junkyard car antenna, or a replacement car "whip" antenna. That's as good as it gets. Don't worry about height, just install it as near vertical and inside the cabin, as you can. This is NOT a critical complex antenna, what is most important is that it is designed for the "car" stereo and not piggybacked with any of your other radios.

#4 probably should be connected to a backstay antenna on your boat. The "DSC" that it uses is HF-DSC, not VHF-DSC, so they CAN NOT share an antenna for that. Icom's manual is unclear if there is any actual purpose or gain to be had form plugging in a second HF-DSC antenna on the 802, you might want to ask them about it. But I wouldn't share that with any of the VHF equipment. If they say another antenna here will have some benefit, you might want to just mount it up the mast, on a spreader. And keep it separate from the rest.

You probably should consider an "emergency antenna" for the VHF, that comes with a 25' length of coax and can just be plugged in and used if the mast itself falls. Cheap, about $30. Similarly, there are jury-rig antennas that can do the same for the 802. Coil it up, stow it, with any luck you never use it.
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