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Closet Powerboater
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Discussion Starter · #1 · (Edited)
Since I had both masts down for trucking my new boat across country, I figured it was a great time to replace the mainmast VHF coax cable and to run a cable up the mizzen to another antenna.

The mainmast VHF is home-run to the VHF radio without connections or splitters and the signal is great. I'm pretty sure I received a coast guard transmission in Japanese the other day. :D

I had a VHF whip antenna put on the mizzen because I figured it'd come in handy one day. It is currently not connected to anything. At the time I had it installed, I thought the most likely use for it would be as an AIS antenna and a backup VHF antenna.

I have since learned that there is such thing as an AIS antenna. Is this significantly different from a VHF antenna?

Also I might like to split this antenna so that it can supply weather radio info to my Furuno Navnet thingy and perhaps even use it for the spare VHF radio. I have 2 splitters aboard right now (not in use) one is the type that is push-button and you choose 1 of 3 cables to connect to the output, the other is a regular 2 to 1 split. Splitters are evil I hear.... why?

MedSailor
 

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No its not significantly different. I have one of each, vhf antenna at mast head and ais antenna on stern rail BUT as each unit is mounted in the nav station next to each other I can plug either in to either. So at sea my AIS is on the mast head antenna and vhf lower. In port when I dont need AIS much but want to blabber on the radio I swap.

Net difference in antenna? ZIPPPERDY! Except for height of antenna, of course.
 
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Mermaid Hunter
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I have since learned that there is such thing as an AIS antenna. Is this significantly different from a VHF antenna?

Also I might like to split this antenna so that it can supply weather radio info to my Furuno Navnet thingy and perhaps even use it for the spare VHF radio. I have 2 splitters aboard right now (not in use) one is the type that is push-button and you choose 1 of 3 cables to connect to the output, the other is a regular 2 to 1 split. Splitters are evil I hear.... why?
AIS runs on two VHF channels: 87B and 88B. A conventional VHF antenna, tuned for best performance on VHF channel 16, will do fine. For a dedicated AIS antenna an AIS peaked antenna is nice, especially since a lot of transponders are fussy about VSWR. An "AIS" antenna will do fine as a back-up for voice VHF.

Splitters are evil. Unless you spend a lot of money splitters will add a good bit of loss (on the order of 2.5 to 3.2 dB) plus the loss associated with two extra connectors (0.2 to 0.5 dB) plus the impedance bump that increases VSWR.

Even with high end splitters with low-noise pre-amps there is a loss in transmit.

Splitters are evil. Did I mention that?

I can elaborate, because nothing is simple. A splitter for out of band services (like FM broadcast radio) is easier to do without a big performance hit. Pulling FM radio out of a TV antenna is trivial. Dividing a received signal in-band (like VHF to two radios) is going to have a significant loss. Switching and impedance issues for two transmitters, like a marine VHF and an AIS transponder gets unfortunate.

Although a separate issue, putting two antennas on the same band within close distance of one another is poor practice. That means that while "avoiding splitters" would seem to justify putting two VHF antennas on a single masthead it is not a good idea. Ketchs, schooners, and yawls make life easier in this respect. For sloops and cutters secondary VHF antennas should go on a spreader, a radar mast, the backstay, or pushpit.
 

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Closet Powerboater
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Discussion Starter · #4 ·
AIS runs on two VHF channels: 87B and 88B. A conventional VHF antenna, tuned for best performance on VHF channel 16, will do fine. For a dedicated AIS antenna an AIS peaked antenna is nice, especially since a lot of transponders are fussy about VSWR. An "AIS" antenna will do fine as a back-up for voice VHF.
...
Pulling FM radio out of a TV antenna is trivial. Dividing a received signal in-band (like VHF to two radios) is going to have a significant loss. ...
Thanks Dave! I forgot that AIS transmits on VHF channels, so the tuning for a channel makes sense. Seems like a trivial difference. I won't worry about it and I'll use my 2 mast mounted VHF antennas (one on each) with confidence.

Splitters are evil. Splitters are evil. I will keep repeating until it sticks. What about switches? One of the devices aboard has push-buttons so you could choose which device is going to the antenna. It'll require connectors, which = loss. Is it evil too?

BTW, your comment above reminded me of another question. I have a car stereo aboard and it works, but the FM radio was cut as well. What's the best option for really good FM radio reception from a car radio on a boat? I really like listening to local FM radio and enjoy sampling the local news and music wherever I go. I'd like to have a really really good FM reception setup and with my 2 masts and all that rigging, there must be a good way...

MedSailor
 

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Splitters are evil. Did I mention that?
I agree! And 2 vhf antennas are cheaper than one splitter incl cable so why do people like splitters? Because boys love complicated electronic toys! Crazy!
 
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Mermaid Hunter
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Splitters are evil. Splitters are evil. I will keep repeating until it sticks. What about switches? One of the devices aboard has push-buttons so you could choose which device is going to the antenna. It'll require connectors, which = loss. Is it evil too?
Not evil. Just worrisome. Send me the make and model and I'll let you know what I think.

Good quality coax switches are no worse than the connectors.

BTW, your comment above reminded me of another question. I have a car stereo aboard and it works, but the FM radio was cut as well. What's the best option for really good FM radio reception from a car radio on a boat? I really like listening to local FM radio and enjoy sampling the local news and music wherever I go. I'd like to have a really really good FM reception setup and with my 2 masts and all that rigging, there must be a good way...
Pulling FM off a TV antenna is probably best. No TV then a long wire will do fine.
 

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Since I had both masts down for trucking my new boat across country, I figured it was a great time to replace the mainmast VHF coax cable and to run a cable up the mizzen to another antenna.

The mainmast VHF is home-run to the VHF radio without connections or splitters and the signal is great. I'm pretty sure I received a coast guard transmission in Japanese the other day. :D

I had a VHF whip antenna put on the mizzen because I figured it'd come in handy one day. It is currently not connected to anything. At the time I had it installed, I thought the most likely use for it would be as an AIS antenna and a backup VHF antenna.

I have since learned that there is such thing as an AIS antenna. Is this significantly different from a VHF antenna?

Also I might like to split this antenna so that it can supply weather radio info to my Furuno Navnet thingy and perhaps even use it for the spare VHF radio. I have 2 splitters aboard right now (not in use) one is the type that is push-button and you choose 1 of 3 cables to connect to the output, the other is a regular 2 to 1 split. Splitters are evil I hear.... why?

MedSailor
New Garmin AIS 600 has a built-in active splitter that allows the use of an existing VHF radio and with Garmin's 'Clear Track' technology ensures there's no interruption of AIS traffic position while the VHF radio is in use.
 

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Closet Powerboater
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Discussion Starter · #8 ·
Not evil. Just worrisome. Send me the make and model and I'll let you know what I think.

Good quality coax switches are no worse than the connectors.

Hehe, this was different than I recall it being when I rummaged around the cabinets of the boat. I'm guessing you won't approve. ;)

While we're at it, I found this gem in with all the junk. Do these things really work? <raises eyebrow of suspicion> If so, what kind of antenna do you plug it into?



MedSailor
 

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Hehe, this was different than I recall it being when I rummaged around the cabinets of the boat. I'm guessing you won't approve.
TV is pretty straightforward. Even if the switch is cheap the signal levels are usually high enough that it doesn't make much difference. For over-the-air signals compare to a female-to-female connector. The performance will be readily apparent.

While we're at it, I found this gem in with all the junk. Do these things really work? <raises eyebrow of suspicion> If so, what kind of antenna do you plug it into?
I don't know that particular unit. Digital Antenna has a reasonable reputation. That isn't a splitter - it's a pre-amp (on receive) and an amplifier (on transmit) for your cellular phone. Do you have a way to connect your phone? Is it on the right bands for your cruising bands and your service provider?
 
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