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Old 27-01-2020, 23:07   #1
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Connect Handheld VHF to boats antenna

Hi!
I want to be able to share boats antenna to handheld VHF. This is a kind of backup solution as well too have some DSC functionality etc. New functions which my old Simrad radio dont have. This solution is primary for long passages over the oceans. We have an advanced antenna splitter for AIS transponder from Comar.

Now I wish to add a more simple splitter and adapter for handheld ICOM that have DSC alarms etc.

Found some components on Amazon.
Will this solution work together with Comar AIS antenna splitter and current old Simrad VHF?

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Old 28-01-2020, 05:12   #2
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Re: Connect Handheld VHF to boats antenna

Jonas,

Short answer: No!
No, it will NOT work....and you will damage/destroy either or both radios as soon as you transmit on one of them!


My advice:
Replace your "old Simrad" radio!!
{how in the world do you still have an old / non-DSC radio? The GMDSS (and hence DSC) has been with us since the 1990's....fully implemented worldwide by Jan 1999...so, how it possible that you haven't upgraded your primary communications device / primary safety device?}
Even if you have budget concerns, replace it!


Second piece of advice:
Replace your primary VHF antenna and all coaxial cable.....'cuz if it as old as your Simrad radio, it should be replaced as well...


Third piece of advice:
A "vhf/AIS splitter" is actually a "splitter" and an RF-sensed "relay" in one box....some (like Vesper's SP-160) are very good, but some are pretty bad...
So, please have a close look at your Comair AIS/VHF splitter....as many (most) AIS/VHF "splitters" are pretty bad (too much thru-loss)



And, finally....
If you're planning on crossing oceans (as I, and many others here, do) and desire some communications advice, it's all here for the asking...for free...
Avail yourself of it...

Particularly have a look at the "stickies" on the top of this Marine Electronics page....
And, have a look at some Youtube Playlists that might apply to your applications...

VHF-DSC
https://www.youtube.com/playlist?lis...J6QugtO2epizxF


HF-DSC Comms
https://www.youtube.com/playlist?lis...ga2zYuPozhUXZX


Maritime HF Comms
https://www.youtube.com/playlist?lis...ZDo_Jk3NB_Bt1y


Offshore Weather
https://www.youtube.com/playlist?lis...zdjTJjHlChruyY


Icom M-802 Instruction Videos
https://www.youtube.com/playlist?lis...rC-8QKVyMb4tVr


Offshore Sailing
https://www.youtube.com/playlist?lis...KgTCj15iyl6qoY



I hope this helped?

Fair winds.

John
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Old 28-01-2020, 05:29   #3
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Re: Connect Handheld VHF to boats antenna

John, would you recommend a standalone AIS antenna over a splitter/relay?

Jonas, all the best for your circumnavigation!
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Old 28-01-2020, 05:51   #4
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Re: Connect Handheld VHF to boats antenna

Quote:
Originally Posted by Spot View Post
John, would you recommend a standalone AIS antenna over a splitter/relay?

Jonas, all the best for your circumnavigation!

I prefer a stand alone ais ant ...it represents redundancy

This dedicated ais ant is normally mounted on a spreader

I can't count how many times that my masthead vhf ant had been destroyed by lightning strike. Bird strike ....

If you loose use of this masthead vhf ant, it's a simple task to re route connections to your spreader ais ant

On a very small boat this two ant system may not be possible
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Old 28-01-2020, 09:11   #5
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Re: Connect Handheld VHF to boats antenna

You don't want a splitter, you wnat a switch.



If the splitter fails you can have RF striking the other device attached. The switch will require you to manually change the RF path from the antenna to whatever device is attached. It is bidirectional so you can have two antennas and one radio or two radios and one antenna.
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Old 28-01-2020, 09:58   #6
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Re: Connect Handheld VHF to boats antenna

Do remember that splitters etc, will result in some loss of signal.
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Old 28-01-2020, 11:00   #7
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Re: Connect Handheld VHF to boats antenna

Spot,
Couldn't you have asked a less controversial subject??
Quote:
Originally Posted by Spot View Post
John, would you recommend a standalone AIS antenna over a splitter/relay?

Jonas, all the best for your circumnavigation!
Seriously, the actual answer isn't controversial, but just complicated and therefore misunderstood by a lot of sailors....hopefully once you read this, you'll understand why it's confusing to some...



The short answer is:


a) For most sailors, it makes sense to have a separate VHF antenna for their AIS transponder....as long as it is at least 3' - 4' separated vertically (or 6' - 10' horizontally) from your primary VHF antenna, neither will damage each other....the farther away the better, as this will help reduce each transmitter from "de-sensing" the other's receiver...


b) For those venturing offshore, expecting to be in heavy seas, etc., where a low-mounted VHF antenna can have its signal blocked by waves, etc...then making sure that you AIS transponder's VHF antenna is mounted up high enough is a very good idea....




So, if you look at both of those criteria, it makes sense to mount a VHF whip on a spreader / top spreader.....

But FYI, in order to keep the mast from becoming "part of the antenna", and making your AIS antenna directive, you need to keep this VHF antenna at least a 1/2-wavelength (approx 3') away from the mast....and preferably 4' or more....(this isn't too practical on some boats, and impossible on smaller boats)....and even if you can accomplish this, the mast still will produce a null in the antenna pattern (a sort-of shadow) that will reduce your AIS range (receive and transmit) in the direction of the mast....on many boats, especially in heavy weather, the yawing of the boat will usually keep you from having this null in the exact same bearing for too long, BUT....but, since you have no way to knowing where this null is when your AIS transponder transmits, and/or when others AIS transponders transmit, so it is possible that you can miss some targets' signals and some targets will miss your signal....and, of course on some boats / some rigs, this spreader-mounted antenna can be fouled by your sails, and/or it can foul/tear your sails, if not mounted/secured properly...


So, a low-mounted VHF antenna that is installed/mounted in the clear (without obstructions nearby), will usually be more reliable!

So, for an AIS transponder installing a dedicated VHF antenna about 8' - 10' off the water, in the clear....on a stern rail, etc., is what is typically done..





c) But, this of course doesn't solve the issue with having its signal blocked or reduced because of a heavy sea state (if you're in a 12' trough and you antenna is only 10' off the water, your AIS range is very very limited)....

So, in these situations / for this application, then utilizing the masthead VHF antenna for your AIS transponder, or use the masthead VHF antenna for both the AIS transponder and your primary VHF radio, using a "splitter/relay", is what is typically done...

The better "splitter/relays" add very little loss into the transmit path, and usually have a receive pre-amp built-in that can improve receive S/N by a few Db....so, as long as you don't have too much lossy-coax run up to the masthead VHF antenna, they don't adversely effect your VHF range at all, and improve your AIS range significantly versus a low-mounted antenna when down in the trough of some big seas....(but, of course this is another piece of electronics to buy [ ~ $250] and another piece that can fail...so, again this is only recommended when needed, not for everyone!)

Have a look at test results of the Vesper SP-160 here:
http://www.cruisersforum.com/forums/...ld-130803.html



SO...
So, as you see, the answer depends on the boat, where/how you're sailing her, and what your needs/desires are regarding AIS range/reliability, and how risk-adverse you are to any "equipment failures"


For me, my application (offshore, some heavy weather), I have BOTH a stern-rail / above bimini mounted VHF whip that can be used as a dedicated VHF antenna for either AIS transponder or my primary VHF radio (which is my "back-up")....AND a Vesper SP-160 splitter/relay connecting my AIS transponder and primary VHF radio to my masthead VHF antenna....










{fyi, I used low-loss cable inside cabin/in-bilge to compensate some for the added loss of the splitter, but doubt anyone else will do so, and of course isn't necessary at all!}



So...
So, as you see, the answer is simple and complicated....

Use a separate VHF antenna, unless specific reasons point you to an alternative approach.





Hope this clears things up.

Fair winds.

John
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Old 28-01-2020, 11:03   #8
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Re: Connect Handheld VHF to boats antenna

Thanks for all answers regarding splitter. Our primary device for SOS is Iridium Go and PLB. Regarding old radio it was good enough to replace 20 years old contacts. Over the Atlantic and Pacific our Comar AIS with antenna splitter worked just fine. There were ”tons” of equipment we needed to consider before we left Sweden for circumnavigation 2018, we did many good choice soo far. We have had amazing help in this forum .
Thanks again for all helpful answers during current refit in Opua, New Zealand.

Jonas
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Old 28-01-2020, 11:14   #9
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Re: Connect Handheld VHF to boats antenna

Quote:
Originally Posted by Segelplaner View Post
Hi!
I want to be able to share boats antenna to handheld VHF. This is a kind of backup solution as well too have some DSC functionality etc. New functions which my old Simrad radio dont have. This solution is primary for long passages over the oceans. We have an advanced antenna splitter for AIS transponder from Comar.

Now I wish to add a more simple splitter and adapter for handheld ICOM that have DSC alarms etc.

Found some components on Amazon.
Will this solution work together with Comar AIS antenna splitter and current old Simrad VHF?

Attachment 207692
Attachment 207693
NOOOOOOOOO





You can take the antenna cable off the installed VHF and onto the handheld VHF. I have done this on boats and airplanes with good results. You cannot use a T fitting and do both at one.
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Old 28-01-2020, 11:21   #10
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Re: Connect Handheld VHF to boats antenna

Quote:
Originally Posted by Stewie12 View Post
Do remember that splitters etc, will result in some loss of signal.
Splitters and all connectors introduce some capacitance and/or resonance into the antenna line. This can change the impedance from the 50 ohms that matches the radio. Any mismatch will create a standing wave, which cripples your radio. When newer radios sense a dangerous standing wave, they limit the transmit power to prevent the standing wave from destroying the radio's transmit diodes.
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Old 28-01-2020, 11:30   #11
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Re: Connect Handheld VHF to boats antenna

I learn a lot about radio here and how complicated it can be. Regarding new solution for new radio and AIS, I consider coming Vesper Cortex. Current refit of boat is expensive - so new radio have to wait. More important to have a rebuild of rig and engine.
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Old 28-01-2020, 11:51   #12
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Re: Connect Handheld VHF to boats antenna

As an emergency backup allowing me to plug the handheld into the masthead antenna I have a short pigtail similar to this
https://www.amazon.ca/Coaxial-Cable-.../dp/B07DYR38BT
It significantly improves the range of the handheld.
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Old 28-01-2020, 13:04   #13
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Re: Connect Handheld VHF to boats antenna

I use a B&G V50 VHF with NMEA 2000 for my primary radio and two H50s handhelds. The VHF can talk to the handhelds, and the handhelds can talk to each other. The handhelds transmit VHF through the primary, so range is good. The NMEA allows direct connection to the GPS in the chart plotter without having to convert between 0183 and 2000 protocols, and it also allows the radio to send AIS data to the chart plotter. One H50 has a mount at the helm and is used as a remote mic. Since they can talk to each other I use the other to communicate with any crew on the bow when anchoring or if someone is directing me through a tight area.

If the primary radio is knocked out, I would guess the antenna would be toast too. A secondary antenna would be a good idea as well.

- - -

My understanding is if you transmit VHF (I would extend to AIS as well) without an antenna, the radio fries. If that is true, would an antenna switch not cause this if you forget to turn the connected transceiver off before switching?
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Old 28-01-2020, 13:30   #14
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Re: Connect Handheld VHF to boats antenna

There are splitters, and there are splitters. An active splitter than can amplify and feed the received signal to both ports (radios), and sense AIS transmit pwer and switch the antenna to that port, should work to allow the main VHF and the handheld to share the antenna peacefully. Not sure what will happen if both transmit at the same time, but if there is only one radio operator aboard, that's acceptable. Not sure if this is what your Comar splitter does.



An AIS-receive-only splitter divides the incoming signal to both radios, and merely switches out (disables) the AIS connector when the main VHF transmits, to protect the AIS receiver from full transmit power. This works for an AIS receiver, but will NOT work in this application.


A coaxial T-connector will NOT work and is likely to damage one or both radios.


The coaxial switch would work but is very manual, and could be a problem if left in the "wrong" position.


If going for an upgrade, a new main VHF with AIS receive capability and a cockpit remote would remove the need to use the handheld for DSC. The handheld antenna adapter is still a good idea for a *manual* backup in the event of a failure of either the main VHF or the ship's battery - in which case the antenna would be physically unplugged from the dead radio and connected to the handheld (not the OP's use case, but still a good capability).
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Old 28-01-2020, 13:40   #15
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Re: Connect Handheld VHF to boats antenna

Yes, I can go for a backup solution. Splitter is too risky. Thanks
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