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VHF Antenna

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Old 09-07-2018, 02:17 PM
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Default VHF Antenna

Please excuse my ignorance, but this will be my first boat where I'm installing a vhf radio. Flush mounting it in a 22ft custom aluminum cc that will mostly be used inshore in southeast Louisiana. My question is, do I actually need to install an external antenna or would it work as is in inshore waters? Thanks in advance
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Old 09-07-2018, 03:56 PM
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Will need an antenna.
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Old 09-07-2018, 08:31 PM
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^ x10,000
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Old 09-07-2018, 08:41 PM
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Don't push the transmit key of the powered radio w/o an external antenna attached! (And the higher the better for range. But suggest not going over 6dB gain antenna for a 20' boat.)

Not sure if it is the case with modern marine VHFs, but I believe in the past that could sometimes turn your radio parts into a momentary toaster.

https://www.westmarine.com/WestAdvis...-a-VHF-Antenna
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Last edited by TTaxi; 09-07-2018 at 08:48 PM.
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Old 09-08-2018, 09:17 AM
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Originally Posted by TTaxi View Post

Not sure if it is the case with modern marine VHFs, but I believe in the past that could sometimes turn your radio parts into a momentary toaster.

https://www.westmarine.com/WestAdvis...-a-VHF-Antenna
They have more protection than they used to, but it's still a bad idea and the manuals of all modern radios have warning against it.
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Old 09-08-2018, 09:02 PM
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Kaboom when you press transmit. You will eventually blow you output finals. Always need an antenna.
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Old 09-11-2018, 11:03 AM
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Yep. As that West Marine article posted above states, the antenna is crucial.

However, it's worth mentioning that nearly any size will do, depending on your use case. West Marine sells VHF antennas in nearly every size you can think of, all the way down to 15", although antennas that short are typically installed at the top of a sail boat mast. While a very short antenna would suffice for extremely short range communication, you do need to consider the fresnel height.

You can type antenna in the search bar on West Marine's site to see their entire selection of antennas. I'd guess an 8 foot antenna would be about perfect for your use case.

I can't post URLs yet(I'm too new), but google Wikipedia Fresnel Zone to read more about how height affects radio transmissions.

I called West Marine at one point, and their sales people are extremely helpful. I ended up getting an 8 footer with -6 db gain for my 22' river boat, and have no complaints. The mounting was the hardest part, but only because I couldn't reach both sides of the mount while attaching the hardware(I attached the inside of the mount under my dashboard).
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Old 09-13-2018, 06:48 PM
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Originally Posted by bubba102105 View Post
...[for use on] a 22 [foot] custom aluminum cc that will mostly be used inshore in southeast Louisiana...do I actually need to install an external antenna or would [a VHF Marine Band radio transmitter] work [without an antenna]...?
You are a bit confused. A VHF Marine Band radio transmitter is designed to work with an external antenna.

The size of your boat, the material the hull is constructed with, the notion that the design and fabrication was bespoke, the location of the body of water within the United States, and the distance from shore you will be boating have no effect, because VHF Marine Band radio transmitters are not sold according to boat size, the boat structural material, the nature of the design, the body of water they will be used upon, or the distance from shore. They are designed and certified for all boats of all sizes in all waters.
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Old 09-14-2018, 10:39 AM
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Originally Posted by jhebert View Post
You are a bit confused. A VHF Marine Band radio transmitter is designed to work with an external antenna.

The size of your boat, the material the hull is constructed with, the notion that the design and fabrication was bespoke, the location of the body of water within the United States, and the distance from shore you will be boating have no effect, because VHF Marine Band radio transmitters are not sold according to boat size, the boat structural material, the nature of the design, the body of water they will be used upon, or the distance from shore. They are designed and certified for all boats of all sizes in all waters.
I have no argument about what jhebert is saying here, but wanted to add:

The only real consideration for using any given VHF base unit in any given boat is the MMSI number, which is specific to a boat. However, that would only apply in the case of a Used VHF base unit. In every other way, your VHF radio transmitter is boat+antenna agnostic. Many VHF units lack an MMSI number altogether, which is fine for many boats. You can also change your antenna pretty easily if your use case changes, but you'd rarely have any reason to change out the VHF unit itself.

It still needs an antenna no matter what.

Concerning MMSI numbers specifically, some manufacturers permit end users to reset the MMSI number, and some do not. Some manufacturers don't officially allow end users to reset the MMSI number, but have secret button combinations that inevitably leak, which will allow you to reset your own anyway. Still others have hard limits on the number of times a given VHF unit can have it's MMSI number reset.
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Old 09-14-2018, 04:21 PM
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Originally Posted by Throe View Post
...some manufacturers permit end users to reset the MMSI number, and some do not.
That may have been true prior to the establishment of the Class-D category. Class-D DSC radios typically do not allow the change of the maritime mobile service identity (MMSI) once it has been set, without advice from the manufacturer. That typically means the radio must be sent back to the manufacturer or his service agent for the MMSI to be changed.

Older DSC radios--which are no longer allowed to be manufactured, imported, sold, or installed in the USA--may have allowed the change of the MMSI once it was entered.

But this aspect of a DSC radio has no effect on the need for an antenna for the proper operation of the radio.

Last edited by jhebert; 09-18-2018 at 11:09 AM.
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Old 09-16-2018, 01:21 AM
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Does it really damage the unit if you try transmit without an aerial plugged in?
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Old 09-16-2018, 05:18 AM
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Originally Posted by [email protected] View Post
Does it really damage [ an unspecified VHF Marine Band DSC transmitter] if you try transmit without an aerial plugged in?
There are no mandatory required behaviors for a Class-D DSC radio transmitter for the intentional abuse of attempting to transmit without a proper antenna connected to the transmitter by a proper transmission line, so the outcome is not predictable.

if you wish to discover what will occur you should perform your own experimentation and report you findings.
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Old 09-16-2018, 08:52 PM
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Originally Posted by [email protected] View Post
Does it really damage the unit if you try transmit without an aerial plugged in?
it can. so can a bad antenna or bad antenna connection.
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Old 09-17-2018, 01:27 PM
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Thats interesting, I didn't know that. You would think they would build some kind of protection into the unit
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Old 09-17-2018, 01:46 PM
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It's probably a matter of how much you want to pay for the unit. I'd expect a more expensive base unit to have better protection circuitry, and cheaper ones to have perhaps none at all.
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Old 09-18-2018, 06:37 AM
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Originally Posted by [email protected] View Post
...You would think they would...
Here is what I think:

Many modern transmitters provide protection of their transmitter final output stage. Whether or not the protection will provide immunity to damage from the intentional abuse of transmitting without any antenna connected is difficult to know. Again, if you wish to establish which radios can tolerate this abuse, I recommend you begin testing them yourself and report your findings.

I recommend you read the instruction manual for each radio for which you wish to determine if that radio can tolerate intentional abuse. Many VHF Marine Band radios contain clear and highlighted warnings against the use of the transmitter without an antenna. For example, an ICOM VHF Marine Band radio instruction manual for their model IC-M330 states:

CAUTION: Transmitting without an antenna may damage the transceiver.
If you want to verify the accuracy of that warning statement, try your own testing.

The user guide for a Standard-Horizon GX1300 radio contains this advice:

Taking the following precautions will prevent damage to the transceiver:
--Never key the microphone unless an antenna or suitable dummy load is connected to the transceiver.

Last edited by jhebert; 09-18-2018 at 11:14 AM.
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Old 09-18-2018, 01:46 PM
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jhebert - Thanks for the info
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