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Need help to amplify my VHF marine radio for fishing offshore/ increase range

xrayengineer@cfl.rr.com said:
Another thought, folks here have mentioned the higher quality cable like the LM240, but all these antennas have the cables already connected at the antenna end. Are there better antennas for boats that have just a female PL-259 connection on it instead? Otherwise how would you retrofit?
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The antenna usually comes apart at the base with a set screw or two and you should find that there is an SO-239 (a "female PL-259") at the base of the antenna with the coax attached to it. It's either done that way or with a "lug" type connection at the base. Take it apart and you should be able to see how it's done.
 
The antenna you linked to is a pretty typical 6db style antenna. It is rated for 100 watts. If you try to hook up a 200 watt amplifier to it, you will turn the antenna into a nice fuse on top of your boat. Part of the problem of installing an amplifier is finding an antenna that can handle the additional power output.

A quick search turned up this antenna: http://www.digitalantenna.com/pdfs/DA_16-21ftVHFAntennas.pdf

It's rated at 10dbi and 200 watts. 10dbi is 4dbi better than the antenna you linked to. A 4dbi difference is equivalent to more than doubling your transmit and receive power with just an antenna change. See why everyone says put a better antenna on first?

I agree with Packrat also. Crimp on connectors suck bad. Get some solder on connectors. If you don't know how to do it, learn or get someone to help you who does. It's worth it. If you want an AM/FM antenna for the stereo, install a separate one. The splitter is going to introduce some loss into the system, which is defeating the whole purpose.
 
My point earlier in the thread, you add a linear, so now you say to yourself, I have power, now I can out even further :headbang

Now you are in the "same boat" pun intended :p

You still need to know your limits and respect them. Like Moleculo said
The ocean is a big place and it is not your friend.
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Just an FYI, AT&T now sells a sat phone,

AT&T launches satellite phone | Wireless - CNET News
 
moleculo said:
The antenna you linked to is a pretty typical 6db style antenna. It is rated for 100 watts. If you try to hook up a 200 watt amplifier to it, you will turn the antenna into a nice fuse on top of your boat. Part of the problem of installing an amplifier is finding an antenna that can handle the additional power output.

A quick search turned up this antenna: http://www.digitalantenna.com/pdfs/DA_16-21ftVHFAntennas.pdf

It's rated at 10dbi and 200 watts. 10dbi is 4dbi better than the antenna you linked to. A 4dbi difference is equivalent to more than doubling your transmit and receive power with just an antenna change. See why everyone says put a better antenna on first?

I agree with Packrat also. Crimp on connectors suck bad. Get some solder on connectors. If you don't know how to do it, learn or get someone to help you who does. It's worth it. If you want an AM/FM antenna for the stereo, install a separate one. The splitter is going to introduce some loss into the system, which is defeating the whole purpose.
Click to expand...


This antenna looks great. 16 feet tall. Would the 10db antenna be too directional on rolling seas?
 
office888 said:
:blink:

RG8X isn't that good on VHF, not only that, if your radio is only 6 ft away from your antenna, your antenna definitely is not high enough.
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My radio is about as high as my belt, and the antenna mount is just over my hear at about 7 feet, so I don't think I understand the comment, please elaborate.
 
xrayengineer@cfl.rr.com said:
This antenna looks great. 16 feet tall. Would the 10db antenna be too directional on rolling seas?
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A vertical antenna - by virtue of its design - is 'omni-directional (radiates in all directions equally).

That 10 db gain antenna would be the antenna that I would choose. Also using LMR-400 with non-crimp connectors. Between these two changes, you would have vastly improved transmit and receive.
 
moleculo said:
Remember, most VHF amps include a pre-amp. I don't think an amp is the best/only route, but I do think it is an additional tool that could be helpful, even if you can't hear the other stations. Your EPIRB doesn't RX anything - it's just a beacon. So it's not useful because it can't hear? Even if your VHF can't hear another station because it's able to talk farther distances than other stations, that doesn't prevent THEM from hearing you calling distress with your GPS coordinates. Also don't forget that the VHF also can send the DSC/MMSID info when activated, which is a data mode that includes the GPS coordinates. That can also be used without any reception on your part to help the Coast Guard locate you, just like a beacon. If you're going to go places on the ocean that can put your life in jeopardy, having every tool available isn't really that bad of an idea.
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I am confused about the VHF amp. Please elaborate if you can. I am assuming that the amps I am looking at would have a pre-amp that would be of some value. If I were to have a top quality 16 foot Digital antenna as mentioned above with a top quality cable, would the amplifier help add additional TX and RX distance? I can totally agree on the reasoning of getting the radio/cable/antenna as optimum as possible. But after that, would the amp be a good idea or not?

Would an amp like this be automatically compatible with a standard VHF marine radio? I am just wondering if the "pre-amp" circuit on the amp might overload the preamp circuit in the radio.

Can anyone recommend an amp to do what I am talking about?

here are a few of the amps i have been looking at:
vhf amplifiers 156-161 MHz

Mirage

RM High Band KL-145 VHF Amp-H&Y Electronics
 
An amplifier is putting you on the bad side of a legality issue. You handle that as you see fit. If your boat is USCG inspected regularly, that can get sort of expensive.
Your best bet is an antenna with some gain and more height. Of those two things, height is the most important one with VHF. The only biggy with a tall antenna is clearance, and you'd know more about that than I would. (You can always use the appropriate mount and tilt the thing over.) There are limits to everything and it seems you may have reached yours with marine radio.
SAT phones.
If you think radio stuff is expensive you ain't seen 'nuthin yet! There have to be less expensive kinds, but I have no idea what/where you'd find one. They certainly are an option though.
- 'Doc
 
I am confused about the VHF amp. Please elaborate if you can. I am assuming that the amps I am looking at would have a pre-amp that would be of some value.
Click to expand...

The Pre-amp amplifies your received signal to help you hear distant stations. Of those links, only this one appears to have units with a pre-amp

vhf amplifiers 156-161 MHz

My radio is about as high as my belt, and the antenna mount is just over my hear at about 7 feet, so I don't think I understand the comment, please elaborate.
Click to expand...

If there is any way to get the antenna mount higher, that will help a lot. That may not be very realistic from a structural perspective in a center console boat. You'll have to evaluate that for yourself.
 
xrayengineer@cfl.rr.com said:
My radio is about as high as my belt, and the antenna mount is just over my hear at about 7 feet, so I don't think I understand the comment, please elaborate.
Click to expand...

What I'm trying to say is:

You need to have that vertical antenna higher in the air!

Get it on either one of those extension rods, or a mast, or something. Don't be afraid to move the antenna to the front or rear of the boat. Even if you put the antenna farther away from the radio itself, if you replace your coax with some LMR400, you'll probably still have less loss with a 25 ft run of LMR400 than you would with your little jumper of RG8X.

Bottom line, get that antenna higher in the air!
 
Is there anyway you could just take a picture of the boat so we can see the space you have and maybe can tell what would work best for the antenna?

If you decided on the VHF amp, I would go with the CMSR 100, that would more than double your legal power from 25 up to 100 watts. The reason I say the CMSR 100 is because the maximum input to that amp is 25 watts. So you can run your radio at full power and not ruin the amp or radio.

If you get an amp that needs only 1-5 watts input, it is easy to just put the radio on low power and let the amp do the work. The problem is, during an emergency, that may be the furthest thing from your mind and you key that radio up at 25 watts and the amp can only take 5 watts in, you may have just smoked your amp, and possibly your radio. Now you are "up the creek without a paddle", pun intended again LOL :LOL:

Again, the CMSR 100 can handle the full power of the radio, when your just worried about keying up and talking.
 
An amp will also draw more current from your batteries. If they aren't getting charged, that can become a problem. HH's amp choice would be mine too. But if the boat is inspected - you will get warned at minimum - and fined at worst.

The 10 db gain antenna won't draw any more power; it will just radiate the power that you do have far more efficiently. It will receive better too. The difference between a 4 db gain antenna and a 10 db gain is significant. It is also taller - which means that part of the height problem you have - has been solved if used. It is legal to use - as well.

A piece of cheap coax - if that is what you have - will inhibit radiating all of the power that your radio has to use. If it has been exposed to sea water for a long period of time and it has crimped connectors; that may create a point of excess resistance that will further the loss to the antenna - even if it is a short run/length.
 
moleculo said:
The antenna usually comes apart at the base with a set screw or two and you should find that there is an SO-239 (a "female PL-259") at the base of the antenna with the coax attached to it. It's either done that way or with a "lug" type connection at the base. Take it apart and you should be able to see how it's done.
Click to expand...

Mole, marine antennas don't work that way. The coax is sealed into the antenna to avoid corrosion. He will have to cut the provided coax short, solder on a PL-259, and use a barrel connector to add a length of better, low loss coax if he chooses to go that route.
Personally, I think his best investment would be in a higher gain antenna, and an extension, mounted on the t-top.
 

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