Electronics and VHF Radio Concern

Builder's Forum
1

I'm building a Pocketship and was considering not installing any battery or electronics system into the boat - until I became aware that I might only have the use of a handheld VHF radio - which is a concern because of it's limited range.  Any thoughts/suggestions on how a full-power 25 watt VHF radio can be used without the usual 'hard-wire' battery/electronics system?  Maybe a solar system?  Maybe bring aboard a small fully charged motorcycle type battery to hook up the VHF radio; other??  Many thanks.  Jimmy V

 

 

 

 

2

Yes, a VHF radio is an important safety device (even if it's not technically required by the USCG).  If it helps, you nominally get 1 nautical mile of transmission per watt, so a fixed mount will send a signal around 25 nm.  Another thing is that it's also "line of sight", so you can transmit/receive a long distance toward the horizon, but you can't necessarily talk to someone two miles away on the other side of a large hill.

You can totally bring a PWC battery that's easy to take home and charge as long as it's 12V.  Wire some alligator clips or even better some rings that fit over the posts or terminal screws and use wing nuts for easy on/off.  Also, some batteries have different sized posts to keep you from reversing polarity.  Some batteries don't have posts at all, but just a place to thread in a screw or your own bolt/wing nut.

Also, if your VHF has the ability to have an MMSI number, you should definitely register it on BoatUS.com with your PocketShip.  This is another important safety feature and might also allow you to DSC (Digital Selective Calling) other boats for more private conversations on the VHF.

You can then use a 2W trickle charger with quick connect ends for the battery of your choice to at home.  This is how I manage the small battery for my trolling motor.

3

  

Where will you be using the boat?  If you plan to go far offshore (>20 nm), then I would advise a fixed mount system with the antenna mounted on the mast head.  That will give you the absolute maximum range.  If you are not going >20 nm offshore and/or are unwilling to mount the antenna on the mast head, then you can save yourself a lot of money and hassle by sticking with a handheld.  VHF radio is basically line of sight, so with a low antenna the maximum communication range is limited by the radar horizon and not power of the transmitter.  To check the VHF coverage where you will be sailing, go here:  https://www.navcen.uscg.gov/?pageName=mtNds  Note that the Rescue 21 system is designed to provide communications with a 1 watt transmitter with antenna height of 6 meters out to at least 20 nm off shore.  1 watt corresponds with the low power setting on most hand-held VHF units.   You may also want to read this: https://www.westmarine.com/WestAdvisor/Selecting-a-VHF-Handheld-Radio.  One final note is that VHF radio can be completely useless in many inland areas, like where I boat/sail/kayak in central Florida.  There is no USCG coverage and very few other boats equipped with VHF.

 

4

Capt Skully and Mark

So many thanks!!  Great ideas all; very much appreciated...I'm on it!  BTW Mark, I'll be using the Pocketship in the northern Chesapeake Bay primarily so concern here is diluted thanks to your/Cpt Skully's suggestions

Jimmy V 

 

5

We have a VHF antenna mounted at the masthead of our Menger 19 catboat.  The cable runs down through the aluminum mast, out the base of the mast in the tabernacle, and to a connector in the foredeck near the mast tabernacle.  From thence the wiring is run behind the hull liner to the aft cabin bulkhead.  We have no built-in VHF radio set, but I use the masthead antenna when I want to extend the range of handheld VHF units, for which purpose it works really well.

.....Michael

6

I've had my ham radio license for almost 40 years and been asked by friends to help them fix their transmitter installations for most of that time. Usually it's been along the lines of adding more power because they didn't have enough range. In all those years, I've never had to add more power to get them the range increase that they wanted. The problem was always in the antenna system/installation.

First, as the folks above mention, get that antenna as high up as possible.

Next, get/make an antenna  that's optimized for the band you're operating on. Otherwise, it's just going dissipate the radio energy as heat. A good antenna doesn't need to be expensive. I made one that I was able to contact the Mir space station with out of coat hangers. See the ARRL Amateur Radio Handbook for designs and instructions.

Then, there's the coax and the connectors. For many people that's just an afterthought, like an extension cable. The wrong choices here can easily eat up 3/4 of the power coming from your radio, effectively turning your 10 watt transmitter into a 2.5 watt device. Use the highest quality coax and connectors you can afford. You really do get what you pay for. Buy them through a radio distributor instead of a marine supply place so that you're paying for the quality and not the "marine" markup.

Next, match all the impedances. If the radio has a 50-ohm output, use 50-ohm coax, connectors and antenna. Same for 75-ohm. Unmatched impedances will cause the radio energy to bounce around in the antenna system, eventually dissipating as heat. If too much is reflected back into the transmitter, it can be damaged or it may automatically reduce the power to avoid damage. Either way, it's not going to be getting out to the other boats where it's needed.

You can go the extra mile and install matching networks between the antenna and coax and coax and radio to get a perfect end-to-end match. That way you'll end up losing almost no power and your transmitter will operate full power.

Now that you've spent all this time, money and trouble - protect it. Make sure that everything is watertight and weatherproof. It should not be bothered by a knockdown that puts the masthead into the water. It should stand up to a driving rain and and all-day fog. It should be protected from fresh and salt water, as well as sunlight and bird crap. Spots of corrosion can act as non-linear mixers with the result that instead of transmitting on the marine bands as you intend, you'll be accidently transmitting on the aircraft bands as well. Not only will your signal to the Coast Guard be weaker, you could be covering up air traffic control instructions to a plane. So make sure that there's no corrosion in the system, ever.

By making your sysem this efficient, you can get away with a low-power transmitter, especially in the VHF bands. Not only can you use a hand-held, as Michael does, but you'll be able to run it on low power. It also works both ways - a good transmit antenna is a good receive antenna. You'll be able to hear weaker signals more clearly.

So, my advice is to spend the money on the antenna system and save it in the transmitter and power system.

Have fun,

Laszlo

 

 

7

As an example on the opposite end of the spectrum.  When sailing my 12' Passagemaker in salt water between the islands of the PNW, I have a waterproof, floating, 6W handheld VHF clipped to my lifejacket on channel 16 with me at all times.  I'm also constantly updating my mental chart so if I have to tell the USCG where I'm at, it'll be withing a few hundred yards.  This means doing your homework and knowing your local geography.

8

"Amen" to Laszlo's remark about improved receiving with a better antenna.  When we've been blessed to have Virginia Mae down in our happy place around Cape Lookout, NC, I remember having no trouble picking up the National Weather Service VHF weather from KEC84 out of New Bern when we were anchored down in the Bight near the lighthouse, a distance of over 40 miles, with the marine VHF handheld hooked up to her masthead antenna.  Without the masthead antenna, it was iffy, at best, as a look at the NWS coverage map would suggest.  Even up near Morehead City or Beaufort, it is a marginal business to get decent weather radio reception with a handheld VHF or an ordinary landlubber's weather radio.  With the masthead antenna, I was able to pull in some of the neighboring signals, as well.

.....Michael

9

Our handheld ICOMs and Standard Horizons both specifically warn against connecting to external antenna. Legal or electronic limitation?   

10

Probably a little of each. As long as the signal meets FCC spectral purity requirements, there's no law against using an external antenna on the marine bands. As long as the antenna system impedances are correctly matched to the transmitter, there's no technical harm from using an external antenna (as long as you disconnect during lightning storms).

But as soon as you hook to an external antenna, the manufacturer has lost control of the system. They can get into all sorts of PR and legal messes about warranties, interference, etc., so my thought is that they say "No" to cover their sterns. That way they are not responsible for the problems cause by a poorly designed, built or maintained external antenna system.

Laszlo

 

11

My son, who is knowledgeable about radio stuff and a licensed ham operator, gave me some sort of adapter cable for connecting the handheld to the masthead antenna to handle whatever electrical mismatch that might have entailed.  He assured me that, since the arrangement did not boost the output power, I was not breaking the law by do doing.  Not my area of expertise, I'm afraid.  As Laszlo suggests, we don't leave it connected during electrical storms.  In fact, we don't leave it connected at all unless we are trying to hear from or speak to a station far away.

.....Michael