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ContinuousWave: Small Boat Electrical
VHF Marine Band Radio Shore Stations
|Author||Topic: VHF Marine Band Radio Shore Stations|
posted 12-06-2005 11:07 PM ET (US)
I am aware of both the legality and controversy over operating a vhf radio from shore. Most fishermen here in Guam who spend any amount of time on the water have base stations. Usually, they are nothing more than an old radio they took out of their boat and an 8-foot antenna clamped to the side of their house as high up as they can get it. There are a variety of reasons why people do it here (and why the FCC does not enforce the law) but the bottom line is personal safety. It is just one more backup "system"
Leaving the ethics and legalalty aside, who has operated a makeshift vhf base station and what was the best setup? I am particularly interested in a power source other than a 12v battery:) Is it an "inverter" I need to convert AC to DC?
posted 12-06-2005 11:17 PM ET (US)
An inverter goes from DC to AC. You want the other way
around. You want a DC power supply that will generate a
nominal 12V at at least 6A, preferably about 10A. That
nominal 12V is probably more like 13.2V really. The exact
amperage requirement is a function of the radio, but some
head room will be good. Those little wall wart transformers
from Radio Shack won't cut it on TRANSMIT. They would be
fine for receive, probably.
Put the antenna as high up as possible. A big 9 dB antenna
posted 12-07-2005 01:04 AM ET (US)
Buy a small lawn tractor battery to power it, and connect a battery maintainer to it. This way you won't have a buzz when you transmit.
posted 12-07-2005 07:21 AM ET (US)
Thanks for the ideas guys.
posted 12-07-2005 08:52 AM ET (US)
Here is something like what I use
posted 12-07-2005 09:03 AM ET (US)
We have had an effective "base station" at our remote camp in the North Channel of Lake Huron for many years, an old boat VHF in the cook cabin with an 8' whip antenna mounted on a 50' single-pole tower held in place with guy wires. We have used both the power supply Chuck describes and the battery arrangement CC25 describes. There is less buzz with the direct battery connection, but for other reasons too complicated and insignificant to explain here, we usually use the power supply. Only rarely is the interference strong enough to be any kind of a problem.
posted 12-07-2005 09:11 AM ET (US)
The battery plus trickle charger approach is workable. If you have distorted modulation on transmit when operating from a 115-Vac power supply, your power supply is not very good.
Use a larger diameter and lower loss transmission line to connect the radio to the antenna, particularly if there is more than 20-feet between them. A half-inch diameter coaxial cable like RG-8/U will have much lower loss than the small stuff commonly used on a boat.
posted 12-07-2005 10:08 AM ET (US)
Forgot about the cable. I don't know for sure what we have is what JimH describes running between the radio and the antenna, but it must at least be close. It is *much* larger than the cable in your boat, and could very well be 1/2". I would guess there is a 75' lateral run to the base of the antenna and another 50' in height, so we've probably got a cable that is about 125' long in total.
posted 12-07-2005 10:09 AM ET (US)
My experience is that a lot of battery chargers, especially the higher tech ones, use a chopper power supply, or chopped sine wave output which adds a tremendous amount of electrical noise. This overloads the radio and prevents reception of week signals. The cheap chargers use poorly filtered AC current which add a 60hz hum to the receiver audio. A better alternative is a 12 volt power supply especially designed for radios. You can find some nice inexpensive regulated and adjustable supplies from a company called MFJ, which markets to amateur radio operators and hobbiests. Such a supply will not add electrical interference into the radio which comes out as background noise during reception. BillS
posted 12-07-2005 01:54 PM ET (US)
I concur with BillS. I use a MFJ switching power supply to run a whole host of different radios and I have never had any problem with interference from the power supply.
Try this link to see more about the MFJ power supplies.
posted 12-07-2005 04:28 PM ET (US)
Height is everything in a VHF antenna. My place on the shore is 100' up on a steep rise. I found that a 5W handheld with its little 6" antenna works so much better from up there as a shore station that it does down on the boat. It's a very simple solution.
posted 12-07-2005 09:14 PM ET (US)
Thanks for the loads of info and variations on how to hook things up. I'll likely go the power supply route to keep transmission clean. I think with the antenna installation I have in mind at home, we should be able to get about 10-12 miles of range and we do most of our fishing in the 10-15 mile out range. This is more for the wife's peice of mind but its also a plus being able to monitor the fishing reports in the morning while having that first cup of coffee. Also, as Chuck points out, being able to assist another boater in distress in this small, tight-knit community is very satisfying.
posted 12-08-2005 12:21 AM ET (US)
Here is a vendor of coaxial cable who has information on sizes and attenuation. For best performance, use something like BELDEN 9913:
posted 12-08-2005 09:59 AM ET (US)
Regarding my earlier comments in this thread about "buzz" or "hum" present when operating our base radio from a power supply, it has been suggested (and very well could be so) that the background noise was not coming from the power supply but from the generator behind it. We are not on the grid up there and anything electrical (including the power supply) is supplied power from a 6.5 KW diesel generator.
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