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  #11  
Old 05-26-2007
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There is actually an organized "Strange Antenna Contest" running on Field Day this year, proving that light bulbs, lawn chairs, and barb wire fences can all make effective antennas. Sometimes.
I have nothing against splitters and think sometimes they are a good idea. But all considered...a car stereo works so well with a plain cheap whip antenna, or a dipole, that personally I wouldn't spend $100-150 to split it into the VHF at the masthead. And, I confess that I prefer a nice SIMPLE and robust antenna system for a transmitter, because it is always the "Oh, it can't be that, those never fail" that breaks things.
I just don't see much need for the splitter in a typical sailboat boat application, unless you really really want to use the car stereo for dx'ing.
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Old 05-27-2007
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Quote:
Originally Posted by RickBowman
If you split a signal, guess what happens? Signal loss. I left my VHF wire alone, and installed a dedicated AM/FM dipole antenna. It cost about $10.00 from an audio electronics car stereo store. I needed to install a 6 foot interference/shielded cable between the radio and the antenna as there is sufficient electronic signal/noise where the radio is installed from other electronic circuits of 12 volt and 110 volt. Then I routed the cable on top of the aluminum fuel tank where it would be out of the way.
In case your wondering, AM/FM signals go through fiberglass like it isn't even there. Great reception!
If i read this right you have your antenna for your AM/FM sitting on top of a fuel tank.Aluminum.
I am new to this so i ask do you worry about lightning strikes?How is she grounded?
Thank You
Mark
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Old 05-27-2007
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Quote:
Originally Posted by travler37
If i read this right you have your antenna for your AM/FM sitting on top of a fuel tank.Aluminum.
I am new to this so i ask do you worry about lightning strikes?How is she grounded?
Thank You
Mark

Mark,

I asked the same question, yesterday.
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Old 05-27-2007
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Quote:
Originally Posted by travler37
If i read this right you have your antenna for your AM/FM sitting on top of a fuel tank.Aluminum.
I am new to this so i ask do you worry about lightning strikes?How is she grounded?
Thank You
Mark
Umm... if the antenna is completely within the boat's interior, I don't see how it would be more susceptible or capable of incurring a lightning strike. It isn't very high off the water, if it is lying on top of a fuel tank, which is usually in the lowest part of the boat, for stability sake. Also, the fuel tank is very likely to be well-grounded, especially if it is a gasoline fuel tank.
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  #15  
Old 05-27-2007
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I bought the Shakespeare splitter and it works very well. I haven't noticed any loss in the VHF performance and the AM/FM performance was drastically improved because the antenna is now 55' higher. The splitter works through the use of electronic filters. Since VHF is an FM signal (most channels in the range 156 MHz - 163MHz) and commercial FM radio is a different frequency band (87 Mhz - 108Mhz-ish), transmitting on the marine channels will cause interference with the AM/FM stereo. Since the filter in the splitter will prohibit the marine FM signal from getting to the stereo (analogous to a check valve), it will not be fried when the marine raido is transmitting. The AM portion of the stereo is unaffected because it's a completely different type of signal (Amplitude modulated) than the Frequency Modulated VHF or stereo.

Shakespeare knows what they're doing. I'm sure that they've considered the lawsuits if they were responsible for frying radios.
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Old 05-27-2007
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"The AM portion of the stereo is unaffected because it's a completely different type of signal (Amplitude modulated)"
Not quite. The AM band used in the US is a RADICALLY DIFFERENT FREQUENCY and that makes it very easy to isolate from the marine VHF frequency.
The splitter electronic components are typically a coil and capacitor combination known as a "trap" that simply block the higher frequency marine VHF output from getting into the car radio side. Simple and reliable--but still able to fail, like any electronic parts.
Some AM radio transmitter antennas are literally 1000++ feet tall. For them, it doesn't matter if your boat antenna is at 5' or 55' above waterline. FM stations are more problematic...but they also have a way more limited range because they are comparably low power.

Shakespeare does know what they are doing--that doesn't mean the product is meaningless for the average boater. These are niche products. As to liability? Read the warranty. They've got insurance to deal with the rest. $150 for 10-20$ worth of parts leaves a LOT of room for profit.
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  #17  
Old 05-28-2007
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Good points, hellosailor. I agree that AM is radically different; I was trying to separate it from the discussion. Not having taken apart a splitter, I defer to your description of the coil and cap. I figured that something of this sort was needed (hence my description of the filters & "check valve" analogy), but couldn't precisely recall from my EE days long, long ago.

I totally agree that something could fail and have an adverse effect, but was attempting to point out that the original design is valid (though not fool proof as you correctly point out). Thanks for the clarifications.
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Old 05-29-2007
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One extra issue with splitters..

With a regular RF splitter (no extra filtering), there is an input port or connector, and two output connectors.

If I understand the application, you are using it in reverse of this, with the two radios on the output connectors and the antenna on the input port. Just to be clear, it is fine to operate the splitter like this as it can combine just as well as split.

But, in a normal splitter, there is about 20dB of isolation between the two split ports.

So if you transmitt watts into one of the split ports, the other will see a much smaller amount of that transmitted signal leaking over to it.

That is probably why the radios described in the previous posts didn't burn up.

Adding filtering in would only make the isolation higher, if needed. But it would make it much more expensive than a general purpose splitter.

*****also

I did have the same idea about combining the use of the one mast mounted antenna (sailboat). I took the VHF antenna (shakespeare) in to work and checked it out. It didn't look all that good at the FM band. I still might try it after reading some of the above posts. Also wondering about TV reception which goes down to 54MHz (ch 2). The antenna didn't look that good for TV either.

It had some spots across the TV and FM band that might work, but not the whole band.

TV band has the FM band between ch7 and 8 I think.

Somebody should make an antenna that works in all three bands.
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  #19  
Old 05-29-2007
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If you are going to use a standard radio antenna for am/fm reception make sure you get the type that requires no ground plane. Sold for fibreglass truck cabs and plastic car bodies. They usually have a coil half way up the antenna. they are worth the extra few bucks for good long range reception.Had one tucked away under the cockpit side coamings and it worked great on my previous boat. This one is a bosun chair job which \I intend to change.
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Old 05-29-2007
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Quote:
Originally Posted by sailingdog
Umm... if the antenna is completely within the boat's interior, I don't see how it would be more susceptible or capable of incurring a lightning strike. It isn't very high off the water, if it is lying on top of a fuel tank, which is usually in the lowest part of the boat, for stability sake. Also, the fuel tank is very likely to be well-grounded, especially if it is a gasoline fuel tank.
Wondered more about making a "path" to the well grounded fuel tank once the charge starts bouncing around the cabin.Was hit once and the things that fried were not what i would expect.Compass on the wheel.Wheel pully under deck.Forward bildge pump but not rear.CB radio,SSB sitting on top of it and also on was not affected.
Old pair of shorts were extreamly affected.Guessing that well paid up insurance helps.....
Thank you.
Mark
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