VHF FM Radio Antenna question

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Kelly Hanson East
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VHF FM Radio Antenna question

Post by Kelly Hanson East » Sun May 10, 2009 8:43 am

Question for the Radio folks on the board

Im putting in a FM stereo into Catigale for use on cuttyhunk (10 miles off shore) and am trying to decide on best location

Part of this might be dictated by whether I have to tap into my VHF antenna (portside) to get Fm reception. I stay within 10 miles of shore, so Im wondering if I can just use one of the small deck mount or freestanding FM antennas to get reception ?

I would like to put it in starboard side over the head door, if I can squeeze in a DIN chassis there.

Could I also tap into a simple wire running up the mast to help reception (already have that from pulling a 6 wire loom up the mast for future expansion previously ?

What say the Hams..??

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Trouts Dream
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Re: VHF FM Radio Antenna question

Post by Trouts Dream » Sun May 10, 2009 9:23 am

Excellent question
I am looking at running a line to the mast top and installing dual use antenea so i am curious what I need.
There was a great mod posted recently where the antenea is flipped down istead of trying to remove it for trailering that helped me decide this is the way to go

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RussMT
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Re: VHF FM Radio Antenna question

Post by RussMT » Sun May 10, 2009 11:40 am

I'm no expert, but as I understand it, FM requires a specific length of antenna for reception. I think 33 inches is the middle of the FM bandwidth. Too short or too long and it doesn't work as well. Smaller antennas coil the lead to effectively create the correct length.
Therefore, a wire (or even your mast) may work but only if it's the correct length.

Our dealer installed a dipole antenna inside the cabin. It worked okay, but just okay. The other problem was reception faded as the boat turned.

Since with VHF/FM height matters, I opted for a masthead antenna like this one. The mod mentioned above is clever, but I just unscrew it and flip it 180 degrees and screw it back on to trailer it.
I then installed a splitter like this one. I know that splitting coax and adding connectors reduces efficiency but I'm okay with a little loss, especially since I'm gaining altitude. The FM reception was a LOT better as was AM. I don't notice any VHF loss although I'm sure there is a little.

There are many debates over masthead vs. deck mounting VHF antennas. For me, we have a lot of hills and junk in the way of VHF's line of sight limitation, so masthead is for me.

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bastonjock
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Re: VHF FM Radio Antenna question

Post by bastonjock » Sun May 10, 2009 12:47 pm

i was looking at this also,there is a splitter on the market that covers VHF,FM and AIS,its set up so that the VHF is never interrupted by the FM signal,when theres a transmittion on ch16 it cuts out the fm.There was no need to run new cables up the mastthe unit uses the existing aerial and VHF cable,you just connect the FM and AIS if required along with the VHF cable into the same box.

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Re: VHF FM Radio Antenna question

Post by SkiDeep2001 » Sun May 10, 2009 2:42 pm

Here is a link for an FM signal booster by Crutchfield. I used these all the way back in the late 70'- early 80's. Worked in the city for boost so I would think on water with no obstructions they would give you a much better signal. :) http://www.crutchfield.com/S-CKLZKQFvVr ... ifier.html This is just one of many products out there so if you do a search you may find something even better like this 8X signal booster. http://www.sportsimportsltd.com/fmra8xsibo.html

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Re: VHF FM Radio Antenna question

Post by Night Sailor » Sun May 10, 2009 5:14 pm

FM signals are a line of sight signal. The higher the antenna, the farther from shore you can recieve a good signal over water.
I"ve always used an antenna splitter shared with my VHF or CB and it's worked with a variety of makes and models of antenna. I curently use on my X a 5' Shakespeare fiberglas whip mounted on my stern arch where the base of the antenna is 75" above motor well deck level and the FM reception via splitter is fine.

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Re: VHF FM Radio Antenna question

Post by Kelly Hanson East » Tue May 12, 2009 8:37 am

Im intrigued by the product reviews on the VHF FM splitter (Shakespeare, sold on both WM and Defender sites)

6 out of 8 report no improvement on FM reception, while 2 people report dramatic improvement. Im trying to decide if I should use a dedicated FM antenna or put the splitter on my masthead.

You radio guys - do you think the people who didnt see an improvement screwed up their installs??

The splitter isnt cheap - about 40 USD plus another 20 for cables all done.

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Re: VHF FM Radio Antenna question

Post by Hamin' X » Tue May 12, 2009 9:31 am

Non laboratory reception tests tend to be very subjective. As a for instance: With antenna at deck level, station A is received with much static and fading. Move antenna to masthead. Station A is heard much better, but station B is now being received and is interfering with station A. The net result is that neither station A, nor B are useful. Remember, FM broadcast frequencies are more or less line-of-sight. Sometimes, more is not better.

~Rich

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Re: VHF FM Radio Antenna question

Post by kmclemore » Tue May 12, 2009 10:31 am

I have the Shakespeare splitter and it seems to work for me... but then I've never run the radio without it! :)

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RussMT
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Re: VHF FM Radio Antenna question

Post by RussMT » Tue May 12, 2009 10:34 am

Kelly Hanson East wrote:Im intrigued by the product reviews on the VHF FM splitter (Shakespeare, sold on both WM and Defender sites)

6 out of 8 report no improvement on FM reception, while 2 people report dramatic improvement. Im trying to decide if I should use a dedicated FM antenna or put the splitter on my masthead.
That is very interesting.

One thing I noticed were that several hooked it up to an 8' whip. Very strange reviews.

I can say that mine works great attached to the 3' masthead antenna. Much better than the dipole antenna in the cabin. The device is obscenely priced as is most boat merchandise. I bet if I took it apart, there is only a capacitor or some such thing inside.

It's possible that the negative reviewers installed it wrong. It comes with the need to solder one coax connector. However, I would expect their VHF performance to drop as well. Or maybe they tossed it before testing VHF.

I just found this one. It is powered and has a pre-amp.

The more wires you have snaking up the main mast, davits or mizzen, the more potential problems there are. So an innovation which will service several pieces of electronic gear at once is at least worth considering.

Even if you had multiples of these, they could act as back-ups for each other, rather than single use antennae. Naturally, you want the reception to be unimpaired.

Italian company Glomex has recently introduced into the market the new RA201 splitter, thanks to which it is possible to use just one VHF antenna to simultaneously receive the AM/FM and AIS radio signals; furthermore, the VHF transceiver can also be used.

The company describes the splitter as 'a compact component, easy to install in any place, requiring only a 12V power supply, from which a maximum of 25 mA is drawn, a negligible current draw. It is provided with a coaxial input for the antenna and three outputs for VHF, AM/FM radio and AIS.

'Equipped with a built-in preamplifier, it ensures the usual performance of the VHF antenna installed onboard, allowing it to be used for multiple applications. This means a simpler and less expensive system.


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Re: VHF FM Radio Antenna question

Post by Hardcrab » Tue May 12, 2009 12:39 pm

I installed an amplified FM dipole antenna used in autos from Kragens/Auto Zone/NAPA ---$9.00 or so.
The 12vdc comes from the FM radio itself when it's powered up.
That's cheap enough to try it out in your location before you mount it.
Not much to lose if it doesn't work out for you.

I decided on an "auto" type radio over a "marine" type radio.
My theory is that my boat sits on the trailer, out of the salt water, much more than floating in it, lessening the need for the more expensive "marine grade" product.
It works fine for our use.

I mounted the antenna behind the daggerboard trunk mirror because I installed my AM FM CD radio in that space above the forward dinnette seat.
Pretty much self contained because I tapped the 12vdc feed for the mastlight connection there, and I hardly ever use that light anyhow.

Somewhat of a pain because I dump all the radio presets and clock when I kill the mastlight switch, but I'm into simple answers over stringing a new power wire.
Last edited by Hardcrab on Tue May 12, 2009 12:52 pm, edited 1 time in total.

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Re: VHF FM Radio Antenna question

Post by waternwaves » Tue May 12, 2009 12:45 pm

If you want the new digital hi def (read between channel) FM

Get an FM dipole of the proper length, orient it vertically, connect it to coxaial cable ( I believe the new vehicle FM systems are 75 ohm systems also), and I would definitely mount it on the mast top next time and live with the losses of a coax connector pair instead of having it inside the shower/head like the previous owner put in.

I cannot understand why people remove the shower capability fro m x boats. 8) :P :D

for example

http://store.xmfanstore.com/pixel-techn ... afhd4.html

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Scott
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Re: VHF FM Radio Antenna question

Post by Scott » Tue May 12, 2009 12:48 pm

I cannot understand why people remove the shower capability fro m x boats.
Im slow but I still dont get it?

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Re: VHF FM Radio Antenna question

Post by waternwaves » Tue May 12, 2009 1:26 pm

Scott...

The PO for my 96 X put a square D AC electrical panel in the head, along with a plastic tray parts organizer to shield the 12V bus connections, removed the sink facet, and then stuck an AM/FM CD player chassis in the head. not to mention the 50A 12 V unshielded connections for the lectrasan and sanipotty head, as well as the back of the 30A (120 V ac) shorepower without a heatshrink

Basicly he turned the head into a sitting closet .....

whereas I am changing it back into a watercloset/shower....

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Re: VHF FM Radio Antenna question

Post by SkiDeep2001 » Tue May 12, 2009 3:59 pm

Oh, he must have been one of the unwashed masses :wink: I have a 32Gigabyte Sansa mp3 player, maybe I'll just say to heck with the FM and play my own eclectic collection of music. I certainly don't need any talk show host blabber while on the water :P

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