Groundplane? - Fiberglass RV


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Old 03-30-2008, 04:47 PM   #1
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I have a little automotive FM antenna for the stereo mounted on the Burro, but the reception leaves something to be desired. Here is where I'm totally lost: fiberglass is not like metal-bodied cars, so does it make a difference to the reception? Should the ground of the antenna be connected to something in addition to the radio? How do the Corvettes do it?

If there should be some kind of "ground plane" would the foil of the insulation be useful to connect to or am I misunderstanding the whole thing?
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Old 03-30-2008, 04:59 PM   #2
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Ground Plain is important when you have a transmitter however I don't think it has much to do with receivers. Most antenna elements simply reflect the signal to one small element of the antenna.

Your receiver should be grounded through the AC or DC power connection.

On a home receiver there are 2 wires that plug into the receiver and they go to a loop antenna. No place to connect to a ground plain.
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Old 03-30-2008, 05:33 PM   #3
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You could ask at a marina store about options as they use them all the time with FG hulls and sailboats. I did connect my FM antenna, on our boat, to the bow rail to act as a ground plane and got extremly better recption. Perhaps a temporary connection to your frame will let you know if it will make a difference.
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Old 03-30-2008, 10:19 PM   #4
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A note about receivers and Scamps -- The foil insulation has an reducing or shielding effect on an antenna inside the egg, be it a receiver only or a transceiver (wifi, cell, etc.).

As Darwin pointed out, a ground plane is more important with a transmitter than a receiver, but it does help. This is a case where the marine world doesn't help much, because a boat will typically get a ground plane for its antenna from a special alloy plate mounted on the hull in the water.

Dyna-Plate
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Old 03-31-2008, 11:41 AM   #5
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I have a little automotive FM antenna for the stereo mounted on the Burro, but the reception leaves something to be desired. Here is where I'm totally lost: fiberglass is not like metal-bodied cars, so does it make a difference to the reception? Should the ground of the antenna be connected to something in addition to the radio? How do the Corvettes do it?

If there should be some kind of "ground plane" would the foil of the insulation be useful to connect to or am I misunderstanding the whole thing?
Without a ground plane you only have half of an antenna so reception will be pretty dismal.

Using the foil insulation for a ground plane could work if you can make good connection to the metal in the insulation. Some insulation has a plastic coating on the metal which will, of course, render a connection ineffective.

I would suggest connecting at least one 1/4 wave wire to the base of the antenna. More is better up to a point. Just clip the wire on temporarily to test it before making major modifications. You should see a big difference in reception.

Another possibility is copper or stainless steel tape. I've seen some antennas on fiberglass ambulance roofs with an X of thin copper tape on the inside where the antenna mount penetrates the roof with the antenna base at the junction of the X. Again, about 1/4 wave for each leg will work fine. You can get the stainless steel tape at auto parts stores.

Aha! The next question would be "How long is 1/4 wave?". An FM radio signal at 100MHz has a wavelength of 3 meters so 3/4 meters (about 30") would be 1/4 wavelength.

Ready. Set. Tinker.

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Old 03-31-2008, 02:53 PM   #6
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While this is still a mysterious subject, your answers do shed some light on it. Orlen, I think you may be onto something here and some quick experimentation may be in order. Thanks, everyone.
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Old 03-31-2008, 06:23 PM   #7
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Here's a DIY that you could mount on a piece of PVC:

http://www.geocities.com/tomzi.geo/antenna/antenna.htm
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Old 03-31-2008, 07:34 PM   #8
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Antennas are most complicated to say the least. They are still inventing new antennas every day. A close friend of mine has a radio-jamming device that the military is using to stop IEDs and he contributes its success to the antenna he invented.

The following sites give u more than you would ever want to know about them:

http://en.wikipedia.org/wiki/Ground_plane

http://www.electronics-tutorials.com/anten...enna-basics.htm

http://electronics.howstuffworks.com

I can tell you that the ground plane on a transmitter will shape the direction the antenna will transmit and that on a short-wave radio, the antenna should be cut to the correct length and the antenna "Loaded" to get optimum performance. (Collins KW-M2)

On a radio receiver only, a proper length antenna gets optimum results.
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Old 03-31-2008, 08:06 PM   #9
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One thing I wonder is what type of radio are you using? If it is car radio the antenna and the radio are grounded to one another through the body of the car.
If it is not a car radio then there needs to be two seperate leads from the antenna to the radio I imagine.
You said you are using an automotive antenna? With that type of antenna the tip of the connector is one lead and the body that slides into the car radio connector is the other lead.
If you are adapting this to a non-auto type radio,the antenna may not be fully connected to the antenna input which also has a two lead connection.

I can not think of a reason an adequate ground plane would be determental and it should be a simple matter to fashion one from almost any conductive surface.
Baking sheets or Pie Plates are commonly used in amateur radio circles for a ground plane but any metalized tape would work well too as others have suggested.

A radio and antenna are a system though so it will help to further understand the setup.
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Old 04-01-2008, 09:14 PM   #10
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I went to my handy dandy HAM radio class and all I can say to this conversation is ... hmmmmm.

Brain leaks. Bad.

Paula
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Old 04-01-2008, 09:47 PM   #11
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I went to my handy dandy HAM radio class and all I can say to this conversation is ... hmmmmm.

Brain leaks. Bad.

Paula
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Yeah I don't remember my standing wave math either.
Doug KC0EDT
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Old 04-01-2008, 10:00 PM   #12
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Yeah I don't remember my standing wave math either.
A link on the first of Darwin's nifty links leads one to this quarter wave GP antenna calculator:

http://www.csgnetwork.com/antennagpcalc.html
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Old 04-01-2008, 11:23 PM   #13
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Thanks for that chart. I need tools like that.

I want to eventually put in a HAM setup in my camper to help with search and rescue stuff when I am "out of county". I guess I could trot "down the hill" to Orlen and bug him, but since he doesn't know me that might be kind of presumptuous, eh?! Actually, I have folks that can help me up here. But, can I still bug you Orlen?!

Paula
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Old 04-02-2008, 06:48 PM   #14
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"I want to eventually put in a HAM setup in my camper to help with search and rescue stuff when I am "out of county"..."
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Just don't get bitten by the Ham Bug as bad as me, otherwise your dinette table
will look like this...
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Next to Camping, Ham Radio is the best hobby I've ever found... fun and a valuable community service.
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