Antennas

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Antennas

Postby boatbobber » Tue May 17, 2011 11:08 pm

First time posting!!!
Looking for some guidence on antennas. I am working on the design of a small boat and I would like not to
have an antenna protruding through the outer the shell of the boat. Is it possible to get good range with an inside antenna???
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Re: Antennas

Postby dannyzz » Wed May 18, 2011 4:35 am

is it 2.4ghz?
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Re: Antennas

Postby boatbobber » Wed May 18, 2011 10:22 am

Yes it is 2.4ghz
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Re: Antennas

Postby kaptain_zero » Wed May 18, 2011 5:48 pm

What is the boat to be made of? Common materials for radomes include fiberglass and ABS plastic (radomes are the covers over transmitting/receiving dishes and horns). Other materials may or may not attenuate the signal, such as dry wood and some other plastics.

An antenna mounted inboard will likely be lower to the water, again risking an increase in attenuation of the signal. Most important is to have the receiver antenna mounted in the same orientation as the transmitter antenna (polarization) and vertical would be the way to go. You have not indicated what type of boat you are building... some have masts, light posts (nav lights) that extend upwards and could be made from a hollow material that could house the antenna in an elevated, vertical position without affecting signal strength.

Quoting from Astronwireless:

On line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more.

As with any remote control project, range testing will be required before the maiden voyage.

Regards

Christian
"I'd like to live as a poor man with lots of money."
-- Pablo Picasso
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Re: Antennas

Postby boatbobber » Wed May 18, 2011 6:24 pm

The boat will be injection molded abs.
The shell is completely sealed and designed to self right after it is submersed.
When I test the rx/tx on land with the wire inside the boat we are at about 150',
when we go on water it is reduced to 70'. The problem could be with the electronics,
they are proto type made in China and all I know is that they are supposed to be 2.4ghz.

I appreciate you time....Jeff
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Re: Antennas

Postby kaptain_zero » Wed May 18, 2011 9:17 pm

boatbobber wrote:The boat will be injection molded abs.
The shell is completely sealed and designed to self right after it is submersed.
When I test the rx/tx on land with the wire inside the boat we are at about 150',
when we go on water it is reduced to 70'. The problem could be with the electronics,
they are proto type made in China and all I know is that they are supposed to be 2.4ghz.

I appreciate you time....Jeff



Jeff, when you say you have the wire "inside" the boat, what is it's orientation? The antenna should be pointing straight up like a flag pole and be as high up inside the model as possible and NOT laying flat in the bottom of the boat. The latter would result in a 20db+ signal loss! Yes, there will be signal loss when you have the antenna that close to the water, so you need to orient it straight up, and do the same with the transmitter antenna. Water attenuates microwave signals quite well.... as all satellite TV viewers can attest to, when there is a heavy rain/snow storm... it can completely wipe out the signal.

Regards

Christian
"I'd like to live as a poor man with lots of money."
-- Pablo Picasso
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Re: Antennas

Postby boatbobber » Thu May 19, 2011 12:43 am

Christian, the electronics compartment is in the upper section of the boat and the end of the antenna wire is at the top of the boat.
My problem is the boat is small in size and only projects out of the water about 3". I got much better range when I used an off the shelf
Spektrum DX5 with a marine rx in my previuos proto type. Will more power help with range....Jeff
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Re: Antennas

Postby kaptain_zero » Thu May 19, 2011 1:57 am

More power can achieve greater range, but there are limits imposed on the power output of transmitters, which varies by Country. On the other hand, receiver sensitivity can be improved without flirting with the transmitters power output. In your case it sounds like one or both ends of your prototype antenna/electronics is not up to snuff and it's impossible to determine where the fault lies without physically examining and testing the devices.

You appear to have things placed correctly, so it only remains to determine if the antenna systems are working correctly, and if they are, then it must be either the receiver or the transmitter (or both) that is the cause. Knowing that the Spektrum DX5 and proper RX works, proves that the idea is valid, just not necessarily with the current (and no doubt much lower cost) proto TX/RX system.

My experience comes from Amateur radio and most of our efforts go into the receiving end, as this is the most effective way of increasing range. In the case of 2 way radio communication, it is an absolutely necessity.... If you cannot hear the other station, you cannot communicate with them.

I hope this helps,

Regards

Christian
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Re: Antennas

Postby boatbobber » Thu May 19, 2011 11:53 am

Thanks for your time and obvious knowledge. I have a clearer picture now and it appears
my problem is not so much antenna but the electronics around it....Jeff
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Re: Antennas

Postby kaptain_zero » Thu May 19, 2011 4:21 pm

Jeff, I have to quote myself and add some emphasis to the key words in that sentence. Just because you have visually inspected and determined that your RX antenna is correctly positioned, it does not mean that it is working properly. The antenna must be resonant at the frequency you are operating at for maximum efficiency. The antenna connection, transmission wire etc. etc. can all have a high impact on your RX system. You cannot ASSUME anything. You must measure/check/confirm before decided that it's this or perhaps that. In my experience, assumptions waste far more time and money that taking the time to properly test and evaluate a faulty system.... You can spend an hour at a test bench or days trying this and then trying that without ever having a clue of what really is wrong. 2.4GHz gear is all around us, but while it seems simple, it requires a great deal of accuracy in the length/diameter of the antenna element, good solid connections and the proper transmission line which, without, can ruin an otherwise well working receiver.

Even at 440 MHz where I spent 12 years operating a fully automated Satellite Gateway station, if the Satellite signals seemed to get weaker, my first suspect was the antenna/cables.... the slightest ingress of moisture into my cables could wipe out those weak signals and only by using sensitive measuring gear could I determine if the cable or connectors were compromised, and if they weren't, it was the antenna that was next on the inspection list.... The electronics came last, as they were least likely to be the problem and if they were, it was usually pretty obvious as they would just die.... not always of course, but most of the time.

This is just some food for thought.....


kaptain_zero wrote: In your case it sounds like one or both ends of your prototype antenna/electronics is not up to snuff and it's impossible to determine where the fault lies without physically examining and testing the devices.
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