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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 11-28-2006, 03:18 AM   #1
JGMM_BC
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Question Lets talk antennas...

So here is my question... I have seen many planes that have the receiver antenna streaming in the wind behind the aircraft. I have also seen many ‘scale’ planes that have no antenna’s showing and in build pictures the antenna is laced into the wing or fuselage.


What are the pros and cons of each setup? Does having the antenna streaming full length behind the plane really give you that much better range as opposed to snaking it through the wing or fuselage?

Thanks!

John
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Old 11-28-2006, 06:00 PM   #2
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Most RC receivers are set up to use an antenna that is 39 to 41 inches long. The LC circuitry inside the receiver is adjusted to make this approx. 1 meter long antenna efficient at the designed frequency. This is done for nearly all brands and all frequencies from 27 MHZ through the 72MHZ range. If you google RC-Cam you will find some interesting tests where antenna length is delved into quite deeply. You will aso find some advertisments where shortened antennas are touted and sold. While many of these work well, there is a loss of range wheather the manufacturers admit it or not, it is just that most of the better receivers are still performing well with the reduced signal input from the foreshortened antennas.
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Old 11-29-2006, 12:32 AM   #3
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in scale planes i use this http://www.allerc.com/product_info.p...products_id=10

with a berg RX and plastic/balsa fuses i've always had good results.

only con for me so far is that they cost $10, oh and i always have the antenna setup in the back part of the fuse, ie away from the ESC, BEC, servos and motors. i tape them down so they don't move around.

ps these are a must on Heli's and 3D planes....
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Old 01-19-2007, 08:44 PM   #4
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Here is what I use!!!!


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Old 01-19-2007, 09:59 PM   #5
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To answer the question actually asked....it is the physical length of the antenna that is important. It doesn't much matter if that length is presented in a straight line out back of the plane or if it travels up and down a wing etc. It shouldn't touch or cross over itself but that's about all.

Steve
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Old 01-19-2007, 11:34 PM   #6
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Slipstick said it right. It's the physical length. The antenna is actually part of the load of the TX/RX circuitry and should be 1/4 wavelength of that frequency. An antenna can be shorter than the 1/4 wavelength if it is "loaded" to appear to the TX/RX that it is 1/4 wavelength. The higher the frequency the shorter the antenna. On a RX the antenna will pick up the signal radiated from the TX and induce a current in the antenna wire. This current will cause the wire to produce a magnetic field that will be picked up by adjacent wires. So long as the distance between the adjacent wires is not a multiple (in this case read that as a fractional multiplier) of the 1/4 wavelength there is no problem. If it is it can either multiply the received signal or cancel it. The odds of wrapping your antenna in a way that puts it in one of these multiples is very slim.

More important is the orientation of the "E" and "H" fields of the TX and RX antenna. In short layman's terms if the transmitting antenna is vertical (in relationship to the earth) the receiving antenna should also be vertical for the best possible reception. In our planes that fly in all orientations this is impractical so the TX power/RX sensitivity is designed to avoid this issue. However its a nice piece of information to know when dealing with TV, CB, Ham, Phone and other antennas.
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Old 01-20-2007, 12:08 AM   #7
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The other quite interesting thing to know about Tx antennas particularly is that you get best range with the Tx antenna sideways on to the model. The worst possible range is with the tip of the Tx antenna pointing at the model.

If you normally fly with the antenna pointing at the model and you lose signal you're very likely to get it back if you raise the Tx and orient it so the antenna is at 90 degrees to the model.

I'm always a bit surprised how many people don't know that....but then I've saved of couple of people's models just by taking the Tx off them and holding it correctly so perhaps I should have kept quiet and maintained the mystique .

Steve
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Old 01-20-2007, 01:06 AM   #8
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Originally Posted by slipstick View Post
The other quite interesting thing to know about Tx antennas particularly is that you get best range with the Tx antenna sideways on to the model. The worst possible range is with the tip of the Tx antenna pointing at the model.

If you normally fly with the antenna pointing at the model and you lose signal you're very likely to get it back if you raise the Tx and orient it so the antenna is at 90 degrees to the model.

I'm always a bit surprised how many people don't know that....but then I've saved of couple of people's models just by taking the Tx off them and holding it correctly so perhaps I should have kept quiet and maintained the mystique .

Steve

It surprises me as well sometimes. The antenna radiates along the length of the shaft in a 360 degree pattern. The tip is weakest point in the field.
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Old 01-23-2007, 03:22 PM   #9
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What are the pros and cons of each setup? Does having the antenna streaming full length behind the plane really give you that much better range as opposed to snaking it through the wing or fuselage?

Thanks![/quote]

I mount most internally usually along the inside of the fuz with no problems. Where problems may occur is shielding from carbon fibre, which is commonly used in construction of composite glider fuselages these days, then I go external.

The range test, conducted at the field is essential and will normally warn you if there is a problem!
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Old 02-16-2007, 11:06 PM   #10
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On one of my RC boats a RC Laser, the antenna is wound and stuck around the 'hatch' This is a common thing that is done on this 'class' boat.
OK it works, and I know that normaly boats do not travel as far away as aircraft.
I feel that when the antenna is wound like this it becomes an helical antenna or maybe it is 'loaded'.
Which some antennas can be to shorten them.
But before someone tells me, I know you cannot beat a 1/4 or if possible a full wave antenna.
It is an interesting subject antennas.
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