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-   -   Antenna Length on 2.4GHz (http://www.rcuniverse.com/forum/rc-radios-transmitters-receivers-servos-gyros-157/10094483-antenna-length-2-4ghz.html)

fwilson 10-25-2010 10:57 PM

Antenna Length on 2.4GHz
 
I have an Art-Tech 2.4GHz receiver that the antenna has been cut off. Anyone know how long it should be? It is now about 1/2 inch or so. I know people who fly FM seem to want to shorten the antenna, but will it work to lengthen it? I noticed the antenna was cut after the second repair job, and I would like to avoid the third one.

Thanks

Fred

dirtybird 10-26-2010 03:06 PM

RE: Antenna Length on 2.4GHz
 
Its about 2.5cm

Here is how to calculate the wavelength:

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

The antenna should be 1/4 of the wavelength

Rodney 10-26-2010 03:31 PM

RE: Antenna Length on 2.4GHz
 
2.4GHz antennas are quite a different animal than those for the 72, 75, 35, 50 and 53 MHz units. They are sometimes only a 1/4 wave stub right on the PC board or more often, a 1/4 inch stub on the end of a 50 ohm coax line which can be several centimeters long. If on the end of a coax, you need to be somewhat careful of how you handle that coax; no sharp bends or anything that will dent or deform the line between the receiver and that little bitty antenna at the end.

Zor 10-26-2010 05:39 PM

RE: Antenna Length on 2.4GHz
 


Quote:

ORIGINAL: dirtybird</p>

Its about 2.5cm</p>

Here is how to calculate the wavelength:</p>

http://en.wikipedia.org/wiki/Wavelength</p>

The antenna should be 1/4 of the wavelength
</p>

Using dirtybird posting to comment for all readiers.</p>

My Spectrim DX7 receivers R7000 have antenna lengths of 1 /1/8 inch sticking out of their case.</p>

Some of the antenna lengths are partly inside the case.</p>

I believe those antennas are half wave long end to end which would include any lenth inside the case.</p>

I measure end to end _ _ _
Main Rcvr ............ 3 1/16 inch ( 77.7875 milimeters)
Satellite Rcvr ,,,,,, 3 1/16 inch ( 77.7875 milimeters)</p>

I did not do any mathematics.

Perhaps these dimensions can be useful.

Zor
</p>

dirtybird 10-26-2010 10:10 PM

RE: Antenna Length on 2.4GHz
 
A full wavelength of 2.4GHZ is 12.5 cm.
A 1/2 wavelength is 6.25 cm
77 mm is two long for a 1/2 wave antenna. I believe what you have is two 1/4 wave antennas. One sticking out each side.

Zor 10-26-2010 10:37 PM

RE: Antenna Length on 2.4GHz
 

Quote:

ORIGINAL: dirtybird

A full wavelength of 2.4GHZ is 12.5 cm.
A 1/2 wavelength is 6.25 cm
77 mm is two long for a 1/2 wave antenna. I believe what you have is two 1/4 wave antennas. One sticking out each side.
Hello dirtybird,

You are making me do some thinking.
From your figures then a 1/4 wavelength would be 6.25 / 2 = 3.125 or 3 1/8 cm.
This is 1.23 inch.

My measurement quoted earlier was 1 1/8" (1.125 ) stiking out of the case on each side.
So I agree that each wire is just about 1/4 wavelength.

Now ___Would these two wires radiate in phase?
If they do which is what I think then it would be equivalent to a half wave antenna radiation.
Would it not ?


Zor



dirtybird 10-27-2010 02:40 PM

RE: Antenna Length on 2.4GHz
 
They would be equivalent to a 1/2 wave antenna provided they are not connected together and were driven from a separate source. If they were connected together it would result in a loss due to mismatch. You could eliminate the mismatch with coils but I don't why you would do that when all you need to do is shorten the wire.

Zor 10-27-2010 04:42 PM

RE: Antenna Length on 2.4GHz
 
<span style="color: #ff0000">Hello,

This will likely be my last posting on this topic.
</span>
Quote:

ORIGINAL: dirtybird

They would be equivalent to a 1/2 wave antenna provided they are not connected together

<span style="color: #ff0000">They certainly are not connected together to form a straight wire having nearly 3 inch in length.
I think that is quite obvious; however they are connected to a common source of supplied energy that generates the modulated 2.4 gigahertz.</span>

and were driven from a separate source.

<span style="color: #ff0000">They are driven from a common source as mentioned above.and are in phase; thus the radiated field is identical to a dipole.</span>

If they were connected together it would result in a loss due to mismatch.

<span style="color: #ff0000">I tried to open the satellite receiver to look inside (2 small screws). I was not successful due to some binding at the antenna wire end of the case. The case would open only about 10 degrees and I did not want to force it. So I could not see inside.

Now imagine that between the two wires that are coming out of the case, there would be inside the equivalent of a half wave lengh voltage fed as a coupling for the energy. There would be no mismatch.</span>

You could eliminate the mismatch with coils but I don't why you would do that when all you need to do is shorten the wire.

<span style="color: #ff0000">We obviously do not have a shorter wire. The reason being that some method of feeding two 1/4 wave in phase has to exist. I was hoping (by opening the cse) to see how it is done. Perhaps some day I will say "the hell with the warranty and will open that case. That would be for my own satisfaction. Who else care about this kind of thing. It works, just use it. LOL .</span>
Thanks for your comments and the postings.

Zor.


Skinny Bob 09-13-2013 10:49 AM

I have the Tatic tt650 2.4 system with standard receiver, can I increase the antenna length to 1/4, 1/2 etc wave length to increase range while I'm waiting for my back ordered twin antenna receiver to arrive?

Bob

Rodney 09-14-2013 08:09 AM

The length of the antenna on a typical 2.4GHz receiver is 28.8 to 32 mm long, most are about 28.8 mm. The antenna is that length of bare line often at the end of a longer coaxial cable to move the antenna farther out from the receiver. Yes, the length of this is somewhat critical and can greatly vary the distance that the signal can be reliably received. To long can be just as bad as to short unless you can accurately make sure it is some odd multiple of an electrical quarter wavelength; i.e. 3/4, 5/4, 7/4 etc. Note that electrical wavelength can be different than a simple measurement as it depends on the velocity factor of any coax or other line involved.

Skinny Bob 09-14-2013 09:00 AM

Thanks Rodney, the 650 receiver's range is limited to about a 1000 ft. I lost control of my Cub when it went past that distance. I have the twin receiver on back order, late Oct., Bummer. Oh well, it's getting late in the flying season, next year. I don't know if I want to experiment with antenna length or not.

Bob

chuckk2 09-20-2013 10:15 PM

It might be useful to remember that the 2.4Ghz RC band goes from about 2.4Ghz to 2.485Ghz when considering antenna length.
There is also a propagation factor that enters into things.

LesUyeda 09-21-2013 06:46 AM

"There is also a propagation factor that enters into things."

And the formulas given for wavelength are given for free space, and since there is no such thing in reality, various "fudge factors" must be incorporated, like propagation factor, physical dimensions of conductors, etc, etc, etc,.

Les

JPMacG 09-21-2013 07:32 AM

A convenient formula for those who use inches is: wavelength = 11.803/GHz.

Half-wave dipoles and quarter-wave monopoles/sleeves are actually slightly shorter than their names. A resonant 1/2 wave dipole is a few percent shorter than a half wavelength. The amount that it is shorter depends mostly upon the diameter of the wire and the frequency.

My recommendation regarding replacement of a 2.4 GHz Rx antenna is to find an identical model and make your antenna look just like that one's antenna. Or, send it back for repair.

chuckk2 09-21-2013 09:05 PM

Since the 2.4ghz band spans .085Ghz the receiver antenna length isn't as critical as you might think!
However, I'd likely use a length that has the lower part of the band optimized.
Receivers are not a critical as transmitters.


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