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Permalink Reply by Andrew Fernie on September 8, 2012 at 6:08am

You should be able to replace it with another piece. I measured mine (900MHz) and the antenna length is 86mm from the top surface of the PCB at the point that it comes through the hole.    Because the wire goes down through the hole in the PCB (insulated, not soldered) then goes horizontally for a few mm before it is soldered to the pad I think that the total length is about 90mm.   I suggest that you cut a longer length and route it through the hole and solder it in place. Once in place measure the 86mm and cut it off. The attached diagram should help.

Andrew

Attachments:

• XBee900Antenna.jpg, 7 KB

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Permalink Reply by Daniel on September 8, 2012 at 7:04am

Quarter wave for the frequency's used by the 900 xBee is between 80mm and 83mm. (902 MHz-928MHz)

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DeveloperPermalink Reply by R_Lefebvre on September 8, 2012 at 7:35am

Oh really?  I used this other calculator thing, and it said 68mm?  Why are there these discrepancies?

And how come the original antenna was very much shorter than that?  It was probably 40mm.  1/8 wave?

Now, is it the total length that matters, the length that's out from the board?  ie: it comes soldered to the board, and then weaves through a hole as strain relief before emerging.  The strain relief probably loses 5mm.  Should it be 5mm longer, or exactly the same length?

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Permalink Reply by Andrew Fernie on September 9, 2012 at 5:12am

I have three of the modules. Two have 86mm length from the point it comes through the strain relief hole to the end, the third has only 80mm. Strange, but that is what I have and I don't believe that the end has been cut off.

Andrew

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Permalink Reply by Daniel on September 9, 2012 at 4:55pm

I assume variation in manufacturing.

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Permalink Reply by Daniel on September 9, 2012 at 4:54pm

Which calculator thing did you use ? I used four different ones on the web and came back with the same result.

http://www.csgnetwork.com/freqwavelengthcalc.html

http://www.wavelengthcalculator.com/

http://www.1728.org/freqwave.htm

http://www.onlineconversion.com/frequency_wavelength.htm

(http://www.mcsquared.com/wavelength.htm gives me the same result with a comma error)

Quick addon: Google Calculator

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DeveloperPermalink Reply by R_Lefebvre on September 18, 2012 at 2:01pm

Daniel, I can't remember exactly which I used.

But actually, I ended up ordering this:

http://www.nghobbies.com/cart/index.php?main_page=product_info&...

And this:

http://www.nghobbies.com/cart/index.php?main_page=product_info&...

Hoping to get a more robust antenna, and also hopefully eliminate the EMI problems caused by the airborne Xbee with the wire antenna not having a ground plane? (I don't completely understand, but I know I have severe problems with EMI when the Xbee is running and somebody said it was because of the crappy wire antenna.)

Think it will all work?

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