Replace broken 2.4GHz transmitter antenna wire?

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Replace broken 2.4GHz transmitter antenna wire?

Postby JensR » Mon Feb 28, 2011 1:56 pm

Dear all,

as I wrote here (sorry for cross-posting, I think me posting this in the review section was a bit stupid):
viewtopic.php?f=6&t=164&p=6132#p6132
I am currently modifying two Turnigy 9x transmitters and I broke the 2.4GHZ antenna wire.

I found this DIY:
http://azureengineering.blogspot.com/20 ... e-mod.html
So could I just get a replacement antenna of suitable length, cut off the plug they typically have and solder the wires of the coax cable to the same spot on the module?


Like these ones:
http://2.4ghzantenna.internetfreeblogho ... sm-review/
http://www.wonderlandmodels.com/product ... r-antenna/
http://www.fast-lad.co.uk/store/spektru ... -1916.html

Some things I should mention:
I am not interested in huge range, 50m would be more than enough.
The plastic thing supporting the antenna wire is still in one piece.
I have trouble even seeing the two solder points, so would ask some colleagues for help when soldering...

Thanks very much for any help.
I did quite a bit of searching, but most stuff I found was receiver soldering and I am not sure how different this is on the transmitter end.

Cheers
Jens
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby RCModelReviews » Mon Feb 28, 2011 9:29 pm

Unfortunately I couldn't see the link you referred to - can you post a picture here?

Any 2dBi 2.4GHz antenna should work, especially if you're only looking for 50m range. In fact, to get that range you could simply solder a 22mm length of stranded (insulated) wire to the transmitter board where the center of the antenna wire used to go and it'd work.
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby JensR » Mon Feb 28, 2011 9:56 pm

Thanks very much Bruce!

There are still around 2 inches of coax wire attached to the board - would that maybe work for my use?
I found some reports (not of the 9x) that said that without an antenna their module was fried.
(That's why I didn't just try it - I did not want to break even more...)

Are the 22mm a precise science? Or could it be 25mm, too?

The first link I meant to post was
http://azureengineering.blogspot.com/20 ... e-mod.html

Thanks again
Jens
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby RCModelReviews » Mon Feb 28, 2011 11:26 pm

If you're going to use the wire that's still attached, peel back the outer insulation and screen for a length of 22mm so that the inner wire is exposed (but leave it's insulation on). That will produce a 1/4wave antenna that will work just fine. Make sure it's not going to touch onto anything though and try to keep the end away from the circuit board.
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby JensR » Tue Mar 01, 2011 1:50 am

Ah, of course. Speed of light divided by frequency gives wavelength #duh#
Thanks Bruce!
(
But shouldn't it then be closer to 125mm/4 then?
3e11mm/s / 2.4e9 Hz = 125mm
)

This sounds as if it is worth a try (even with my limited skills).
I am sure I can route the antenna so that the exposed end does not touch anything apart from the inert plastic parts.

Best wishes
Jens
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby RCModelReviews » Tue Mar 01, 2011 1:58 am

Yes, you're right -- it should actually be (3e11/2.44e9)/4 = 30.75mm (duh). :-)
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby Allan Warner » Tue Mar 01, 2011 1:14 pm

Thats for free space. Slows down in a conductor.
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby JensR » Tue Mar 01, 2011 3:37 pm

True.
http://en.wikipedia.org/wiki/Speed_of_electricity
""
Propagation speed is affected by insulation, such that in an unshielded copper conductor range 95 to 97% that of the speed of light, while in a typical coaxial cable it is about 66% of the speed of light.
""
However, with the last tip being the "real" antenna and non-coax (if I understand that properly), would we expect like 95% of the vacuum speed?
Meaning 30.75*0.95=29.2
Or would it still be 66% of the vacuum speed?
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby RCModelReviews » Wed Mar 02, 2011 12:23 am

Just trim it for minimum SWR :-)
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Re: Replace broken 2.4GHz transmitter antenna wire?

Postby JensR » Wed Mar 02, 2011 12:42 am

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

Umm. Yes, Sir, yes! :D
Probably only need a brief introduction into high-grequency osciloscopy and I'm set?

Nah, I'll do it MechEng style: trim 22mm first and then peel off successively more of the outer mesh until I get a range that is satisfactory. ;)
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