Tuesday, 13 October 2015

Replacement Aerial for a Taranis X9D

On Saturday, while packing up, I broke the aerial off my Taranis, I have to admit the method of assembly isn't particularly great - the aerial simply clips into the case which means to replace it you have to de-solder the coax lead off the XJT Transmitter board. This is the second aerial I have broken.
I have decided to make a proper repair - something that I think FrSky should have done in the first place.
I bought the bits from T9 Hobbysport
This was the aerial I chose to buy.

The pigtail with SMA connector (250mm)

I also bought the high gain 5dB Tx aerial

I haven't stripped it, but it looks like its a 5/8 over 5/8 collinear.

Assembly was fairly straightforward.
De-solder the old aerial using a clean and very fine pointed soldering bit
Remove the old aerial by unclipping from inside and pushing it out
As you can see, the old and new aerials are identical except for the different bases

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Fortuitously, the SMA connector is a perfect coaxial fit inside the hole vacated by the old aerial
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The nut is only used to centre the connector. Screw the aerial fully into place and then screw the nut up so that it 1/2 thread adrift
When happy with the fit, solder the shortened pig tail to the Tx board. You will need to cut to length, strip the outer sheath and then solder/tin the coax outer. Cut the inner so that the dielectric is about 1-2mm longer then another 0.5-1mm of inner which is very carefully tinned and soldered to the track

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Not brilliant soldering, but before proceeding check that there are no shorts. There are 2 ground pads in the photo both are linked to the ground plane. The original lead is soldered between them, its slightly easier just to use one as I have done.
Check for connectivity for the inner to the pin in the pigtail SMA. If all OK proceed.
I simply epoxied the connector into the Tx casing hole
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and checked that the aerial will screw in fully..
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It does!
Obviously, I need to test it but I am not expecting any problems or change in directivity.
The high gain aerial will be interesting. To get gain, you need to sacrifice directivity. When aerials are stacked - if this is a collinear, lobes will form and also associated nulls. So in addition to the normal nulls off the end of the aerial you will get nulls out in the general direction (usually about 30 degrees out) of maximum radiation.
Not sure I'll use it, but it will be worth a test or two.

Footnote:

The aerial has been tested out to several hundred metres flying a T240 with a FrSky Delta Receiver. It has also been range checked with no discernible difference between this and the original aerial.