1090 MHz ADS-B PCB antenna from eBay

About a month ago I bought a 1090MHz PCB aerial on eBay and immediately forgot about it. It arrived a few days ago and I had a good look at it before I connected it to anything to try and work out what it actually was. I decided from the construction that it was a vertical half wave dipole.

As with all new aerials, I decided to put it on one of my analysers so see how it appeared to perform. I chose the straightforward vector impedance analyzer (sic) rather than the full VNA due to the simplicity.

I was very surprised to see the SWR showing as a disappointing 6:1 on the analyser.

PCB aerial showing 6:1 SWRPCB aerial showing 6:1 SWR
PCB aerial showing 6:1 SWR

I did a visual inspection of the aerial which showed that one side of it wasn’t even soldered – Effectively this was working as quarter wave vertical with no groundplane whatsoever.

Unsoldered 'connections'
Unsoldered ‘connections’

I fired up the soldering iron and it only took a few seconds to fix this.

The connections soldered in place
The connections soldered in place

You can see that both sides are now nicely soldered in place to the board. With that done, I put it back on the analyser again and it showed a much more pleasing SWR curve.

That's better - The repaired ADS-B PCB antenna
That’s better – The repaired ADS-B PCB antenna

For completeness, I also tested the aerial on my VNA. The marker here is at 1090 MHz and shows an SWR of 1.22:1. I do appreciate that SWR on a receive aerial isn’t anywhere near as important as when one is transmitting but at least it’s a good indication that the aerial is resonant on the required frequency.

ADS-B PCB antenna SWR
ADS-B PCB antenna SWR

I haven’t yet had a proper chance to test the effectiveness of the aerial but I expect it to be a bit worse than a simple quarter wave vertical with radials (spider). The main reason for this post is as a advisory – If you’ve bought one of these types of aerials then it’s worth checking to make sure that it’s actually soldered properly.

1 Comment

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  1. Beware cheapie bits from China eh? A simple enough fix though curious as to what you’re using it for. Pi relatedness?

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