Tiny LoRa ~900MHz copper coil antenna

[meshnerd]

Hey all, I got a handful of tiny 900MHz copper coil antennas that I wanted to use with my Pycom boards that support LoRa.

I got a larger antenna and connected it up to the uFL connector and it works great.

Now if I wanted to use one of these little copper coil antennas how would I go about it?

[robert-hh]

@meshnerd Throw them into the bin. That's the best you can use them with a Pycom device.
You could attach a UFL cable AND assemble the antenna on a ground plane, but that's not worth the extra money and effort.

[meshnerd]

@robert-hh I was afraid someone might say that.

Let's say for the sake of argument I wanted to attach one to a uFL cable, like the ones that come with the larger antennas for example (uFL to RP-SMA antenna adapter cable). How would I do that? Can I just cut off one end of the cable and solder the spring antenna to it?

Can I just solder to each end of the antenna?

[kjm]

You could try soldering the core to one end of the coil but I like Roberts idea better. If you want to play antennas you need something like https://www.ebay.com.au/itm/PS100-137-5MHz-2-7GHz-UV-RF-Antenna-Analyzer-SWR-Meter-Tester-Alloy-Shell-B/174082019208?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200520130048%26meid%3D3f3479dbc9d34a418208dff5bfb41f2d%26pid%3D100005%26rk%3D1%26rkt%3D4%26mehot%3Dco%26sd%3D353094490302%26itm%3D174082019208%26pmt%3D1%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851 otherwise you're just stumbling around in the dark.

[robert-hh]

@meshnerd Like @kjm said: you have to solder the core to the hook end of the antenna, and the shield of the cable to a kind of ground plane, e.g. a 8 x 8 cm piece of metal. In the intended use of the antenna the PCB acts as ground place.
You can also make a reasonable good antenna yourself: https://www.element14.com/community/community/project14/rf/blog/2020/01/11/building-a-poor-man-s-quarter-wave-433mhz-antenna-antenna-s-construction
For 900MHz, the wires have a length of 95% wavelength/4 ~ 8 cm.

[meshnerd]

@robert-hh @kjm Thanks for the explanations.

I apologize in advance for the newb question but I'm still learning about electronics. Is there a reason why I can't just take the shielding from the uFL cable and solder it to the GND pin on the board?

[robert-hh]

@meshnerd The shielding is already connected to GND via the UFL connector. The problem is the missing radiation GND at the antenna. The coils is just one half of the required wavelength/2 antenna. The other half would be the ground plane at the antenna.
But that's just nitpicking. At the low power Lora is transmitting noting will happen. It's just a bad antenna. Even a 8 cm long cable sticking out of the core of the UFL cable would make up a better antenna.

[meshnerd]

@robert-hh Thank you. This has been enlightening. I ended up just getting another antenna but thanks for your explanations.