LoRA GP antenna
LoRA GP antenna
Hamradio is all about experimenting, so why not do that for my LoRA WAN / TheThingsNetwork setup?
One of the most common antenna's is the GroundPlane antenna which is basicly a 1/4 lambda driver element and 3 or 4 reflector elements (creating a artificial ground). It's a simple antenna to build with a good bandwidth, it doesn't have any gain over a dipole because it's dipole. Ok for the record it has a +2.15dBi gain (so you 3$ ebay 5 dBi antenna only has a 2.85dB gain over a dipole) ;-)
More info at : Electronic Design
Note : length adjusted for best SWR (see SWR measurement below).
- aprx 50cm of 2mm diameter brass or copper wire cut to 5 pieces of 10 cm.
- 4 x cable ends M4 / Blue
- 1 x N-style chassis part
- 4 x M4 10mm cylinder screws
- 4 x M4 lock nut.
Remove the blue plastic parts.
Solder the cable ends to one end of the tubes.
Solder the tube to the center pin of the chassis part.
Mount the ground plane tubes to the chassis part with the M4 10mm screws and the M4 lock nut. And trim the tubes to the correct length (see : design).
Bend the groundplane wires to a 45 degr. angle.
You're almost done. When you want to use the groundplane antenna outdoor. Please apply a bit of silicone sealing around the top of the chassis part (so no water is collected on top).
SWR measurment result
After the inital building I took the antenna to my local Hamradio club (Veron/VRZA Twente) to have it tested with a RigExpert AA-600 (which when connected to the computer can work up to 1.4Ghz) from a fellow Ham. Some minor tweaking (I made it for a lower frequency so I could trim it for the 868Mhz) the SWR dip was right on the 868Mhz.
This groundplane antenna can be easily installed on a 32 mm PVC tube.The connected cable will pull the groundplane antenna to his place.
LoRA GP antenna - in TheThingsNetwork LoRa crash course
In the LoRa crash course by Thomas Telkamp (a must view when you into LoRa or IOT) at 30:33 this design is referenced.
Thomas, thanks for the reference :-)
LoRA GP antenna - in TAntenna Modelling video
In the Antenna Modelling video from Richard Wenner this design is referenced.
Richard, thanks for the reference :-)
LoRA GP antenna - simulation
I have tried to simulated a 868Mhz groundplane in freespace and serveral heights above good ground.
For these simulations I used the 4NEC2 software which can be download here. Tutorials in 4 parts can be found here : part0, part1, part2. Another good tutorial set is this serie of 4 article publisched in QST : part1, part2, part3, part4 (but off-course you can also google for "NEC antenna tutorial pdf").
Groundplane in freespace
The NEC file : 868_GP.nec for this simulation.
CM CM CE SY Len=0.07875 'Element length (1/4 lambda) SY Height=0 'Height above grond SY Corr=0.70710678118 'SIN(45 dgr) GW 1 8 0 0 height 0 0 height+len 1.e-3 GW 2 8 0 0 height len*corr 0 height-len*corr 1.e-3 GW 3 8 0 0 height 0 len*corr height-len*corr 1.e-3 GW 4 8 0 0 height -len*corr 0 height-len*corr 1.e-3 GW 5 8 0 0 height 0 -len*corr height-len*corr 1.e-3 GE 0 GN -1 EK EX 5 1 1 0 1 0 0 FR 0 0 0 0 868 0 EN
The NEC file has 3 variables :
- Len : 0.07875
- Height : variable (in meters)
- Corr : 0.707 (used for bending angle)
Groundplane 0.25 m above realground
Groundplane 0.5 m above realground
Groundplane 1 m above realground
Groundplane 5 m above realground
The higher the better ;-)