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

The design

Note : length adjusted for best SWR (see SWR measurement below).

Materials used

  • 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.

 

Step 1

Remove the blue plastic parts.

Step 2

Solder the cable ends to one end of the tubes.

Step 3

Solder the tube to the center pin of the chassis part.

Step 4

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).

Step 5

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.

Installing

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.

https://youtu.be/T3dGLqZrjIQ?t=30m33s

Thomas, thanks for the reference :-)


LoRA GP antenna - in TAntenna Modelling video

In the Antenna Modelling video from Richard Wenner this design is referenced.

https://youtu.be/L7Vveme4DUA

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

 

 

Conclusion

The higher the better ;-)


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