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GNSS Antennas and Recycling

Nail as antenna
DIY GNSS (GPS/Galileo/Glonass/Beidou) Antenna

Everybody talks about protecting the environment and recycling. The nail antenna from the land of poets and thinkers (Germany) follows this trend. We’ve hit the nail on the head with this design.  We don’t need a new nail – no we use old, superfluous, rusty nails and recycle them into valuable, perfect GNSS antennas. This nail antenna was tuned without using a Vector Network Analyser (VNA). To adjust the nail antenna you only need a belt grinder. You shorten the nail with the saw to approximately Lambda/4, check the number of visible GNSS satellites in the NMEA string and then further shorten the nail by grinding it. We do this until we see a maximum number of satellites in the sky. And as you can see, we are saving twice because we use old nails as antennas and save money on the purchase of an expensive VNA. If you don’t have a belt grinder, you are welcome to use a hand file. If you don’t have a hand file, you just ask your friendly neighbour. Everybody who sends me a picture of their nail antenna for GPS, LoRaWAN, Sigfox, Bluetooth, NB-IoT, or LTEM by e-mail up to October 31, 2019, can get a 30% discount on my IoT M2M Cookbook.

Kidding aside – Back to real LPWAN and GNSS antennas

The antenna above is real. The HW developer has the same MegiQ Vector Network Analyzer (VNA) as me.  His VNA is in the laboratory and he wanted to repair the PCB at home. The GPS patch antenna was broken and at home there were only nails and a belt grinder. How a Lambda/4 antenna works is basic knowledge. From time to time we exchange home made antennas. He constructed an antenna from old nails and/or metal rod and I constructed one from two two cent coins (total cost therefore 4 euro cent).  A nail antenna can be adjusted to SubGHz (LoRaWAN, Sigfox, NB-IoT) and Bluetooth or Wi-Fi .  My coin antenna is nearly impossible to tune for SubGHz.

Nails or coins – from both you can develop antennas

The right conductive structure in the right arrangement always results in an antenna. You only have to know which structure fits which application.

GNSS DIY Antenna and Receiving

GPS App Results
GPS Test app on Android

How many GNSS satellites can be received and which are visible in the sky can be determined by an Android app called GPS-Test. GPS-Test shows us which GNSS satellites the phone is currently receiving and Sat-AR shows us which satellites are where in the sky. The screenshot of GPS-Test shows us 12 satellites in the display window and the scroll bar shows us that more than 12 are being received. GPS-Test shows not only the GPS satellites, but also the Glonass satellites. In the upper left corner of the display window we can see that 20 satellites are visible. On the right we can see that 18 satellites are in use. Below left one sees in which angle the satellites are in the sky. With the Trimble GNSS Planning web page we can see the number of satellites spread over the day. The chart below shows the number of satellites for Neustadt am Rübenberge near Hannover. In the worst case only 6 American GPS satellites are visible but 10 Chinese Beidou satellites. Besides there are 7 Russian GLONASS satellites and 6 European Galileo satellites.

Visible Satellites
GNSS Satellites visible in the sky over time

GPS DIY antenna: Smith chart and return loss

Smith Chart
DIY GPS antenna – Smith Chart

Return Loss
DIY GPS antenna – return Loss

The red curves show the antenna not matched to 50 Ohm in the return loss diagram and in the Smith chart. The blue curve shows the attempt to simulate matching. The return loss in the blue curve is better than -35 dB. However, the antenna cannot be adjusted to 50 Ohm and simultaneously pulled to 1575 MHz medium frequency. The 50 ohms are almost reached at 1655 MHz. The frequency is too high and the nail should be a bit longer. The red curve is perfect for this, which was adjusted without VNA. But it also shows that only shortening the antenna without VNA will not achieve the optimum. The blue curve would shift towards the red curve with a slightly longer antenna.

Anyone who has problems with their antenna or radio can contact us.  It does not have to be a nail antenna or a 4 cent antenna. We take care of the design of almost any antenna from 400 MHz to 6000 MHz.

December 20, 2019

Author: Harald Naumann

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