Antennas in regards to UKHASnet is an area that is under explored. I have used a number of different types both homemade and commercial and am yet to find something that works well. Many nodes have a single wire antenna cut to a 1/4 wavelength (82mm) – often just put in place for testing and then never upgraded to something more. Its also suprisingly hard to test antennas as they are influenced by so many environmental factors and the equipment to test it scientifically is expensive. On the flip side the key is more how well they work so I decided to start a simple experiment using my home gateway.
- Ebulobo Gateway (ESP8266/RFM69HW) running up to date code
- Short section of RG58 coax with an sma male header
- Monitoring using Russs’ Grafana Gateway Dashboard
Short section of RG58 coax with an SMA connector on one end. Stripped the outer insulation and shield to expose 82mm of the core and then attached the antenna with tape on my desk so that it wasn’t close to any other object. No ground plane was attached and so this antenna acted like a single wire antenna.
The graph shows received packets by AB gateway, each colour is a different node and the y axis is RSSI in dB, the red line is the noise floor. As you can see the ‘green’ node, ‘orange’ node and ‘blue’ node all have a better RSSI then before, the ‘yellow’ node is right next to the gateway so probably is at its best already. By adding 2 radials the antenna is performing better.
Same setup but now 4 radials (just to note the laptop is off). Adding the extra two radials didn’t really make much difference to the performance. Out of interest I then detached the antenna and left the gateway running without an antenna. You can see a significant deterioration in performance for all the nodes as well as a smoothing of the noise floor as its less sensitive to nodes and local noise.
From these simple experiments it seems sensible to put a ground plane onto a 1/4 wave antenna and you can probably get away with just 2 radials. Next step is developing directional antennas especially as I’m planning some long range links.