Lightning Protection For The Flexradio Transceiver

What is needed is an automatic system that grounds the antenna when not in use.

Given: When there are no users on, the antenna needs to be grounded. A remote coax switch normally grounds antennas when not in use but this installation only has one antenna and no remote coax switch. This project will perform that function.

Certain parts are already in place. A Polyphaser lightning arrestor offers protection but when a lightning event occurs a Polyphaser will let through 1000 volts and destroy equipment. A relay that grounds the antenna when the power is off is already installed but now it must be activated manually over the Web. Here is a white-board sketch proposing an automatic solution. It uses Node Red software.

The Weeds

Node Red

Node Red will listen over the LAN for a user to be logged in and then activate the grounding relay. It sounds complicated but the flow below shows how simple it really is. A Raspberry Pi running Node Red is already on site being employed to log the usage. For this new project all that needs to be done is to add a new flow.

Explanation: On the left is a node that queries the Flexradio for information including any clients who might be logged in. In the center is a “function” node that looks only at the data field for the client’s identification. If the field is empty, null, the function outputs a boolean “false”. If there is a client logged in, the function outputs a boolean “true”. On the right is a node labeled “PIN: 16”. PIN 16 is a digital output pin on the Raspberry Pi where a relay module will be connected. The contacts on the relay control the existing antenna grounding relay. The debug nodes above are used only for testing.

Here is a look at each of the configurations of the nodes mentioned above. First, the “flexradio-discovery” node. There is very little here except the port number for the radio. Written by Steven Houser, the Flexradio nodes are quite easy to use, with default settings of “automatic”. The node will find the radio on the LAN and use port 4992 to poll the data.

Below is the function node. The function node contains a Javascript Function. In the first line the command examines the data “client_stations”. If the data is not empty, that is, does not equal a null, it returns a payload of true. Else it returns a payload of false.

Note: How was this function code written? With the help of the new tool, chatGPT, of course. (Yes, chatGPT does more than write essays) Here’s how:

Finally, the output node “PIN 16” tells the Raspberry Pi to make pin 16 (GPIO 23) high or low. The Raspberry Pi nodes are easy, like the Flexradio nodes. Just click the radio button for the pin to use. It even has a sketch of the pin layout that matches the layout of the Pi itself.


This is a Raspberry Pi with the relay module attached, ready to be moved to the remote site.

Close up of the relay module. It is a little unusual because it is designed for 3.3 volts so it can match what the Raspberry Pi uses on it’s GPIO pins.

Status: Currently the Node Red flow has been tested in the lab and seems to work without a hitch. The flow has been deployed into the existing Raspberry Pi at the remote location. Next, a site visit to install the 3.3 volt relay between the Pi and the antenna grounding relay, is scheduled for Monday, May 8, 2023. Update: …….Installed at the remote site, complete with heat shrink to protect the relay module.

The existing grounding relay, now activated automatically, is mounted on the single-point-ground-panel where the cables enter the building:

A week with several thunderstorms in May and no lightning damage. Of course, the big improvement is, no one had to worry about manually activating the grounding relay.


Node Red might suffer a crash which would prevent users from having the use of an antenna. The current Raspberry Pi has been running 4 months without failure, logging away with Node Red. And there is a backup copy of the Node Red flow that could be used to restore this Pi or a replacement Pi if needed. Hopefully the odds are in our favor on this one, too.