How to Viewshed with Radio Mobile (Rebel Edition)

Mount Independence

Cyntony is located in historic Lexington, Massachusetts, home of the “shot heard ‘round the world” that started the American War of Independence. After receiving a signal via lantern light from Boston, Paul Revere and others set out to warn local militias of the British army’s route and approach, as memorialized in Henry Wadsworth Longfellow's iconic poem excerpt:

"He said to his friend, “If the British march
By land or sea from the town to-night,
Hang a lantern aloft in the belfry-arch
Of the North-Church-tower, as a signal-light,—
One if by land, and two if by sea;
And I on the opposite shore will be,
Ready to ride and spread the alarm
Through every Middlesex village and farm,
For the country-folk to be up and to arm.”

Now for some alternate history -- what if instead of using lanterns, the patriots had access to Doodle Labs Mesh Rider® radios outfitted with Trival Antene high-gain dual-band antennas? How much farther could they have communicated?

We can use Viewshed analysis, a crucial aspect of communications engineering that focuses on determining the unobstructed path or, line-of-sight (LOS), between transmitter and receiver locations.

Radio Mobile

We're going to use Radio Mobile, a free software developed by Roger Coudé (VE2DBE) that simulates RF propagation.  Don't be fooled by the '90's vibe of this website, Radio Mobile is widely used in the amateur radio community for planning and optimizing radio networks. Here’s how to get started:

Installation

• Download Radio Mobile from the official website
• Download and install Google Earth Pro
• Create a folder C:/radio_mobile (or in another directory of your choice)
• Extract the zip file to the folder you just created
• Launch Radio Mobile by double clicking on the rmweng.exe file

Data Input

• Import terrain elevation data (DEM files) for your area from NASA’s SRTM database. These files provide topographical information.
  • Click on Options > Internet > SRTM.
  • Then change the internet ftp directory to SRTM – Best data – Site 2.
• Click on File > Map Properties
  • Set the location of the center of the map by entering a latitude and longitude or using the Select a city name button
  • Click Extract. The elevation map should render on the screen.
  • Click Edit > Fit to a window

Network Configuration

Now we will configure the network with the assumption that we are using Mesh Rider radios in 900 MHz mode.

• Click on File > Networks Properties > Parameters
  • Name the network whatever you like. I used Doodle MANET network.
  • Set the minimum frequency to 900 MHz and the Maximum to 928 MHz
• Click on File > Networks Properties > Systems
  • Name the system whatever you like. I used Doodle Labs Mesh Rider.
  • Set the transmit power to 30 dBm.
  • Set the receiver threshold to -90 dBm.
  • Set the antenna type to dipole and the gain to 3dBi

Order of Battle

The patriots must select their radio locations strategically to ensure signal propagation, with attention paid to both line of sight and Fresnel zone. A high point along the expected path of the British march along Massachusetts Avenue is in modern day Arlington Heights, then called Menotomy. With radios placed on the belfry in Boston and on the heights in Arlington, we should have a good link, but Radio Mobile can help confirm this.

Figure 1: Map of the Battles of Lexington and Concord

Unit Configuration

• Create “units” which are individual radios in your network
  • Click File > Units properties
  • Select Unit 1
    • You may rename it if you like, I named it North Church
    • Set the location, I set it to the north end of Boston
    • Set the elevation if it will be elevated. I chose 40 meters for the position in the belfry of the church.
  • Select unit 2
    • I set this position Arlington Heights on the path of the British march.
  • Repeat steps for any additional units. I also made one for Cyntony HQ in Lexington

Generating Maps

• Click on Tools > Radio Coverage > Single Polar
• Select your two units as desired. The analysis will run radially from your center unit
• Select Worst Case for link direction
• Select Rainbow and Fill area for plot
• Select dBm for Threshold
• Click Draw!
• See figure 2 below for an example

Radio Link Analysis (Fresnel Zone)

• Click on Tools >Radio Link
• See figure 3 below for an example

Add to Google Earth

• Click File > Save Picture As
  • Choose a filename and a directory
  • Click Save
• Open Google Earth Pro (installed earlier)
  
  • Click File > Open
  • Navigate to the picture you just created
• Now the coverage map will be able to be viewed as an overlay on the map.

Discussion

As can be seen on the viewshed coverage map (Figure 2), our network of Mesh Rider radios could have warned patriots stationed on a hill along the British route far ahead of Paul Revere. With additional viewshed planning, patriots could have created a MANET network covering the entire Boston region. Maybe the revolution could have been won in a day!

Figure 2: Boston area bi-Directional MANET radio coverage map (centered on North Church), as revealed by Radio Mobile viewshed analysis

Figure 3: Fresnel Zone visualizer showing the North Church (right) to Arlington Heights (left) propagation path

Conclusion

In this blog post, we’ve traveled back in time to the American War of Independence, reimagining the “shot heard ‘round the world” not with the flicker of lanterns, but with the invisible threads of radio waves.

Learn more about the Battles of Lexington and Concord.

Let us know what you think in the comments below. If you're interested in learning more about Mesh Rider radios, or any of Cyntony's other products