In October 1937, a small crew of eight men climbed to the summit of Mount Washington to erect a radio tower under the direction of Edwin Howard Armstrong, inventor of frequency modulation (FM) radio. They spent three weeks on the summit and were able to work only five days due to severe weather. What they built became one link in one of the most ambitious radio relay systems ever constructed.

This system was the Yankee Network’s FM relay chain. It stretched nearly 300 miles, from Alpine, New Jersey, to the summit of Mount Washington, New Hampshire. It proved that FM radio could cover entire regions, not just cities. And it depended entirely on one principle: height.

The Problem: FM Radio Needed Elevation

FM radio behaves differently from AM radio. AM signals can reflect off the ionosphere and travel great distances, especially at night. FM signals do not. They travel primarily in straight lines.

This means FM is limited by the curvature of the Earth.

This limitation is called the radio horizon.

The higher the antenna, the farther it can reach.

Edwin Armstrong understood this immediately. Instead of building many small relay stations, he built fewer relay stations on mountains.

This was more efficient and more powerful.

The Core Yankee Network Relay Chain

The Yankee Network used four primary relay sites:

• Alpine, New Jersey
  
• West Peak, Meriden, Connecticut
  
• Mount Asnebumskit, Paxton, Massachusetts
  
• Mount Washington, New Hampshire
  

These sites were carefully selected based on elevation and line-of-sight geometry.

Site Elevations and Antenna Heights

Alpine, New Jersey (W2XMN)

Ground elevation: 520 ft

Tower height: 400 ft

Total antenna elevation: 920 ft

This was Armstrong’s primary FM transmitter.

West Peak, Meriden, Connecticut (W1XPW)

Ground elevation: 1,024 ft

Tower height: ~120 ft

Total antenna elevation: ~1,144 ft

This was the first relay station.

Mount Asnebumskit, Paxton, Massachusetts (W1XOJ)

Ground elevation: 1,007 ft

Tower height: ~150 ft

Total antenna elevation: ~1,157 ft

This was a major relay hub.

Mount Washington, New Hampshire (W1XER)

Ground elevation: 6,288 ft

Tower height: ~50 ft

Total antenna elevation: ~6,338 ft

This was the highest and most important relay station.

Distance Between Relay Sites

Alpine, NJ → West Peak, CT

Distance: ~85 miles

West Peak, CT → Mount Asnebumskit, MA

Distance: ~70 miles

Mount Asnebumskit, MA → Mount Washington, NH

Distance: ~130 miles

Total relay chain length:

~285 miles

This was extraordinary for the 1930s. Most engineers believed FM was limited to about 40 miles. Armstrong proved otherwise.

How Radio Horizon Made It Possible

The radio horizon is the maximum distance an antenna can see over Earth’s curvature.

Formula:

Distance (miles) ≈ 1.23 × √height (feet)

Each antenna has its own radio horizon.

Maximum communication distance equals:

Max distance ≈ 1.23 × (√height₁ + √height₂)

Example: Mount Washington to Mount Asnebumskit

Mount Washington antenna elevation: 6,338 ft

Radio horizon: ~98 miles

Mount Asnebumskit antenna elevation: 1,157 ft

Radio horizon: ~42 miles

Maximum theoretical distance:

98 + 42 = 140 miles

Actual distance:

~130 miles

Within range.

Example: Alpine to West Peak

Alpine antenna elevation: 920 ft

Radio horizon: ~37 miles

West Peak antenna elevation: 1,144 ft

Radio horizon: ~42 miles

Maximum theoretical distance:

37 + 42 = 79 miles

Actual distance:

~85 miles

Atmospheric refraction and transmitter power made this possible.

Why Mount Washington Was the Key

Mount Washington’s antenna elevation exceeded 6,300 feet.

Radio horizon: ~98 miles

From Mount Washington, FM signals could reach:

• Maine
  
• Vermont
  
• northern New Hampshire
  
• southern Quebec
  

No other relay site had comparable reach.

This made Mount Washington strategically essential.

Construction Under Extreme Conditions

Original FCC license records preserved in the National Archives document construction in October 1937.

A crew of eight men spent three weeks on the summit.

They were able to work only five days due to severe weather.

Edwin Armstrong personally inspected the installation.

Despite extreme conditions, the tower was successfully constructed.

National Archives photographs show Armstrong standing beside the tower during construction.

Why This Mattered

This relay network proved FM radio could cover entire regions.

It demonstrated FM was practical.

This directly led to widespread FM adoption.

Today, FM remains the dominant broadcast system for music radio.

Mount Washington played a direct role in making that possible.

The Legacy Today

The Armstrong tower on Mount Washington represents:

• early FM broadcast infrastructure
  
• experimental relay engineering
  
• mountain-based communications design
  
• proof of regional FM coverage capability
  

Modern communications still rely on the same principle: height extends range.

Nearly 90 years later, Mount Washington remains one of the most valuable communications sites in New England.

Sources

• National Archives — Building a Radio Tower atop Mount Washington
  
  https://text-message.blogs.archives.gov/2019/02/12/building-a-radio-tower-atop-mount-washington/

• National Archives and Records Administration — Record Group 173, Federal Communications Commission
  
  https://www.archives.gov/research/guide-fed-records/groups/173.html

• World Radio History — Historic Broadcast Engineering Journals
  
  https://worldradiohistory.com/

• FCC Experimental Station Records (W1XER, W1XOJ, W1XPW, W2XMN)
  
  https://www.fcc.gov

• Mount Washington Observatory — Summit Infrastructure and Communications History
  
  https://mountwashington.org