Using NOAA Weather Radio
to Monitor VHF Propagation

This page is a collection of information about measuring VHF radio propagation, particularly for weather-related or diurnal signal enhancements.

The basic idea is to monitor the signal strength on seven channels in the 162.40 - 162.55 MHz range used by the National Weather Service to transmit weather and emergency information. There are now over 1000 of these transmitters across the United States, and nearly every populated or travelled area is covered by one of these stations. And, what makes things interesting for my purposes, many areas get one signal that is quite strong, but transmitters on the other channels are just out of range. So, monitoring these frequencies can show us when VHF propagation enhancement exists; the normally weak out-of-town signals may pop up in strength.

I've written a program that controls an HP 8920 service monitor with a spectrum analyzer function. It measures the signal strength on each channel at an interval (usually 5 minutes) and logs the data to a disk file.