FM Log

I rate FM radio performance by counting local stations I can hear down on my patio in the middle of the day. That’s simplistic, because daytime propagation varies and E-Skip happens. Not all stations are necessarily local and consistent.

Sporadic‑E (Es) is a propagation mode where radio waves in the 30–300 MHz range reflect off dense patches of ionization in the E‑layer of the ionosphere (≈90–120 km altitude). On the FM band (88–108 MHz), this produces long‑distance reception of stations 600–1500 miles away, often with strong, local‑quality signals.

Es clouds form when wind shear and atmospheric tides compress metallic ions (mostly Fe⁺ and Mg⁺) into dense layers. When the electron density spikes high enough, the layer becomes reflective at VHF frequencies.

Key triggers:

• Summer solstice season (May–August)
• Winter minor season (December–January)
• Strong wind shear in the upper atmosphere
• Thunderstorm complexes (sometimes correlate)
• Jet stream boundaries🤖

I’ve come to realize that the key thing in refining ones radio listening is logging, and on FM distinguishing between stations usually heard from ones usually not.

Because many radio stations carry syndicated material, identifying them can be non-trivial — and you can only pick up one ID at the “top of the hour” ID per hour. When a station carries RDS information, it can be fairly easy. My Qodosen DX-286 and MLite-880 display the PI segment of RDS. Other RDS segments may identify the station also. See RDS / RBDS: FM on Display. My Eton Elite Executive apparently decodes the PI and displays the call sign.

All that introduction introduces a project, to log all the FM stations I hear. I already have a starter list of local stations from Radio-Locator. I created a Google Sheet for the table that I’m embedding below. It will automatically update the article as I add to it.

The National Radio Systems Committee maintains a database of PI assignments. I use this as a definitive identification tool for “FM full service transmitters;” however, FM stations use translator services that rebroadcast their signals to serve extended areas, and those transmitters may also have PI codes, codes not in the database. I’m using multiple sources to identify stations:

1. RDS PI
2. Off air station identification, checked against frequency to identify translators
3. Educated guesses, confirmed by frequency and matching streamed program content

The project got off to a grand start, thanks to some E-skip today. Note two stations from Minnesota on the list, over 1,000 miles away.