VHF Low Band Skip is caused by a phenomenon called Sporadic E skip. Sporadic E skip occurs when patches in the E layer of the ionosphere, about 65 miles above ground, become ionized. This layer normally refracts shortwave and mediumwave signals but is transparent to VHF radiation. When patches of the E layer become ionized, great skip opportunities from 28 MHz to 75 MHz occur, allowing you to monitor communications in this band cross-country, and sometimes worldwide when "double-hop" skip occurs.Hunting for skip.
One very valuable tool for looking for E skip patch openings is the DX Sherlock 1.7 - V-UHF QSO real time maps tool. This tool, provided by vhfdx.net, shows real time contacts made by amateur radio operators on 6 meters (50-54 MHz). Usually, when a number of contacts are being made cross country, a sporadic E skip opening is occurring.
Another valuable tool is of course your scanner. Some precursors to sporadic E skip come from meteor scatter transmitter sites which broadcast near 40 MHz for telemetry and weather reporting. Meteor scatter transmissions are similar in nature to sporadic E skip transmissions, except the radio communications broadcast bounces off on ionized trails from naturally occurring meteors vaporizing in the atmosphere. These vaporization trails allow ground stations to communicate over long distances from remote areas. Some frequencies commonly used by Meteor scatter systems include:
40.53 SNOTEL - Snowpack Telemetry in the Western States
44.20 Meteor Communications Corporation
Plug those frequencies in and scan them often. If you hear data (you'll know it when you do, it is a loud buzzsaw sounding data transmission) on these frequencies, chances are a nice band opening is occurring.
Common Reported Skip
Some of the more commonly public safety agencies that show up on skip across the nation include:
42.00 - 43.00 MHz Missouri Highway Patrol
42.00 - 43.00 MHz Tennessee Highway Patrol
33.90 Hamilton County (Cincinnati) Fire / EMS Dispatch
39.00 - 40.00 MHz California Highway Patrol
Some of the more commonly heard Military stations include:
30.45 Fort Hood Range Control
38.90 Fort Irvwin CA Range Control / Fort Knox TN Range Control
In addition to those public safety agencies and military operations, there are numerous other fire departments, police departments, SOs, pagers, Mexican taxi drivers, military range controls, military helo towers, public works, and other operations that occur.
The full set of low band allocations in the United States are:
30.0000 to 30.5500 U.S. MILITARY
30.5800 to 31.9800 PARK SERVICE
32.0000 to 33.0000 U.S. MILITARY
33.0200 to 33.1000 HIGHWAY SERVICE
33.1200 to 33.4000 BUSINESS RADIO
33.4200 to 33.9800 FIRE DEPARTMENTS
34.0000 to 35.0000 U.S. MILITARY
35.0200 to 35.6800 PAGERS
35.7000 to 35.9800 BUSINESS RADIO
36.0000 to 37.0000 U.S. MILITARY
37.0200 to 37.4200 POLICE
37.4400 to 37.8800 BUSINESS RADIO
37.9000 to 37.9800 HIGHWAY SERVICE
38.0000 to 39.0000 U.S. MILITARY
39.0200 to 39.9800 POLICE
40.0000 to 42.0000 U.S. MILITARY
42.0200 to 42.9400 POLICE
42.9600 to 43.1800 BUSINESS RADIO
43.2000 to 43.6800 PAGERS
43.7000 to 44.6000 BUSINESS RADIO
44.6200 to 46.0400 POLICE AND PARK SERVICE
46.0600 to 46.5800 FIRE DEPARTMENTS
46.6000 to 47.0000 U.S. MILITARY
47.0200 to 47.4000 HIGHWAY SERVICE
47.4200 to 47.6600 EMERGENCY SERVICES
47.6800 to 49.5800 BUSINESS RADIO
49.6000 to 50.0000 U.S. MILITARY
50.0000 to 54.0000 HAM RADIO 6 METERS
Search through those frequency ranges and see what you hear! Most Sporadic E Skip occurs from sun up to sun down, however some of the best sporadic E skip openings can occur well till midnight.
Antennas
You might ask, what antenna do I need on my receivers to pick up this skip? Well, most people reporting activity have received low band skip just using a rubber ducky on a handheld scanner, however using a dipole wire antenna cut for 40 MHz will probably give you the best results.
Whatever you hear, whenever you heard it, be sure to post your findings and logs to the Skip / Tropospheric Ducting Forum on RadioReference.com.
Have fun!
