Increased VHF/UHF Transmitting Range

Most two-way radio enthusiasts are aware of distant communications during atmospheric conditions commonly known as “skip”. Skip occurs when “sky wave” signals in the HF range (frequencies between 3 and 30 MHz) are refracted off the ionosphere excited by sunspot activity or cosmic radiation. 20 MHz is considered the best frequency for distant skip communications, however, skip can occur up into the lower VHF range under certain conditions.

Because the higher VHF and UHF signals are line of sight and will normally shoot straight out through the ionosphere into space, range is normally increased through antenna height and higher transmitter output levels. However, certain weather conditions will allow for VHF and UHF signals to greatly extend their range. Such conditions are known as tropospheric ducting that occur in the lowest layer of the atmosphere called the troposphere. The troposphere, or lower atmosphere, is where almost all weather occurs. The troposphere begins at the Earth's surface and extends from 4 to 12 miles high. Tropospheric ducting happens during weather when the signal encounters a temperature inversion.

A temperature inversion flips the normal change of atmospheric temperature in the troposphere from warm to cold with increasing altitude. During an inversion, the normally warmer surface air temperature is colder than the warm air mass above it. During an inversion the higher refractive index between the inverted layers will cause the signal to be refracted or bent. Tropospheric ducting will affect all frequencies, and signals enhanced this way can travel up to 800 miles.

Generally speaking, mild temperature inversions occur in the mornings and evenings when the angle of sunlight is hitting the upper troposphere, heating it up to a higher temperature than the lower surface layer. This effect will typically last for a couple of hours before and after sunrise and sunset. During temperature inversions when a warm front enters an area over the top of a colder layer of air, the intensity and area covered increases tropospheric ducting allowing for greater range and clarity of VHF and UHF two-way communications. The duration of a tropospheric ducting event like this depends on how long the inversion lasts.

Inversions are caused by a number of factors and will often cause fog to develop, or in urban areas smog will increase. One way to be aware of tropospheric ducting is through the observation of broadcast TV signals. Apparently all long-distance reception of broadcast digital television occurs by tropospheric ducting, so when you’re monitoring broadcast TV on an antenna and notice an increase in signal strength and the reception of distant channels, then you should have an increase in range when communicating on VHF/UHF two-way radios.

Due to the limitations of the unlicensed multi-use radio service (MUR) and family radio service (FRS) two-ways, communications on these frequencies during a temperature inversion would be the best opportunity to increase your range from a mile or two to considerably farther. A well matched, full wave outdoor antenna mounted as high as possible in a flat open area always helps and in the case of handheld two way radios, a higher elevation in flat open topography is best for communications range as well. Using a directional antenna will increase forward gain as well as range and if pointed skyward it will help project sky waves toward the refractive atmospheric layer during a tropospheric ducting event.

Fascinating and useful. Thanks

Thank you for the information..

Question for anyone that cares to answer...

What is a good quality base station, not a hand held I have several of those... I mean a sit in my house put up the antenna and scan the airwaves base station.

So many out there, it is hard for new folks (like me) to figure out the best bang for my buck.

a reply to: MichiganSwampBuck

Great info.. thanks.

Comms related, just saw this clip of a new 40W GMRS radio that may interest some..

a reply to: MichiganSwampBuck

S&f. Thank you for the info, I use ham utility (iOS version) can't remember if it is a paid app but great app to have for enthusiast alike.

vk3

I swear they taught in flight weather at 80,000 feet....the temp is 80 degrees.....in a short layer.....ionosphere.!...70 degrees anyway.......anyone remember that far back for me ....ha....ha

a reply to: JacKatMtn

I like the GMRS, you can purchase a 5 year license without needing to take a test, are allowed to use repeaters and transmit data.

The General Mobile Radio Service (GMRS) is a licensed radio service that uses channels around 462 MHz and 467 MHz . . . There are 23 GMRS channels and each channel is 25 kHz.

That is in the VHS frequency range.

The GMRS is available to an individual (one man or one woman) for short-distance two-way communications to facilitate the activities of licensees and their immediate family members. Each licensee manages a system consisting of one or more transmitting units (stations.)

Normally, you and your family members would communicate between yourselves over the general area of your residence, such as an urban or rural area. This area must be within the territorial limits of the fifty United States, the District of Columbia, and the Caribbean and Pacific Insular areas. In transient use, mobile station units from one GMRS system may communicate through a mobile relay station in another GMRS system with the permission of its licensee. The communications may also be with mobile station units from other GMRS systems also with permission from the licensee to communicate through the mobile relay station.

A GMRS system consists of station operators, a mobile station (often comprised of several mobile units) and sometimes one or more land stations. A small base station is one that has an antenna no more than 20 feet above the ground or above the tree on which it is mounted and transmits with no more than 5 watts ERP. The use of some channels is restricted to certain types of stations.