What About Inversions

Lately many of us have heard stations from rather distant areas on the 147.315 repeater. It is interesting to hear those stations that we normally do not hear but often it is just due to a weather phenomenon called and inversion. I expect that some amateurs sit back and wonder just what is this inversion thing that some offer as an explanation for the unusually distant stations heard and some stations that we can even carry on a QSO with. Sometimes the stations seem as though they are just audible for enough time to hear a call sign but other times long enough for a typical QSO. Then there are times that you may not even be able to hear or access your local repeater and again you will hear folks offer the explanation as an inversion as well.

Consider the simplified diagram of an inversion below. Note that typically as you increase elevation the temperature lowers but with an inversion the opposite happens! You can see the yellow area depicting the inversion, which actually ends up acting as a boundary layer that can either attenuate the signal to and from the repeater or at times signal attenuation can occur to the extent of both blocking the repeater from hearing your transmitted signal and from you hearing the repeater’s transmitted signals. This occurrence can lead one to believe the repeater is off the air. I recall years ago there were trips made to the repeater site when we could not use the repeater, only to find the repeater operating. All due to an inversion. Sometimes the inversion layer is well above what the diagram depicts too, leading to other stations that you will be able to talk with that you would not ordinarily be able. There is another term used for this phenomenon which is called ducting that enables more distant than typical communications to occur, especially on VHF as well as UHF.

Inversions, ducting, tropo and what ever other titles the phenomenon of having radio signals reflected and refracted is an interesting and vast topic of which you can read up on. Look for propagation of radio signals either on the Internet or the ARRL Handbook for Radio Communications, what was previously called the Radio Amateur’s Handbook.

Inversion

       

Share

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>