Guest Post: What is FM Lightning Scatter DX?

Photo by Olivier Lance on Unsplash

Many thanks to SWLing Post contributor, Bruce Atchison, who shares the following guest post:


What is Lightning Scatter DX?

by Bruce Atchison (VE6XTC)

Believe it or not, it’s possible to receive distant FM stations during a thunder storm. While lightning makes it difficult to hear AM and shortwave broadcasts, its crackles aren’t as evident on the 88 MHz to 108 MHz band.

When lightning strikes, it temporarily ionizes the air around it. Radio signals are reflected by the charged gasses and come back down to earth.

From my experience with this kind of DX, the signal became noticeably stronger during lightning strikes. This effect lasted for a second, then the signal level dropped to its former strength.

While a thunder storm raged overhead on July 7th, I used my CC Skywave SSB radio to check out the FM band. Instead of hearing E-skip as I had hoped, I found that tropo-like conditions reflected stations down to my home. I heard signals from a hundred miles away or further.

As just one example, I found a low-power station with the call letters CKSS on 88.1MHZ. They call themselves 88.1 The One. Find out more about this station at the http://www.881theone.ca/ link. It’s located in the town of Stony Plain, Alberta. This station plays country music and airs local news events.

At a guess, I’d say the transmitter is about 120 miles from my QTH in Radway. It normally doesn’t come in at all. The signal strength varied too, showing that it wasn’t a local.

In my instance of catching CKSS’s signal, a form of tropo ducting was also present. Rain can produce reflections of signals but it’s much more pronounced in the UHF and microwave bands.

When a thunder storm is ruining AM and shortwave reception, try DXing the FM band. You’ll be surprised at what occasionally comes in.

For further information on weather-related DX, check William R. Hepburn’s article.

To see a demonstration of lightning scatter on amateur TV, watch the
following video:

To hear what FM lightning scatter sounds like, watch this video:


Thank you for sharing this guest post Bruce. I’ll be the first to admit that I’ve never tried to hear lightening scatter DX, but I will certainly give it a go.  This time of year, we’ve numerous thunderstorms in the afternoon and evening, so I’ll certainly have the opportunity!

Post readers: Have you ever caught FM DX off of Lightening Scatter? Please comment!

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10 thoughts on “Guest Post: What is FM Lightning Scatter DX?

  1. Mike N7MSD

    This makes sense as you can scatter off anything else ionized or of sufficient wavelength:

    Aurora Scatter, common in polar regions
    actual Tropo Scatter of course, as well as the Tropo Ducting referenced in the article
    Non-Tropo Forward Scatter like off airplanes
    regular Back Scatter the usual way mono-static radar operates along with some comms
    (Meteor Scatter goes both directions)

    And, of course, the Big Bubba of them all, EME aka Moon Bounce: compared to that lightning should be trivial 🙂

    Reply
  2. Marco Antonio Macalusso Núñez

    TNX Robert.
    Hola, ahora entiendo aquellas capturas de emisoras en FM comercial.
    Parecía de que el cable ó la antena del RX estaba conectada en forma defectuosa. Aparecía bruscamente la estación y en el lapso siguiente se oía ruido y así continuaba la escucha de la estación.
    Otras escuchas las realizaba en horarios definidos , en ocasiones recibía estaciones de FM , ubicadas muy lejos, hacia el norte de mi ubicación (centro -sur de Chile), la escucha era de corta duración pero mas estable que aquella producida por rayos. Estas eran rebotes de emisoras en el cuerpo de aviones comerciales, los horarios en que las sintonizaba, se repetían de acuerdo a los horarios de vuelos.
    CE6SAY, from FF31 qr.
    73

    Reply
  3. Babis

    by the way i forgot … is also risky … here in a rural village (more close to nature) in the past very strong lighting had destroyed 2 broadband modems, electric fridge, 1 weather station (was at the roof) one usb port at pc … so waiting to get fm dx signals, is not the best option, it will happen once to get hit by strike & thats it … if you can get signals inside home is safer, but for me dx signals pass better & more stronger about 50 away from my home

    Reply
  4. Babis

    i confirm but not always … i am sure 1000% that summer times during the daytime here in corfu greece … with some large party parts of clouds (not all sky covered) ^ having some good lighting around my location & about 100-200 km far, i get sporadic-e fm signals from middle east, maybe spain, france, russia, turkey… i believe is a mix of specific barometric pressure, temperature (maybe around 24-30 c) low to middle moisture (even if is raining summer time daytime here, moisture does not usually go over 60% in most cases) causing kind of electric generate at the atmosphere which helps fm to boost … at my case is not necessary to have lighting direct into my location but around me, still good … users reported the same at OIRT band (getting sporadic-e from eastern countries) but i do not have oirt radio yet (now i wait for the new pl-330) … how ever is not the same case for vhf dab+

    Reply
  5. Mangosman

    The ABC Classics transmitter is at Mt Baranduda,,(near Wodonga) in Victoria It has an effective radiating power of 80 kW and the horizontal and vertically polarised antenna is 78 m above the ground. Unfortunately the receiver location is not known.

    Reply
    1. Mangosman

      On viewing the Utube video Numeralla NSW is 224 km away as the crows fly but there is a mountain range about 1000 m above than a straight through “path”. So the signal definitely had to be through tropospheric ducting.

      Reply
  6. Roger Fitzharris

    Ben Franklin would be proud of whoever is holding the Tecsun PL-390, in the vicinity of a thunderstorm, with its stainless steel antenna extended. Shocking!

    Reply

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