Trophspheric Ducting of VHF radio signals

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Trophspheric Ducting of VHF radio signals

Postby CPSK » Wed Jun 20, 2018 12:48 am

Hi'
I was writing a sort of memoir of my early rail scanning days when I recalled one night in August 1975 listening to my Heathkit scanner at my home in Teaneck NJ and hearing on the PC River Line channel (160.800) a train crew reporting that their train had derailed in Mount Marion NY.
At the time it happened, I wasn't sure whether it was in Mount Marion NY or at Marion Junction in Jersey City NJ.
Considering the nearly 100 mile distance between my receiving antenna (at about 25ft above ground) and the source of the radio transmissions, I found it difficult to believe that the right band conditions had just occurred on this fateful night when there would be a wreck in upstate NY.

I had never before heard even the dispatcher's radio from that far north, and this was when the radios were still on high towers like the one in Alpine NJ. I would regularly hear dispatchers on the Alpine radio, and the one somewhere north around Haverstraw? Or maybe it was on Mount Beacon on the other side of the Hudson. I would hear trains north on the River Line up to about Haverstraw.
But on this night I was hearing strong signals from both the dispatcher and the train crew. I think I may even have heard the caboose radio.

A week or so later I was hanging out with a train crew - they would often stop for a long time on the passing track in Teaneck awaiting another train - and asked about the derailment. That is when I learned that indeed it had occurred at Mount Marion NY and not Marion Junction in New Jersey.

A few years later when I became a ham operator, I began to realize just what had caused this phenoma. It's referred to as tropospheric ducting. It occurs when there is a temperature inversion at an altitude of between 500 and 1500 meters, and can 'guide' VHF radio signals for hundreds, or even thousands of miles.
Oddly, while I was hearing the radio transmissions of that train crew at Mount Marion from my Teaneck home, another listener somewhere in-between may not have heard anything. That's the way this type of radio propagation works. Kind of the way normal e-layer propagation works on HF.

Today I Googled "Train derailment in Mount Marion NY" and got a hit that took me to the article in a newspaper from August 1975. There was a paragraph saying that 15 cars of a 135 car train had derailed. I would have needed to sign up for a subscription to the website - newspapers.com - if I wanted to read more, but decided not to go that far.
But later when I tried to read that article again, it would not come up in the same Google search.
I've tried deleting cookies in my browser, and my Google search history at Google, but still I cannot get that hit I got the first time. It's almost as though someone at newspapers.com knew that I chose not to sign up and changed the Google search results...

anyway. I was just wondering if anyone has had any similar 'DX' listening experiences on the railroad band.

CP
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Re: Trophspheric Ducting of VHF radio signals

Postby radio » Thu Jun 21, 2018 8:12 am

US east coast was open to Japan on the 6 meter band yesterday, I heard.
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Re: Trophspheric Ducting of VHF radio signals

Postby CPSK » Thu Jun 21, 2018 10:21 am

radio wrote:US east coast was open to Japan on the 6 meter band yesterday, I heard.

I should be listening to 6m. My 40m dipole with 15m stubs will resonate on part of the 6m band. Perhaps I should at least try some FT8 up there...
But isn't 6m propagation mainly e-layer, and not tropospheric?
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