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Author Topic: Tropospheric Ducting  (Read 18881 times)
KK4APV
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« on: June 03, 2013, 02:53:00 AM »

My ham radio buddies joke that I'm in a "magic RF zone," because I can get VHF from far away.

For several months (yes, MONTHS), I was getting a repeater in Mecklenberg, Virginia that is 140 miles from my house (next door to the Norfolk, VA airport). Every morning, from 5:00 - 6:30 pm, I could not only hear them, but I could reach the repeater.

Amazing.

Now that we're into the hot weather, it has stopped, and yet, this went on from August to May.

I've done some reading on Tropospheric Ducting, but most of my reading suggests it's a weather/temp related anomaly. And yet my "connection" with Mecklenberg continued for several months.

Conversely, no matter how many machinations I attempt, I can not hit the Franklin repeater or the Richmond repeater, both of which are much closer to my house.

Any explanations? Or is it really just magic?  Smiley

Rose in Norfolk
KK4APV

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W1JKA
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« Reply #1 on: June 03, 2013, 12:10:23 PM »

Your correct,weather related,basically temperature inversions causing ducting effect.Common seasonal occurrence in different parts of the world i.e being able to pick up LA and San Diego,Ca. television stations after departing the Panama Canal and heading North bound up the Mexican coast to Baja
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RENTON481
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« Reply #2 on: June 06, 2013, 02:57:52 AM »

Here's a very useful website that has a page with Tropo ducting forecast maps.

A lot of FM DXers use them.

You can select which area of the World you want a forecast for, i.e. Eastern North America, Western North America, etc.

The link to the Tropo ducting section is in the middle of the webpage.

http://www.dxinfocentre.com/
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WB2WIK
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« Reply #3 on: June 06, 2013, 09:52:07 AM »

My ham radio buddies joke that I'm in a "magic RF zone," because I can get VHF from far away.

For several months (yes, MONTHS), I was getting a repeater in Mecklenberg, Virginia that is 140 miles from my house (next door to the Norfolk, VA airport). Every morning, from 5:00 - 6:30 pm, I could not only hear them, but I could reach the repeater.

Not so amazing.  Ordinary temperature inversion can create this quite reliably and repeatedly, and then suddenly stop.  140 miles isn't that far for a repeater.

"Ducts" are often a whole lot better than that, and provide propagation that gets better as you go up the spectrum into the GHz range.  Very common here for us to get a duct the whole length of the San Joaquin Valley (like 400 miles) and use it to make contacts on 144-222-432-902-1296-2304 MHz, sometimes up to 10.3 GHz, and 144 MHz is at the "bottom" of the spectrum regarding where it really works.  Signals are usually stronger on 1.2 GHz than on two meters when this happens, pretty reliably.  It almost never works on 50 MHz, the frequency is just too low.





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KD4LLA
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Posts: 454




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« Reply #4 on: December 07, 2013, 12:46:40 PM »

When I drove truck in Alaska there was a certain segment (10 mile) of the highway where our business band (UHF) radio could be used to contact another truck driver 50-75 miles away, due to "knife-edge refraction".  What is the terrain like between you and the distant station?

Mike
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W4KYR
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« Reply #5 on: December 08, 2013, 11:20:35 AM »

And then there are those legendary Hawaii to California paths.

http://www.arrl.org/w1aw-bulletins-archive/ARLP030/2005

"The tropospheric duct to Hawaii is open again. I worked Paul Lieb,
KH6HME last night (Sunday) at about 0150 UTC July 18 on 144.170 MHz.
Paul's signal was up and down, peaking S6, but he was easy to work.

"I use 100 Watts from an FT-736R and brick amplifier to a Cushcraft
124WB (4-element wideband) Yagi at about 70 feet on my tower in
Garden Grove."

Chip continues, "A number of other Southern California stations
worked Paul, as well.

"The beacon on 432 MHz was also being received well at the time."

He concludes, "The tropospheric ducting maps look very favorable
over the next 48 hours, so we have high hopes for more openings to
Hawaii this week."

The regular propagation bulletin will be out on Friday, July 22,
2005 as usual."
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Still using Windows XP Pro.
HURRICAINE
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Posts: 0




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« Reply #6 on: January 01, 2014, 08:25:18 PM »

Look at the map, the OP lives next to the water.

The only thing between him and the repeater is the hills up in Emporia.

The repeater is next to the Occoneechee park - right next to the water.

In the morning, the air warms before the water does and in the evening the air cools faster then the water does.

The mirage from the land mass heating up causes the signal reflections, along with both locations.

Now if you could talk in the other 3 directions an equal distance, that would be amazing.

In the morning, there is a repeater in Ohio that is on the same frequency as one here - 40 miles away.  The repeater here has no PL - hence when the people on the border between the two talks on their morning nets, they key both repeaters because they do not reduce their power when they know that they are causing harmful interference to the other repeater.

The Heterodyning in my receive is so bad I have to block the frequency when that happens.  The Ohio repeater is 120 miles away.

The problem was caused by two repeater councils that refused to relent when the other gave permission to use the frequency even though they were too close together.

How would you like to live in Florida where one television station in the middle of the state could serve the whole state when the signals were analog.

One good two meter repeater atop a 300' tower with a 250 watt PA could effectively cover most of the state and could offer handheld coverage for everyone within 50 miles of the repeater in all directions.
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