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Author Topic: NVIS  (Read 2652 times)

Offline ChrisSmolinski

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NVIS
« on: December 17, 2011, 1441 UTC »
While shortwave radio is commonly thought of as being used for long distance communications, it also functions for local and medium distance links. This is accomplished by a method known as NVIS, or Near Vertical Incident Sky Wave, and is in fact what most US pirate operators are using, even if they have never heard of it before....

http://www.hfunderpants.com/?p=245
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Offline John Poet

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Re: NVIS
« Reply #1 on: December 17, 2011, 2135 UTC »
Yep.  Unless they can get their horizontal dipole up 60-some feet, which hardly any can manage, most of the signal is NVIS, and most landing within the first 300-500 miles... unless its very long after local darkness in December, in which case most of it is not landing at all due to MUF absorption which you cite in your post.

Ideally, everyone with many listeners within that 500-mile range should be down around 3-3.5 mHz after dark, especially during December and January; but generally from November through February.

I recall operating one Christmas eve around 3.3 mHz until well after midnight and 1 am, and being heard well regionally, even short-skip into Ohio. You could almost run all night down there, with little loss of regional coverage.  By contrast, 6.9 mHz would be closed to me for much of the eastern half of the US this time of year by 6pm local, except for the deep south and Gulf coast, from this Michigan locale..

On the other hand, MORNING operations around 6.9 mHz as long as three hours after daylight would be at their most efficient this time of year, with signals losing strength much later in the day than in, say, June.... :D and the noise levels are reduced after daylight as well.

Through January, the window is from 7 am to almost noon.  Best coverage would probably occur between 8-10 am local.  Someone posted a log after 12pm today of WMPR, coming in at 4s & 5s



« Last Edit: December 17, 2011, 2146 UTC by John Poet »

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Offline ChrisSmolinski

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Re: NVIS
« Reply #2 on: December 17, 2011, 2142 UTC »
Ideally, everyone with many listeners within that 500-mile range should be down around 3-3.5 mHz after dark, especially during December and January; but generally from November through February.

I recall operating one Christmas eve around 3.3 mHz until well after midnight and 1 am, and being heard well regionally, even short-skip into Ohio. You could almost run all night down there, with little loss of regional coverage.  By contrast, 6.9 mHz would be closed to me for much of the eastern half of the US this time of year by 6pm local, except for the deep south and Gulf coast, from this Michigan locale..

Yes, I recall hearing you on 3 MHz, and several other ops used it years ago. As you said, it works great all night long, well after 7 MHz has closed.  In the past, I think the largest obstacle was that no one knew to listen there, so few transmitted. Now, with instant reporting via HFU/FRC/IRC, ops can feel more assured that someone will hear them.

Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline John Poet

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Re: NVIS
« Reply #3 on: December 17, 2011, 2159 UTC »
Well, the antenna lengths being doubled from those for 6.9 mHz can also be an issue for the ops....

For a dipole, we're talking almost 70 feet per leg.

THIS is a very interesting alternative design, which uses 'linear loading' to employ a reduced-height vertical leg as well as a horizontal or angled leg.  They call it a vertical, but it would really employ both vertical and horizontal polarization:

http://ke4uyp.tripod.com/80m_160m_Antenna.html

Use a good antenna tuner, and you wouldn't have to worry so much about painfully "tuning" the thing to the exact frequency you want to use...

The 2-inch PVC would seem to be "overkill", 1 inch would seem adequte to me. I would also think the two-foot spacing between wires a little more than necessary.

The mast could easily be eliminated.  You could haul the top portion of the PVC pipe into a tree with a rope, using the usual sling-shot methods... For that type of configuration, seems like even 3/4 inch PVC would be quite adequate-- the caveat being that it may tend to break down quicker over time with exposure to weather.

John Poet

"A treasonous voice of dissent"

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Offline fpeconsultant

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Re: NVIS
« Reply #4 on: December 22, 2011, 1817 UTC »
Chris - you mentioned "HFU/FRC/IRC" - what are you referring to when you list "IRC".  I get the other two.
Thx
Near Chicago, IL USA.  Drake R8, Ten-Tec RX340, JRC NRD545, Watkins Johnson HF-1000, Wellbrook loop at 28', 43m inverted vee.  Please QSL to fpeconsultant@aol.com thanks.

Offline ChrisSmolinski

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Re: NVIS
« Reply #5 on: December 22, 2011, 1933 UTC »
IRC - Internet Relay Chat. A real time messaging system. You can chat with other radio enthusiasts, share loggings, etc.

Here's some basic details: http://www.hfunderground.com/wiki/Internet_Relay_Chat
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline Zoidberg

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Re: NVIS
« Reply #6 on: December 22, 2011, 1939 UTC »
"...what are you referring to when you list "IRC"..."

Internet Relay Chat, usually just referred to as chat or chat room.  Real-time text messaging with other folks in the same channel or chat room.

Old tech, relatively speaking, but still useful for certain niche hobbies and interest groups where real-time messaging with a group is desirable.  Works great for the pirate radio hobby and radio DXing in general, since participants can notify others to activity on a particular frequency.

And it's very resource efficient so even folks with older computers or on dialup can participate.

Click here for the: Pirate Radio IRC Chat Java Client.  Java clients are just oh-kay but after trying it you may prefer something else.

There are several popular free chat client software packages around.  I mostly use Pirch98 for StarChat, and occasionally an old copy of GAIM (now Pidgin), but there are others that work as well: mIRC, mibbit, others.
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Offline fpeconsultant

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Re: NVIS
« Reply #7 on: December 22, 2011, 1956 UTC »
Dang - you guys are GOOD!  Ok, now for another question: in the formula (in Chris' artcile linked) for MUF, what is the variable "D"?  Distance between the transmitter and the receiver?
Near Chicago, IL USA.  Drake R8, Ten-Tec RX340, JRC NRD545, Watkins Johnson HF-1000, Wellbrook loop at 28', 43m inverted vee.  Please QSL to fpeconsultant@aol.com thanks.

Offline ChrisSmolinski

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Re: NVIS
« Reply #8 on: December 22, 2011, 2022 UTC »
Dang - you guys are GOOD!  Ok, now for another question: in the formula (in Chris' artcile linked) for MUF, what is the variable "D"?  Distance between the transmitter and the receiver?

Yes, distance in km. Good catch, I really should have specified that.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

 

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