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Author Topic: NVIS regional comms with low-slung end-fed on 80m.  (Read 2613 times)

AK4YH

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NVIS regional comms with low-slung end-fed on 80m.
« on: November 06, 2018, 03:33:19 AM »

Check out my latest video:

https://youtu.be/6aWgNdaPGDk

Gil.
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ONAIR

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #1 on: November 19, 2018, 11:47:37 PM »

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K7AAT

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #2 on: December 01, 2018, 02:39:17 PM »

I simply do not understand why someone would want to make a video on the subject of an outdoor antenna.....IN THE DARK!

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KB2WIG

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #3 on: December 01, 2018, 03:25:31 PM »




 Radios work better in the dark.


klc
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EXTRALight  1/3 less WPM than a Real EXTRA

ONAIR

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #4 on: December 01, 2018, 05:19:44 PM »




 Radios work better in the dark.


klc
  Especially on 80 meters NVIS!!  ::)
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WB6BYU

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #5 on: December 02, 2018, 10:52:28 AM »

Quote from: ONAIR

Quote from: KB2WIG

 Radios work better in the dark.

 

Especially on 80 meters NVIS!!  ::)



Not always!  As we approach the bottom of the sunspot cycle, here in Oregon
80m NVIS is only available during the day.  We need to use 160m at night.

It depends on your latitude, among other factors.

A lot of problems that folks report with NVIS propagation are due to trying
to use too high of a frequency, in accord with "conventional ham wisdom"
of 40m during the day and 80m at night.  That certainly isn't true up here,
except during the summer if we have enough sunspots.

W7ASA

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #6 on: December 02, 2018, 07:43:25 PM »

If you camp even just one day, it's going to get dark. (Arctic/Antarctic excepted)
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N9AOP

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #7 on: December 15, 2018, 07:10:20 AM »

I enjoy video about ham projects.  However when they don't get to the point  immediately and drag on endlessly I get bored and cut the feed.
Art
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NEVBEN

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #8 on: March 12, 2019, 04:44:38 PM »

Great video.  Thank you.

What I don't understand about NVIS is how do you know it is skywave and not groundwave?  I don't have much experience with 80m, but 150 miles is a distance that is quite possible for groundwave with 2m or 6m.

I might be convinced the ionosphere was involved if I was in a valley with a horizontal wire and contacting someone on the other side of the mountains receiving with a vertical where it only worked at night, but how else could you be sure it wasn't just groundwave?  My local club has a weekly 80m net, and the guys with a particular interest in Emcom are determined to use NVIS antennas to extend their range beyond our immediate region but without the skip associated with other kinds of 80m skywave propagation.  Just the occasional check-in from 150 or 200 miles out isn't compelling to me that we have skywave propagation happening.

Noticing a big difference in propagation between daylight and nightime conditions would be some evidence the D layer was interfering with skywave propagation, but simply noticing the band was quiet during the daytime could just mean that other amateurs are using 20m at those times.
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W1VT

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #9 on: March 12, 2019, 05:41:37 PM »

One way tell the difference would be to measure the polarization.  Ground  wave doesn't shift polarization, which is why it is so important to match polarization.
NVIS involves a conversion to circular polarization.
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NEVBEN

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #10 on: March 12, 2019, 05:48:45 PM »

Right, that's why I thought the mismatched polarization in my example would suggest skywave was happening.
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WB6BYU

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #11 on: March 12, 2019, 09:27:09 PM »

Quote from: NEVBEN

What I don't understand about NVIS is how do you know it is skywave and not groundwave?  I don't have much experience with 80m, but 150 miles is a distance that is quite possible for groundwave with 2m or 6m.



I think you are mixing your modes...

Groundwave propagation must be vertically polarized, and travels in contact with the ground.
Maximum range depends on soil conductivity and output power, but might run out to 100 miles or
so on 80m with high power, though signals would be weak unless you are over salt water.  Coverage
drops with increasing frequency:  you aren't going to get very far at VHF with ground wave.  (Hint:
ground wave coverage would be just as good for a ground mounted quarter wave whip as for one
much higher in the air.)

Space wave, or direct propagation from one point line-of-sight to another.  That's much more
common on VHF.

Most longer distance contacts on VHF that aren't line-of-sight are typically troposcatter or something
similar:  signals are very weak, signals need to be propagated at low angles.

F-layer ionospheric propagation is most common at HF, at least for distances beyond groundwave
range.  NVIS is a subset of this (though there is some evidence of paths via the E-layer instead on 80m)
that works when the operating frequency is below the critical frequency.  In this case, a low dipole
or similar horizontal antenna) radiates (mostly) straight up to the F-layer and straight back down
to cover out to a few hundred miles.  Because path losses are low, signal strengths are good.   Generally
you have to change frequency as ionospheric conditions change over the day / year / solar cycle.
During the winter, especially with low sunspot counts, we typically use 80m during the day and 160m at
night to communicate around Oregon, while during the peak of the cycle during the summer we would
be using 40m during the day and 80m at night.  The critical frequency rarely gets above 12 MHz or so,
and that only in the tropics, so for most of North America we only have 40, 60, 80, and 160m as options
for NVIS coverage.

With good sunspots the F-layer does occasionally support propagation on 6m, in which case things really
get wild!  But generally the only ionospheric enhancement at VHF is due to the E-layer.

W1VT

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RE: NVIS regional comms with low-slung end-fed on 80m.
« Reply #12 on: March 13, 2019, 04:04:54 AM »

https://youtu.be/ryiQjrNtnYo

CW NVIS Polarisation Ellipse during o-/x-mode transition


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