Author Topic: Introduction to NVIS  (Read 24441 times)

Offline Carl

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Introduction to NVIS
« on: September 01, 2015, 06:40:56 PM »
  NVIS is often thought of as a special antenna though it is more of a skill and method of communication on HF (short wave) radio.
NVIS or Near Vertical Incidence Skywave is a great way to communicate in a zone that is otherwise a void for radio.
Most radio ,VHF,UHF,HF work line of sight to about 15 miles and after this the curvature of the earth pretty much blocks the signal as radio does not penetrate earth well. A high position or repeater allows for VHF/UHF to be heard farther ,a 200 foot tall repeater can be heard 27 or so miles away.

But HF bounces off the "F" layer of the ionosphere and can communicate hundreds and often thousands of miles...but leave the area between 15 mile ground wave and the 300 to thousands of miles away zone where the signal is normally NOT HEARD...while you
can talk thousands of miles away there is a area of coverage that you often need that is SKIPPED OVER..



Well with NVIS ,we point you power UP (almost straight up) to be able to bounce a small percentage of it back to earth CLOSER TO YOU and this allows coverage BEHIND HILLS,IN VALLEYS and places you can not reach without the effect of hosing (like a water hose) your signal almost straight up and scattering it from the reflecting layer 75 to 125 miles above earth...Kind of a pool shot that makes your signal rain down all around you from right at your feet to about 300 or so miles away. :)



With NVIS...you are able to talk closer in the 'normal' HF signals and have much more reliable 0 to 300 or so mile area of coverage ...
PLUS distant stations will still hear and be heard by you with the NVIS  antenna...just not quite as strong of a signal.

The NVIS signals are normally effective on 80-60-and 40 Meters as the higher frequencies penetrate the ionosphere while the
lower frequencies 'bounce' more readily.The antenna is just a horizontal dipole or other antenna placed about 1/10 wavelength
above the ground (I use 10 feet ,so no one gets clothes lined) and have ,on occasion just tossed a wire on the ground to demo that antennas don't have to be high to work (though they do work better when not in the dirt.

So this is how you get the best area coverage and most consistent communications in wood,hills,and valleys and with this simple
explanation ,maybe you could be convinced to give it a try to fill in the giant HOLE in your communications.

I will do my best to help with any questions of this interesting method of communication and better describe the antennas as needed.

Offline Greekman

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Re: Introduction to NVIS
« Reply #1 on: September 02, 2015, 12:31:56 AM »
Will you cover the need for Power for NVIS (yuo have elsewhere mentioned)?

Offline Ken325

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Re: Introduction to NVIS
« Reply #2 on: September 02, 2015, 05:11:49 AM »
Thanks for info.

Offline Carl

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Re: Introduction to NVIS
« Reply #3 on: September 02, 2015, 06:54:45 AM »
Will you cover the need for Power for NVIS (yuo have elsewhere mentioned)?

With NVIS , your signal must travel a long way up to the "F" layer in the ionosphere and due to the scattering of atmosphere and partial absorption of the signal (not ALL of it bounces back to earth)you get less signal to where it is wanted....but more than with conventional antennas and methods. The high angle  radiation gets MORE to bounce back CLOSER TO YOU and though still capable of long range communications....not quite as good at long range as a high antenna...BUT a low NVIS antenna has LESS NOISE and so it is often a better antenna to receive with as noise often is stronger than the signals. A low power signal still works,but with so little bouncing back,you need at least 20 watts as discussed in military manuals...for consistent communications...the more power you start with gets you more to bounce and return to earth and often low power NVIS is overpowered by the noise.

I don't recommend low power radios because communicators who depend on their radios want and need every advantage and while a cute ,low power radio may work,do you want to take that chance? The FT-817 runs for TWO to THREE hours on AA batteries and then must be turned off for a 10 to 12 hour recharge cycle while producing a FLEA FART of power when you can turn down the power on a 100 watt radio if you want but have the full power when you NEED communications. QRP (low power) radios do work and a man on foot has to compromise power for weight of radio and power BUT MOST QRP distance communications are done with MORSE CODE as code is more effective and often heard when voice can not.

How many preppers will carry their tons of necessities into the woods without a vehicle? Save the low power for when your welfare does not depend on it..I love QRP ,but you don't want to whisper a cry for help.

  Just a note that when man first set foot on the moon,a Ham designed VHF radio was used on their suits and they could talk through the void of space with these 1 watt radios DIRECTLY to ground stations even though they had 'repeaters' in the command module and the lander ...and on their rover vehicle..BUT in the absence of atmosphere ,their 1 watt was heard 240,000 miles away!
I recall reading this in a Ham magazine long ago ...QST I think.

A place to begin reading:  http://www.w0ipl.net/ECom/NVIS/nvis.htm

and here :  http://www.tactical-link.com/field_deployed_nvis.htm
« Last Edit: September 02, 2015, 07:07:05 AM by Carl »

Offline armymars

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Re: Introduction to NVIS
« Reply #4 on: September 02, 2015, 07:38:44 AM »
  Today is a good example of when you need more then QRP. I just finished my net on 60 meters and had to use Olivia to stay in contact with stations in Michigan (my state). I could make out stations in IL,MN and Ohio on phone. We did a radio check on 74 meters at 1220z and it was a little bit better then 60 M. By 1245z no one could hear anyone on 74 M because of D layer absorption. That left us 60 M again and that was going down hill. Most stations were running 100w with NVIS antennas. Without though's antennas not even Olivia would have helped much.
  At night many stations will drop down to 20 watts because that's all you might need. Right now I'm listening to IL and MN on Olivia, it's 1328z . Even with the lighting strikes noise they are printing out OK.  I now see WI is in there to. He just told MN was the loudest stations on the net. I can cpy one MN station on phone , but the other is just printing QRK4 . Right in the noise.
  Olivia or PSK 31 may be the only way you can talk to each other when the band is bad and that's with a 100 watts.

Offline Chemsoldier

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Re: Introduction to NVIS
« Reply #5 on: September 02, 2015, 08:25:36 AM »
 :popcorn:

Offline Carl

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Re: Introduction to NVIS
« Reply #6 on: September 02, 2015, 09:09:40 AM »
Good Idea     :popcorn: :popcorn: :popcorn: :popcorn:

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #7 on: September 02, 2015, 12:06:23 PM »

Offline idelphic

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Re: Introduction to NVIS
« Reply #8 on: September 02, 2015, 02:59:22 PM »
I would rather use my FT-817 over the FT-857,..  But I am interested in the NVIS system and have been looking for a good antenna design for a while (off and on) to set up in my yard.  While I wish to chat local (KY), I'd like to be able to reach central VA as well.

Offline Carl

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Re: Introduction to NVIS
« Reply #9 on: September 02, 2015, 03:19:46 PM »
I would rather use my FT-817 over the FT-857,..  But I am interested in the NVIS system and have been looking for a good antenna design for a while (off and on) to set up in my yard.  While I wish to chat local (KY), I'd like to be able to reach central VA as well.


A 40 or 80 meter dipole at 10 to 15 feet of the ground will work OK and does not have to be all in a straight line to work and cover as NVIS to 400 or so miles ,but NVIS still has some distant ability...just not optimum for distance only. I also think you can do well with low power,just not consistently well as military testing has proven about 20 watts or more is needed for consistent coverage. I have run low power in the range of ten watts or so often ,but the noise level is often tough to overcome the last year or so.The lower antenna receives less noise and if BOTH parties use NVIS antennas,you have better chance of success though rarely do you find 80 meter wires 120 feet in the air ,so they are partially NVIS anyway and 80 meters is a better choice for "F" layer reflection also.

  Last thought is ,I encourage the use of a 4 to 1 CURRENT balun at your feed point as that has proven successful in many tests.
Running without a balun is OK also ,depending on trees,growth,and soil conductivity.

I welcome any other suggestions .

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #10 on: September 02, 2015, 03:29:37 PM »
I'm not sure if it was Carl's idea or my own, but I run with this balun.  I'm on the air, haven't burned up my station (or house) and all my bands tune up with the modest 3:1 built-in tuner on my IC-737.


http://www.amazon.com/gp/product/B00OU5KEDO

Offline Carl

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Re: Introduction to NVIS
« Reply #11 on: September 02, 2015, 03:34:52 PM »
Yes,low cost and it works...

Offline armymars

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Re: Introduction to NVIS
« Reply #12 on: September 03, 2015, 12:01:11 PM »
  So much depends on the time of day. 40 M at night with the antenna at seven feet will go as far as 1000 miles on the first hop. On Wednesday at 1340z all stations jumped at least 1 S unit. Even the MI stations were S5  on 60 M. I have found 60 meters to be about the best during the day till 2pm local time. Then 41 and 40 meters is better. Learn to use the VOCAP software or check WWV.
  Real early in the morning I often get one way propagation. I can hear stations west of me, but they can't hear me. This happens most during the gray line (dawn).
  You know when your going to loose a band because there will be a big jump in signals just before it goes dead. You'll have about five minutes to change bands. Antennas are important, but you must learn about propagation. It changes with the sun spot cycle, time of day, Ozone and a bunch of other factors. I've been in Mars for over 25 years and spent much of that time running nets with out using all of the information I had available. Now I take advantage of everything that will help me set up circuits and keep them running 24 hours a day, any day. This includes running multiple nets and relaying between nets to pass traffic.
  If you have to run QRP then set up your scheduled for before dawn or after sunset to improve your chances. 73 dit dit

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #13 on: September 03, 2015, 12:52:52 PM »
two big things for me to improve

1) understanding signal reports (sometimes when I get a good copy I just tell them "599" because that's what they want to hear, but I just have an analog meter bouncing on my rig)

2) understanding propagation and band conditions - sometimes where the bands are reported as bad - they actually are, but last night after dark I hit coastal NC over PSK31 on 20meters.  Furthest QSO on that mode I've made, but conditions were "red".


Offline Carl

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Re: Introduction to NVIS
« Reply #14 on: September 03, 2015, 02:27:04 PM »
two big things for me to improve

1) understanding signal reports (sometimes when I get a good copy I just tell them "599" because that's what they want to hear, but I just have an analog meter bouncing on my rig)

2) understanding propagation and band conditions - sometimes where the bands are reported as bad - they actually are, but last night after dark I hit coastal NC over PSK31 on 20meters.  Furthest QSO on that mode I've made, but conditions were "red".

1...Signal report with three numbers

R = READABILITY
1 -- Unreadable
2 -- Barely readable, occasional words distinguishable
3 -- Readable with considerable difficulty
4 -- Readable with practically no difficulty
5 -- Perfectly readable

S = SIGNAL STRENGTH
1 -- Faint signals, barely perceptible
2 -- Very weak signals
3 -- Weak signals
4 -- Fair signals
5 -- Fairly good signals
6 -- Good signals
7 -- Moderately strong signals
8 -- Strong signals
9 -- Extremely strong signals

T = TONE
1 -- Sixty cycle a.c. or less, very rough and broad
2 -- Very rough a.c. , very harsh and broad
3 -- Rough a.c. tone, rectified but not filtered
4 -- Rough note, some trace of filtering
5 -- Filtered rectified a.c. but strongly ripple-modulated
6 -- Filtered tone, definite trace of ripple modulation
7 -- Near pure tone, trace of ripple modulation
8 -- Near perfect tone, slight trace of modulation
9 -- Perfect tone, no trace of ripple or modulation of any kind

2 ..

It often depends on where measurements are taken for propagation and this is why I use the reporting site of DX MAPS to see who is talking to whom and what bands and mode SSB/CW are being used.

 http://www.dxmaps.com/spots/map.php?Lan=E&Frec=7&ML=M&Map=NA&DXC=N&HF=S&GL=N

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #15 on: September 03, 2015, 02:35:24 PM »
Thanks Carl.

Does "tone" apply for digital modes then?

I suppose it would for CW to some extent...

Offline Carl

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Re: Introduction to NVIS
« Reply #16 on: September 03, 2015, 04:10:56 PM »
Thanks Carl.

Does "tone" apply for digital modes then?

I suppose it would for CW to some extent...

From the days of CW,but just like "Q" codes,it is often given to indicate quality of voice...QOK? (made up 'q' code)

Offline Greekman

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Re: Introduction to NVIS
« Reply #17 on: September 04, 2015, 12:59:23 AM »
From the days of CW,but just like "Q" codes,it is often given to indicate quality of voice...QOK? (made up 'q' code)
No you did not....(the nerd in me speaks  :egyptian: :egyptian:)
QOK means "Have you received the signals of an emergency position-indicating radio beacon on...kHz(or MHz)?" (MARITIME USE ONLY)

(yes, I am that screwed I had to find the whole list)

Offline armymars

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Re: Introduction to NVIS
« Reply #18 on: September 04, 2015, 08:24:47 PM »
  Smurf Hunter,
Yes tone does apply to digital. You can often here someone over driving their radio by the distortion in there tones. (Olivia, PSK31)

Offline Carl

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Re: Introduction to NVIS
« Reply #19 on: September 05, 2015, 06:46:41 AM »
No you did not....(the nerd in me speaks  :egyptian: :egyptian:)
QOK means "Have you received the signals of an emergency position-indicating radio beacon on...kHz(or MHz)?" (MARITIME USE ONLY)

(yes, I am that screwed I had to find the whole list)

OK,but not a Ham radio "Q" code

Offline armymars

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Re: Introduction to NVIS
« Reply #20 on: September 06, 2015, 07:48:22 AM »
  We use QRK for digital on Mars. I have often seen 599 on PSK31 transmissions for signal reports just like you would on CW. To confuse matters we all use Z codes which were for RTTY. Pick whatever you like. Grin.  dit dit

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #21 on: September 06, 2015, 09:26:52 AM »
Had a contact use QTU yesterday.  I confess I had to look it up.

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #22 on: September 13, 2015, 10:08:12 PM »
Learned some things from my first attempt at NVIS.

I setup a 15 ft tall pvc pipe mast and ran 40m wires in an inverted V.  I also have 80 meter wires but my yard isn't large enough to accommodate so they were tied off short.

Google sa2259 if you want an idea of the design.

7.100 tuned pefectly.  No kidding, the entire band had no reflected watts on my meter.  80m tuned but was 5:1, and expected given it wasn't setup, so I focused on 40m.

I was able to hear far away stations in the southeast.  Lots of k5 and k4 calls.  NVIS?

Sunday nights are our weekly emcomm checkin, and in addition to a voice NET we send winking email.  I tried every winmor station within 300 miles and either got weird digital noise or no response.  For amusement I chose a station in NV, almost 600 miles away.  I connected, though it took 3 times for my message to send.

Summary:  this 15ft high 40m wire in a V is intended to be NVIS specific but just ended up being a solid 40m wire antenna, better than the one in my attic.

Other thoughts:

The mast is a pain.  It's a two man job to do this right.  I ended up using duct tap me around the coupled pipe segments, as it would flex and come apart.

RFI was a little hot, but with no balun choke etc, this is expected and there are various tricks.

I set this up at the edge of a 2:1 sloped hill.  Maybe the RF thinks it's higher from "ground" than I do.

I would like to setup in the field behind the nearby school and see if things work better.

Offline Alan Georges

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Re: Introduction to NVIS
« Reply #23 on: September 13, 2015, 10:37:12 PM »
I was able to hear far away stations in the southeast.  Lots of k5 and k4 calls.  NVIS?
...
Summary:  this 15ft high 40m wire in a V is intended to be NVIS specific but just ended up being a solid 40m wire antenna, better than the one in my attic.

Last weekend I had a 1200 mile 80m contact on my backyard NVIS antenna, at a time when conditions were supposedly poor on all bands.  Admittedly it was PSK31, but still it should have been impossible.  Sometimes these inexplicable openings just happen, especially as weird as the sun has been this past month or so.

Offline Greekman

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Re: Introduction to NVIS
« Reply #24 on: September 14, 2015, 12:05:18 AM »
Quote
I ended up using duct tap me around the coupled pipe segments, as it would flex and come

you did not use any pipe clamps, did you?

Offline Carl

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Re: Introduction to NVIS
« Reply #25 on: September 14, 2015, 05:33:26 AM »
An NVIS antenna is NOT a short range only antenna ,it is optimum for TRANSMITTING a short range signal but can hear and be heard at a distance . This is why I use ONLY NVIS antenna as they generally have lower noise than a high antenna and you tend to have LESS capability at long distance,but you still have enough signal to be heard well.

Offline armymars

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Re: Introduction to NVIS
« Reply #26 on: September 14, 2015, 01:50:04 PM »
  On the pvc pipe. I use 4" thin wall drain pipe with "no hub couplers" at the joints. I remove the rubber gasket an put it on the pvc after I fit the pipe into the hub ( so the smaller end is built up to match the bigger end ). The coupler with the two hose clamps go over the joint so one hose clamp is on each pipe. I can go up to 30' this way and put it up by myself. For a base I use a 2'X2' square of plywood with a pipe flange bolted to it. I screw in a 3/4" X 12" pipe nipple into the flange and add a weight from a barbell set. Then the mast slips over the nipple and you can walk it up no problem. I have pictures of my son walking it up when he was 12.
  I did add guide ropes on all four sides before it went up. Three were stacked down the forth was taped to the mast. You walk the mast up then grab the last guide rope and walk it out to the last stake. If the mast is not straight, slide the base around until it is.  Look Ma no adjusting the ropes. Don't forget to add a pulley and rope to the top before you put it up. HI
  The 4" pvc pipe is about seven to seven and a half dollars for ten feet. The No Hub Clamps about five dollars each.

Offline Greekman

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Re: Introduction to NVIS
« Reply #27 on: September 14, 2015, 02:09:49 PM »
I cannnot follow you a 100% cos i see unfamiliar terms and items.
But here is my system
https://imagizer.imageshack.us/v2/464x309q90/r/713/webigp7153.jpg
Three sections nest inside each other for 5-6 inches and a total of 15 feet.
There is also the option if adding a wooden broomstick to gaina yard or more.
there are 2 sets of rope attachements that can be moved anywhere on the pipes.
the pedestal is amde for a car wheel to lay on it, has a hole for a bolt joining pedestal and pipe and also a hole for a half meter stake to be drinen in the ground

Offline Smurf Hunter

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Re: Introduction to NVIS
« Reply #28 on: September 14, 2015, 02:16:41 PM »
  On the pvc pipe. I use 4" thin wall drain pipe with "no hub couplers" at the joints. I remove the rubber gasket an put it on the pvc after I fit the pipe into the hub ( so the smaller end is built up to match the bigger end ). The coupler with the two hose clamps go over the joint so one hose clamp is on each pipe. I can go up to 30' this way and put it up by myself. For a base I use a 2'X2' square of plywood with a pipe flange bolted to it. I screw in a 3/4" X 12" pipe nipple into the flange and add a weight from a barbell set. Then the mast slips over the nipple and you can walk it up no problem. I have pictures of my son walking it up when he was 12.
  I did add guide ropes on all four sides before it went up. Three were stacked down the forth was taped to the mast. You walk the mast up then grab the last guide rope and walk it out to the last stake. If the mast is not straight, slide the base around until it is.  Look Ma no adjusting the ropes. Don't forget to add a pulley and rope to the top before you put it up. HI
  The 4" pvc pipe is about seven to seven and a half dollars for ten feet. The No Hub Clamps about five dollars each.

Is this the "no hub" coupler you are talking about?




On my 1 1/2" PVC I cemented the PVC coupling to one section.  If the outer coupler was longer, it would help.  Is this the idea of these no hub connectors?

Maybe I could just slip those over what I've got now as an incremental improvement. 

I also like your idea for a base.  I bent the 1/2" threaded rod several times, and hammered it straight.  I think a flange and heavy base is more practical.

Offline armymars

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Re: Introduction to NVIS
« Reply #29 on: September 15, 2015, 04:01:30 PM »
  Yes that is a no hub coupler or clamp. On 4" drain pipe you have a hub (bell) on one end and a just the pipe on the other. Like what you see on the gray pvc conduit. Drain pipe is SCH 10 and very light. For the clamp to work right you need to build up the pipe that does not have the hub. I used the rubber liner and it works OK.
  Remember to put half the clamp on the pipe and half on the hub.