Let's talk NVIS- best solution for comms 0 to 100+ miles?

[xsquidgator]

I got into amateur radio a year ago primarily due to interest in prepping.  After getting going with a Technician license and a dual band HT, I started to hit up on the various distance limitations of simplex VHF comms.  Repeaters are nice and they help a lot, but I'd really like to be independent of reliance on them.  I live in central Florida and a number of my friends w with radios live within VHF simplex range of me, especially if I take an antenna up on the roof of my house and use more than 5 watts.  But several friends are a few miles further out than that.

Knowing a little bit of the theory left over from the study guide, i began to think HF might have more to offer.  Got my General license and some HF gear, and began trying that too.
Initial experiments with a mobile screwdriver-whip antenna were disappointing, almost never have I been able to make HF contact and when we could, it was weak and almost impossible to copy.

We're now trying out NVIS antennas and I think this will work better, but we're still early in the process.  A couple of us in our group of friends have made our own copies of the military AS 2259 - I'll see if I can't attach a picture in a minute.  Mine works pretty well I think, and it doesn't seem difficult to get out to 300 miles away on only 15 watts or so.  The NVIS antenna is supposed to be optimized for 0 to about 200 iles I think, but I've  so far gotten contacts as far away as New York City while I was trying to find more local contacts. If I can get mine set up at the same time as my for ends, which will happen one of these days, we'll get a better idea of how well it works in much closer, say in the 10 to 40 mile range. 

Couple of questions for you experienced operators out there, about NVIS and this type of antenna in particular.
1) is there a minimum effective range for making contacts on 20 and 40 m with this setup?
2) for the type of comms that I'm talking about, do all parties have to have NVIS antennas for two way

Comm?    A friend of mine 20 miles away couldn't hear me at all but he has been using a sort of horizontal dipole on his roof.  Perhaps it can't pick up near vertical incidence HF?
3) are either  the 20 m or 40 m bands always or almost always open enough to support NVIS at these close distances?
4) any other recommendations for a radio setup to allow reliable radio comms from zero to perhaps a hundred miles out or so?  This NVIS seems just like what we're looking for, I think, but we aren't done figuring it out and testing it.

[xsquidgator]

http://www.globalsecurity.org/intell/library/policy/army/fm/24-18/24180049.gif

I don't have a picture of my antenna setup handy, but it is very much like the one in the link.  Four legs, each 45 feet long total. Each 20m wire is 25 ft long and each 40m wire is 38 feet long, each connected via insulator to 550 cord and bungee to a total length of 45 feet, staked at the ends.  Center-fed with 100 foot of 450 ohm ladder line.  Due to small lot size, I put it up in the neighborhood common area behind my house, and take it down when I'm done.  By myself it takes about 20 minutes to put up or to take down.
That isn't bad but I'd sure like to be able to leave it up for a while.

[Alan Georges]

XSG, thank you for starting this thread!  Like you, I'm a new ham who's experimenting with NVIS too, for much the same reasons.

First, from what I can answer, here're my answers to your questions:
(1) No, it's straight up and straight down, so it'd be really unusual to have a local skip.  BUT... 20 meters is way too high in frequency for NVIS to work.  (more on that in a minute)
(2) Nope, works fine for about any orientation.  Irregularities in the ionosphere randomize the polarization.  You may get the signal knocked down by a few dB, but it'll get through.
(3) 40 is good now, near solar max, but may be too high in a few years.  Scroll down to the plots on page 5 of this presentation: https://www.txarmymars.org/downloads/NVIS-Theory-and-Practice.pdf  And of course, 20's never open for NVIS.  (Or if the sun's active enough that it is open, I'm wearing heavy sunscreen and a lead hat that day.)  Even 80 can be too high when the sun's particularly quiet.
(4) Setup... I'm going to refer you to a review and discussion about my 40/80 meter set-up http://thesurvivalpodcast.com/forum/index.php?topic=44578.0   The main point is that it can do 80 meters but doesn't take up much more room than a 40.

The one other place I'll point you is to this presentation:
http://www.w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf
It has a lot of practical advice for different configurations, as well as discussions regarding less-than-perfect setups.

Central Florida?  I've talked over that far on 80 meters at night... Maybe we should try to talk on 40 meters one day this weekend.  If you're interested, PM me and we can set something up.

[armymars]

   I'v been running NVIS since about 1990. Right now my Mars Nets are using 60 meters. This works well till about noon. Then it falls off till about 6 pm. Late at night in the winter we might go as low as 2 MHZ. The last few days, our MUF has been as high as 6.2 MHZ.
   I find there is a dead spot from 0-20 miles or so. Not completely dead, but 12 db down from the other stations. One way to beat this is add some vertical component to the antenna so you get some ground wave mixed in. The off center fed dipole from Radio Wave might work if mounted low. My 60 meter dipole is only 7 feet off the ground or so. and I work the U.P., OH and WI. off it during my 8 am net. The loudest antennas are feed with open wire feed on the nets. The dipole is at lest as long as 80% of the lowest frequency. (200 ohms impedance at that frequency).
   There are times when it looks like nothing will work, but we have found Olivia, or JT65 will get through under the worst conditions. 64 tones, 2K band width. The nice thing about digital is the average person has no idea what is being said.
   My portable antenna is like the AS-2259, but I use resonate antennas cut for 3.3 MHZ and 60 meters which are near my Mars frequencies. This way I can feed it with co-ax with little loss. The less loss the better. My mast is 16 feet tall, the ends are 5 feet off the ground.
   One of the best places to get started with NVIS is the TX Mars site that's been listed. They have information in there that took me years to figure out for myself. The best height I've found for the dipole when vacationing in Fl was 17 as a flat top. Be leave it or not it changes a little with changes in Latitude 73's .

[Alan Georges]

   I find there is a dead spot from 0-20 miles or so. Not completely dead, but 12 db down from the other stations. One way to beat this is add some vertical component to the antenna so you get some ground wave mixed in.

Hmmm, good to know.  I'm pulling in stuff across town (2-3 miles) and next town over (~10 miles), but with my inverted V there's a significant vertical component.  I was thinking about modifying to a full flat-top to squeeze out a few dB more performance, but now I'm thinking to leave well enough alone.  Thanks, AM.

[SCWolverine]

My random wire antenna (75+/-' at 8'AGL) has worked really well for NVIS.  I've talked as close-in as 12 miles;I'm sure it was Groundwave Prop, but we still did it    (and all up and down the East Coast),  we've found the lower the freq the better we do-minus 10m with both of us running a Vertical.

That same Random wire also got me to AZ on AM and Japan on 20 

if you google "ar15.com NVIS" you may find some of the discussion we've had over there.

[xsquidgator]

Everyone - thanks!  This is exactly the type of experience and info I was hoping to hear.

Fwiw we had a successful test last night, me with the as2259 copy antenna and a friend of mine at about 10 miles away using an end fed sloped wire.  We had strong excellent comms on 40 m and use able comms  on 60m.  Nothing at all on 20m even though I was picking up a fair amount of 20m traffic.  Apparently the muf was (well) below 14 MHz.

I'll have to think on some of what you guys have posted and I'll certainly check out the ar15 dot com discussion too.  Even if there's a 10 mile dead zone, I find that I can get out to 10 to 15 miles simplex with a vhf j-pole on a 15 ft mast.  While on that subject, any recommendations for the best type of mobile or at least portable vhf-uhf antenna for this shorter range stuff?
Ii'm running an ICOM 7000 with ah4 tuner off a battery.  I have two mil surplus sets of fiberglass poles, one for the NVIS and one for the vhf-uhf antenna.  I keep the NVIS put together enough so that I just have to run out the end wires and stake them, then put up the center pole, connect feed line to the tuner, and ready to operate.  By myself it takes me about 15 to 20 minutes from out of the car to on the air.  The NVIS wires-rope, stakes, and feed line all fit a 5 gal bucket when put away for storage or transport.

[armymars]

In my earlier post I mentioned Radio Wave, I meant Radio Works. They also make good Balun's. 73

[doublehelix]

Really, REALLY not a fan of Jpole antennas due to tuning and swr issues.

In a local EMCOM test here we did real-life testing of Jpole vs/ 1/2 wave dual-band mag mounts, and the mag mounts were at least twice as effective in coverage.

Throw in a ground plane kit and a 20ft push up fiberglass mast, and you have a VERY solid setup.

You can even hang it upside down from a tree branch with paracord.

Used NVIS here between base and BOL about 50 miles away.  Rock solid.

[xsquidgator]

Really, REALLY not a fan of Jpole antennas due to tuning and swr issues.

In a local EMCOM test here we did real-life testing of Jpole vs/ 1/2 wave dual-band mag mounts, and the mag mounts were at least twice as effective in coverage.

Throw in a ground plane kit and a 20ft push up fiberglass mast, and you have a VERY solid setup.

You can even hang it upside down from a tree branch with paracord.

Used NVIS here between base and BOL about 50 miles away.  Rock solid.

Which bands have worked well for  you for comms  with your BOL?  So far, 40m seems to always work for us nvis, sometimes lower frequencies too.  Right now, thinking of making vhf, then 40m our comms  plan mainstays if phones didn't work.

[SCWolverine]

http://www.n9tax.com/Slim%20Jim%20Info.html

work Really Well for a Roll-Up EMCOMM answer.  I bought one early on for my primary base antenna (my base rig at the time was my only rig at the time-Wouvun HT) and had great success with it here on the farm.  It now hangs behind the curtain in the Den to use in case of Incitement Weather.  Need a few more to toss in our 'bags'!  You can build them yourself if you are so inclined, but N9TAX sure makes 'em pretty 

[idelphic]

J-Poles can be useful.  I don't remember what kind of antenna I have in the attic, and I need to put the coax back up to it again.

It's about a 6' tall dual band base antenna that gets good coverage.  If you want a decent base antenna that should fit in tight spaces, try this:

The Comet GP1 dual band, single section, fiberglass vertical base antenna is for 2 meters and 440 MHz. It mounts on a mast (shown in photo but, not supplied) from 1.5 to 2.25 inches.

GP1 Specifications
Frequency: 2M/440
Gain: 3/6 dB
Power: 200 watts
VSWR: 1.5:1 or less
Connector: SO-239
Height: 4.2 feet

[xsquidgator]

A little update on this NVIS project.  I've learned a couple of little handy things over the past month or so.  One thing was that I don't seem to need all 4 wires to make it work well.  I removed the shorter 25 foot wire sections and ended up placing the center support pole in one corner of my rectangular lot, with each of the two wires going down one of the sides.  That is much lower-profile than the original, and it seems to perform as well radio-wise as the 4 leg NVIS antenna.  I kept my original 4 leg antenna for a field setup, with the stealthier 2 leg sloper antenna at home.

So far in the past month, 40 m has always seemed to be open for local comms.  I have gotten a few distant contacts, well 'distant' relative to the central part of Florida.  Several times I've been able to make good contacts out to 1000 plus miles, and once out to 1850 miles (Florida to Arizona).  For local contacts, it seems to work if the other end is using an NVIS setup too.  Not so much success contacting a local friend running a conventional dipole, it must not have enough gain vertically I'm guessing.

So far so good with the NVIS.  Now I just have to keep on the other hams I know a round here to put up an NVIS antenna too.

[Alan Georges]

A little update on this NVIS project.

Cool, thanks!

[armymars]

I was talking to Barker & Williams the other day and they were telling me that for in close NVIS 0-10 miles you didn't want your antenna more then 10 feet off the ground. Also it should be a flat top if using one of their TFD. 73 Magazine had a great article called a Super 40 Meter Antenna. It was a 40 meter folded dipole 7 feet off the ground with 3 reflectors under it just off the ground 6 feet apart. I think it was Oct. 1968. 73

[Greekman]

Is this it?
http://www.hamuniverse.com/supernvis.html

It is oen of the articles in my "to read" list

[armymars]

  I doubled check my info. The year the artical came out was 1969. October, page 8. the formula is 458/fMz in feet as a folded dipole fed with co-ax. The low impeadence is because the antenna is only 5% of a wave lenth above ground(7'). The 3 reflectors are 5% longer then the antenna.
  The name of the artical is "Super-gain antenna for 40 Meters" Also read "Viditos That have known Me". Even my mother was laughing so hard while I read it to her she had to stop ironing. 73

[doublehelix]

40M seems to work best for my distances between group members and the BOL.

I'm currently experimenting with an NVIS antenna setup OVER a 3 acre pond (used as a counterpoise/reflector) at the BOL. Looking for surplus harbor buoys on which to mount some insulated standoffs for the antenna wire to sit in the middle of the pond.

 

Which bands have worked well for  you for comms  with your BOL?  So far, 40m seems to always work for us nvis, sometimes lower frequencies too.  Right now, thinking of making vhf, then 40m our comms  plan mainstays if phones didn't work.

[armymars]

  That's almost as cool as the ham I talked to in NC who mounted all his antennas over a salt marsh.  73

[Alan Georges]

There's been a lot of discussion about NVIS over at an antenna review (http://thesurvivalpodcast.com/forum/index.php?topic=50876.0 ), but I'm trying to drag the NVIS-specific discussion away from there over to here.  So... jumping in in mid-conversation:

When antennas go higher,they pick up more noise. When dealing with NVIS,your signals are just a tiny percentage of power reflected back to earth. I always opt for LESS ,it noise and signal go down equally then your change does little as "S" unit is just a number. I have found that lowering the antenna removes way more noise than it does signal. I would do a true dipole (not inverted "V" I use now) at 8 to 9 FEET and benefit from low noise and good reflection.

Carl, are you doing this for 40, 80m, or both, or maybe some other bands?  PVC masts to 10' are really easy, and I might re-arrange my 80/40 antenna one of the days.  It would be nice to get rid of some noise, and even if the signal goes down too, as long as the noise goes away faster it's a win.

Also a slightly longer wire on the ground as a reflector will better define 'ground' and improve receive strength PLUS help stabilize the transients that received signal often fades in and out.

It also narrows the bandwidth of the antenna.  I initially put reflectors under my 80/40, and on 80m (where it relies on the trap coils) the bandwidth was about 2/3 of the General phone band.  After I read this http://www.w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf , I pulled up the reflectors and was able to talk across the entire General phone band.

Also, about half-way through that presentation there's a figure showing gain vs. antenna height.  I think EZNEC was used, but I can't find exactly where the model is mentioned.

[Alan Georges]

A question for you fellows, as this seems like the group who could give me the advice I need.

the back yard I've got to use is about 17' (though I might be restricted to about 13-14') by approx. 30', perhaps a bit longer, and there's a balcony on the second floor from which I could probably hook up the center of an inverted V. The problem is that I'd have to not only keep the wires fairly low (perhaps a good thing) but that I'd probably have to tie both ends down at the far North end of the yard just 10-12 ' apart from each other (like a v shape from above). Perhaps I could alternately do something with two crappie poles at either end of the yard, but those would at best be only 30' apart. Thus even a half length 40m G5RV or the MFJ that's the subject of this thread could hardly fit into such a yard and even that's with the dubious setup.

I'll be adding some extra radials to my portable vertical today and am not giving up on it, but I'd like to try something different and even an NVIS setup would have practical application for me, but it's all about playing with such limited space. Perhaps once I set up my power system for more portable use in a park I'll be able to properly setup a 50-100' dipole, but in the meantime I'm trying to play around with other options. If those end up being fairly portable that would be a bonus, as the ability to deploy with my kit is a medium term goal.

CDP, the two legs will probably be too close together yielding a too-low impedance for the antenna.  You may or may not be able to adjust it with a tuner.  Maybe for your case, a tuner, a single wire, and a really great ground system may be a better answer.

Hang on a sec, I'm going to run outside and measure the linear footprint of my 40/20m (or more like 20m antenna, but they go in the same spot).

(towels of some sweat)  OK, I'm back.

The whole thing is 34' end-to-end on the ground, but there's a couple of feet of paracord on either end too, so you could rig this in 30' (just barely), or maybe you could even zig-zag the legs a little to make it all fit more easily.  Remember, that's with single center pole and a 45deg vertical angle between the two legs.  Sounds like you could fit that, perhaps if you go diagonally.

[armymars]

  With the antenna that close to the ground a flat top might be better. I did run an inverted V for years with the center as low as 13 feet. You want to keep the angle shallow. The book says 120*. More than that and losses go up. When you pulled out the reflectors the antenna may have become broader, but the losses higher. Of course if this is the only way you can work them, go for it.
  Is there any way you can run open wire feed. On Mars these are the loudest antennas on NVIS. The next are the antennas with remote couplers and the last are G5RV's at 37 feet. All stations are close in performance to each other. It's only when the band is bad you can really tell the difference.
  Last but not lest don't over look 60 meters for NVIS. It works very well until Noon or so then picks up at about 5 pm or so. In winter it may work 24/7. When the sun spot numbers drop think 160. 73

[Alan Georges]

  With the antenna that close to the ground a flat top might be better. I did run an inverted V for years with the center as low as 13 feet. You want to keep the angle shallow. The book says 120*. More than that and losses go up.

It works out to 130deg on my 80/40m, so it's in bounds.  The feed point is 20', ends are at ~5'.

When you pulled out the reflectors the antenna may have become broader, but the losses higher. Of course if this is the only way you can work them, go for it.

Yeah, that's about how I'm looking at it too.  The small dB hit for the extra bandwidth is a good trade.

  Is there any way you can run open wire feed.

No, not really.  It was a contortion to get the 80/40m in the yard at all, running ladder line to it would be major yard re-building task.

  Last but not lest don't over look 60 meters for NVIS. It works very well until Noon or so then picks up at about 5 pm or so. In winter it may work 24/7. When the sun spot numbers drop think 160. 73

I'll start listening in for traffic on 60m, even if I can't tune it yet.  If there's much talk on it regionally, it may be worth the effort of yet another antenna.  160... maybe as the sun calms down in this cycle I'll get desperate enough to go there.  It'll be interesting, to be sure.  May just do a tuner and a long wire to dip my toes in at first.  Got a year or so before it's time.

Thanks armymars.

[armymars]

  Canadian Prepper said his yard was only 30 feet long. That got me to thinking about early radio. With the operating frequencies down around 137 KHz no one had a yard big enough for a 1/2 dipole. They got around this by running short folded dipoles with 5 to 7 wires in parallel. It won't raise your radiation resistances any but it does raise your feed point impedance. The parallel wires also cut losses by dividing the current.
  I tried this on the ham bands by making a folded dipole only 7 feet long with 13 wires and window line. It worked better then my G5RV at 30 feet as an inverted V on 40 meters. It's true that I was in the parking lot of a Red Cross building with cars all over, but on 40 it worked better. On 80 it sucked. I didn't have time to try it on any other bands.
  If you could get a mast 60 feet tall you could make a skeleton slot antenna.  This would give you horizontal polarization even though the antenna is vertical. ( Strong H wave , weak E wave. )
  Last you could try an antenna I read about. It was short so you had to make a impedance transformation. Think of a delta antenna, but two of the legs are the transformer to the feed line. The math is heavy and I need to reread the article. 

[Canadian Prepper]

CDP, the two legs will probably be too close together yielding a too-low impedance for the antenna.  You may or may not be able to adjust it with a tuner.  Maybe for your case, a tuner, a single wire, and a really great ground system may be a better answer.

Hang on a sec, I'm going to run outside and measure the linear footprint of my 40/20m (or more like 20m antenna, but they go in the same spot).

(towels of some sweat)  OK, I'm back.

The whole thing is 34' end-to-end on the ground, but there's a couple of feet of paracord on either end too, so you could rig this in 30' (just barely), or maybe you could even zig-zag the legs a little to make it all fit more easily.  Remember, that's with single center pole and a 45deg vertical angle between the two legs.  Sounds like you could fit that, perhaps if you go diagonally.

I'll have to dig up my measuring tape to get more precise dimensions in the daylight, but a quick check reveals closer to 40ft of workable space, and perhaps another 10 feet that can be used on one end to tie down on end. And  just by chance I came across a local ham selling a 30ft vertical pole in 9 segments, with supporting cables, etc. for $65, whom I think I'll call tomorrow. That could probably be set up at the optimum height for either a conventional or NVIS type dipole. So a 20/40m dipole might just fit in my space, and the pole would be easily transportable for portable use elsewhere.

Pardon me for taking the threads a bit away from the NVIS theme, but all of your assistance has been most helpful.

[Alan Georges]

Pardon me for taking the threads a bit away from the NVIS theme, but all of your assistance has been most helpful.

Always happy to help.  Now 20m's not gonna do beans with NVIS but 40m can if you flatten things out the way armymars describes, or the whole thing can be set up as an 45deg-ish inverted V and you're sure to get some use out of both bands that way.  You'll get contacts either way!

Please keep us posted. 

[armymars]

  If all else fails, go for an inverted L antenna with ground plane. 30 feet up 30 feet across. You now can work 80 meters to. Or 15 feet up 30 feet across you can work 60, 40, 30, 20 meters with a tuner and have NVIS on 60 and 40 meters. In fact your signal will be about the same for all stations. A remote tuner works best for this set-up.

[Carl]

As I was in a series about a MFJ 20-40 antenna and it mutated into NVIS ,I read some of this and though I would inject my thoughts.

NVIS is a 40-80 meter anomaly that rarely works at higher frequencies well due to composition of upper atmosphere.

1/10 to 1/4 wave above earth is accepted as best height for NVIS antenna (BEST...not only) as in variable conditions and inverted "V" allows more consistent use and a true dipole allows slightly better effectiveness.

Any antenna that is shortened by traps and coils will be less effective than a proper length wire at NVIS and all HF for that matter, coils and traps make for a more convenient size ,but are a compromise.

HF ground wave will extend to 20 miles or so and is not NVIS as your signal is not bouncing off of the atmosphere .

Wire ground reflectors do help,but they also help define ground (earth ground varies and is not a finite depth of the surface)
so that tunes and effective angle may also be effected.

The AS 2259 is a command antenna that offers much for a portable effective GROUND WAVE,NVIS,and Long distance antenna. And when used with a good antenna tuner can be your ONLY antenna needed for HF. The link below is to some 2259 variations I have hosted on my GOOGLE DRIVE, I found them free and offer them FREE,any claim to ownership and I will be happy to take them off the drive. Anyone with this link can download and use these files...ENJOY keeping the VERB in HAM radio.

The LINK:  https://drive.google.com/folderview?id=0B5ZIZLZV4AwIY3NoMkthTEVQRE0&usp=sharing

[Carl]

As I was in a series about a MFJ 20-40 antenna and it mutated into NVIS ,I read some of this and though I would inject my thoughts.

NVIS is a 40-80 meter anomaly that rarely works at higher frequencies well due to composition of upper atmosphere.

1/10 to 1/4 wave above earth is accepted as best height for NVIS antenna (BEST...not only) as in variable conditions and inverted "V" allows more consistent use and a true dipole allows slightly better effectiveness.

Any antenna that is shortened by traps and coils will be less effective than a proper length wire at NVIS and all HF for that matter, coils and traps make for a more convenient size ,but are a compromise.

HF ground wave will extend to 20 miles or so and is not NVIS as your signal is not bouncing off of the atmosphere .

Wire ground reflectors do help,but they also help define ground (earth ground varies and is not a finite depth of the surface)
so that tunes and effective angle may also be effected.

The AS 2259 is a command antenna that offers much for a portable effective GROUND WAVE,NVIS,and Long distance antenna. And when used with a good antenna tuner can be your ONLY antenna needed for HF. The link below is to some 2259 variations I have hosted on my GOOGLE DRIVE, I found them free and offer them FREE,any claim to ownership and I will be happy to take them off the drive. Anyone with this link can download and use these files...ENJOY keeping the VERB in HAM radio.

The LINK:  https://drive.google.com/folderview?id=0B5ZIZLZV4AwIY3NoMkthTEVQRE0&usp=sharing

YEP..I am replying to my own post. with more thoughts.

A 34 foot antenna for 20 and 40 is a 20 meter antenna that sorta works on 40. For convenience and size it is OK,BUT as very little signal it reflected at the HIGH ANGLE of NVIS ,3 or 4 DB can be all of your signal. My full size 40 wire is an inverted "V" but as my space is too narrow ,it "V's" toward the back yard as well as to the sides.

WIRE antennas are drawn as straight lines because straight lines are easy to draw , the ends of a dipole can make a 90 degree angle and still work great. If folded back within 2 feet of itself ,some length will need to be added for tuning but the RF works very well ,even bent RF is heard as straight at the other end.

[TiredOldGrunt]

If dont 40m NVIS, a dipole about 6 ft above ground works a treat.  Ive also done a dipole as a sloper, tall side toward intended direction, high side about 12 ft and low side about 3 ft.  WORKS.

Best advice I can give you, is experiment and try for yourself!!

TOG