Mobile NVIS
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- Опубликовано: 23 сен 2019
- In this video watch me attempt to take a Little Tarheel 2 mobile HF antenna and attempt to convert it to an NVIS antenna. NVIS or Near Vertical Incident Skywave is an antenna configuration designed for efficient communications on 40 or 80 meters at a range up to 500 miles. Often used for emcomm or ARES groups to communicate when 2M won’t make the trip or when amateur radio repeaters are off line or nonexistent. NVIS radiates almost straight up and returns in a cone shaped pattern.
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Portable vertical antenna still works NVIS, but a horizontal wire off your feed point, I have a icom AH4 tuner installed on the truck
Hey, Jason.
The antenna you have will work, and it will work well. You just need to tweak your methods a bit.
First, you have to be familiar with Maximum Usable Frequency (MUF). At our current point in the Solar Cycle, 80M is generally better than 40M during the day.
Here's a great propagation prediction website: www.voacap.com/hf/
Move the cursors: one to your location, the other somewhere within 50-100miles away. Set the antenna heights for both stations to 17ft dipoles on 40,60,80M. Choose your mode and power. Click on the Prop Wheels to get an excellent graphic of the percentage of success between the two points around the clock. It's not a perfect match, but it'll get you on the right track.
For NVIS reading: www.universal-radio.com/catalog/books/5444.html This book is a compilation of articles LTC Fiedler and others wrote for the military. It is an excellent resource.
Also: Army Field Manual FM 24-18. Read Appendix M: Near Vertical Incidence Skywave Concept.
Ocean County ARES in New Jersey has used an antenna design similar to yours to communicate all around our region -- from 15mi out to 308mi (and all over in between) using SSB and various Digital modes.
When you play with the VOACAP page compare 100W SSB to 5W CW/Digital with all other settings the same. You'll see why Digital is far more efficient for EmComm than SSB -- but I guess that's no surprise.
As for vertical whip antennas. Again, you have to look to the military. I'm sure you've seen whips tied down over jeeps and Humvees. That's not to get under bridges. It's to raise their take off angle from low to nearly vertical. Now if you read their manuals you'll find that while that works, it is a compromise. The whip radiates best when bent off the BACK of the vehicle. However, it's not practical to drive with a 16ft whip sticking out the back, so they bend it over the front when moving and off the back when stationary. I've experimented with bending a 75M Hamstick on a spring off the back of my truck. It's a huge compromise, but it does work. I've gotten ~75mi away with 30W SSB.
So anyway, I hope this helps you on your NVIS quest. Like I said earlier, you're well on your way with your wire antenna. Check my QRZ page for more info on the OCARES ANA-1 NVIS wire antenna that Ocean County ARES uses. It's cheap and easy to make, light weight, super portable, easy to deploy and tear down, can be used on 40/60/80M and....It works!
This is not to say that you can't add reflectors or raise the height or slope it or whatever else to get some better performance out of it -- or better yet just get an endfed inverted V or an AS2259 dipole. But for our portable needs in ARES, it works great as is. Good antennas don't always have to be complicated.
Best of luck, 73
NJ2N
Thank you for taking the time to include all of the info. I ordered the book you recommended. I have considered a 102" whip bent over the front of the jeep. My only concern is side loading the tarheel. I am afraid the tarheel might not be able to take that much force. An inverted V would certainly be a better choice. I tested this setup trying to find something that has a super quick deployment that was also small to pack around. One thing you learn when you drive a 2 door jeep.....every inch has to be accounted for. There just isn't that much room in them. I still might try the 102"whip though. If the tarheel can handle it then it could be used while actually mobile. The stationary design of mine limits it's use. 73, de KM4ACK
@@KM4ACK I’m guessing you’ve experimented even more since you published your video 3 years ago. In a response to a comment you said an inverted V would be a better choice. One only needs to look at what the military does for mobile HF where the rear mounted whips are bent over to secure to the front of the vehicle. Of course, an inverted V would not work on a vehicle.
Re the inverted V, many are likely aware of the RACAL AS-2259/GR crossed inverted V. Cut for US mil frequency bands, cloning one doesn’t work well on the amateur bands. This antenna uses a coaxial transmission line 15’ mast to feed the dipoles at the top of the mast. The dipole elements slope downward at approx. 30 degrees. I constructed one cut for 80M, 60M, and 40M (lower bands with loading coils). I compared its 40M performance to a straight 40M dipole that was strung at the same height of 15’ as the V’s feed point. Expectation was that, though both were at nearly ideal height (1/8-1/4 wave length above ground), the horizontal dipole would out perform the V. Contact with a cooperating station approx. 400 miles distant using a horizontal NVIS array resulted in 2S units better with my V than the horizontal dipole.
A friend of mine camps in the Yosemite Park valley. The valley is at about 4k’ and surrounded by 6k’ to 8k’ mountains. The valley is only a mile or so wide - making a v-e-r-y challenging HF path. He regularly checks into an evening 80M net. To get out of the valley, he rotates his vehicle antenna to a horizontal orientation which results in very good comms with the net.
This month’s QST (July ’23) has an excellent article with the application of NVIS to overcome lumpy real estate issues with a public service event in Maine. Well worth the read.
Tennessee here also (W4TJP) 🙂 Keep on doing the work. Enjoy your content.
I use your EFHW kit parallel to the ground about 6.5’ above the ground and can communicate across the the State of Hawaii with 6W. The closer stations about four miles away on Oahu works fine, albeit a bit weaker than the stations in Hilo on the Big Island.
An HF Kit EFHW set in an inverted Vee is both an excellent NVIS as well as DX to South Africa 12K away.
Great stuff!!
Great vid. Answered a few simple questions I’ve had for awhile, and found few answers. 73’s y’all
That airplane was flying in a circle because he left his blinker on lol! :) Fun vid!
I love your bloopers. VA2SOB - 73.
Thanks Claude! 73, de KM4ACK
I was planning something similar with an FT-857D in my pickup truck. The plan was a 3/8" mount on the edge of the pickup bed where I count mount an MFJ HamStick for DX or an end fed dipole with an impedance matching box for NVIS. I'm due for a new truck so I postponed that installation. Thanks for the WSPR testing.
That sounds exactly like the web article I referenced in the video. That's where I got the idea. Need to do some more testing soon. I managed to get my hands on a 102" whip that I want to try. Keep us informed of what you settle on and how it works. 73, de KM4ACK
Thanks to your video I was motivated to experiment with my Little Tarheel 2 during the recent OH ARES NVIS Day.
Using a modified quick disconnect to SO239 connector and ran 50ft of coax out at 10ft in the air. (The coax cable is what I normally carry in my go kit, 10 ft up using the mast sections and mounts I normally carry, plus cargo straps and a handy tree).
Had good results on 80M copying the state EMA at 40+ and they received me at 57.
It would not tune at 40, I think the coax was too long as the Tarheel only came up as far as it normally does at 20M. Didn't think to check tuning on 160. Need to check that next time, along with experimenting with shorter coax runs to get it tune up on 40M.
Thanks again for the idea!
73 Randy KAØAZS
Nice video. Thanks for taking the time to test it. With the new band hopping scheme on wsjtx, there is an order that is no longer random to optimize when stations are listening and transmitting to maximize the number of stations on a band at a time. It may have been that some stations in your area weren't on 40 when you were TX.
Adding a ground screen of horizontal elements will help in general because of the amount of loss of signal into the ground. What most antenna modelling doesn't show is the radiation pattern into the ground. In Ground Penetrating Radar, GPR, we use that energy, which is significant.
Thanks again
Brandon W0GPR
I didn't realize the band hopping feature was timed so stations were on the same frequency at the same time. Makes sense. Thanks for the tip! 73, de KM4ACK
Nice test. Thanks. I use a 96" whip on a Chameleon base. When I want to go NVIS I bend the whip over my roof and tie it to my luggage rack. It works quite well. 73, Charlie - K0CKH
I've considered a 102" whip for the tarheel but I am concerned about side loading the coil with the force of bending the whip over the jeep. 73, de KM4ACK
Great and informative video Jason. Have you tried to lay another wire on the ground below the antenna wire, like a reflector? I have heard this gives it more of a "cloud warmer" type of take off angle.
I have heard that but never tried it. May have to test again with that and see if I notice a bigger difference. 73, de KM4ACK
The counterpoise on the ground really works quite well. I used for some emergency comms on hf from the bottom of some deep canyons in the Sierra.
"Turns around a point," it's a thing, hey, even prospective pilots have to have a little fun too!
That was my go to antenna for my vehicle. Ground reflector was also incorporated. I'm local to you, will have try making contact.
I need to try the ground reflector. Thanks for watching! 73, de KM4ACK
Interesting results ? Good comments on here also from other viewers. Thanks for putting this together Jason. 73 de 2E0IEH
Thanks Tim. I have enjoy the comments on this one. Lots to think about. 73, de KM4ACK
Hi Jason. In wspr you can add delimiters such as VK1MIC/A and VK1MIC/B etc. saves having to wait.
Thanks for the tip. That's worth it's weight in gold! 73, de KM4ACK
Maybe someone has already mentioned it, but foF2 was 4.65 MHz at the time of the video according to the nearest Lowell Digisonde I found (looking at an ionogram), which means the 40m band would not have worked for high-incidence skip-zone-free comms. 80m would have worked great, right at the sweet spot, there was even a double hop trace above it in the 80m portion of the band. Nice setup though!
Good stuff Jason , would definitely be interesting to see what a large whip antenna would do like a 102". Glad you were able to get past the airplane attack !!
Just picked up a 102" from a club member. Another test coming soon. 73, de KM4ACK
I guess the key measure of success is to determine if you've eliminated the skip zone.
Bingo
The "incessant Cessna" is what I call those low, slow, and noisy aggravations to the out-of-doors. When they get stuck in a headwind, they hang up there forever! Is 20m too high in freq for NVIS? I should work up a mount so I can deploy my half-wave all band from the car. Thanks for vid.
LOL. Yep, 20 won't work for NVIS. 40 & 80 are your best bet. 73, de KM4ACK
Would a ATU be needed for 80M on your wire which you manually tuned for 1/4 wavelength of 40M?
Sure you can build a towel bar antenna and it will work too
Great video, I've wanted to do the same test with my Yaesu ATAS120. Does adding the whip back on top of the wire create an L type or does it mess things up because the screwdriver portion and the whip would put the wire in the middle?
I can’t say as I have never tested that configuration.
How long was the antenna wire you used. That was not mentioned.
Interesting results. Not what I expected, but I love the experiment. What mount are you using on the Jeep? I’m picking up an FT-857D and ATAS-120 this weekend. You have no idea how much I appreciated your out takes. It’s part of the content producer game. 73
Diamond K-400 mount. Absolutely great mount that has been rock solid for almost 5 years now. I like including the outtakes from time to time. Let's folks know we don't get it right every time on the first take.
I suspect WSPR is so sensitive that your results are skewed indicating they are similar. I agree that SSB voice would result in a more significant difference.
Great point! Why didn't I think of that? 73, de KM4ACK
Ya - compare with a dipole for a reference. I test using two antennas, two transmitters, etc, in WSPR band. That way fades affect ALL antennas under test. Even testing 1-2-1-2-1-2 alternately fades occur and skew results. Plus, testing over 24 hrs one sees how the ant does for DX vs NVIS.
@@uploadJ Running both at the same time would be nice but don't have to 2 HF rigs in the mobile to test with. Testing against a dipole is a great idea. I have been frustrated lately with the maps being down. wsprnet.org/drupal/wsprnet/map 73, de KM4ACK
3 questions: When you removed the whip and switched to the wire, did you retune the Little Tarheel? I have that setup in my truck with a IC-7000 and use a Turbo Tuner to adjust the LTH. What length of wire did you stretch out? And, lastly, do you have corrosion issues with that quick disconnect? Even in dry Arizona I have had issues.
LARRY TAYLOR yes. I re tuned each time. The wire is ~30’. No corrosion issues with the quick disconnect and my whip is off 3/4 of the time. Can’t fit in the garage with it attached. 😀
KM4ACK I had never thought of using the quick disconnect to solve that problem. I have to unscrew it every time. And, of course, I have forgotten about it a few times and bent the whip badly going into the garage.
Shouldn't that counterpoise be connected to the vehicle ground ? Didn't see if you did that
Did you take into account that you changed the whip length and in doing so changed the SWR? And the resonant freq.
Cut the wire to a 40 or 80 meter freq and put it on without the coil.
Yes. The coil has to be moved to account for the additional wire and keep the SWR at 1:1. The wire is cut to a length that takes almost 100% of the coil out of the equation on 40M. The some coil has to be added when working 80M with the same length of wire to keep the SWR at 1:1. 73, de KM4ACK
Another excellent video. I looked too fast and I read NCIS oupsssss. Did you have time to have a solution for the Raspberry Pi 4 ?. 73 VA2SOB - 73
Yes. I gave made progress on Buster and the pi 4. Script used in the Easy as Pi video should now work with Buster. 73, de KM4ACK
That's /P NVIS (portable) as you can not drive with a wire in a tree ;)
How would an inverted V fan dipole work out you think? 73 de ke4ooo
I'm certain it would out perform this setup. I chose this for a couple of reasons. 1. Quick Setup 2. Small and easy to store the extra piece of wire. 73, de KM4ACK
For some reason I can't consider this to be "mobile". Just because the antenna is mounted on the car and the radio is in the car doesn't mean it's mobile. Seems to me that to be considered to be mobile, one must be able to operate while driving down the road. If one can drive down the road, stop, and continue operating without making any station changes, it could be considered fixed mobile. But there is nothing mobile about this. Take the Tarheel and mount it on the hood of the car and lean it way over the top of the car. Does that work?
I do not think a mobile is a true NVIS antenna. I think that is where the problem is. The true NVIS antenna has a crazy elevation angle, pretty much straight up. I've not done much personally but have read some, and see examples of NVIS antennas with huge metal "reflector" arrays under them. They are not ground planes, but instead reflectors. That seems to be crucial for a good NVIS antenna. Antennas really are taxing from the brain power side, and the programs which try to help in computers can be a direction to go to. Great to experiment with an attempt at using ft8 or ft4 mapping as a results graph, couldn't do that 5 years ago.
You are correct sir. The horizontal wire helps but probably not a great NVIS. Just fun to experiment. 73, de KM4ACK
Agree. The typical pattern resembles a isosceles triangle. I've done with with a 20 ft mast with the 40m dipole (1/4 wavelength) legs running towars the ground, spliced with rope to it terminates a few feet above ground.
@@KM4ACK
Actually, no, N6GRG is not correct. The antenna you have will work, and it will work well. You just need to tweak your methods a bit.
First, you have to be familiar with Maximum Usable Frequency (MUF). At our current point in the Solar Cycle, 80M is generally better than 40M during the day.
Here's a great propagation prediction website: www.voacap.com/hf/
Move the cursors: one to your location, the other somewhere within 50-100miles away. Set the antenna heights for both stations to 17ft dipoles on 40,60,80M. Choose your mode and power. Click on the Prop Wheels to get an excellent graphic of the percentage of success between the two points around the clock. It's not a perfect match, but it'll get you on the right track.
For NVIS reading: www.universal-radio.com/catalog/books/5444.html
This book is a compilation of articles LTC Fiedler and others wrote for the military. It is an excellent resource.
Also: Army Field Manual FM 24-18. Read Appendix M: Near Vertical Incidence Skywave Concept.
Ocean County ARES in New Jersey has used an antenna design similar to yours to communicate all around our region -- from 15mi out to 308mi (and all over in between) using digital and SSB modes.
When you play with the VOACAP page compare 100W SSB to 5W CW/Digital with all other settings the same. You'll see why Digital is by far the best NVIS mode for EmComm.
As for vertical whip antennas. Again, you have to look to the military. I'm sure you've seen whips tied down over jeeps and Humvees. That's not to get under bridges. It's to raise their take off angle from low to nearly vertical. Now if you read their manuals you'll find that while that works, it is a compromise. The whip radiates best when bent off the BACK of the vehicle. However, it's not practical to drive with a 16ft whip sticking out the back, so they bend it over the front when moving and off the back when stationary.
I've experimented with bending a 75M Hamstick on a spring off the back of my truck. It's a huge compromise, but it does work. I've gotten ~75mi away with 30W SSB.
So anyway, I hope this helps you on your NVIS quest. Like I said earlier, you're well on your way with your wire antenna. Check my QRZ page for more info on the OCARES ANA-1 NVIS wire antenna that Ocean County ARES uses. It's cheap and easy to make, light weight, super portable, easy to deploy and tear down, can be used on 40/60/80M and....It works!
This is not to say that you can't add reflectors or raise the height or slope it or whatever else to get some better performance out of it -- or better yet just get an endfed inverted V or an AS2259 dipole. But for our portable needs in ARES, it works great as is. Good antennas don't always have to be complicated.
Best of luck, 73
NJ2N
Great video Jason. It inspires me to do some more experiments.
If I had a big van I would do something like in this SGC 231 manual page 19, 20
www.sgcworld.com/Publications/Manuals/231man.pdf
Maybe this is what Ronny Julian s talking about
You could use your antenne base instead of the SG231
Thanks for the link. 73, de KM4ACK
Ever thought of a roof mounted fold up magnetic loop?
I have zero experience with a mag loop of any description but another friend has been on me for months to try one. Might have to break down over the winter and DIY one. Do they work for NVIS? 73, de KM4ACK
@@KM4ACK Peter has many examples. There is a nice group on FB that Julian moderates. ruclips.net/video/Cv_RnLpZ9gw/видео.html
@@KM4ACK ruclips.net/user/results?search_query=nvis+loop+antenna
My fav mag loop video from Kevin. ruclips.net/video/L7DSkqy2siI/видео.html
Nice video (perhaps the airplane was looking for other activities in the woods...). 73, kk4zuu
That is always a possibility. 73, de KM4ACK
When you see a HUMV running around with its antenna pulled forward and tied to the front bumper, they are operating NVIS, usually digital.
Also, those funny bars over the top of WW-II German Army Command Cars were not for RollOver or Rain Protection but was an NVIS Antenna which was in standard use along with their ENIGMA Code Machines via hand sent CW.
The German Army was using NVIS at least as early as the 1920s as were German U-Boats during WW-I when close to their shore bases. Out to sea the same antennas used Skip at higher frequencies. All during WW-ONE!
Many National Guard buildings have a 40M Dipole NVIS Antenna about 20 ft above the metal roof of their building operating Digital/SSB.
In the 80s I used 40M and 80M Hustler Resonating Elements folded over the roof of my Ford StaWag on the installed hinge mount while both Mobile and Portable. I also used a 20M Resonator with a length of wire clipped to its top and stung out to a tree to operate 40M. I made many 40M NVIS Contacts using both setups with a TS-430 and a few on 80M, all SSB Phone.
At this QTH I have an 80M EFHW Slopping Inverted ELL going up on a 40 foot SpiderBeam Mast and slopping out to a tree limb 100 ft away. Works NVIS SSB like a champ and occasionally a marginal SSB phone from NH out to MI/OH.
A 40M or 80M EFHW is a multiband antenna. I can hear good on 20M but haven't been able to make a solid contact yet. Drats! Must cut a 20M EFHW wire and try that as a virtical W/WO a few radials.
73 OM KA1RUW.....
Thanks for the video. NVIS propagation can really be different from day to day and lately it seems like it's been a little on the long side. Last week I tried to make a 40 meter QSO with a station 150 miles away and couldn't do it all day or the next but on the third day it worked great. Switching to 80 meters fixed the problem and I could make the contact all day long every day. So right now at least, 80 meters is a much better bet for NVIS. I've found this website very useful for checking on realtime and historical NVIS conditions.
lgdc.uml.edu/common/DIDBFastStationList
I pick the Austin station as it's closest to me. Then go through each page picking your date and time. When you finally get to the report page look at the top left "foF2" number. That's the highest frequency that was shot straight up and came straight back down again. If you want true NVIS distances you need to operate at that frequency or lower. At the bottom of the page gives you max frequencies for 100, 200, 400, etc NVIS ranges in kilometers. I have found it to be pretty accurate to real life communication abilities.
Your antenna setup will work fine for NVIS as it will radiate a good chunk of your signal up just as it is. Lengthen the wire some and drop to 60 or 80 meters for our current conditions.
Next time out, I will be trying 80M. Thanks for the link! 73, de KM4ACK
unfortunately this is a portable configuration, not a mobile configuration, but an excellent video. I am looking for something that will be truly mobile when off roading
The title was a little misleading. If you're tied off to a tree you're not "mobile," you're operating portable. I was hoping for ideas on how to get NVIS performance while driving down the highway.
What would it do if you did a full 1/2 wavelength center feed?
Not sure but it would be worth testing. Please share your results :-)
@@KM4ACK I am a new ham. At this time I can only do 2m, 70 cm. I love your videos and spend a lot of time watching them. I am 73 disabled retired saving up my SS check to get what I want to get for radios. Living in south Florida I have worked mostly on sheltering at home for hurricanes. I have a Anytone AT D878UV Plus, that gives me 2m, 70 cm analog, and DMR! Still working on getting DMR working. Also have a Anytone AT D578 that gives me 144, 222, 444, analog and DMR. I got 4 -25 ah LiFePo4 cells and 2 sets of 4 - 60 ah LiFePo4 giving me 24 v to power a UPS that I have. I have 5550 watt generator and a good supply of gas. I have 100 ft RG8 going up a tower behind my house with a dual band antenna with 9 & 11 db gain. I don't know if you know about the Florida SARNET! With this I have talked to someone about 300 miles away. on 70 cm repeaters. When you see a hurricane, look for WX4NHC on HF. National Hurricane Center! They are also one the SARNET! So when a storm is coming I have a hotline to the Hurricane Center, but mostly lesson unless ask for something. I want to get a weather station, only have basic one now with pressure, temp, humidity. As soon as I can save up enough I will get HF! I will be getting a Pi soon and start doing things with it. Want to get some things going with what I can. Sorry I can't test that now. But as soon as I can I will test that. I may have enough room to a 20m long wire low down
Outstanding, many thanks for that. 80m may be a better choice for NVIS depends on what part of the world you reside in. The important thing is that you get out and try it which is exactly what you have done and made a very interesting video at the same time. Good stuff.
Thank you! Many good comments on this video. Leads me to believe there is more testing to be done in a future video. :-) 73, de KM4ACK
Best Wishes from the Uk. Larry M3 MPD 73s
Other NVIS..."OH5ZN´s mobile magnetloop 3 - 16Mhz"; www.dropbox.com/s/8sasnor7gxu1igz/mobile_mag_loop.jpg?dl=0
Nice looking setup. 73, de KM4ACK
Your propagation is still NVIS