NVIS Round 2
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- Опубликовано: 2 июн 2024
- Testing NVIS mobile antennas again for my Jeep. This time includes the 102" Whip on top of the little tarheel screwdriver antenna.
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A horizontal loop near the ground is the best NVIS antenna you can get. The noise is lower and the pattern is reflected upward at a very high angle. You can place a remote tuner at the feed point and work all bands. As the frequency goes up the pattern moves closer to the horizon. Exactly what you want...
I'd say in a true NVIS situation the 102" whip achieved its purpose - POSSIBLE coverage within the skip zone. Thanks for the experiments.
Testing is a good thing. However, doing a little modeling with EZNEC goes a long way toward understanding what is going on. A short antenna on a vehicle always has a lot of NVIS performance on the lower bands. And as the frequency goes up the radiation pattern gets closer to horizontal. You can easily model a vehicle and antenna on a vehicle with EZNEC. The other thing to remember is that the screwdriver antenna has most of the current and therefore RF emission below the coil. Keeping that coil above the vehicle metal structure can make a huge difference. Also, being mounted low to the ground or metal structure increases the capacitive ground loss. Modeling and testing together is the best way to understand what to expect. Have fun modifying and testing. Enjoyed the video.
From the things I have read, you may of had the whip tied too close to the vehicle. I would have to go back and recheck but IIRC, you are supposed to have 1m distance from the vehicle metal and your whip so I expect it was throwing your SWR off a bit. An excellent video, and confirmation that this is the approach I may want to look into when I upgrade my license. I want something other than satellite that can get out of the mountain valleys when I need to. Most of the time running the whip vertically should do the job just fine, but on occasion, NVIS will be more useful.
Jason - interesting tests. The results did not surprise me at all. The 102" whip, bent over the vehicle and tied down, will never exhibit a performance improvement in my experience. Remember that the vehicle is the ground plane, and the whip is the radiator. When placed in such a distorted configuration, efficient radiation is virtually impossible. Keep up the good work! 73, Lyn W0LEN
Lesson learned. It was still a fun experiment. Think I'll be sticking with my wire off the back of the jeep. 73, de KM4ACK
@@KM4ACK I am enjoying the NIVS videos. I have been experimenting recently trying to find a reliable and portable one to keep with me. regarding the 102 whip, its supposed to be bent backwards . bending it forward is just how they do it while in motion . Thanks for your time.
Hi Jason. Yet another interesting video. A lot of time and effort gone into making it clearly. Interesting results as others are commenting. Thank you again for all you do for other operators. 73 de 2E0IEH
Thanks Tim. I think this video has generated as many interesting comments as the first one I did on the subject. 73, de KM4ACK
You may want to try a 12 foot whip with the tip of the antenna at least a foot above the metal on the vehicle. Also 60 or 75 meters might give better local results in mid day for local coverage.
The whip bent over not getting distance is what you want for NVIS you are aiming for 0-300 miles at most.
I think it would do better if you don't bend it so far down. Keep it as close to a meter above the vehicle that you can. You had it down almost touching the metal. You are aiming for as much of the antenna horizontal as possible.
Gday Jason. Have a look at how Codan do NVIS with there mobile antennas. You need to keep a minimum distance between car and antenna. I've done testing with a larger whip(4.5m) and then bending it over. The larger whip increased my signal by 3db (greater radiating efficiency) and bending it over increased it by another 3db again but it was no where as close to the vehicle as your whip was. Keep up the experiments. Cheers Lance VK6LMK
Didn't cross my mind that the distance to the vehicle would have that much of a negative impact. Thanks for the info. 73, de KM4ACK
What distance did you have between the car and antenna? Also wondering where you found a 4.5m whip to purchase, would you be willing to share where you found one?
I don’t recall exactly but probably a couple of feet.
Outstanding sir !!
The thing about NVIS is that if the receiving station is also NVIS it receives about twice as good as non NVIS so if the others were vertical and you were horazontal it's a 20 db loss in reception
AA4CP Chuck
Enjoyed this, great video
Thanks! 73, de KM4ACK
The whip will be more effective if tied down "away" from the vehicle. In other words 180 degrees from the setup you had. Not for mobility of coarse. That's why you might use it the way you had it.
Great test. I was more surprised how well the basic tarheel did. 73de KF7VUT
Always fun to experiment. The results surprise me on a regular basis. 73, de KM4ACK
Excellent testing. I'm guessing N9CB is direct ground wave. Your variation in results may be due to when stations are listening more than anything (except for the bent whip). The database query on wsprnet is great for looking at statistics. I've used it to look at transmitter frequency stability and variations in other stations. Consider using the results of each antenna and determine average SNR for each test and for different distance groups (bins) like 0-50 km, 50-200, 200-500, etc.
Great tests and always appreciate your content.
W0GPR
It's possible that N9CB was ground wave but I would have expected the bent whip to reach him as well. 73, de KM4ACK
Very interesting. I love real world experiments. Thank you for sharing.
I assumed you were going to bend the whip horizontal off the back of the jeep and not bend it into an arc over top of the jeep. I didn't expect much radiation from the half loop so close to the virtual ground of the vehicle.
I need to get HF in my truck, and based on your WSPR data I think I'll stick with my original plan when I bought the equipment several years ago - coil loaded resonant Hamsticks for DX and resonant end fed dipoles for NVIS (both while parked).
That seems to be the best advice right now. The wire coming off of the back works fairly well but limits travel. Just trying to find something that could be used while actually mobile. 73, de KM4ACK
102 whip .. try . Fully extended vertical .
Great video! Can you try another test when you get a chance? I've seen a diagram in a military manual (I forget which one) regarding NVIS where they had the whip in the same location as yours, but they bent it over away from the Jeep, not over it. They used a rope and a ground-stake to hold the whip over about 45-degrees. Who knows what the close proximity of the vehicle's metal has on the whip when the whip is bent over so close to it? Anyway, I wonder what the comparison would be between the vertical whip, and when it's bent horizontal away from the vehicle.
Not sure I want to try it bent away from the Jeep. It might produce better results but I am concerned about the strain it would put on the little tarheel coil. Also, I'm not sure that the mount would remain upright as pressure was applied. Bending the whip forward allowed the tarheel coil to rest against the body of the jeep and take some of the strain off of the coil & the mount. Hope that makes sense. Also, I was looking for something that could be used for NVIS while actually mobile. Maybe the bend was too great and less of a bend forward would produce better results? Maybe it's not possible at all? More testing needed. 73, de KM4ACK
That EM66wd station is pretty close; might it be possible that it was hearing the ground wave component of the antennas and not the NVIS components?
Try bending the whip away from your jeep. You jeep might be doing something to your signal .
Maybe I can try that next time. Thanks. 73, de KM4ACK
That's how the military does it.
It almost makes a horizontal dipole.
And being close to the ground becomes NVIS.
From what I could see it looks like you were transmitting at 100 watts on the original whip and you lowered it for the wire and even lower for the 102" whip
Power level remained the same (5W) for each antenna. 73, de KM4ACK
@@KM4ACK I was judging by the green bar that went across on what looked like FLRig. It went all the way across on the first test.
Cool video, interesting tests. I honestly struggled for a while with the usefulness of mobile HF, but I decided it wasn't worth the investment when most like I would have man portable HF gear anyway. Of course the argument can be made that even man portable HF gear is kind of pointless unless you are clandestinely TXing in some sort of civil war or revolution where you need to TX and move. Investing money in a system that sits in a vehicle that will eventually have no fuel, battery, oil, or tires just didn't make sense to me. But during peacetime it's a fun bragging right I'm sure. ;-) Great video. Btw, are you in AmRRON? I am in the Corps and thought I've seen you on the airwaves, don't feel pressured to answer.
When I first installed the HF in the mobile, I wasn't sure how often I would use it. While I don't turn it on in town very often, it is almost always on when I hit the highway. I have past tons of highway hours chasing a contact or having an HF QSO. 73, de KM4ACK
Jason how did you generate your signal reception maps?
www.pskreporter.info/
@@KM4ACK thanks
Can you share the app you use or software used . It would be a pleasure to know
www.physics.princeton.edu/pulsar/k1jt/wsjtx.html
Why did you test the 102” whip with it in a tied down position?
Trying to achieve a NVIS propagation pattern. 73, de KM4ACK
102" didn't get out as far Isn't that the point of the video?
Flip that whip backwards