Hello all,
Have any of you tried a deliberate set up for NVIS (Near vertical incidence skywave) on 80 or 40 meters was it any good ? VHF/UHF is near dead near me and I thought this maybe an option for inter G contacts, The problem I have is I’d have a max of 10 watts due to EMF regs and don’t wish to go to the expensive of HF equipment ( I have none at present) only to find it is useless for this purpose.
Thanks all
Brad
Brad, If your 40m wire is 6 or 7m off the ground, NVIS is already at play, however, solar conditions still come into play, as you’re still relying on the ionosphere to refract the radio waves.
LOS is also possible for close contacts. Often, @GM4JXP and I hear one another on 40m when we’re both chasing the same activator. We live around 8 miles apart.
This is what I found on the internet.
The OPTIMAL NVIS antenna height is about 30 feet between 80 and 40 meters! Please note the following trends when we reduce the antenna height from approximately 16 feet to 40 meters or approximately 32 feet to 75 meters: At 0.06 wavelengths in height (16 feet at 80 meters, 8 feet at 40 meters), the field strength is 3 dB lower.
A horizontal dipole is used as the radiator.
73 Chris
Thanks for the reply, I’ve only used HF for a very short while when I first got the A licence converting from a G7. At the time it just wasn’t for me so I have very little experience of HF and NVIS was something I only heard of recently as a deliberate thing. 160 meters sounded like the ideal thing but to this day I have never heard a single person on the band.
Fraser, you was faster than me 
… and this in such a special way as it has had an effect in recent times and also today, hi
Propquest NVIS
Short answer: No. But Yes, for the 60m (5 MHz) band having had success in a few trials with low power with a ham in the neighbouring county, and many more times with ‘accidental’ non-pre-arranged QSOs.
I’ve always been fascinated about how to make HF contacts beyond the groundwave but still in the [low-angle skywave] skip zone, which led to my interest in NVIS, especially in very hilly terrain like G/LD where I live and where the HF groundwave doesn’t get very far.
At high latitudes (e.g. northern Europe) and during the daytime, 60m is usually the most effective amateur band for NVIS, 40m a bit less so. Due to high daytime D-layer absorption, NVIS on 80m is best after dark.
I read that military NVIS comms typically use frequencies between 2-4 MHz at night and 5-7 MHz during the day.
Horizontal, inverted V or sloper wire antennas work best and having them only 4-6m off the ground is fine for NVIS.
Hi Brad,
One thing that the others have touched on is that even with an antenna set that “should work” for NVIS, you still need the propagation to work for you as well - specifically the Critical Frequency needs to be high enough before NVIS will occur. While the CF is often around 3 MHz and hence 80 & 160 m are covered, you won’t always get NVIS on 60 and 40 metres. It effectively “never” (don’t ever say never, but…) occurs above 10MHz. So when someone says they have just worked someone via NVIS on 20m, I would doubt that they understand NVIS.
As also stated above, a good place to see what the CF (look at FoF2) is at is propquest.co.uk.
73 Ed.
Brad,
I think you should always use the best antenna you can. As high as possible and as clear as you can of vegetation and buildings. Whatever is practical. As already pointed out most SOTA activators are using NVIS on 7 MHz or lower as typically the average height of the antenna is between 3 and 7 m.
On one occasion I was packing up after an activation. The mast was telescoped and in the car when I discovered a potential S2S on 80 m. I unwound the ant wire to the full 80 m half wave length and left it on the ground. Then I called the other guy and we completed. SWR? Ignorance is bliss.
Doesn’t get more vertical incidence than that. Or was it ground wave in a literal sense? Distance was 50 - 100 km. Sorry not sure exactly.
That anecdote is to illustrate that even a terrible antenna will yield you contacts. Don’t hold off waiting for a perfect design. You will die of old age before that happens.
73
Ron
VK3AFW.
Not directly NVIS but hopefully this will help.
The experience in central Europe:
For distances up to 50 miles you can use the 10m band. For distances up to 350miles sometimes even 1000miles you can use 60m or 40m. With focus on 40m as there are more chasers listening. However there is a deadzone.
20m currently varies with sometimes short skip but usually no contacts below 75 miles. Usually on 20m we have contacts from 350 miles to traditionally around 1000 miles. E.g. from Frankfurt 20m works ufb to OE9, S5 or OH6.
In the last weeks we often had conditions when only 40m worked fine. 30m was working somehow, while on 20m we had bad conditions with a strange QSB changing from almost no signal to S9+ in 1-2 seconds. And back again… It is completly unpredictable how long the propagation is on S9…
Keep in mind that the time of the day needs to be taken into consideration as well.
The type of antenna used will have a strong impact on the coverage. Vertical antennas are usually dx antennas. They cover dx areas but nothing or in bad cond. areas up to 175 miles. Wire antennas, that are not vertical polarised, have a good signal for the range you are looking for.
Although not directly about NVIS I hope this helps to at least mitigate your problem.
73
Ingo
The need to limit yourself to 10 watts should not be a problem. I bought an FT817 in 2003 and installed a G5RV antenna at 6 metres agl, I got lots of inter-G contacts on 80 and 40 and on the higher bands I had worked 100 countries n less than a year. Things are probably a bit more difficult now as noise levels are much higher but I still use the 817 successfully on 60m from home. When the propagation is good QRP does the job!
Hi Brad,
HF propogation has been rather mixed of late. Under normal conditions you can expect to have a lot of fun speaking to local stations on a SOTA activation on 40m or 60m. I would recommend joining an experienced HF SOTA operator on a joint activation before buying a new rig. There are many UK and European SOTA chasers waiting to speak to you, who will soon become familiar callsigns.
Your antenna only needs to be good enough.
Don’t discount 160m. If you build it they will come.
73, Kevin MW0KXN
Sporadic E?
Brad
Three things:
1 As many have noted, a low dipole or similar is fine for NVIS. As ever, do check the condition of feeders and connectors frequently; SWR with an analyser, and DC resistances with a multi-meter.
2 A transmit power of 10 watts is fine.
3 Good CW skills can be worth perhaps another 10dB? Acquiring these can require a lot of work. Routine SOTA QSOs won’t help much, you’ll need some kind of a plan.
Much like running, if you just go out a couple of times per week for a jog, benefits will be limited. But taking advice, making a plan, running with others, and so forth, can bring real improvements. Hard work but fun 
73 Dave
Out of curiosity, I looked at how EZNEC sees a dipole laid out on the ground (the ends insulated). The ground was chosen as the EZNEC default value, Average: pastoral, heavy clay (conductivity 0.005 S/m, dielectric constant 12).
Based on the results, the frequently read reports of portable radio contacts achieved with such antennas seem quite credible to me, even without NVIS having anything to do with them, hi.
Propquest NVIS - Critical Frequency
Maybe this is of interest:
In addition Morgain-antennas seem to have a similar characteristic…
73
Ingo
I have an 80m loop for NVIS, designed by K6HPX and later added to the catalog of Force 12, with mine bearing S/N 0001. Seven feet high, 12 feet wide, radiused corners, made with 2" aluminum tubing, tuned with a big motor-driven vac variable. We tried it out at my place, 400 feet atop a hill in San Francisco. Thirty watts SSB got us S-9 plus from a station 300 miles away and no line of sight.
I have used a low dipole / inverted vee many times on 40m and 80m for comparatively local contacts (sometimes over 1000 km). Success depends on conditions, time of day, time of year, latitude, etc. I haven’t used 60m yet, but 2 to 5 watts to an inverted vee up about 4m seemed to work well enough, although I wasn’t necessarily the strongest signal on the band. (Note that I generally use CW, which has about a 10 dB advantage over SSB for the same output power, although I have still made SSB contacts on occasion.)
An introduction to NVIS, including a plot of relative signal strength vs. distance, is here:
https://practicalantennas.com/applications/nvis/
I generally use an inverted vee hanging from a branch at whatever height is available. My backpacking coax is only about 8m long, but often the available trees may limit me to about half that. (There is little advantage in exceeding 6m on 80.) Yes, an 80m dipole might be a bit long for a small, crowded summit with lots of people, but that hasn’t been a problem in the types of places where I have operated. The wires for 80m only add about 140g to my dipole kit (they go on the same coax and center insulator along with wires for the other HF bands that I plan to operate) so the added weight shouldn’t be an issue.
I would agree with the others that accompanying an experienced operator would be a good way to start. You might even be able to borrow a radio from someone to try it yourself before committing to purchasing one of your own.
And pay attention to the propagation forecasts. I like the Local Area Mobile Prediction (LAMP) chart from the Austrailian SWS:
http://sws.bom.gov.au/HF_Systems/6/5
It shows you the likely open bands vs. time of day for your current conditions.
edited to add:
I’d note that there is both a minimum and a maximum frequency that will support NVIS propagation with any specific set of ionospheric conditions. The maximum is set by the F layer Critical Frequency (although the E layer may come into play at times). The minimum is set by absorption passing through the D layer, and varies somewhat with the power level. So expect that you will have to change bands if you are going to spend some time up on the hill. You may find that 160m is most useful when you are camping on the summit overnight.
Listen at night and learn CW or use FT8. You should hear plenty of stations on a long wire even during the summer once it gets dark.
73 Phil G4OBK
