HF NVIS Frequency Selection – Idaho ARES


Understanding propagation is critical to successful cloud burning.

NVIS requires using a frequency that is below the Critical Frequency, the highest frequency at which NVIS communications can operate at, but above the frequency at which the D-Layer absorption results in excessive attenuation, or the Lowest Usable Frequency (LUF). NVIS communications is not possible below the LUF or above the Critical Frequency. Use of frequencies below the LUF or above the Critical Frequency will result in a loss of NVIS communications.

via Idaho ARES – HF NVIS Frequency Selection.


In the arena of grid down communications, wilderness plays a big part. In a SHTF scenario you will most likely find yourself operating outdoors at some point. With this in mind, your training should focus on operating in a less than perfect environment.

Don’t expect your shack station to work ‘field-portable’ the first time you need it to. One of the reasons I’m skillful with HF field comms is because, since the beginning, field-comms has been a purposeful constrain on my station and I operate from camp or go portable at least monthly, year round.

Can you carry your stuff a mile?

How long does your portable power keep the tubes warm?

Do you know how to get a wire un in the trees?

These are all skills to understand before they become necessary.

Practice. Practice. Practice.


Burning the Clouds

My first trip into the local ham radio store was made with one question in mind; what do I need to do to listen to lots of stuff, and talk locally for 0-200 miles(ish); similar to what we did with radios in the Army. The person I was talking to looked quite confused at my question and thus began my quest.

Now that I have enough comfort with the science, skill, gear, and art that I thought I’d present the case for Near Vertical Incident Skywave (NVIS) and share my learnings and experiences regarding this important radio art.

Let’s start with the why. I’ve played with technology and traveled enough to experience regional power outages, communication outages, and other mayhem that happens when infrastructure fails. Thus far NVIS is the one reliable communications that is low power, field portable, and zero infrastructure.

Now, let’s establish what NVIS is; Wikipedia has a nice description here – https://en.wikipedia.org/wiki/Near_vertical_incidence_skywave

If you’d like a simple demonstration, go into your yard, point a hose straight into the sky and turn it on. One quickly notices the water pattern falling back to the ground. That is what NVIS essentially seeks to accomplish; but reflecting RF off the F-layer of the ionosphere and then creating a pattern roughly a few hundred miles in diameter.

Understanding NVIS is one thing, being able to use it in a true grid-down / field-portable environment require understanding and enough practice so you can rely on your knowledge, skill, and gear if it ever needs to be put into practice. In future articles we will cover aspects of this; radios, antennas, propagation (band conditions), power, etc.

Thanks for reading and I hope you get something from my ramblings. Post a comment and let me know your questions, comments, and thoughts.