Concerning the length of the wire to use, in my case, I am using 40 meters for the Ohio NVIS Antenna Day. One would think that the classic formula for a quarter wavelength vertical would do the trick. However that seems to not be the case. Since this NVIS antenna is so close to the ground, and close to the car, my first attempt using the formula 234 / freq. to get the length of wire gave me a resonance of 8.6 mHz. By the way, having a MFJ antenna analyzer helps greatly with this process. So armed with this data, I did some back figuring and came up with my own constant for calculating the proper length of this type of NVIS antenna. That is not to say this is cast in stone, but this is what worked for me, at least this time.
The new formula I have come up with is as follows:
Length (ft.) = 261 / F (mhz)
Here is another photo of my NVIS antenna fully deployed. Notice that at the far end I am using two 4 ft. military fiberglass tent poles that I picked up locally.
DIY NVIS Antenna using a Mag Mount
My preliminary results show that is seems to work well for a NVIS antenna. I will also be adding a 75 meter leg to the setup in the future as well. That is a simple matter of measuring out the wire, adding the clamp to attach to the mag mount, and deploy.
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