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.
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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Great idea! One could also use an old used 11 meter mag-mount antenna with the interior modified and a bolt or eye hook as the attachment point. I’ve bought some of those at garage sales and auctions for $1.
Thanks!
I have thought about buying old CB antennas and doing as you say, I just haven’t found any.
Good call!
— Mike WB8ERJ