http://arrl-ohio.org/SEC/nvis/NVIS%20-%20DX%20Engineering.pdf

I'm wanting to use this as a basis for my first nvis antenna build. Something portable I can use on 40/80m. It is detailed how to build it. My question to you is how does it know which antenna wires to use or does it just use both. There seems to be nothing seperating the 40 pos side from the 80 pos side, same for neg side. How does the radio know what to use?

Electricity takes the path of least resistance

That is a good antenna. There was a whole thread about emergency type antennas, that doesn't always mean NVIS (to me it does) but had a lot of good info in it.

Don't try and just stick some wire out 2' feet off the ground. I like to get at least 8' but at that low of freq you aren't going to get too high to lower the take off angle. I have been wanting to make a knock off 2259 with a reflector using some painter poles but havent gotten around to it. The 2259 is a great antenna.

What he said about path of least resistance. Also 15-20 feet off the ground is a good compromise height for 40/80m. It's better to get it higher for 80 if that's your primary band of interest but then your 40m starts to be less good on NVIS (but better for mid range).

What kind of reliability do you get out of NVIS?

Ask the freewheelers net

I have had great luck with 40m between MUF and antenna size. I talk on my mobile to locals every now and then on my drive in.

Much like a fan dipole for several bands this will tune to the point of resonance for the band selected.

These have been, in the past, referred to as a "maypole antenna" and they're a good design where the angular separation of elements lessens the inductive coupling. I've made them before for up to 3 bands for portable ops.

The only real pain is when you get the elements snarled up during transport & storage...tape all elements rolled up separately.

15 ft is a reasonable height for my location and you clear peoples heads by a decent margin.

Give one a try... I think you'll like it..

73..FN

"nvis build"?


The radio energizes whatever it's connected to. An element that is a reasonable impedance match will accept the energy readily and radiate.

The lengths in that article make no sense for amateur use. They are a direct copy of the military antenna which is, unsurprisingly, intended for use on frequencies used by military forces, not amateurs. For amateur use you would be far better off to cut the elements for the amateur bands.

What would be the lengths for 40/80m? Still new to hf

I'd probably start with 60' per side for 80 meters and 33' per side for 40. There are various ways to add loading to shorten the 80m elements, with corresponding reduction in efficiency and bandwidth.

I started with a LDG 4:1 balun, 103' of random wire and 1 ground radial.
Had a BLAST with NVIS early on.  The JA contact and AZ on AM were fun too!

103' of 14ga wire, 8' above ground, 100 watts.  Worked Wonders for me.  build you an 80m dipole, hang it at 8-10' and see what happens

Pick a center freq (80m is a huge band). I know in my area 3.916MHz is a very active freq. Let's call 3.916MHz f.

So now we know f it gets real simple, we divide 468 by f. That tells us the overall length of a half wave dipole. I said overall because that is important. You can feed (hook up coax) in different places i.e. Off center fed, but let's keep it simple and feed it in the middle for a center fed dipole.

468/3.916 = 119.5 (let's call it 120ft)

Because you will need to adjust in and out to effect frequency add another foot (6" per side)

Now you are at 121' of wire. Fold it in half and make a cut. I recommend picking up a 1:1 balun and using that as an easy way to adapt the coax to wire plus adding a little isolation.

Put the ends through some insulators and fold it back on itself so that the total length is 120' (you should have 9" of wire folded back on itself per side)

Put it in the air and check swr

Great info coming in. I was afraid it wouldn't be as easy as illustrated. Trial and error will prolly be most of it.