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The characteristic you are talking about for a NVIS effect off the whip is simply changing the orientation of the main lobe. I am sure you have seen diagrams showing how the waves propagate off of the whip. The image usually looks like a large doughnut with the whip in the center. The gap being directly off of the tip of the antenna. Laying the doughnut on its side gives you a vertical radiation which can assist in a NVIS effect. Of course use of a ground may be required in order to really achieve the takeoff angle you are looking for.
Using a counterpoise is helpful in situations where earth-ground is not conducive to the takeoff angle you wish to achieve. Of course all of this is dependent upon proper frequency selection in order to achieve the near-vertical bounce you are looking for. For that reason, NVIS operations tend to be the area where everyone's lunch gets eaten, particularly in that area where the ground wave and sky wave may cause some fading.
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Thanks for the reply. I am going to to try to read back what you said in 11B language to make sure I understand.
The radio set comes with a small ground rod and a length of braided copper. My understanding is that this should always be used when practical, but I also understand that while better than nothing, this may or may not be a very suitable ground. In cases when there is a little more time and/or space to get set up, ground radials may help what otherwise might not be a very good ground through the grounding rod, and should help performance of the antenna somewhat. Is it correct that this effect is regardless of the orientation of the antenna?
I guess in my mind I am trying to sort out a logical sequence for trying to establish HF (short-medium range) with the least amount of time and setup. Here is what I am thinking, maybe the fine gentlemen here can tell me if this makes sense.
- On the move - radio in ruck, whip antenna, no ground other than a grounding tail (mentioned in some of the above referenced articles)
- At a brief halt - radio stays in ruck, whip antenna, deploy single ground rod
- Long halt / Hide site - radio out of ruck, whip antenna, grounding radials
- Long halt / Hide site - radio out of ruck, RF-1941 antenna or field expedient antenna if can't make commo with long whip
Frequency selection will be out of my control, but my assumption in this scenario is using ALE mode where hopefully at least some of the freqs are suitable for NVIS.
And I think I understand about ground wave/sky wave interference - the basic idea being that in the zone where the receiving station gets both signals, they may have a canceling effect.