NVIS or ground wave?

Started by vwflyer, October 03, 2016, 01:53:33 am

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Big back story here.
I've started playing around with QRP NVIS to see what it's capable of. I set up my computer to auto start a recording of my home radio's audio at certain times. I then turn the radio on and tune it to the freq I want to try. I then go out into the mountains and set up my QRP rig and simply string my EFHW from tree to tree as high as I can reach. When I know the computer has started recording I call CQ. If someone answers great. If not no big deal, I just want to see if my home QTH recorded me and how strong I was. So far I've only made three attempts but plan on many more at different distances, on different bands, at different times of day and in different terrain. The first attempt was at 130 miles on 40 meters in the mountains at 9:00 AM. My recording heard absolutely nothing. Then it occurred to me that my noise floor on 40 at my home QTH is always S7 or more. That could be why I didn't hear anything. If my signal was S5 it would have been buried in the noise. So I decided to try 30 meters out as it's a lot quieter than 40 at home. On the second attempt  my recording never started for some reason so who knows.

On my third attempt I was just going to a friend's house in town about 12 miles away from me. He has a big yard so I figured I'd take the little rig along and try a 30 meter contact from there. Long story not so short, my recording picked up my CQ quite well at 12 miles on 30 meters at 3 PM.

So here's my question. Was I using NVIS or ground wave to reach home? Both of our houses are in low spots so while there are no big hills between us there is also no chance of line of sight communications. My 2 meter FM base station at my home can't get more than about 8 miles towards town when talking simplex with my mobile rig and both are running 50 watts, not 4 watts that my QRP rig runs. The antenna was oriented for NVIS and not ground wave but at 12 miles it might not matter. Any opinions?


Hi, I think your 2m performance answers your question, if the antennas are at the same height.. It could be either or both.. Are you sure you didn't have line of sight between the antennas?


Horizontal polarization is much worse for ground wave; like 10s of dB worse.  But like you said, at 12 miles it might not matter. 

I think the only way to tell if it's NVIS or ground wave is to try several distances.  If the signal drops off rapidly with distance it's ground wave.  If for a distance out to 100 or 200 miles it is fairly constant, then it is probably NVIS.


Why didn't I think of that!? :-)


Hi Gil. My 2 meter antenna is on the same pole as my inverted vee dipole, about a foot or two above the dipole's apex. I've never tried a 2 meter contact between our houses because 2 meters has always died out about 4 miles shy of his house, about the time I start to get into town. If it weren't for all the buildings in town I think the 2 meters would go a little further.


I think you're right Bob. I do plan on doing a lot more tests. I don't have any trips to the mountains planned in the near future so my next test will be another local one. This time though I will be going east out of our valley and putting a 1000 foot mountain ridge between me and the house. I would think that even at only 10 miles, ground wave at 4 watts would have trouble getting over that.


My most puzzling contact was 200mi on 11m.. Never quite figured that one out.. Bob is right, try a bit further to see if the signal decreases.. I've had great NVIS contacts here but on 80m.. I have not used 30m enough to volunteer an opinion..



QuoteMy most puzzling contact was 200mi on 11m..

We pretend that all this is understandable through science but in reality it's all magic. Therein lies the draw.