NVIS Distance Help

[blhar15]

I am trying to setup communication between two sites about 80 miles away from each other. We have been experimenting with NVIS, 40 meter but have not been getting good results. I am wondering if anyone else has experience with this type of communication under 100 miles on HF? I think our incident angle needs to be higher, because I think we are in the skip zone for our distance.

I have also considered looking into Tropospheric scatter.

Does anyone have some suggestions?

Thank you

 

[mastr]

I respectfully suggest that "have been experimenting with NVIS, 40 meter" supplies practically no useful information about how you are trying to make your 80 mile contact.

List the type of antenna in use, power level and the results you are getting now (signal level and time of day/night) and maybe you will get more useful answers.

 

[blhar15]

I guess it was a more general question if anyone has had experience, successes with NVIS under 100 miles and what they used. We have tried using a Buddipole setup for NVIS, early evening (still daylight hours, towards dusk), power level one radio was at 10 watts and other station was at 100 watts. The one station thought they could faintly hear the 10 watt radio coming through, but nothing coming back on the 100 watt radio.
We are located in Iowa.

Thanks

 

[mastr]

Right now I am listening to a station about 75 miles from me on 7.258, he is 20 over S9 and says power is "about 500 watts".

The following is my opinion, based on 35 years of NVIS experience -

(1) a plain old wire dipole at modest height will perform better than the Buddipole. Adding a reflector under it will help if you have time, room and motivation.

(2) 10 watts is a waste of time. A 100 watt radio is 10dB better. Add a 1kW amplifier for 10more dB.

(3) 40meters is not going to be a 100% 24 hour a day band for NVIS. Consider trying 60 or 80 when 40 doesn't work.

 

[kb5udf]

I second what Mastr said. I would add that basically, 40 during daylight if it is working well and 80 otherwise ( around sunset +/-)
as a general rule. Sometimes, when propagation is poor you may have go down to 80 or try 60m. Pretty much any fuller length antenna is going so work better than a compromise portable one. So basically what mastr said a dipole, though a bit below the optimum height for DX which helps with your NVIS propagation. In my experience most verticals aren’t that great for NVIS. 10 watts is near QRP. levels; given the typical noise level on 40 and 80, you want more power. Usually, 100watts is enough, assuming proper antennas, but not absolutely always.

 

[KB4MSZ]

I communicate with a fellow ham friend on a fairly regular basis on 40 meters between his house in St. Cloud, Fl and my mobile in south Tampa, Fl. The distance is about 85 miles. He is using an end fed halfwave broadside to the east and west, I am using a hamstick on my pickup truck. Our signals vary between S7 to 10 over 9 during the late afternoon. When it starts to get dark the signals start dropping rapidly to just about nothing. Both of us are using 100 watts.

 

[K6GBW]

Buddy poles are not the best antenna for getting a signal out. Try a 40 meter dipole at 15 to 30 feet. Make sure it's as horizontal as you can get it. NVIS works best when both stations have low horizontal antennas otherwise one station will be talking over the other. Keep in mind that HF has good days and bad days. Some times you can do everything right and the bands just won't cooperate. Also, you should ground the coax and use a common mode chock near the shack. It helps make your station safer and reduces some of the noise.

I routinely talk to a buddy of mine that is 54 miles away. We both use low dipoles with 100 watts or less.

 

[prcguy]

Propagation will vary some across the US but you can typically do what the OP wants much of the time using full size horizontal dipoles. The maximum gain straight up will be near 1/4 wave high or about 32ft so consider that the highest you want to go. Lower heights will have reduced NVIS performance although the receive noise floor will go down as the antenan is lowered. Some days you can communicate just fine with dipoles laying on the ground right in the dirt and some days 1500 watts may not work as propagation will change. But it should work most of the time at 100w levels on both stations with dipoles at each end.

You might want to consider using 60m and 80m for backup as propagation will sometimes favor those bands over 40m. An end fed multiband antenna is an easy way to combine all the bands in one antenna, basically a resonant end fed half wave made for 80m works great on 40m but you will need a tuner for 60m. Put that 15-30ft high and you will have a good chance of meeting your goals.

 

[blhar15]

I appreciate the replies.

I guess everything I have read about NVIS is calling for an antenna that looks more like an inverted V, to get better antenna pattern more vertical. Based on what I am hearing, a basic dipole or endfed that is horizontal closer to the ground will work just as well, is that correct? What kind of distance above ground would be ideal and recommendations for the best reflector material?

Thank you

 

[mastr]

Give this a careful read - you may decide that a simple dipole at about 25 feet will do the job.

http://on5au.be/content/a10/wire/n2.pdf

 

[AK9R]

I don't think flat-top or inverted-V makes a difference. What the previous posters are trying to tell you is that you need to get some copper in the air. A full-length dipole for 80/75m or 40m is going to work much better than a Buddi-anything. At the longer waves, full-size antennas work better than antennas with traps or tuning coils.

I check into a net on 75m every morning at 8:30am local time. One of the regulars is 20 miles from me. The other regular check-ins range from 40 miles to 150 miles from me. We hear each other just fine. I'm running 100 watts and so are most of the other guys.

 

[oldradioguy2010]

Field day we did NVIS at 80meters less than 100 watts.
From So. Cal (Ventura) we worked Oregon to the Mexican border and over to Las Vegas Nv.
Check your loading.

DW
So. Cal

 

[prcguy]

I appreciate the replies.

I guess everything I have read about NVIS is calling for an antenna that looks more like an inverted V, to get better antenna pattern more vertical. Based on what I am hearing, a basic dipole or endfed that is horizontal closer to the ground will work just as well, is that correct? What kind of distance above ground would be ideal and recommendations for the best reflector material?

Thank you

As I mentioned in my previous post, about 1/4 wavelength off the ground and horizontal will give the most gain upwards. For 40m that would be about 32ft off the ground but 25ft is fine. The lower you go the more inefficient it will get but the receive noise floor will get quieter as you lower the antenna from 32ft for 40m.

Since 40m is about the highest band you can make use of NVIS 32ft would be the highest you would want to go and that will also work fine for 60m or 80m. If you were only going to use 80m then higher like 50-65ft would give the highest gain upward at the expense of a higher noise floor. I would not recommend a ground wire reflector as that can sometimes provide a slight benefit but in many cases it degrades things due to a lossy untuned element sitting in the dirt. The only type reflector that will give constant good performance would be a very large ground screen at least 1/2 wavelength long and very wide under the dipole. Not practical for most installations and even that would only be a slight improvement over just dirt.

 

[K6GBW]

prcguy is correct. Right around a quarter wave length works best. If you go below that it still works...the pattern is the same, but you start loosing more and more power into the ground the lower you go. That said, if you are running 100 watts at ten feet and you are only putting 15-20 watts into the air, you'll still make contacts. So don't sweat the small stuff, just get a wire at the best height you can manage and don't look back. For me, I have mine at 20 feet because that's what I can do without having to go to extreme lengths. Guess what, I talk on 40 meters from northern Arizona to north of San Francisco all day long. Perfect for me needs.