I have a HF TVIS stored in the biological main computer and ram , one day . TVIS Paul , with just another acronym to remember .
Truthfully, I enjoy regional conversations, and focus on that 'one-tank-of-gas distance'. Maintaining scheduled conversations with friends in the region is enjoyable and - as in the recent case of Hurricane Florence - the 'one-tank-of-gas' range proved to be very important for news &etc. Having lived much of my life in The Rocky Mountains, NVIS's ability to reach down into deep valleys and over peaks using my little CW QRP rig was much appreciated! Nice series of short pod-casts on your site. Thanks you for letting us know. >Ray ..._ ._
New Hampshire has PLENTY of peaks and valleys, along with granite walls and magnetic ore. Full wave loops work great for NVIS. I have two full wave 80m loops, one 12' high, and the other about 30' high. The low one gets me pretty much all of NH, the high one gets me New England. In a pinch both are great up to 10m with a tuner. As KL7JR says: "Not bad for a piece of wire, eh?" 73 Jim, WQ2H
My condominium association rules prohibit any type of outside antenna. So I strung up an inside end fed dipole which enabled me to work 40 meters CW. With tall buildings and terrain obstructions surrounding me, my signal really had no other place to go but straight up. So for me, it was NVIS or nothing!
I didn't watch the video here, but if you want a free presentation here is one I gave multiple times in north Texas back in 2009. Below are the links to the PDF and Powerpoint versions. I heavily based my presentation on the great works of L. B. Cebik, W4RNL, SK (2008). And the presentation is FREE. Aren't hams supposed to help one another out for free, hence the term "Amateur" in Amateur Radio? One good application for NVIS is EMCOMM when you need to set up close in communications during disaster relief. Another good use is for getting those close in states for contesting that your big beam will shoot right over. Unfortunately NVIS in Texas means picking up those damn grumpy old opinionated Geritol Nets from the jerks out in west Texas, but just stay clear of 3.8xx MHz and you will be okay. BTW, I pronounce NVIS as "enn viss" or as "enn vee eye ess". But you can call it whatever you like! http://w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf http://w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.ppsx Enjoy...
A T2FD with a length of about 40 meters hanging about 5 meters above ground would be good for the most common range of NVIS frequencies.
The Army did a study on NIVS the 80s. A lot of it based on HF communications during Vietnam. apparently they found that the optimum antenna for this technique is a dipole 1/10 of the wavelength above the ground. I am not a rocket scientist but from my observations in the field height above ground is key.
That's wrong. A dipole at 1/10 wavelength high is a popular misconception and mis-reading of NVIS recommendations. For RECEIVE NVIS, 1/10 wavelength (0.1 wavelength) is the height for optimum SNR (Signal-to-Noise-Ratio) , in a perfect ground site. For TRANSMIT NVIS, 0.2 wavelength is approximately the optimum height. There is only a 1dB NVIS advantage at 1/10 wavelength for Receive (compared to 0.2 wavelength). But, there is a 3dB NVIS advantage for 0.2 wavelength for Transmit. What this all boils down to, is that 0.2 wavelength is probably the best overall height for an NVIS dipole, above typical (farmland) damp soil. Over other types of ground, it varies quite a lot. Generally, the lower the dipole, the more of your transmit power (gain) gets absorbed by the ground soil. But, with HF receive, the SNR is often more important than gain or loss. Then, there's the modern reality of SNR... the RFI received due to nearby RF noise sources. Whatever height for the receive antenna which achieves the lowest receive RFI, is probably now the best NVIS receive height Unless your QTH is totally noise-free, you can throw out the NVIS myths about low dipoles being better. Also, a little-known fact is that a transmitted signal from a dipole, when it goes thru an NVIS path, gets converted to approximately circular polarization by the ionosphere See chart below (source: B. Witvliet, 2015) hRX is Receive optimum height hTX is Transmit optimum height
I do not think there is a such of a thing as NIVS How is NVIS different from conventional propagation Theory ?? Not something called NIVS It is called conventional propagation theory ! Most every dipole I have ever seen for 40 and for sure 80 were at a sub 1/2 wave height ! Some very much less If what I say is true ! And everyone knows well it is ! What is this chatter ???? I think working toward a efficient antenna will go much farther than nonsence chatter about NVIS
This gets mentioned often. Putting up an 80 foot tower in the field might draw some unwanted attention. I believe the army found a solution that met their needs. You can model a 80m dipole and see that the pattern doesn't really change much until you go beyond 60 feet. What does change is ground loss. The lower the dipole the higher the ground loss. Same pattern but less efficiency.
I see what you did there KB1ARM , post: 4804011 thanks , ok i'll retract my comment on "no mention of SNR" , just did not see it/words as it ended with ratio's . Click bait is staying , it baited me for instance and it's up to me if i want to buy anything or not , or mention it or not , with or without any mistakes included or not , and at the end of this post you'll notice absolutely no advertising of anything , but you are welcome to send a dollar to my paypal account if you like just because i'm a nice person too . Back to NVIS And whilst i'm here and not directed to anyone specifically , whats all this talk on only short distances , many a time from QTH to Eastern Russia , Japan , VK6/7/8/9 and the usual VK2/3 and ZL has never been a issue , some distance's over 8000klm (5000M) all on 80 night and 40M any time , that's with a reference 1/2 wave dipole to switch over to and compare also , and when switched to 1/2wave practically inaudible on a real crashy 80m band , switch back to the NVIS and the signal jumps out generally with no more head-aches from the crashes either , with Tx one needs another 3 to 4dB of gain to compensate for the loss imo , but i never used any gain and still worked the dx ok with 100W . There always is around at least 2 S points lower difference with the NVIS yet that is compensated with much lower band noise and SNR , sometimes i had to go out and check everything to make sure the coax was still connected and wires still up the noise floor was so quite . The NVIS i used was 7Ft off the ground with reflectors copied and modified from a website ie:superNvis , dual band 80/40 from the feed-point with balun and 2 sets of reflectors everything wood and wire , i had it for a couple of years or more until a new owner in the next 70Ha paddock and the 1st thing it did was put up fences everywhere including around here on this small block , the previous owner let me do what i like in his paddock . I found i always defaulted to the NVIS and eventually took down the 1/2 wave dipole up at 60Ft , all that stuff has gone now and i use a 5 band vertical due to the restrictions . I miss that NVIS , especially on 80M in summer with S9 and plenty more crashes which were S4 or 5 on the Cloud Burner , 40M was like having a automatic Squelch . Paul .
