Welcome to Tropical band

To most people the phrase "tropical bands" bring a pretty clear picture to mind - a bunch of shirtless guys playing calypso music. But to experienced shortwave DXers those two little words express the most challenging and enjoyable part of the radio hobby. The phrase kindles memories of a DXer's best catches and favorite QSLs, of exotic stations, music and of early morning listening sessions. (Don Moore)
I like the "Tropical band" name for new 60m allocation. (OK1RP)

Effective from 1st Jan 2017 please paper QSL via OM-bureau only.

Sunday, August 14, 2011

NVIS - The phenomenon of last few years only?

Hi all,

did You heard about the NVIS already?

The NVIS - shortening of the Near Vertical Incidence Skywave utilizes high-angle skywave paths between stations instead of ground-wave or surface-wave in order to communicate via HF radio equipment. Although it seems to be the phenomenon of the last few years and lot of ham radio guys talking about it and using it to reach local stations the NVIS technique is definitely not new!

The NVIS was originally evaluated by U.S. Army Forces in Thailand during the Vietnam conflict in the mid of 1960's. It was found that the mobile stations using whip antennas bent parallel to the ground could communicate more reliably with their base-stations instead of standard vertical whips mounted in it's original vertical position. Signal strengths would be weaker using high-angle skywave but communications would be more reliable less subject to fading known as QSB in ham radio and consistent between all stations. This was because the intervening terrain was less of an absorber of signals. Terrain obstructions between stations such as hills, mountainous areas, jungle growth, built-up areas with tall buildings no longer become path obstructions with stations when NVIS techniques are employed.

I do not like so much the NVIS technique simply because I am looking for long distances communication on the 60m - 160m bands in general. Nevertheless I realized that I am also using the NVIS technique on 60m band to reach close areas. My half sloper originally tuned for 160m band with really bad ground system worked pretty poor over there. I was not able to work comfortably UK stations and I got very poor reports from there.

After few weeks I decided to build new antenna for 60m but unfortunatelly I had not tower or another support to put planned dipole enough high. So I installed the Inverted Z (legs are folded to Z letter) with 10m apex only. (see here http://60mband.blogspot.com/2011/01/experimental-60m-inverted-z-for-pocket.html)

Immediatelly after the installation this antenna I found that my sigs rapidly increased in nearby location. The reports gotten from UK stations from now are superior and I have no serious problem to work station around Europe. When I though about it in fact I have just 0.16 lambda apex feed point so it can be called NVIS technique on 60m band too... and it really work well for these kind of ranges.

If You are interesting more in the NVIS techniques then click over here:

or You can read the famous presentation of Jack, W5JCK here:

73 - Petr, OK1RP

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