Near Vertical Incidence Skywave (NVIS) Antenna for Local HF Contacts

The Virginia QSO Party is just around the corner and this year I am going to be better prepared for making local HF contacts.  In the last few years of contesting, I have been plagued with poor local performance from my HF operating station.  I employed two multi-band HF antennas for making contacts but found that I could mostly reach non-Virginia stations, typically > a 500 mile radius from my location.  My current antenna setups are great for long distance contacts, often times reaching all over the US and Europe.  The antennas are great for making DX contacts due to their take off angle, but not as great for local contacts for the same reason they are great for DX.  My current HF station is comprised of an Icom 7300 HF radio, seven band off center fed (OCF) Buckmaster dipole, and six band MFJ 1796 vertical.  I can switch between antennas using an LDG AT-100ProII antenna tuner which also has an Alpha Delta antenna switch hanging off the ANT2 connection (more to come on that later).  A little research yielded interesting results and a positive outlook to my local contact problem.

When researching my problem I found a solution that the military has used for a very long time to establish local coms with ground units using HF.  They use a technique called Near Vertical Incidence Skywave (NVIS), which generally speaking, shoots the signal at an extreme angle into the air.  The signal then bounces off of the Ionosphere and comes back to Earth, proving effective 30-500 miles from the originating station.  This type of antenna is said to work best between 2 and 10 MHz (primarily 80m and 40m bands).  Further research led me to a plan for an NVIS antenna that can be built easily and  inexpensively.

DX Engineering, which is my favorite place to source my amateur radio needs, has a great PDF that explains the technical details behind the NVIS antenna as well as the plan and parts list to build an antenna for yourself.  Please check out the PDF for a deeper technical explanation as well as the parts list.  I ordered all the parts I needed to build an NVIS antenna and also purchased a very sturdy, telescoping fiberglass painters pole from Lowes to mount the antenna to.  Once the parts were received, which for me usually only takes a day from DX Engineering (another reason I love them), I was able to assemble the entire antenna in an hour or so.  The listed “kit” includes the assembly instructions which are easy to follow.  I chose to only build the 40m NVIS dipole due to the location where I was going to be mounting it.

After assembly I attached the center “T” to my telescoping fiberglass pole and set it to a height of 15 feet.  I mounted the fiberglass pole to a fence in my back yard which runs parallel with some evergreen trees that boarder my property.  The pole extends upwards into the evergreen trees with it’s wire “legs” making an inverted “V”  with the ends extending out and mounted roughly 3 feet off of the ground.  This position is what I found to work best during testing after installation.  Results may vary and should be tested to meet your needs.

After getting everything mounted and attached, I ran a new length of RG-8X into my basement and connected it to my Alpha Delta antenna switch.  I tuned the Icom 7300 to the 40m band and put the LDG AT-100ProII through a tuning process to see how things turned out.  According to the tuner, I achieved a 1.1 : 1 SWR on 40m which is what I expected.  Just for fun, I tuned to the  80m band and ran the tuning process to see what would happen.  I was pleasantly surprised to find that it tuned almost as perfect as 40m!  Since I received such great results on 80m and 40m, I decided to try 20m  and found that it tuned perfect there too (as well as a few more bands)!  With that said, I do realize that this is not a formal antenna analyzer so other numbers may be off.  Regardless, I was very happy that the NVIS antenna was tuned in and was working properly!

Antenna building is a very fun part of the amateur radio hobby, especially when the expected results are so easily achieved.  Not only was I able to build an effective antenna for very little cost, I was able to solve a problem that had been occurring for the last few years during the Virginia QSO Party.  Next month will mark my 3rd Virginia QSO Party and I look forward to making contact with many local Virginia stations as well as out of state contacts with the new NVIS antenna!

Look for me on the airwaves on March 16-17.

73 de W4LAN

If you have any comments or questions about my NVIS antenna, feel free to leave them in the comments section below.

 

**The Virginia QSO Party is sponsored by the Sterling Park Amateur Radio Club (SPARC).

**Although I am not affiliated with DX Engineering, I HIGHLY recommend them.  They have great products (and prices that almost always beat Amazon), great information,  and shipping is VERY fast!

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