[KLQRP] NVIS Antenna

[Richard Hayter]

Interesting Bob,

Did you measure the impedance at the feed point to the antenna and if so
what was it? I believe that is another advantage of this particular design.
Ie. feedpoint impedance should be around 50ohms at 16 ft.  As the Antenna is
lowered the feedpoint impedance decreases? 

Also NVIS antenna is supposed to minimize the ground wave. Can you model the
ground wave on EZNEC?

You state 1000miles range. In the article I read it talks more about ranges
of 200-300miles. 

72 Dick N4HAY

-----Original Message-----
From: klqrp-bounces at knightlites.org [mailto:klqrp-bounces at knightlites.org]
On Behalf Of Bob Kellogg
Sent: Thursday, July 12, 2007 8:11 PM
To: John Paul
Cc: KLQRP
Subject: [KLQRP] NVIS Antenna

John Paul,

I've modeled the antenna using EZNEC and also modeled the N6VNG 
antenna.  Ours seems to be far superior as far as matching is 
concerned.  Both send the signal straight up, but ours works like a fan 
dipole on 40 and 80.  The N6VNG  antenna is actually an off center fed  
(OCF) antenna cut for 40 meters.  So it may work on  7 and 21 MHz pretty 
well, but it is lacking on other bands.  Ours works on 3.5, 7, 21, and 
at least as well as the N6VNG on the other bands.  (Actually it should 
be better on some, like the 30 meter band)

Although, it's strength will be operating in the 1000 miles or less 
range, so the only reason to try to use it on the higher bands would be 
to make contact in the near skip range.  I'd like to get some practical 
experience using it for that purpose before  we make a lot of claims for it.

The best wire dimensions based on the model are 65'-2" and 31'-4", guyed 
so the ends of the wires are about 5' off of the ground.

As I mentioned earlier, the mast is 16-1/2' high on my version, made of 
1-1/2" PVC pipe.

The balun I used is a current balun, made by cutting two 20" lengths of 
#18 magnet wire and taping them together so the wires are parallel.  The 
parallel wires were wrapped 11 turns around a 1-1/4" core.  I used an 
Amidon FT-125-K.  I don't think the core is critical.  The red, yellow 
and plain cores would also work if we are operating at low power.  My 
balun will handle over 100 watts.

The balun is housed in a 3" section of the PVC pipe, with a PVC cap on 
one end and a PVC coupling on the other.  The cap is drilled  for two 
stainless steel screws to make the antenna connection.  I cut a plastic 
disk to fit inside the coupling and mounted an SO-239 socket on it for 
the coax connection.   The plastic disk is trapped between the pipe and 
the coupling as they slide together.  The two wires on one end of the 
balun  coil connect to the antenna terminals and the two wires on the 
other end connect to the SO-239.  The coupling end of the balun sits on 
top of the mast.  The coax enters the mast through a hole near the 
bottom and runs to the top inside the mast, connecting to the SO-239.

Knightlites who are not familiar with the basic design should look at 
the pictures on  this web site: http://www.vcars.org/tech/NVIS.html

This really a simple antenna to build, costs about $20 for materials, 
and has minimal space requirements
 

-- 
Best Wishes,

Bob Kellogg
Greensboro, NC
Prolably, not nececelery - Benny Hill

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