New NVIS Ideas

[VE3WI Dave]

I've seen designs for a couple of cloud-burner NVIS antennas, basically 2 el. vertical Yagis (dipoles with reflectors directly underneath). 

• One was a full size 40m dipole at 35' el. with a 5% longer reflector at 7'.  Author claimed good results for nearby contacts during Field Day. 
  

• The other was a short centre-loaded 80m dipole with four 10' sections and two 70 uH loading coils.  It was located at 12' el. with a 5% longer reflector at 2'.  Author also claimed good performance.
  

A balun works better if you wind a single layer on some kind of form (non metallic), rather than just a random coil.  Tom VA3TS used a plastic coffee jar (Folgers I think) as a coil form.


Off-topic:

A crossed dipole inverted-v is a simple, easy to erect antenna for portable ops.  The antennas are also the guys.  They don't interact when they are at 90°, and they can be fed by a single feedline.  80m/40m is pretty big, but an antenna for 40m/20m or higher bands is very manageable. 

The 4' stackable mil surplus fibreglass poles are great.  I bought a bunch from Bob Morton (Maple Leaf Comm) but I don't think he has any more.  Princess Auto used to have some but maybe Bobby bought them all :-)  If we can ever get back to Dayton, there's always lots of both the fibreglass & aluminum versions in the fleamarket. 

(Hint: much less risk of failure at the joints if you glue hardwood dowels into the male ends and tighten hose clamps around the female ends after assembly.  I had 8 of them assembled like this holding up an inverted-v for two years.)

73
Dave, VE3WI