Saturday, June 4, 2016

20 meter elevated vertical build and testing

Reason for project

Operating during a few state QSO parties and Winter Field Day showed the advantage of using a NVIS 40 meter dipole. This works great for pulling in the county multipliers or surrounding states but causes a low number of state multipliers. My thought was that I needed something on 20 meters to help grab the east and west coast states since I usually cannot put up a high dipole. 

The mast

I use a Max-Gain 32 foot push up mast with a drive on mast holder. This allows me to pull up a inverted V dipole. I have made various PVC adapters to fit the top section of this mast. 
These adapters include: Dual band 2M/70CM antenna, 2M yagi and arms to pull up dipoles.

New PVC adapter

A PVC adapter was made that allows the use of a MFJ 17 foot telescoping antenna to be top mounted on the Max-Gain mast. The adapter has a 3/8x24 threaded fitting for the antenna connection. It has a support guide about 18" above the base to provide support for the antenna and to take the wind loading off of the 3/8 x 24 mount. The 3 tuned radials hook onto to a cable tie with plastic S-clips. The radials have banana plugs that plug into the ground side of the 3/8 x 24 fitting. The PVC dog leg on the bottom is for pulling up the dipole.

Finished product

Here is a picture of it in the air with the base at about 25 feet. Height to the tip of the antenna would be around 40 feet. The 3 radials also act as guy anchors which I have at about a 45 degree angle. During the first measurement I had the antenna at 16.5 feet which should have been just right for 14.225Mhz but it measured resonant at 14.9Mhz. I lowered the mast and extended the antenna to 17 feet. This brought the resonant point to 14.110Mhz which is lower than I wanted but it turns out the VSWR is acceptable for the entire band. 1.25:1 or less for the entire band. Measurements were made with a RigExperts AA-54. I am able to save and view my VSWR graph on the PC but I cannot find a way to display it here on the blog. 

1 comment:

  1. So you'll have a dipole for 40m at around 16 feet hanging off the eye bolt and the 20m vertical starting at 17 feet, extending to 40 foot in the air?