Saturday, October 19, 2013

A modified 30 Meter Ground Plane Antenna. Post #235.

This week, I'm exploring the joys of 30 meters and the antennas that support this intriguing amateur radio band.

Last week, I built a simple 30 meter inverted vee antenna which continues to deliver outstanding performance.

Today, I decided to try a 30 meter ground plane antenna, consisting of a main vertical element and four sloping radials.  Many antenna experts believe that sloping the radial elements by 45 degrees will produce a better match for 50 ohm coaxial cable feed lines. Although my sloping radials don't come off the connector at 45 degrees,  they do seem to produce a usable match for my RG-8X feedline.  Any mismatch is corrected by my standby antenna transmatch--an old MFJ-941 E Versa Tuner.

According to "searchmobilecomputing.tectarget.com", a ground plane "is a variant of the dipole antenna designed for use with an unbalanced feed line such as coaxial cable.  It resembles a coaxial antenna whose lower section consists of straight elements called radials instead of a hollow cylinder.  There are two or more radials, each measuring 1/4 wavelength.  The radials are connected to the outer conductor or shield of the feed line.  The main element is connected to the center conductor."

My homebrewed ground plane is designed for the narrow range of frequencies between 10.100 MHz and 10.150 MHz.  The antenna was made to be resonant at 10.125 MHz--the midpoint of the band.

MATERIALS:

One 33-foot/10.06 meters MFJ telescoping fiberglass mast.  I had a spare mast in the garage at my new home site in the Puna District.

One Budwig HQ-1 coaxial center connector.

Five, 5-foot/1.52 meter wooden support stakes.  One stake would serve as the mast support, while the other stakes would support the drooping radials (ground plane).

Five ceramic insulators--one would support the top of the vertical element at the tip of the mast.  The other four would be used to tie off the drooping radials to their wooden support stakes.

Fifty feet/15.24 meters of RG-8X coaxial cable with UHF connectors.

A sufficient amount of #14 AWG housewire to make one vertical element and four radial segments.

Several 3-foot/0.91 meters RG-8X coaxial cable patch cords to connect the transceiver to the antenna transmatch, low pass filter, and dummy load.

A 30 meter capable transceiver.  In this case, I used an old Ten Tec Argosy II transceiver.

One MFJ 941-E Versa Tuner.  The "tuner" would handle any mismatch in the antenna system.

Basic tools, including wire cutters, soldering station, nylon ties, and vinyl electrical tape.

ASSEMBLY:

The antenna was built on the ground and later hoisted into position.

Using the general formula 234/f(MHz)=L, each radial and the main vertical element were cut to 23.11 feet/7.04 meters.  Some antenna experts recommend that radials be cut about 5% longer than the vertical element.  I decided to keep each antenna element the same length.

I attached and soldered the vertical element to the + terminal of the Budwig HQ-1 center connector.  The connection was covered with a layer of vinyl electrical tape.  I attached a ceramic insultor to the top end of the vertical element.  The vertical element was secured to the fiberglass mast with nylon ties.  The top insulator was taped to the top of the mast and secured with nylon ties.  The Budwig connector was oriented so that the + terminal faced up and the - terminal (with the radials) faced down.

Four radial elements were connected to the - terminal of the Budwig HQ-1 center connector.  The connections were soldered and taped with a layer of vinyl electrical tape.  Ceramic insulators were attached to the end of each radial.

I hoisted the mast on top of its wooden support stake.  The bottom of the vertical element was about 10 feet/3.04 meters above ground.  The radials were carefully spaced out and led away from the mast.  The radials were then attached to 4 wooden posts.  The wooden posts and the drooping radials were positioned to face North, South, East, and West (0, 90, 180, and 270 degrees).

The RG-8X feed line was led away from the fiberglass mast at a 90 degree angle, with the coax being approximately 10 feet/3.04 meters above ground.

The feed line entered the shack through a small hole in the radio room window and then to the MFJ 941-E Versa Tuner.  I also ran a 23.11 foot/7.04 meter "counterpoise" wire from the tuner ground connection.

INITIAL RESULTS:

Like the 30 meter inverted vee previously made, the homebrewed ground plane performed very well.  Owing to the vertical element's proximity to ground and the less than ideal slope of the radials, my initial SWR was between 1.5 and 1.7 to 1 across the 30 meter band.  The versa tuner handled that small mismatch without a problem.

My trusty Ten Tec Argosy II ran without complaint through the late afternoon and into the early evening hours.  With 25 watts output, I was getting reports of 569 to 599 from both Hawaii and mainland U.S. amateur radio stations.  My power source was a deep cycle marine battery charged by solar panels.

I'm enjoying the relaxed atmosphere of the 30 meter band with an antenna I built from materials found in the shack.

REFERENCES:

http://searchmobilecomputing.tectarget.com/definition/ground-plane-antenna.
http://www.csgnetwork.com/antennagpcalc.html.
http://youtube.com/watch?v=4Ex-33Jzp5E.

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I've included a few Amateur Radio News Headlines at the bottom of this post.

Thanks for dropping by today!

Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.