Thursday, July 4, 2013

Antenna Topics: A simple 30 meter vertical antenna

Every now and then I feel the need to get away from the crowded amateur radio bands and just relax with an easy-paced conversation on 30 meters.  The band, which stretches from 10.1 MHz to 10.150 MHz, is quite narrow and is restricted to cw and data transmissions.

The pace of communications is generally more relaxed on 30 meters than in any other amateur radio band.  And since I need more practice in cw, this band is perfect for sharpening my skills.  Along the way I also meet some interesting and helpful people.

In order to use 30 meters, I have to change rigs.  My old Swan 100 MX, Yaesu FT-7, and Kenwood TS-520 don't cover this band, so I rely on another excellent transceiver--the Ten Tec Argosy II.  This rig can run up to 50 watts output, but I prefer the 5 watt setting for most of my cw work.  I can run the Argosy II off my solar charged deep cycle marine battery all day without depleting the battery.

Although I could use my 40-10 meter inverted vee fed by 450-ohm ladder line, I decided to build an inverted vee especially designed for 30 meters.

So, last Friday morning, I used a halyard/pulley combination to lower the 40 meter inverted vee.  I removed the antenna and its Budwig HQ-1 center connector and placed them in a plastic storage bin.

MATERIALS:

One 33-foot (10.06 meters) MFJ telescoping fiberglass mast.  That was already in place.

Two, 7-foot (2.13 meters) tie off stakes.  These were already in place.

A 50-foot (15.24 meters) of RG-8X coax with UHF connectors.  The cable was in the shack.

Two ceramic insulators from the junk box...one insulator would be attached to each element of the inverted vee dipole.

One Budwig HQ-1 center connector.  I had an extra connector in the junk box.

Fifty-feet (15.24 meters) of #18 AWG speaker wire.  I had some of this wire in the shack.  For a permanent  installation, I would recommend stronger wire, such as #14 AWG house wire.

A halyard/pulley system to hoist the vee into position.  I had the system already attached to the fiberglass mast.

ASSEMBLY:

The antenna was built on the ground.  The halyard/pulley system would later hoist the antenna into position.

Using the general formula 468/f (MHz)=L (ft),  I cut the antenna to a length of 47 feet (14.32 meters).  The computed length was 46.33 feet (14.12 meters), but I used the longer length to accommodate for adjustments to the dipole elements.  The dipole was divided into two equal parts--each 23.5-feet (7.16 meters) long.

Each dipole element was attached to a ceramic end insulator.  The top portion of each element was soldered to the Budwig HQ-1 center connector.  Connections were covered by several layers of vinyl electrical tape.

Before I attached the RG-8X coaxial feed line, I wound the top portion of the coax into a 6 turn RF choke to keep RF off the cable.  The coil diameter was 6-inches (15.24 cm).

I attached the coax feed line to the center connector and hoisted the inverted vee into position with the halyard/pulley arrangement.

I tied off the dipole elements to the support stakes.

I ran the cable into the shack through a nearby window and attached the feed line to the Drake MN-4 antenna transmatch.  Small patch cords linked the Drake MN-4 to the low pass filter, dummy load, and the Ten Tec Argosy II.

PRELIMINARY RESULTS:

Without the Drake MN-4 in line, the SWR measured 1.7 to 1--not bad for a hurried half hour of building.  A bit of trimming would come later.  The Drake MN-4 brought the SWR down to 1.1 to 1 without a problem.

So far, contacts have been excellent in the late afternoon hours, with reports ranging from 569 to 589 with the Argosy II running 5 watts.

I had fun making this unsophisticated, but  efficient antenna.  Best of all, I didn't spend any money making the antenna, thanks to my junk box in the garage.  Thirty meters is a fun band with lots of helpful people.  So, get  out your key or keyer and try 30 meters.  This band is quickly becoming my favorite place to catch a good "ragchew".

REFERENCES:

http://www.wm8c.com/60-minute-dipole.htm.
http://www.kd5om.com/build-an-inverted vee.htm.
http://www.youtube/watch?v=fyOWRTWdDKM.
http://www.146970.com/PDFs/Antenna-HFAntennasforbeginners30MetersandBelow.pdf.

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Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM).

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