Friday, March 28, 2014

Simple Ham Radio Antennas: The Ghost of Antennas Past, part 2. Post #268

The Novice Inverted Vee Antenna

Moving to a new QTH can be a lengthy process, especially when you're still working part time and must do all of the transporting yourself.  But in this drawn out activity, you have a chance to find things you were once thought lost forever.

Such was the case this past Wednesday, when a state holiday gave me and my xyl a chance to move some more "stuff" from our rental house to our permanent location in the Puna District of Hawaii Island.

Once most of the small objects, such as books, records, clothing, entertainment equipment, and, of course, amateur radio equipment is placed in their new surroundings, we can hire a commercial mover for the larger items, including beds, various pieces of furniture, and heavier items.  We'll probably take a few more months to get things everything squared away.  After all, both of us are supposed to be "retired".  We both teach school, so retirement is but another word to add to things of yesteryear.  With the cost of living rising ever higher, work becomes a life-long activity.  I don't mind, as long as we both keep active and enjoy our hobbies, including amateur radio.

During our last transport activity, I uncovered a complete set of logs and antenna notes covering the years 1977 to 1980--the years I was a novice, technician, and general class licensee.  I later became an advanced and extra class licensee, but that's a tall story for another time.

It was interesting to see what kind of antennas and equipment I used then.  The rig in those days was a slightly used and very forgiving Heathkit HW-101, a J-38 key, and a Drake MN-4 antenna "tuner".  The HW-101 was later given to a new ham.  The key and Drake MN-4 are still with me.  In those those three exciting years, I worked a lot of DX with some very simple antennas.  Thankfully, I kept the diagrams and associated measurements of those "skyhooks" in a series of school composition books which I filed with my old operating logs.  I still keep logs and antenna pages, but nothing beats re-examining the efforts of the past.

One of my favorite novice antennas was the inverted vee or drooping dipole.  All I needed was one tall mast, two antenna elements cut to my preferred frequency, a center dipole connector, a 75-foot/22.86 meters length of RG-58 with UHF connectors, my trusty Drake MN-4 ATU, and the much repaired HW-101.  When I added a low pass filter and the Heathkit Dummy Load (which I still have), I had a simple, functional amateur radio station.

I decided to follow my original plans and build a 40-meter inverted vee cut to my favorite 40-meter frequency of 7.125 MHz.  With a little nudging from the Drake MN-4 ATU, I could get acceptable performance on 15 meters, using the third harmonic of the 40 meter frequency.  The swr would be a little high because the third harmonic would fall just outside of my permitted 15 meter privileges.  The antenna would be modified later by extending the length of the original 40-meter elements so the resonant frequency would be near 7.088 MHz (the frequency of the Hawaii Afternoon Net).  Using the third harmonic of this frequency would put me near 21.264 MHz--just right for SSB operations in the 15-meter band.

Despite this limitation, I decided to build the antenna as a replica of my original 40-meter inverted vee.

MATERIALS:

One MFJ telescoping fiberglass mast measuring 33-feet/10.06 meters long.

One Budwig HQ-1 center coax connector.

Two antenna elements cut from #14 AWG house wire.  According to the general formula 468/f (MHz)=L (feet) and a design frequency of 7.125 MHz, each segment of the dipole would measure 32.84 feet (32 feet, 10 inches)/10.01 meters.  I probably should have allowed some extra length for swr adjustment, but, following my original plans, I didn't.  The Drake MN-4 would take care of the small mismatch in the line.

Seventy-five feet/22.86 meters of new Radio Shack RG-58 coaxial cable with UHF connectors.  I now use a better grade of coax, preferring RG-8X or RG-8 from Belden and other cable manufacturers.  This is another case of "live and learn."

Two 5-foot (1.52 meters) wooden fence posts to support the ends of the inverted vee.

One 5-foot (1.52 meters) wooden support stake for the fiberglass mast.

Two ceramic insulators to isolate the antenna elements from the wooden posts.

A few short length of nylon rope to tie off the antenna elements to the posts.

Basic tools, nylon ties, vinyl electrical tape.

Shack equipment, including a transceiver, low pass filter, dummy load, and the Drake MN-4 ATU.  Since I didn't have my original HW-101, I used my venerable Swan-100 MX transceiver, vintage 1983.

ASSEMBLY:

The antenna was built on the ground.

I then cut the antenna elements to length, soldered each element to the Budwig HQ-1 center coax connector, and attached a ceramic insulator to each free end of the antenna elements.

Before I attached the coax feed line to the center connector, I made a "choke balun" out of the RG-58 feed line near the center connector.  The balun consisted of a 6 turn, 8 inch/20.32 cm diameter hand wound coil secured with vinyl electrical tape.

I attached the coax to the center connector and ran the feed line down the length of the extended 33-ft/10.06 mast.  The coax was secured to the mast by nylon ties.  All exposed antenna connections were covered by several layers of vinyl electrical tape.

I secured the center connector to the top of the fiberglass mast with nylon ties and vinyl electrical tape.

I then hoisted the mast onto the wooden support stake, led the antenna elements at an approximate 45-degree angle from the apex of the mast, tied off the antenna segments to the pre-positioned wooden posts, and adjusted the antenna for a uniform and balanced appearance.

I led the remaining length of the coax to the patch panel in the shack window.  A short length of RG-58 (6-ft/1.82 meters) went to the Drake MN-4 ATU.  Small patch cords made from RG-58 coax I had in the junk box connected the Swan-100 MX, dummy load, and low- pass filter to the Drake MN-4.

RESULTS:

With the Drake MN-4 ATU in line, I was able to keep swr at 1.3 to 1 across the entire 40-meter band.  Tuning was bit touchy on 15 meters, but I was able to get an swr of 1.5 to 1 on most of the band.  Tuning on 20-meters and 10-meters was a bit more tedious, owing to the high swr present on those bands.  I decided, like in the past, not to push the old Drake MN-4 too far with a severe mismatch.  But for its intended purpose of getting a new novice on the air using 40-  and 15-meters, the antenna works.  Following my past operating procedures, I ran no more than 50 watts from the old Swan-100 MX transceiver.  The finals are a bit "long in the tooth" and I didn't want to begin a search for replacements.

During the course of several hours of operating  from early afternoon to mid-evening, I made many satisfying contacts on 40-meters CW and 15-meters SSB.  I'll play with this antenna for awhile and then I will carefully take it down, repack it, and save if for portable or emergency use.  This was a fun way to connect to my "novice" days as a newly licensed  amateur radio operator.

REFERENCES:

http://www.arrl.org/your-first-antenna.

http://www.arrl.org/file/Technology/tis/info/pdf/0683033.pdf.

http://www.iw5edi.com/ham-radio/?10-meter-dipole, 140.

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Aloha es 73 de Russ (KH6JRM).

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