Saturday, October 5, 2013

A radiating dummy load antenna, part 2. Post #231

In my last post, I recounted a conversation I had with Dean Manley (KH6B) on Monday, 30 September 2013 concerning the use of "dummy loads" as emergency antennas.  The conversation centered around Hank Scharfe's (W6SKC/7) attempt to get some power into his 150-ft (45.73 meters) grounded inverted "L" antenna following the failure of his automatic antenna tuner.  Hank was successful in meeting his scheduled nets when he used his Waters dummy load with a "T" UHF connector to feed some rf to his antenna.  Although most of his power was confined to the dummy load, there was sufficient power delivered to his antenna to complete his schedules.

Dean and I have made several such antennas for field day and portable operations.  In fact, I mentioned my own experience with a dummy load antenna back in September 2012 when I was a newly licensed novice operator.  That contact surprised me, and that experience has kept me interested in radiating dummy loads ever since.  So, while I had some time off from my substitute teaching assignments, I decided to make an emergency antenna using a dummy load and the few milliwatts I could squeeze from the lash up to make some local contacts.  The results were gratifying.  I made some excellent ssb and cw contacts on 40, 20, and 15 meters with my trusty Heathkit  Cantenna dummy load performing most of the work.

MATERIALS:

One 33-ft (10.06 meter) MFJ telescoping fiberglass mast.  The mast supported a 40 through 10 meter inverted vee fed by 450-ohm ladder line running into a W9INN 4:1 balun and a Drake MN-4 antenna transmatch.  I had a spare 40 meter dipole connected to a Budwig HQ-1 coax center connector and 50-feet (15.24 meters) of RG-8X coaxial cable in the garage.

I lowered the inverted vee, stored it in the garage, and hoisted the dipole to the top of the mast where I configured it as an inverted vee.  The antennas were raised and lowered with a halyard and pulley system.

Two 5-foot (1.52 meters) wooden stakes to support the ends of the inverted vee.  The stakes were also used for the vee fed by the ladder line.

One Heathkit Cantenna dummy load.

One UHF "T" connector.

Three-feet (0.91 meters) of RG-8X coaxial cable with UHF connectors.

Shack equipment, including an SWR meter, low pass filter, and the trusty Swan 100-MX transceiver.

ASSEMBLY:

One I lowered the ladder line-fed inverted vee, I hoisted the 40 meter dipole with the Budwig center coax connector to the tip of the fiberglass mast.  The halyard and pulley system came in very handy in making a quick and smooth transition from ladder line to coax feedline.

I ran the RG-8X coaxial cable through a homebrewed window panel to the equipment table.  I screwed the coaxial "T" connector into the Heath Cantenna.  One port went to the Swan 100-MX transceiver and the other port went to the coax leading to the outdoor inverted vee.

RESULTS:

I ran approximately 50 watts cw and 75 watts ssb into the antenna feed line.  The SWR meter showed 1:1 on all frequencies from 7.088 MHz (Hawaii Afternoon Net frequency) to 29.7 MHz.  Although most of the power was channeled to the Cantenna, there was enough "juice" left over to energize the antenna.  Reports varied from 549 to 579 on cw and 53 to 58 on ssb, depending on time of day and band in use.  Ten meters was very noisy, so I didn't spend much time using that band.  My best reports came from 40 and 15 meters.

Despite the absorption of most of the power by the dummy load, some power was running up the feedline.  Like W6SKC/7's experience, I noticed this modification seemed to be quieter than my other inverted vee.

This is a compromise antenna with high losses, but, in an emergency, a dummy load can substitute for an antenna "tuner" if the need arises.  This was an enjoyable and educational experience.  I replaced this temporary antenna with my previous inverted vee fed by ladder line.  If I ever need an emergency antenna, I know what to do.

REFERENCES:

Personal conversation with Dean Manley (KH6B) on 30 September 2013 at the Hilo, Hawaii Jack In The Box Restaurant.

The "Aerials" column from "World Radio", December 1992.  The column was the brainchild of the late Kurt N. Sterba (aka John E. "Jack" Althouse) (K6NY).  Althouse died on 15 September 2013 after suffering a massive stroke.  He was the president of Palomar Engineers.

ARRL Letter, 19 September 2013 (http://www.arrl.org/).

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Aloha es 73 de Russ (KH6JRM).

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