Wednesday, October 2, 2013

The radiating dummy load. Post #230

On Monday, 30 September 2013, I had the day off from my substitute teaching assignment and I decided to meet with some of my amateur radio friends at the Hilo, Hawaii Jack In The Box Restaurant for informal discussions concerning amateur radio.  The Hawaii QRP Club holds daily meetings at the popular fast food restaurant around 0800 W.  Most of the time, the meetings are concerned with the usual topics of rigs, DX, antennas, and the latest HOA restrictions on ham operators.  Monday's meeting was going to be different.

By the time I arrived at 0800 W, most of the group had departed for their jobs and other concerns, leaving only myself, my xyl, and informal club president Dean Manley (KH6B) left to "hold the fort."  Several times in the past I had lamented my fate in using compromise antennas in the various homes I rented while I was fully employed as a news announcer for KKGB-FM and KHLO-AM in Hilo.  Now that I was building a new home on a larger property, I had more space to build "real" antennas without some HOA forcing itself on my operating habits.

Dean handed me an article published in the December 1992 edition of "World Radio", which described how  Hank Scharfe (W6SKC/7) used a dummy load to get back on the air after his "automatic high-speed antenna tuner committed suicide."  I found the article fascinating.  I'm offering a few quotes from the article, hoping that those in similar circumstances can return to the air despite failure of their antenna matching devices.

Although Hank could hear well on his 150-foot Grounded Inverted L, the Icom "781 would not generate any power to what was probably a very high SWR.  The little 'band expander' tuner in the 781 was of no use at all, so I decided I had to trick the 781 into generating some useable (sic) power.  I screwed a coaxial 'T' connector into my Waters dummy load.  Of the other two ports, one went to the 781 and the other went to the GIL's feedline."

"The power meter on the dummy load indicated 150 W on peaks, and the inline SWR bridge indicate the world's finest SWR, 1:1 on all frequencies between 1.8 and 29.7 MHz!  Best of all, instant loading."

"I checked into my normal sked and Tucson (60 miles away) gave me my usual 30 over 9 report.  Then Yuma (250 miles to the west) volunteered that I was the same old 20 over 9."

"Although the power meter in the dummy load was still indicating 150 W, it was obvious that some power was escaping up the GIL's feedline.  The only noticeable difference was that the receiver seemed to be 'quieter.'  Being a low-Q lashup, i.e. broad-banded, the residual noise was down.  I thought the coupler with a 10 to 20 millisecond tuneup time was fast, but zero tuneup time is faster and more convenient when band-hopping."

"Not wanting the big Waters DL on the operating table all the time, I replaced it with a 15 W dummy load from Radio Shack...it handles the 150 W of the SSB rig without getting hot, since the duty cycle SSB is probably less than 5 percent.  For a few dollars more, Ten-Tec and MFJ offer 300 W units that will handle 1500 W SSB easily."

So, there you have it...an emergency antenna using a dummy load to help your random wire radiate.  I've done the same thing using a Heathkit Cantenna, a "T" coax connector, and a simple coax-fed dipole.  Like W6SKC/7, I've made contacts on several amateur radio bands, including 40, 20, 15, and 10 meters.  The reports were a bit down from my usual reports at home, but I did radiate a signal and was able to carry on conversations.  I suppose most of my power was absorbed by the cantenna, but some power in the milliwatt range was "squeezed out" and I had enough energy to make contacts.

You may want to try this temporary antenna project just to see what you can do.

REFERENCES:

Sterba, Kurt N. (John E. "Jack" Althouse, K6NY (SK).  Article published in the Aerials column.  "World Radio".  December 1992.  Note:  John Althouse (aka Kurt N. Sterba) died 15 September 2013 in San Diego, California.  He was the president of Palomar Engineers.

Personal conversation with Dean Manley (KH6B), 30 September 2013, 0800 W, at the Hilo, Hawaii Jack In The Box Restaurant.

http://www.eham.net/articles/9054.

http://www.ehow.com/how_6459249_use-dummy-load-ham-radio.html.

You can follow our blog community with a free email subscription or by tapping into the blog RSS feed.

Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM).

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