Archives

Updated November 26, 2021

Random QRM from the President’s Shack

November 2021

“Don’t assume… verify!”

  Recently I installed a truck stake antenna mount on my pickup in preparation for installing a dual-band mobile rig. I installed a Comet SS-460SB short dual-band antenna onto the mount, and I decided to throw an analyzer on it just for fun. I have been using the SS-460SB on a mag mount for many years, and it was fine—then.

  As I tuned the analyzer to 145.2 MHz, I got a rather unpleasant surprise. The SWR was over 5! At 444 MHz it was around 3.5. I didn’t believe the analyzer.

  I got out my ohmmeter and tested the connectors, feedline, and mount. The feedline was not shorted; the shield connection showed 0 ohms and so did the center connector, and the mount was grounded to the body.

  I tried another antenna: a Comet SBB-5. At 145.2 it showed 1.1, and at 444 it was 1.6. I had just assumed that my little SS-460SB was “just fine.” Well, something had happened to the little guy. I saw no external damage, no corrosion but obviously something was wrong internally.

  This incident reminded me of another one that occurred a few years ago. MARS was doing Field Day at the Carrollton Fire Rescue Training Building that used to be next to Newman Smith High School.

  I double-checked all the connections, and they were okay. I checked the antenna, and it was okay. I asked Andy Parcel, KE5KOF, if he had another tuner and he did, so we swapped the manual tuner for an LDG autotuner. The LDG tuned right up, and contacts were made! The manual tuner was simply broken. Everyone assumed that the 40m station was fully operational including the tuner.

  With the cooler fall weather, it’s a good time for antenna projects. I suggest as you work on your antenna, don’t forget to check the antenna using an analyzer or SWR meter. That antenna that “worked fine” the last time you used it might not do so today. Don’t assume… verify!

 —73, David Gilpin, K5GIL

A Portable Antenna

—Daryl DeVault, KE5SAB

   I’ve been putting together an emergency portable all-band system, and I needed a portable HF dipole antenna. By “portable” I mean:

  • something that doesn’t weigh a lot;

  • something that stands up on its own;

  • something that will break down for transport.

   I decided to use the old Vietnam-era military fiberglass tent poles. They’ve been available for years and I used several of them to build my 30-foot inverted Vee in the back yard. I found more at Omaha’s Military Surplus in Ft Worth—$50 for a bag of 12 poles and 4 bases.

   Each pole is about 44 inches long. I made 3 sets of poles: five poles for the mast to go as high as 18 feet, and two sets of 4 poles to support the antenna legs. These can go up to 14.5 feet. This will make a versatile inverted Vee dipole suitable for uneven ground if needed.