Short, Loaded Antennas – Part 2

Part 2 of the two part series in QEX came in the mail today — woowoo!  This is the “actual measured performance” bottom line results part of the series.   Here is one screen snap taken without permission but with the hope of promoting wider interest in the content.  Results?  It reinforces what Bill, W6OAV has been restating for years.   Moving the loading coil from the base of a mobile vertical up to the center will increase the performance by 2 db.  Notice the gain with the coil at the base is -6.5 db.  The antenna with the coil moved half way up has a gain of -4.7 db.  Almost exactly 2 db improvement.   The author, Barry Boothe, W9UCW,  also reports the bottom line results of decades of testing things like effective ground resistance of different types of vehicles, angle of resonator to mast, capacity hat location, and empirical results of measuring the current in a loading coil from bottom to top.   Does current taper in a loading coil? You’ll just have to get the March/April 2014 QEX magazine from the ARRL to find out.

 

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Short, Loaded Antennas — Part 1

Wowee.  “Short, Loaded Antennas” is part of the title to a feature article in the latest QEX magazine from ARRL.  Barry Boothe, W9UCW has published a pragmatic journey of antenna research.  I was fascinated and I can’t wait for Part 2.  Here’s one excerpt that should whet your appetite:

“The big deal of the day was the comparison of signal strengths between two otherwise similar antennas for 1.8 MHz.  One used a big high-Q coild with a 1:1 length/diameter ratio, 6 inches in diameter, with spaced turns of #10 wire and an air core.  The other used my skinny 7/8 inch diameter close wound coil with #20 wire on a piece of PVC pipe and a 20 to 1 length/diameter ratio. And worse yet, my coil was covered with shrink tubing!

As was expected, the higher Q antenna was better, but by only 0.3 dB.  That’s right, three tenths of a decibel!  That was not expected!”    The journey begins…..   You’ll have to get a copy of QEX to read all 9 pages of the article.

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Aside

Raspberry Pi on the cover of QST!  Right smack in the middle, lying on the Python book is an actual Pi.  It is so impressive that the ARRL is right on the forefront developing ham radio applications for the coolest microcomputer to come down the pike lately, the Pi.  Inside is mentioned what is being developed is a panadapter with TV dongle.  ARRL is also developing a panadapter for the Beagle Board Black and the KX3.   Nice, nice, nice.  I can’t wait.   Go, ARRL.

 

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PAR EF-20

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I moved the PAR20 this morning to an aspen tree using the slingshot launcher. Wow. First qso is HA6ZB in Hungary giving me a report of -14db (JT65 of course). I love it. The antenna is invisible with no fiberglass support pole to give it away. This is where it will stay for the winter, I think. Gotta love these PAR’s, right?

I’m already thinking of replacing the PAR with the CQC antenna to give me more bands.

Gray Line Propagation

On the lower bands signals are stronger from a station where the sun is just going down or just coming up.  This phenomenon is known as gray line propagation because it follows the gray line between darkness and sunlight as the earth rotates.  A good example to demonstrate how well it works came the weekend of the CQ World Wide DX Contest in November, 2013 on 80 meters.  On the map below notice that the DX stations getting through to North America are on the gray line.  This is a screen snap from Reverse Beacon Network. My station is the green dot.  Red dots are all the stations I was hearing.

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PAR EF-80m antenna installation

This is a full half wave length on 80 meters, meaning it’s 135 feet long.  Getting that much wire strung up to be a vertical antenna is beyond me.   As a compromise, I put a bunch of army surplus fiberglass poles together as tall as I could.   The wire goes up the poles for about 25 feet.   From there it slopes at 45 degrees over to my big tower.   Not ideal but it gets the wire somewhat vertical.

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Photo: PAR EF-80 80m half wave dipole is up and running in time for the 80m dx season this winter.  It's in a sloper configuration, running from this fiberglass pole up to an arm mounted on the side of the main tower.  I chose to go with the EF-80 this year instead the quarter wave vertical of past years.  Hopefully this eliminates near field ground interaction, giving a little more gain.  It dips at 3.550 mHz which provides coverage for cw, psk, and JT65. I hope to work you there!

I worked quite a bit of QSOs with this antenna but only stateside.  I was hoping for dx, of course.  I modeled the antenna and the slope kills the low angle takeoff.  Takeoff angle is about 40 degrees, making it a great NVIS, and explaining the lack of dx.  It’s coming down.

Thoughts on next antenna trial:

A K5RP rectangular loop for 80 meters.

Clone of PAR End Fed Antenna Matching Network

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A clone of the PAR EF-20 end fed antenna matchbox under construction at the W0QL radio ranch.  This kit is a prototype from the Colorado QRP Club which the club is thinking about selling.  It would be a fundraising project for the club.

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What we’re doing here is building from a kit of parts to make a matching network that emulates the matching network that comes with the EF-20. The kit consists of a toroid and three pieces of wire, plus the box and hardware. We don’t really know what’s in the EF-20 matchbox because it’s sealed in epoxy.  It’s potted and we can’t see the components without ruining it.  I’ll post some results once I have it up and working.