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2015 - Going Portable

In 2015, I'm going to be operating 100% solar portable, as I'll be traveling to California each week on business. I try to get out after work a couple days each week. Working portable this year has taught a lot about my rig, amplifiers, solar power, propagation and especially antennas.

My latest project is a portable 40M inverted vee 3 element yagi. This antenna is designed to help me operate at the Martinez, CA Marina Pier and make my weekly CW QSO on Tuesday nights with AC9FL, a code buddy in Chicago who learned CW about the same time I did in 2014. I’ve been using a Buddistick or a 20M/40M linked inverted vee dipole during the summer and fall on 20M, but now that we are in Daylight Savings Time, we’ve had to resort to using 40M. These portable antenna choices have not worked very well for the 40M hop between CA and IL. I’ve toyed around with the idea of getting a taller mast to get my 40M linked dipole up higher to about 55 feet, but the SpiderBeam fiberglass mast is a little pricey and according to my calculations the results would not be as good as a 3EL yagi configuration I have in mind.

I already have 3 telescoping fiberglass masts that go up to 30 feet, so I recently cut a reflector and director element to use along with my existing 20M/40M linked dipole as the driver. The driver (middle wire) will be bungeed to a sink that used by fisherman to clean their catch. The reflector will be bungeed to a post at the west end of the pier. The director mast will be bungeed to a post on the east end of the pier. The spacing between these various support structures work almost perfectly for my purposes -- 34' and 38'.

I’ve been using EZNEC to model antennas and AutoEZ to automate the optimization computations. Below is a screenshot from the AutoEZ spreadsheet that shows the 3EL yagi with a 6.62 dBi gain at a 20 degree take off angle – my guesstimated take off angle from CA to IL. The 3EL yagi (red line) has better gain than my 40M BuddiStick configuration at this take off angle and it has a 9.18 max dBi at 40 degrees for shorter distance QSOs when I’m not rag chewing with AC9FL.

As you can see in the legend, the red line is the 3 element yagi. The dark blue line is a 2 element yagi. The light blue line is a simple inverted vee dipole. The purple line is my Buddistick (17.5 foot shockcord whip + extension arms + coil) with 2 tuned radials. The green line is another simple inverted vee dipole but at a peak of 55 feet (Spiderbeam mast). All these models were computed over brackish water, which is what I have at the Martinez Marina pier.

The gain of my original portable anteanna, the simple inverted vee dipole (light blue line), has a -0.38 dBi at a 20 degree take off angle. This is a 7 dBi difference from the yagi. That’s over one S-unit on the receiver!

Below are the EZNEC wire coordinates for the 3EL yagi that were compurte as optimal (given my boom length contraits on the pier) by the AutoEZ programs. 

Below are the actual wire dimensions I need to use when cutting the driver, reflector, director. The height of all masts, the apex angle of the inverted vee and the distances between the 3 masts are all input constraints that AutoEZ used to compute the optimal of wire length of the 3 elements. EZNEC and AutoEZ have been a great set of programs for my purposes.

And this is what the antenna looks like in EZNEC. The curved purple lines are the calculated amplitude of the current at various spots along the wires.

VOACAP estimates that I would have a 92% chance of making the CW QSO with AC9FL using this 3 element yagi with 50 watts – my max power output. 40M looks to be the best band to use at 2am UTC (8pm Chicago Time, 6pm Pacific Time). See the black arrow on the pie chart. If I use just a 40M dipole at 33 feet, VOACAP say our chances go down to 85%. If I try to use 20M at this time of the day our chance go down to 70%.

VOCAP says my yagi should be pointed at 77 degrees (ENE) to hit Springfield, IL (the closest city to Chicago in the VOCAP picklist). It just so happens that the pier at Martinez appears to be angled at 70 degrees.  If actual conditions prove to be close to VOCAP predictions, I should be heard by AC9FL in Chicago at S7 when transmitting with the yagi, versus S6 for a dipole. This 1 S-unit difference computed by VOACAP seems to confirm my guesstimate of a 20 degree take off angle. 

The following chart is the top-down view (azimuth) of the radiation field. Even if my yagi’s direction is off by 5 degrees, the primary radiation lobe should still be transmitting near its peak power.

I loaded the Windows based VOACAP program to compute the optimal take of angle (TANGLE) on 40M at 2am UTC and it came up with 15 degrees.

This take off angle is right at the break-even point between this 3EL yagi and my BuddiStick vertical. See the AutoEZ elevation plots near the top of this web page. Notice how the 3EL yagi (red line) is very close to the Buddipole vertical (purple line) at the 16 degree elevation angle. The reason I'm still interested in using the yagi is the focused shape of the far field radiation; this shape should cut down on the QRM/QRN I hear with the BuddiStick and improve my Signal to Noise ratio. The 75 degree beamwidth on this yagi should still allow me to have a good chance at making contact with folks from Minnesota to Texas and all points in between with this non-rotating portable yagi. I'll update my QRZ page later in December after I've had a chance to try it out on the pier.


KX3 Go Box

Earlier this year, I built a radio rack out of aluminum to secure all my components wired together in order to minimize wear and connection failure. The assembly fits securely in a rugged waterproof case with foam cushioning. 



The ionosphere is a layer of lightweight gases that are held in place in the sky because the earth is just the right size and has just the right gravitational pull to keep them from escaping into space.

Our sun is just the right size, just the right distance away and just the right intensity to energize these lightweight gases into a plasma that reflects HF radio waves.

This delicate layer of plasma is protected from being blown away by these intense solar winds due to a geomagnetic force field that is generated by the earth’s molten iron core that is spinning at just the right velocity deep under our feet.

Maybe all this occurs by chance, but I believe it’s proof that God loves ham radio.



6925235 Last modified: 2015-12-13 18:17:09, 9226 bytes

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