Goodbye Swamp Cooler? Antenna Modeling Notes

Why is it 4:15 AM and why is Ure running antenna models?

The answer is simple:  The end of summer is upon us.  When the weather cools down, things here heat up.  Hot coffee on a cool more, clear head, and a zillion ideas to run down.

But first….

Goodbye Swamp Cooler

A couple of years back I did all the science I could throw at the problem of cooling the shop down for summertime use. 

We are, if you’ll remember, in a kind of gray zone between where swamp coolers are great (low humidity, say under 30% in the summertime) and where it’s insane (over 70% humidity at the day’s low which is generally in the afternoon).

This summer everything was great – in May and June.  May, the “heat wasn’t really on” and in June, per Tyler Texas Weather dotcom, we had 2.33 inches of rain.

But, things went down hill from there. Almost 3.6 inches of rain in July about spoiled it, and although Tyler (45 miles north of us) had u7nder 6-10ths in August, we had an inch and a half, or so.

So far this month, Tyler’s had 7 and a half inches, and our gauge was over 9 inches.  All of which results in high humidity.

Not that it’s  all bad, mind you.  No Burn Bans so far this year, so the burn barrel has run….

To make a “long story longer” though, I went out after yesterday’s column and along about lunchtime it was getting hot in the shop.

” Alexa, turn on Chiller.”



” Alexa, turn on Chiller.”


Hmmm…Investigation showed the ground fault on that outlet was popping. Oh-oh!

Quick – hand me the Fluke meter!  What????  A few ohms – nearly short across the plug?

Opening the unit, the answer was obvious.  The fan prop was locked in position.  Bearing frozen.

68-bucks from Home Despots and the new part will be here when it gets here…

Then the Universe Smiles

You can almost hear it, when it happens…

Psst!  Ure…you know, since you are planning to do a lot of 3D printing over the next couple of years….and since you really don’t need more moisture in your shop…and since next year could be wetter still….why not look at a real A/C unit?”

Ummm… yeah!  Since power’s not a big deal (remember, with our solar add-on this fall, we will be almost dead-even on power in the summer) running a/c in the shop isn’t too insane…

Wait!  What’s this?  A “such-a-deal” on Amazoon for 300-bucks on a kick-ass 10,000 BTU cooler?  Should I….or shouldn’t I?

Aw, what the hell…

It’s not like the swamp cooler’s going to be tossed out:  Remember, I still have a nutty plan for using a swamp cooler to keep the greenhouse cool enough so plants will set fruit up there….and this would be just-the-ticket…..

We shall see.

Don’t misunderstand:  Swamp coolers are great.  It’s just they are only great when the humidity is under 40%, or so.  And under 30% is even better.  20% it’s a slam-dunk.  This past couple of weeks?

Today, thanks to the recent rains, we will only get up to 88F this afternoon, but with that comes 60% humidity.  That will mean a work environment of almost 100% humidity and 80-F.   Thing about  real a/c is not only will the shop drop 10-15 degrees (remember, it’s 10,000 BTU) but the humidity will come down, as well.

Considering 100% humidity at 80F or working in maybe 73F and 35-40% humidity, I couldn’t get the order in fast enough.  When Amazon has a “deal” – as long as you run your a/c for a few minutes every month over winter – setting it up for a year ahead makes sense.

Thanks Universe for waiting until the end of the cooling season for the prompting.  I can’t help but notice this is the last couple of days of hot weather.  The high tomorrow  may touch 90 – and then heat’s off until the Texas Life Grill turns on next Memorial Day.

Antenna Modeling

With cooler weather, (and a new pneumatic antenna launcher to top 100-foot pines) it’s almost times to build this winter’s Super Antenna.

This whole project (compulsive software modeling) is based on always wanting to be the “Big Signal on the bands.”  And, some curiosity about how adding a couple of wires to a “conventional antenna” (like an Off-Center Fed Dipole (OCFD) or G5RV) could dramatically improve its performance.

The current set of wires (if you model antennas) looks like this:

Obviously, Wire #7 is the feedpoint (source) wire.  Drawback:  Weight of 880 feet of #14 wire.  Hole in checkbook of corresponding size.

Wire-Based “Beam Killer?”

What’s driving all this is the sad fact that the 3-element beam on the top of the tower has a blown out trap or disconnected wire.  Unusable. 

An upcoming Peoplenomics article’s title alone will explain why I’m not just writing a check and putting up a new beam and rotator ($1,800).  That article will be titled “Age-Adjusted Return on Investment” (AARoI) and we’ll talk about that on the grown-up side this week.

Back to point, though:  What I’ve got looks great in modelspace:

And with a feedpoint impedance of 90-ohms…it just doesn’t get much better.  A cloverleaf pattern, and the biggest of the lobes from here will come right down over Europe.  Anxious to try it.  But wait…before I get too excited…

Lower Band Trade-Offs

The only drawback I have found with this antenna (so far) is the little matter of gain on 80-meters.  The low bands (80 and 40) are the ones most-used in the winter when we fire up the tube-type gear here.  That way, the office stays warm and the radios work.

Here’s the 80-meter problem in a nutshell:

On the surface it  seems like we ought to kick a dipole’s butt.  Because what you see here is 7.27 dBd (because I set dBref = 2.15 in my models) versus the paltry gain of a simple 2-wire dipole:

You’re thinking “ Come on Ure!  That’s 3-decibels better than a dipole – go for it!”

Except it isn’t that easy.  Because on 80-meters the return loss (think of it as a built-in standing wave ratio) is 2.8 dB.

And when we run out that number:

Cursing Mismatch Loss

While the antenna totally kills everything on 20-meters, down on 80-meters the math works out like this:

7.27 dBd less 3.23 db mismatch loss equals 4.04 dBd  actual performance.

Which – as anyone can see – is still a tiny bit less than the 4.75 dB of the simple Dipole.  Worse, though, is this still doesn’t solve the 40-meter antenna problem.

So off to the drawing board – again – going for the “perfect design” with a maximum of 90-feet on a side because the trees are too big to dig-up and move.

Fan Plans?

One of the ideas is to build a “perfected fan dipole.” 

As you can read with a little research, though, most “fan dipoles” are compromise antennas UNTIL you see that Stanford found feeding them 5-1/2-inches or more at the center, reduced the inter-element interactions that can make tuning such an antenna a beast.  Says an article on Ham Universe:

“They found that the wires at the center feed point had to be separated by at least 5 1/2 inches vertically and the ends separated by 38 inches in the 2 to 18 MHz range.”

For modeling, how about we round this off to 3-feet?

OK, for elements?  A regular-sized dipole on 80 meters, an extended double Zepp (DEZ) on 40 and another on 20…how would that work…stacked – fan dipole fashion…(the mind races)…

Projects never end.  Almost time for more coffee and it’s cool enough in the shop for a couple of hours, so projects there are just ahead…

More as the holiday winds along…. Elaine’s got enough sense to sleep in.

Write when you get rich,

author avatar
George Ure
Amazon Author Page: UrbanSurvival Bio:

8 thoughts on “Goodbye Swamp Cooler? Antenna Modeling Notes”

  1. George

    “running a/c in the shop isn’t too insane…”

    Have you ever considered Geothermal Cooling using ground water?

    Most well water is very cool. My well is at about 55f at 70 feet below grade. In terms of economics it may not pencil out but I find it an intriguing engineering challenge.

    Be careful of that $300 AC! You get what you pay for. I’v been running a Frigidare 25000 btu unit for the last 5 years for almost 6 months out of the year. It’s still going strong. Granted we paid $600 for it but it was cheaper than a whole new AC system for the house and it does the job.

  2. Here is an interesting project to consider for AC… I checked you still can’t buy the solar air conditioner in the USA.. they make low power air but the true solar powered air is not in the usa yet..
    similar to the solar beer chiller.. use the heat of the sun to chill..
    the one below is pretty good basically a swamp cooler but uses a descant cooling ..

  3. George, regarding Age Adjusted ROI, I’m interested. Particularly regarding teeth – if I let my dentist have her way, I’d be dropping serious five figures again! With all due respect, she’s a good dentist. What’s with teeth that they always cost the earth and I have no other medical expenses? Medicare and dental insurance are not useful here. How on earth can you figure ROI when the variance of life expectancy becomes so extreme from 70 onward? With teeth, it’s not always about eating or oral health, it’s about attracting.

    Happy Labor Day Weekend!

  4. You need big, dense Grapefruit trees around the place. Or build a heat buffer canopy over the entire spread. Go to the gas station. Notice the temps are usually cooler under the huge canopy.

    Here in MI I need heat. My painting the wood privacy fence black worked The snow around the perimeter of the yard was melted long before the snow 3 or 4 feet away from the fence. Blueberry bushes would work great along the fence line now.

    Out of all my garden plants this year I got a few cucumbers and five pumpkins. The pumpkins are still growing and larger than a 1970’s Philco 20″ TV.

    None of the cabbages formed heads. None of the Brussels sprouts sprouted Brussels. Spinach and beans all tail-spun.

    Over this winter I plan on obtaining used tires and planting in them next year. The black tires will help with warming the soil and the tries will act as moisture barriers. Instead of watering a spot in the yard around a plant, I’ll be able to dump five gallons of water into the tire…. get it??

    Can any of you think of disadvantages of planting in old car tires? Like, cancer causing chemical from the tires leeching into the plants/fruit? TIA.

    • Not sure about your area and the mosquito. But tires are awful for retaining water in the perfect amounts to breed the pests. I basically cannot go out around my property after 16:00 in warm weather without DEETing up. Since a couple a neighbors don’t really make an effort to keep standing water policed there is little recourse except to try to avoid the end of the day as much as possible. I personally would not put such things around my food.

      Also consider if you change your mind about the tires, you will have to pay someone a disposal fee. Trying to sell property with them onsite could also trigger some hazardous materials review.

      • JoeDish.

        You’re right about water/mosquitoes. I would lay the tire on side then back fill full of a topsoil/peat mix. Basically a raised garden made out of tires. The sun would warm the edge of the tires creating early microbial activity. The tire would retain water. I’ll test during the next grow season.

  5. My Buckmaster OCF dipole is center supported on mil fiberglass mast across the yard from the shack, so lightweight RG-8X (mini coax) is used. Now I just acquired a 1200w linear which is just beyond the power rating of the coax. RG-8 would be too heavy and pull over the mast, so I had to find a high power, lightweight coax. Eureka! LMR195 is the size of RG-58 and will handle over a kw on HF bands, so that will be the replacement. I also have the 90ft of extra flexweave wire to add… on 6″ spacers… to the long side of the OCF dipole for the ‘Ure Gain’. Now waiting on cooler weather to take down the dipole and add all the new wires. Winter project will be a wire-crawl thru the attic/oven to pull some #10 3-wire w/g for a 240vac feed for the linear amp and also new 120vac for the shack circuits… separate breaker from the house wiring.

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