ShopTalk Sunday: Ham Antennas, Printer II, Beryl

There I was on the Fourth. A moment in the recliner. Vibrator setting one, clicker in hand, and wondering about Tree Houses – which would logically follow from my deck plans…

Phone rings.  It’s my buddy Mike who lives on a little patch of dirt (>80 acres) in the East Bay.  Out toward where it’s still civilized.

We hadn’t talked for a while and he’s the Big Brains on CNC while I do what I can in other areas.  Naturally, both being hams, we got on the topic of antennas.

Now, while I can’t tell you where he lives, except in the most general of terms (East of the City of SF), I can tell you he’s tucked in safely behind a hill some several hundred feet high.  From his house, it’s a serious climb in a 4-wheeler to get up to the electronics on his ridge.

“I know you like big antennas,” he began.  “So, I have been looking at a monster long wire from the house up to the top of the ridge.  Say about 1,000 feet worth.  How do you think it would play?”

“Not too well,” I sadly informed him.  “The reason is that as long wire antennas get longer and longer, they tend to “end-fire” more and more.  That was the original way that the BOG (Beverage (antenna) On Ground came about.  Super long wire roughly in the direction of the source you’re trying to tune in…”

“Well, I was wondering….” he continued.

And I volunteered. “Tell you what: Been too damn hot to work in the shop these past few weeks, so let me do some serious modeling for you and I’ll show you how the modeling comes out…”

We have several other ham readers and this “My antenna is bigger than Ure’s” is a popular topic.

A Few Words About Gain

If you are not a ham, some of the terms we’ll use may not be familiar.

• Gain: When a piece of wire is used as an antenna will make a signal stronger or weaker.  Depending on its length, which is related to the frequency in use. And the orientation of the wire.
• Aperture: The Wikipedia nickel’s worth says “The effective area of an antenna is defined as “In a given direction, the ratio of the available power at the terminals of a receiving antenna to the power flux density of a plane wave incident on the antenna from that direction, the wave being polarization matched to the antenna.”  Or, as my friend Ehor summarizes, bigger antennas generally work better.
• Azimuth: This is the local compass direction that the radio signal takes off on.
• Elevation: This is how far over the horizon the maximum beamwidth power flies away at.

Think of the 100-watt lightbulb (in an unenclosed socket) – it throws some light everywhere – and thus is “omnidirectional.”  The 10-watt LED super spotlight won’t light up jack anywhere except where it is pointed.

Which sets you up to learn that the “most basic” antenna is a “dipole.” Two pieces of wire, perpendicular to one another, fed in the exact middle.  The signal from this antenna is a standard reference and its measure is dBd (decibels (power level reference), dBd is usually 2.15 dB less than a dipole in isotropic model space.  Isotropic is a theory number.  So, when antenna makers use “dBi” antenna numbers, run.  dBd is what really matters because hugely important things – like the proximity of ground and ground currents come into play.  It’s math spaghetti, but you get the idea.

A directional antenna works best for far-away places.  Spotlight, right?  But a simple dipole, especially close to the ground with a semi-parasitic ground reflecting wire in a configuration for Near Vertical Incidence Skywave (NVIS)  on 40 or 80 meter bands is great for reliable short to mid-range communications.

Formulas? On Sunday?

Sorry.  If you want to be smart, you have to work at it 7-days a week.

The “standard dipole” is 1/2 wavelength overall.  Each of those two wires is thus one-quarter of a wavelength.

Which is determined by the one formula you need to know for antennas:  Length of a 1/2 wave is 468 divided by the operating frequency in MHz

Because most of my antennas work on the 80-meter ham band, I typically design for 3.55 MHz.  Which means the length of a half wave is?  468/3.55 = 131.83 feet for a halfwave antenna. Each side should be 65.91 feet from the center insulator where the coaxial cable connects.

So far, so good.

Big, Long Antennas, Higher Bands

Now we can begin modeling how very long antennas work.  We begin with a free (Thanks Roy!) download of EZNEC – a great antenna modeling program from here. https://eznec.com

We can generalize a bit about antennas and feeding them now. A half wave antenna is pretty well-mannered on its design frequency.  Let’s call it 3.55 MHz, remember?

But on the second harmonic of that – 7.1 MHz in the 40-meter band – the antenna is now two half waves long and it doesn’t like to match much in the way of transmission lines (Most people use Coaxial cable, I’m an open wire or ladder line guy).

But when we go higher, up to 14.2 MHz in the 20-meter ham band, we’re now at the third harmonic of the design frequency.  3.55 MHz is our primary, 7.1 MHz is the second harmonic, and 14.2 (double of the second harmonic) is our 14.2.

Feed Points

The trick antenna that solves the “second harmonic hard to feed” issue can be reduced when the feed point is offset from the dead middle.  Here’s a very good article to consider if you want to build your own antenna: Multiband HF Center?Loaded Off?Center?Fed Dipoles (hamwaves.com).

The Sleeper in OCFD Antennas

A lot of hams get very fouled up when designing and putting up OCFD antennas because on higher frequencies they stop acting like dipoles.

At their primary frequency, center fed dipoles radiate maximum power perpendicular to the wire. For example, an east-west wire dipole would have a decent lobe to the north and a mate to the south.

But as you get up into higher harmonics, the higher you go, the more than antennas become first cloverleaf and then end-firing.

I am working on which of these two antennas to put up for the coming Winter ham season.  Here’s the short antenna first.

As you can see, the signal from this antenna (modeled with north-south wires and used as an extended antenna on the 20-meter band does have some “model losses” which can be added back in so the total gain (in the favored directions would be about 8.5 dBd.   Sadly, though, physics says there is no free lunch.  We will have some great lobes (clover leaf) but we will not get all things for all people on all compass headings!

Don’t be confused on this, but the cursor azimuth is relative to the horizontal axis…so reference the 90 degrees north, it’s at 35 degrees on the compass.

We pay particular attention to the lobe going off at 35 degrees and then we see which countries a perfect north-south wire will put our signal into from Texas:

A little headwork says “Well, off at 35 degrees, we will be pointing too far east to get much except the NATO countries western Med and east Africa.  But looking out west, we are lighting up very little of interest – save French Polynesia. Won’t even do well into Australia.  (We skip forward past the southern headings discussion, but you have the idea…)

The Final Solution on this one was a wire antenna with 10 dB of gain and a closer (to North) pair of lobes which should be about as close to perfect as we can expect.

Mike’s Antenna

He’s got the land and elevation to put in a bit more than 1,000 feet of East-West off center fed behemoth.  And wow – on 20-meters is a gain monster.

He would end up – adding back modeling losses, somewhere around 13 dBd.

His problem, though is when laid out on his property, he’s boiling the South Pacific…

When we put his antenna on the great circle map, it would work best if he had a huge following in Australia…

What this means?  Simply put, if you want maximum fun/contacts in ham radio, consider the antenna because even a humble off-center fed dipole double-sized and lead to some useful gain lobes.

We both happen to be lucky (try hard working) enough to have enough land to model and build antennas. No everyone does, but sometimes big, long antennas come with (bad pun alert) strings attached.

Printer Adventure II

The new control head for the CR10 V2 printer showed up this week and the eBay seller was kind enough to install the Tiny Machines firmware.

I set to work getting it all ready: Turned it on and this time no BSOD:

So I began to print.  About 5-minutes in, the filament pushed out the Bowden tube (the white PFTE tubing the filament runs down to the print head through this).

Fortunately, I had a spare tube kit so it was no big deal to replace it.  So round II of printing begins. And after a half-hour of printing I got this:

And when I looked at the extruder pinch roller, yes, it was not running smoothly even though I had it set to as “pinchy” as it would go.

I messaged the eBay fellow asking him if he had other ideas. But when the print ain’t printing we’re down to a problem of either bad filament or bad print head, but the new Capricorn tube and a new nozzle are in place – so Ure is sort of stumped but thinking about a fresh roll of filament.

Rain and Pain

I really needed the printer to work. I need lots of stuff to work around here (including more from me, apparently).

But with the Hurricane which should be down to tropical storm by the time it gets here? Ure was out building drainage channels away from the shop – like this one:

And we also got the uphill side of the greenhouse bermed up thinking we will slow the water coming in there:

Elaine and I took turns watering it and we will do more of that today.

People who’ve never lived on a farm/ranch don’t know what a PITA it is just getting ready to move dirt around.  See, the bucket on the tractor has a “tooth bar” on it for slamming up brush piles, carrying logs, and what-not.  For “fine, gentlemanly work” near a house you don’t want to wreck, that comes off.

But no, it’s not a right click on the mouse.  It’s the running out air hose, turning on the compressor.  Digging out the oversized deep sockets (>1 inch nuts – I resemble that remark!) and then the 1/2 inch impact gun. zing-zing

Can of Kroil spray, a pair of Channel-Locks and now we’re ready for 4 minutes of actual work.  Once off, then you reverse the process to pick up the mess… but you see how it goes?

I am sure Hank will remind me that since my “Mercury Retrograde begins 3-4 weeks before the actual (we all have a personal offset…) that we are already “getting close.” (Aug. 5)

I did remember to do some water-diversion work around the house and the shop septic systems, so while the weather will be crap, as least we won’t…er...be.

We’re in the bull’s eye east of Wacko, southeast of Dull-as and north of Who’s town?:

Oh – that Home Depot order I had for a 16-inch Shidaiwa easy-start chainsaw got canceled by me. Ordered on the 3rd, vendor hasn’t shipped yet and we don’t have all day to shag slow orders around here.

OK, more coffee then going around the house on a ladder early to make sure the gutters are all clean.  Yes, I will be careful. My God the glass of red wine at 4 PM daily is getting to be one of the major incentives of life on this side of 75, ain’t it?

Write when it…well, if the internet is up…

George@Ure.net