A Close Call for #3

Seems that New Orleans came all too close to having a third Mardi Gras float run-over last week.  Article at NOLA-dot-com: Woman Rescued at Tucks Afer She Fell Under Float

Whew.

Ten Physics Effects You Need to Know

No, you won't be tested on this, and you really don't have to understand them all either (as if that's even possible for some of these).  It's just that you ought to be familiar with them, the words around them, and have some general idea that they exist.

The 10 Most Important Physics Effects, in both video and text formats.

Carnival Sunday

Another Sunday-before-Mardi-Gras in New Orleans.  Parade-went until we couldn't go any longer.  I am afraid that the only drink shots in evidence were espresso shots, but those were damn tasty.  Lots of friends and their extended family and their friends in attendance, and the food was outstanding.  A mighty good day.

Not a lot else to write here.  Carnival parades in New Orleans have to be seen live to be believed.

Vertical Off-Center Fed Dipole for 6m

An older post on VOCFDs at KB6NU's blog scampered across my field of view this week, so I had to adapt it for 6 meters.  Six meters is a really cool band: low VHF, can sometimes duct as expected of VHF, can sometimes skip like HF, is on pretty much everyone's HF transceiver, and completely is under-used.  Mostly though I'm interested in it for its local VHF properties: line-of-sight, with some ability to crawl around hills and penetrate piney woods.  Throw in that shiny new 9:1 unun (link, scroll to the bottom) and I'd have everything already in house, all ready to go.

Now a note about that antenna design post... it's largely correct, but some of the math is a shade off.  The ultimate result, X1 = 0.131 * X is correct, but if you want to work it yourself, remember that the feed Z is 450 ohms, not 50.  Also, be sure to do the arcsine calculation in radians, not degrees.  But as I said, the ultimate result for X1 is correct, and of course X2 = X - X1 (referring to the sketch at the above-linked post; but X, X1, & X2 are respectively total length, short end length, long end length), so everything's easy.

I wanted things tuned for the center of the 6m band, namely 52 Hz.  Cranking the formulae and tacking on 3% more for insulated wire gave X1 = 1.2157', and X2 = 8.0643'.  Cut some #20 wire, assemble, hang, measure resonant frequency... and get 39.2 MHz.  Hm, that's pretty far off the 52 MHz target.

A half-hour of cut-and-try and I wrestled it down to SWR = 1.5 across the 6m band, for X1 = 1.04' and X2 = 6.46'.  That's weirdly short, but it does seem to work.  Then I recalled about that LDG unun: it's only rated to 30 MHz.  But what's an extra 20 MHz between friends?  Good enough, hook up the FT-817nd and take it for a spin.  Like I said, it seems to work, with low SWR and some unknown digital somethings received.  Didn't make any contacts, but then I wasn't really expecting to under the current conditions.

Testing will continue.  In the meantime though, it was a nice afternoon to spend playing radio on the back lawn.  Here, have some pictures:

  

L: the slightly suspect unun.  R: FT-817nd in its native environment.
As always, click to embiggen.  These pics really do benefit from increased size.

ps: Looking back on this post from Tuesday's perspective, I really needed a slow goof-off Saturday last weekend, and that's what we got here.  Need another.

Like I need another dust collector.

Still, kind of cool in the "books are magic" way.  Miniature Book Nooks Belong on Every Bookshelf.

Solar Cycle Near Minimum

In fact, we may already be there.  As of last December, the NOAA SWPC is picking April 2020 ±6 months.

Not bad.  Not bad at all.  If you can make contacts on 5w and a compromise antenna under these conditions, it's all looking good from here.

Too Many Beads at Mardi Gras?

Article at NOLA dot com, by way of the Darling Daughter.

It is an interesting conundrum.  On one hand, c'mon, it's Mardi Gras.  It's all about the excess.  OTOH, when it's not fun anymore, when it's just clogging the storm drains.... yeah, it's time to dial it back in favor of quality over quantity.  And face it, even a tenth the quantity is still pretty overwhelming.

Interesting though that this whole business is less than a century old.  Anyway, read the article and find out.

Ten Years of Blogging

That's like, what, ten dog years, right?  But only if the dog is traveling at a significant fraction of the speed of light.  Or something like that.

In any case, it's time to mention the occasion.  The question naturally arises (usually in my head, late at night), why am I doing this?  Initially it started as an easy way for family and friends to keep up with goings-on: bike rides, movies, interesting articles, etc.  Later it evolved to have a significant number of how-to posts, on everything from fixing appliances to setting up ham radios.  It's also a convenient place to document coffeeneuring trips.  So... catch-all for writing, pictures, news, and informal documentation.  That's why.

But the best post?  How to Work a Physics Problem in Four Easy Steps

ps: And the most-searched posts?  
DIY Air Purifier  $30-ish bucks and five minutes' work.
All You Really Need  The $4 special ham/shortwave antenna (more on this on the way, btw).
Two from the SWLing Post  High frequency trading, in more than one sense, and rescue radios.
A New Article on Numbers Stations  Reading the mail, if only we knew what it meant.
Meanwhile, Down at the Hamfest  No pork, just technical forums.  And a new solar panel.

pps: I may be taking a few days off from blogging.  It's just a short break due to a few pressing matters, it's definitely not a quit.  Don't worry, this blog's good for decades more of ACME-grade misadventures.

17 Ways to Crash an Interview

Over at The Ladders.

They all seem like common sense, but then common sense isn't as common as we would hope.  In any case, it never hurts to have a checklist to avoid the minor flubs.  Hopefully the big ones, especially #1, are self-evident.

Dirt Rag Calls It Quits

Sad news: Dirt Rag mountain bike magazine called it quits over the weekend.  Announcement Here  They had been showing signs of stress for a while, closing down their sister publication Bicycle Times and such, so it should be no great surprise.  Still, sad news.

1989–2020 was a good run for this sort of magazine.  Born in the 'zine era on an early Mac, they made full use of desktop publishing and the web as they came along.  They covered the boom years of suspension in the 90's, single speeds and freeriding in the 00's, and bigger wheel standards in the teens.  There always seemed to be something to talk about, for three decades.

More and more print magazines seem to be reducing to web-only, or just shutting down entirely.  I'm not sure how much relevance a how-to article has anymore in this age of three different ways to make a bike repair on youtube.

Well, good things come and good things go.  Wonder what's next?

Quasi-Random Wire Results

Following up on last week's post regarding good random wire lengths, we now have a weekend's worth of experimentation to discuss and results to report for the 75' wire.  Also, if you need more background, here's the related Wikipedia article.

The first step was to set up the wire in the side yard nearest the shack, and connect in to the radio gear with 25' of LMR-240 coax cable.  The 9:1 unun was protected by a quart zip-loc bag; coax in through the zipper side, wire out through a small slit in the other end.  This made for comfortable, dry operation on a rainy Saturday afternoon, for both the unun and the operator.  The coax was entirely suspended at 4' to 6' off the ground, and grounded at the shack end.  The radiating wire was suspended roughly horizontally at heights varying between 4' and 7'.  R, X, SWR, reception, and transmission measurements were made both with and without the ~30' counterpoise attached to the ground leg of the unun.  The feedline was routed through a two-position switch, which was also attached to an existing MFJ-17758 loaded dipole.  This allowed for convenient A/B performance comparisons.  The dipole is relatively low-mounted for NVIS work, configured in a shallow inverted-V, from 18' at the feedpoint to 5' at each end.

R, X, and SWR were all within useable ranges across all ham bands from 3.5–10.2 Mhz.  80m in particular benefited from the counterpoise, with SWR dropping from 6 to 2.  60m was relatively unaffected.  40m, without the counterpoise, had an SWR in the 1.4-1.7 range and, as with the dipole, did not require an antenna tuner.  This fortunate coincidence allowed direct comparisons between the two antennas on 40m, without the need to re-tune.  With the counterpoise on 40m, the SWR increased to 2.7-2.3, necessitating the use of the tuner.  30m performance was slightly improved by the counterpoise, with SWR dropping from 2 to 1.4.

The main performance results were that, without the counterpoise wire, noise levels were approximately 18 dB higher relative to the dipole, while signal strengths were approximately 6 dB lower.  With the counterpoise wire attached and draped across damp grass, noise levels were approximately 12 dB higher than those from the dipole, while signal strengths were roughly 3 dB lower.  The handful of QSOs made with each antenna show a similar 3–6 dB decrease in transmitted signal strength.

In other words, there ain't no such thing as a free lunch.  The random wire did work, but it has serious performance drawbacks relative to a dipole.  It's an interesting trick in the toolbox however, and it is much easier to deploy than a dipole.  Experimentation relative to the 21' mini-W3EDP is in store for the next camping trip.

Well, that was also dry as dust.  Again, "just the facts ma'am" fits here.  But, having gotten to the bottom of this mass of data and (hopefully) useful conclusions, have another enjoyable song.

Theme Song for Today's Ride

Twenty-six miles at the Bethel Trails today, all of them good.  Saw some friends, met a few people, etc.

Anyway, this remembered tune popped into my head while riding Couch Trail:

That is all for today.  An early bed calls.

LiFePO4 Batteries, Quantum Mechanics, and You

The other night I was discussing different battery chemistries that are commonly available today with a friend via the local 2m repeater, and naturally LiFEPO4 came up.  "Lithium-ion?"  "No, lithium-iron."  "Well what's the difference?"  "About 3 times the price."  That's the way a lot of these conversations go.  OK, so say it with me, just to get everyone on the same page: "lithium iron phosphate."  Lithium ion batteries are something else entirely.


Just then, the biologist-in-residence drifted through, pulled out his smartphone, and looked up the Wiki page.  We were discussing the way that the one double bond is sort of shared among the four oxygens, in the usual can't-pin-it-down quantum mechanical way, when the friend on the other end of the 2m link said something about all this quantum indeterminacy making his head hurt.  So here's a set of links to some PBS videos to help with the headache:

• The Quantum Experiment that Broke Reality (this has the most to do with "which oxygen?")
• How the Quantum Eraser Rewrites the Past  (but only a little bit at a time, so don't worry)
• Quantum Entanglement and the Great Bohr-Einstein Debate (this is where it gets weird)

Really though, these are all very good videos, and they explain things as best as they can be explained without power lifting the math.  Remember, Einstein struggled with this and ultimately got it wrong, so if it doesn't entirely make sense to you, you're still in very good company.

BTW, LiFePO4 batteries absolutely rock, especially when you have to carry them around.  At 1/5 the weight of conventional lead-acid batteries, they will also significantly lighten your wallet.

As heard on the way to lunch this week...

"Somewhere, sometime in the next few years, some teenager is going to look up at the sky and say 'Betelgeuse' three times, and that's right *fingersnap* when the light from the supernova gets here."

Truly interesting stuff, this prospect of a supernova cracking off fairly nearby.  (don't worry, even if it does happen it's far enough away that it'll only be a cool light show here on Earth)

The Quasi-Random Wire Antenna Revisited

A confluence of several factors have put me back onto these things, following up on an earlier success.  First, their simplicity.  Second, I want an easy NVIS backpacking wire that will cover 160–30m.  Third, I was curious about the analogous results for common shortwave broadcast bands, and developed a program to do the calculation there, which naturally led back to doing the same calculations for the ham bands... you get the picture.  Finally, LDG has extended their balun/unun line to a handy 9:1 unun and I had to get and try one.  A non-resonant random wire in free space has an average impedance around 600 ohms, so a 9:1 transformer should drop it into the 67 ohm range, which is only a small mismatch into 50 ohm coax.

First, the calculations.  Similarly to one from the guy at U Del., my code calculates the "bad" half-wavelength integral lengths corresponding to each of the the band edges, and then eliminates all values in between.  My code uses a knock out array to keep track of the allowable values, and after all selected bands are considered and the corresponding bad areas knocked out, the few remaining values are output.  To convert frequencies to feet, the usual 468 ft*MHz value is used, which includes the usual 0.95 velocity factor.  I added an option for an additional 0.965 velocity factor for insulated wire.  The code rounds inward to the nearest even foot, to eliminate marginal values.  In this calculation, the maximum wire length considered is 140'.  Longer lengths are possible, but this is enough for a 160m antenna.  Finally, where the U Del program limits things to 4 harmonics, the new program calculates how many harmonics can fit a total wire length and goes from there.  Sometime, this went as high as 16.  User input consists of the range of bands to be considered, whether to use the WARC bands, and whether the wire is bare or insulated.

Without showing any nice graphics here (tired; too much work; not needed), the results of the two programs agreed well as long as the insulation velocity factor wasn't included and the harmonics were limited to 4.  Turn these improvements back on, and the results varied a little.  But to cut to the chase, for bands 160m-30m, 136'–140' of insulated wire were the shortest practical lengths.  Drop the 160m band and limit ourselves to 80m-30m, and the shortest practical lengths were 69'–85'.

To test these numerical results, two 20 ga. wires at the average value of the above mentioned bands were cut; i.e., 138' and 75'.  For each test, the wire was hung at approximately 6' above ground from tree branches using loose zip-ties.  The wire did not contact the branches.  This was a reasonable representation of a temporary field set-up.  The feed end of the wire was attached to the hot post of the 9:1 unun.  Optionally, a ~30' ground/counterpoise wire could be attached to the ground post on the unun.  Both configurations were tried in testing, across all bands.  A 25' length of LMR-240 50 ohm coax was used to connect to an MFJ HF-VHF SWR meter.  The meter was ungrounded, however the coax shield was entirely along the ground and likely provided significant inductive coupling to the moist grassy earth.

Across all covered bands (i.e., 160, 80, 60, 40, & 30m, with 160m omitted for the shorter wire), both wires exhibited useable antenna properties.  SWRs were typically in the 2–4 range, and never exceeded 6.  Values for R (radiation resistance) ranged from 22 to 110 ohms for the ungrounded configuration, with X (reactance) values from 20 to 80 ohms.  Generally, the R values were ~50% greater than the X values.  For the grounded configuration similar results were seen; however, the X values were usually ~50% greater than the R values, indicating a lower radiation efficiency.  While sweeping between bands, peaks of several hundred ohms were seen, indicating that the "bad" half-wavelength integral values had been successfully avoided for the amateur bands and buried harmlessly in the inter-band gaps.

Bottom Line: For 160–30m, a 138' quasi-random wire strung horizontally at 6' worked well in SWR meter testing, and similarly for 80–30m, a 75' quasi-random wire worked well too.  The "bad" wire lengths were avoided for the amateur bands, but could be seen as peaks in SWR while sweeping between bands.  For all cases, the ungrounded unun configuration worked better than with the ~30' counterpoise/ground attached.

Testing will continue, beginning with transmission tests and A/B comparisons to an existing NVIS dipole.  Additionally, shortwave broadcast band values and reception testing will be performed and presented in the near future.

Oh man, that post was dry as dust.  Sometimes though, "Just the facts ma'am" is the only approach to take.

A Pretty Good Day

Twenty five miles on the trails today, no crashes, no drama, but no particular speed in the ride either.  It was a "get back on the trails after deer season" kind of ride.  Speaking of which, saw two does zip past just before the Clay Climb on Couch Trail.  That was cool!  Saw a couple of old friends, a ton of campers out at the trailhead (it seems that we've been found by an online 'free camping!!!' site), met a few people, pumped up a kid's back tire so he could ride... a pretty good day in all.

Brexit Happened

Two catch-up links for those of us not directly involved:

"How did we get here?," a two minute video at the BBC

FAQ on the topic at NPR.

Let's all hope this goes better than the last time they pulled a Brexit.  That one did not go so well.