Wednesday, May 30, 2012

The "Cybernator"

I obviously can't take credit for this - and I wish that I knew to whom credit should be given.

Anyway, the story goes something like this:  A friend of mine happened to be on the campus of a local community college (possibly Foothill College in Los Altos, California) in the mid-to-late 70's and couldn't help but notice the following advertisement stuck on one of the bulletin boards - so he plucked off one of the copies and brought it home with him:

Be sure to click on it for a larger version if you have trouble reading it.


The original, which he ran across and gave to me several years ago, is fairly beat up having been folded and torn over the years so this reproduction has been cleaned up.

Wednesday, May 23, 2012

Stared at sun, had fun...

As promised, my dad, younger brother and I wandered down to southwestern Utah, placing ourselves in line with the center of the eclipse - and waited.

Rather than contend with hoards of people descending on well-publicized towns like Kanarraville - almost exactly in line with the eclipse but conveniently located just off Interstate 15 - we headed toward a small almost/former town of Modena located a few miles east of the Utah-Nevada border.  Driving west from Cedar City, Utah on highway 56 we noted that pretty much all of the passenger car accessible side roads and turnouts were occupied by people who seemed to be readying themselves for the event that was to occur just 3 hours later.

Upon reaching Modena, we drove through the town and considered stopping there, taking advantage of the trees and desolate, picturesque landscape and partial ghost town and were somewhat surprised that we didn't see anyone else obviously set up to witness the event.  We decided, however, to continue on the highway and a few miles down the road we left the pavement and followed a well-graded dirt road into the surrounding, low mountains.  After a few miles - and passing one or two other places where people were setting up to stare at the sun - we found a wide area that was excellent both for viewing and throwing our sleeping bags on the ground for the evening.
Figure 1:
Setting up the 8" telescope with sun filter.
Click on the image for a larger version.

With about 2 hours to spare before the first bite was to be taken out of the sun, we lugged our gear about a hundred feet further south to clear a nearby brush-covered ridge and I began setting up my old 8" Celestron reflector telescope, outfitting it with a Baader filter in a homebrew, cardboard mount to enable safe viewing.  Soon, the eyepiece revealed a boiling, bespeckled sun and we then proceeded to set up the rest of our gear.  Soon after this, Gordon, K7HFV arrived having driven down under separate cover.

I had with me an adapter that would convert the 1-1/4" eyepiece mount to a standard Pentax "K" mount and my brother had the foresight to order an adapter that would permit mounting of his Sony DSLR.  With this arrangement we were soon projecting a live image of the sun directly onto his camera's sensor, using the "live view" function to focus the resulting image as precisely as possible.  As expected, only about 80% of the sun's disk would actually fit onto the imager so any "full-disk" pictures had to be taken in two, overlapping parts, adjusting the telescope slightly for each, the pair of images to be pasted together later.

Figure 2:
A solar projecting telescope used to monitor the eclipse.
Click on the image for a larger version.
I had with me a small power inverter to run the telescope's AC tracking motor (I said that it was an old telescope!) and not having set its mount up perfectly, we had to occasionally bump the right ascension to re-center the image, but this was very easy to do - especially considering that we were constantly moving things back-and-forth to get full-disk images, anyway.

One thing that was apparent from our drive in was that there was quite a bit of airborne dust without very much wind, a phenomenon attributed to wildfires burning a few hundred miles south in Arizona.  As the sun set in the west the sky became brighter as the sunlight was scattered by the dust and in our telescope, the image of the sun was slightly fuzzier and less stable than we'd hoped with the sunspots popping in and out of sharp focus randomly. In the images seen through the eyepiece - and on the camera - we could also see a bit of fluctuating colored fringe - something we attributed to atmospheric refraction as the reflector telescope itself should not have imparted a visible degree of chromatic aberration on the visible image by itself:  This effect seemed to increase slightly as the sun's angle dropped toward the horizon.

Within a few seconds of the time predicted, we could see the first bit of the moon's encroachment onto the sun's disk and at about that time (6:26 PM local) I measured the solar intensity as being 84200 lux - a value approximately one third of what one might see during local noon on a clear, summer day.

Figure 3:
The back end of the solar projecting telescope with a solar crescent.
There is a green filter in the optical path to reduce chromatic
aberration.
On the day before the eclipse (Saturday, 5/19) I'd put together a few simple devices for the safe viewing of the eclipse.  One of these was a "solar projecting telescope" seen in the picture above.  This device consists of a double-convex lens at the far end of the tube immediately followed by a pair of "Kelly Green" theatrical gel filters followed by one "Fire" red gel element.  About 1/4 of the way from the "Sun End" of the tube was a strong, plano-concave lens that then spread the image out a bit before hitting a ground glass screen that I'd installed about 1/5 of the way up from the "Eyeball" end in which I'd installed another double-convex lens to permit either direct viewing of the image on the ground glass screen, or a magnified view of that image when viewed from a few inches away.  As can be seen from the picture, a shroud was placed over the tube both to shield the viewer from the direct sun and to aid in aiming by adjusting the device on the tripod so that it cast no shadow on the backside of the shroud itself.  As you can see from the picture, it was all assembled into a stiff, cardboard tube with the lens, filter and ground-glass mounts being constructed of scraps of cardboard and black posterboard held together with thermoset ("hot-melt") and yellow wood glue!

Figure 4:
The moon, encroaching on the sun's disk.
Click on the image for a larger version.
This telescope wasn't intended to provide a crystal-clear image - and it didn't, as can be seen from the above picture - but it was a safe, convenient way to get a quick, safe glance as the current phase of the eclipse.


As the event progressed, it started to get darker as evidenced by the lower lux readings on my light meter.  While it still seemed to be plenty bright, there was an eerie aspect to the illumination of the surrounding landscape that defied description:  Was it the increasing sharpness of the shadows as the sun's disk was reduced in size, or was it the gradual loss of contrast between the highlights and the shadows or was it largely psychological, with the increasing incongruity between the brightness of the landscape and our expectation of what it should look like at that time of day?

Working the camera and telescope, my brother continued to snap pictures every minute or two as the moon made its way across the face of the sun, gradually blocking the visible sunspot groups as it did so.  The rest of us occasionally snapped pictures of each other, the surrounding landscape, and made various attempts to take our own pictures, sans-telescope.

Figure 6:
The "ring of fire" observed during the peak of the eclipse.
Click on the image for a larger version.
At about 7:33 pm local time, the entirety of the moon was contained within the solar disk and the landscape was eerily drab, the colors seemingly muted and the air suddenly feeling cooler than before.  At this point my meter indicated a reading of 3570 lux - a brightness of about 4% of what it had been just prior to the start of the eclipse and roughly comparable to what might be seen in a well-lit room:  To be sure, at least some of this decrease would be due to the lower angle of the sun in the dusty atmosphere.

Resisting the temptation to do so, we avoided sneaking a peek at the sun during the "ring of fire" phase of the eclipse knowing full well that within the ring of sunlight, the light was just as bright as it normally would be - the difference being that a ring would be burned onto the retina rather than a circle!  It was during this period of maximum occlusion that by brother was furiously snapping pictures - one of these being visible to the right.  As can be seen, our location put us almost exactly (within a couple of miles) in the center of the path forming a nearly perfect ring of sunlight around the moon that was visibly changing by the second!  Impressively, in many of these pictures picture one can make out "jaggies" along the edges  from the lunar mountains.

Figure 7:
The last seconds of the annular eclipse.
Click on the image for a larger version.
Too soon, the moon finished its traverse across the sun's face, extinguishing a narrow ribbon of sun along the edge as it did so - a scene captured in the image to the left.

Gradually, the eerie darkness of the landscape was replaced by the warm glow of sunset as the moon moved away from the sun's disk while setting on the western horizon.

In the gloaming, we relocated the telescope to the immediate vicinity of our cars and ate the snacks that we'd brought with us.  Later that night, I pointed the telescope at familiar night-sky objects such as the thin crescent of Venus and the rings of Saturn accompanied by several of its moons.  After putting the equipment away for the night, we bedded down under the stars, occasionally waking to glimpse the rise of the Milky Way as we spun our way toward the sunrise.

In the morning we got up, packed our gear back in the cars and headed off toward Cedar City where he had breakfast before heading back north to Salt Lake.

* * *
Figure 8:
The happy Eclipse God!
Later, I heard from my friend Ron, K7RJ who had been several miles to the east of us, also along the center line of the eclipse, just off highway 56 short of Modena.  There, he had also witnessed the spectacular sight with his wife Elaine, N7BDZ.  Unlike us, they both had plans for the following day (Monday) and they started back to Salt Lake a bit after the eclipse.  What would normally have been a 4 hour drive turned into a 6 hour drive as hoards of eclipse glimpsers - all with the same idea - clogged the 2-lane northbound interstate on their return trips, but he arrived home safely, albeit a bit later than expected.

Clearly, the Eclipse God was smiling upon us, granting us clear skies and safe travels!


* * *

Credits:  All of the telescope-based pictures of the sun/moon were taken by my brother while the picture of us at the telescope was taken by Gordon.  Those of the solar projecting telescope were taken by me while Ron provided a picture of the happy eclipse god.

Friday, May 18, 2012

Staring at the sun - for fun!

Like many people in the southwestern/western U.S., I've been making preparations to (safely) stare at the sun for a few minutes during the upcoming weekend.

I am, of course, referring to the Annular Eclipse of May 20, 2012 that will cut a brief, darkened swath across much of the south to west of the U.S. on that day, mostly blocking out the sun from Texas to the Pacific coast.

Like many, I plan to place myself in the middle of the maximum portion of the eclipse where the moon's disk is predicted to be entirely within that of the sun's for a bit over 4 minutes while we stare through "sun-safe" filters, look at the images on the screens of cameras and makeshift camera obscuras and amuse ourselves with the varying shapes of shadows being cast on the ground during its various phases.

Here in Utah, only the south-west corner of the state will experience "totality" of the annular eclipse but some very good and remote locations are just a few hours away by car:  I'll throw a few pictures up here after it's done.

It should go without saying that unless one has purpose-specific lenses designed for direct viewing of the sun, NEVER look at the sun - or even a portion of the sun with the naked eye - or even really dark sunglasses.  Even though the sun will be "darker" during the eclipse, remember that instead of the normal "sun-shaped" burn that would appear on your retina, you'll get an "eclipse-shaped" burn instead, which isn't any good, either!


Wednesday, May 16, 2012

Duck!

This year I saw the pair again, but now - as was the case last year - there's just the female.

Some mornings and evenings for the past several weeks I couldn't help but notice a female duck just standing in the middle of my back yard.  This seemed to draw the interest of at least one of the neighborhood cats, but it seemed to keep a cautious distance and I never saw anything that would have lead me to believe that there had been or would be any sort of confrontation.

Duck, sitting!
 I'd been wondering where this duck spent most of its time when it wasn't just standing, staring blankly (from what I can tell...) in the middle of the yard but figuring that she was doing something important, I didn't really bother trying to find out.

This evening I was mowing the lawn and doing some minor yard and outside work when I spotted her at home, sitting, staring back from a cozy nook amongst the grape vines.

Now that I know her secret hiding place I'll keep a respectful distance and make an effort to put out a shallow pan of water - something that will likely be helpful once her clutch hatches.

As for the neighborhood cats:  I'm afraid that she's on her own to do what she can to protect them!

(What's a duck doing here, away from any real source of water, anyway?)

Update:

The duck sat for a few weeks more but alas, at about hatching time it seems likely that one of the neighborhood cats (not mine, since they live inside) took advantage of the situation explaining the presence of scattered egg shells and the complete lack of feathers and mother duck.

Tuesday, May 15, 2012

Noise on NOAA images

Figure 1:
A tall, narrow QHA with mast-
mounted GaAsFET preamplifier
below it.
Click on the image for a larger version.
Several years ago (in November 2008) I put together a weather satellite receiver from scratch - that is, I started out with things in my parts bins, parts in the junk box and a few ideas.  I'd never actually built a synthesized receiver from the ground up before and, having no definite plan in mind, I was looking forward to see what I ended up with!

The result is described for all to see on my Weather Satellite Page including schematic diagrams, pictures and descriptions.

Since then I've had the receiver online for pretty much the entire time, originally pressing an old 333 MHz W98SE laptop into service but then switching to a small, low-power desktop computer (an Aopen M945D) that had far more computational horsepower and enough capacity to be used for several other things at the same time - like monitoring my GPS receivers and providing a network time source.

Years before I'd built the receiver I'd constructed a "Tall, Narrow Quadrifilar Helix Antenna (QHA)", a funny-looking corkscrew affair that is purported to have a bit more gain on the horizon than a typical "fat" QHA where the satellite's signals are weak by sacrificing some overhead gain - where the signals are strong.  For a while, I would occasionally mess with this antenna, receiving images using either a service monitor (its IF bandwidth being a bit too wide to work really well) or my trusty FT-817 (its bandwidth being too narrow to work properly.)  Once I'd put together my purpose-built weather satellite receiver, it was a natural fit!

A good idea, in theory.

From some unknown source there's some power line related "buzz" on frequency that seems to be finding its way into the pictures.  This buzz isn't there all of the time, but when it is, I can't seem to readily "hear" it on the audio - or on the nearby 2-meter amateur band.

For decoding the NOAA satellite images I use "WXtoIMG", a shareware program that, for a modest fee, offers even more features than the "free" version.  This program will automatically download the orbital parameters of the satellites, switch the receiver to the proper frequency, receive and decode the pictures from the satellite, place the images atop a map and apply a number of different transformations to the data to better-show various types of meteorological phenomenon and then upload these to a web page - such as the one that contains the images from my receiver.

Figure 2:
A typical image (with noise).
Click on the image for a larger version.
This noise shows up as wavy, diagonal lines in the image - particularly near the north/south extremes where the satellite's signal is a bit weaker.  The picture to the right also has another type of noise evidenced by horizontal bars:  These are due to nulls (e.g. fade-outs) where the signal was momentarily blocked by some other object (such as a tree) or reduced by some aspect of the antenna's pattern and are not due to man-made interference.

Fortunately, WXtoIMG contains a number of filters that can greatly reduce the effects of various types of noise and interference, but these can only do so much!

So, what's the solution?  Several things spring to mind:
  • Seek and destroy!  Find the source of noise and do something about it.  So far, this has eluded me.  As noted before, the noise is not only intermittent, but it seems to defy detection on a portable radio (such as the FT-817) when I attempt to determine its source.  (I'm pretty sure that the noise isn't coming from my own house...)
  • Relocate the antenna.  It's possible that the noise is emanating from something in a neighbor's house or garage.  In this case, moving the antenna from its present location in the back yard, atop a mast to somewhere away and (maybe) more in the clear may reduce/eliminate it - or, if it doesn't, provide additional clues as to its source.
  • Change to a different type of antenna.  Perhaps an antenna with less gain at low elevation angles may reduce the susceptibility to noise as it is presumed that any terrestrial noise source will also arrive at low angles!  A "normal" QHA might work, as might a "Turnstile" antenna.  The ultimate solution would be to construct a circularly-polarized beam antenna (crossed-Yagi or a Helix) and have a pair of rotators automatically track the satellite as it moved across the sky, but this strikes me as overkill!  (But it would be a fun project!)
 Anyway, it's something that's on my huge "to-do" list, falling under a category that I call "YAFP" - which stands for Yet Another Fun Project - or something very close to that!

Sunday, May 13, 2012

A mechanically-powered capacitor flashlight?

A later article about a less-impractical and potentially more useful capacitor-powered flashlight was described in the
August 14, 2012 post which may be found at this link (click here).

You probably saw them in those annoyingly repetitive low-budget commercials several years ago (similar to those for the "Faraday Flashlight" or "Faraday Torch"):   Flashlights that you "shake" to generate electricity with the claim that "you'll never need batteries".

The insides of a "shake" flashlight, showing the magnet, coil, circuit board and the two non-rechargeable CR3032 lithium coin cells.
Figure 1:
Insides of a "shake" flashlight showing the magnet, coil, etc.
Click on image for a larger version.
Why, then, do they have a battery?

Careful inspection of the flashlight - even without taking it apart - will reveal that it has a pair of non-rechargeable CR3032 lithium coin cells - the two edge-on flat metal disks as seen in figure 1Not visible in this picture is a small, green cylinder on the backside of the circuit board to the right of the coin cells which is a 0.22 Farad, 5.5 volt capacitor.  It is this component that is capable of being charged and discharged many times while the disposable coin cells aren't!

The way that these flashlights are purported to work is by the motion of the user causing a magnet to move repeatedly through a coil, this being different from the rotating fields in more conventional, rotary electric generators.  As the strong magnet moves, current flows through the coil and is rectified using a 4-diode bridge to assure that the polarity is always correct.  A simple switch with a series resistor and white LED completes the circuit, providing light.

Why the battery, then?

Several years ago - as an experiment - I took one of these flashlights on a hike with some friends, having removed the battery and discharged the capacitor completely.  As it started to get dark I took out the flashlight to see how useful it actually would be if it were necessary to generate all of the power through the motion of the magnet.

Knowing that it was going to get dark (it always does at night, around here!) I wielded the flashlight while there was still enough light to see and started shaking it, taking partial advantage of my already-swinging arms as I walked along.  It took several minutes before I got even the slightest hint of light from the light, but that was no surprise - and for a very good reason:  The capacitor had to be charged to 2.7-3.0 volts before the LED would produce any light at all and I still had another 1-2 volts to go before enough current could flow through the circuit and the flashlight had any hope of being bright enough to be useful!
Figure 2:
Circuit diagram of a typical "Shake light" - nothing special here!
Click on image for a larger version.
By the time it got dark enough to require the flashlight I'd managed to charge the capacitor to the point where it was quite bright when it was first turned on, a process that had required a mere 10-15 minutes of walking with the flashlight's magnet moving back and forth and occasionally shaking it.

Upon turning it on, the light dimmed dramatically within a few 10's of seconds, but stayed illuminated, providing barely adequate light to avoid large obstacles - but not quite enough to avoid medium-to-small rocks and tree roots in the trail.  Fortunately, being quite tall and fairly familiar with this trail - plus hiking with a group of people who had proper flashlights - I was easily able to lift my feet to avoid obstacles and avoid doing face-plants in the dirt!  I could vigorously shake the flashlight to briefly get more light, causing the light to be pointed in random, useless directions while doing so, but it faded down again soon after I stopped.

What did work was to completely shut off the flashlight and, "mooching" off the lights from the rest of the hiking party, continue on my way while shaking the light as I walked along, only occasionally turning it on.  This strategy of turning off the light while shaking permitted the capacitor in the flashlight to be charged to a higher voltage than it would be if it were on with the LED dragging the voltage back down faster than it was charged and this allowed occasional bursts of bright, useful light.

My suspicions as to why a "free energy" flashlight actually has a battery were confirmed:  It is unlikely that the consumer would actually follow the instructions for a flashlight that required some action beforehand such as:
"Shake vigorously for 3-5 minutes before turning it on.   When it gets dim, turn it off and then shake it vigorously for a several more minutes before using it again."
Thoughtfully including a few inexpensive coin cells allows for both instant gratification and light:  Without having to work just to get the light to work out-of-the-box probably went a long way toward preventing customer returns on flashlights that didn't seem to work because people didn't read and follow the directions!

If you look at the diagram in figure 2 you'll notice that the non-rechargeable battery is placed in parallel with the energy from the coil and the capacitor.  What this means is that after extensive use with the coin cells exhausted, the battery is still in place, adding a bit of loss to the mechanical generation of power as one attempts to "charge" them.  Ignoring this issue, in the case of a light with a dead battery, the user may not be aware that it might be necessary to shake the such a light for a while before it becomes useful - and that assumes that the battery isn't going to badly drag down the charge accumulating on the capacitor!

What's worse, there's the impression by the user that it "never needs batteries" and that it can always be counted on:  While this is (technically) true, it's unlikely that someone finding the battery dead in this thing from having accidentally left it on would be accustomed to shaking it for a few minutes just to get any light at all.  These factors probably explain why it is that one hardly sees these flashlights advertised anymore!

A practical "shake-light" is possible, but the folks that made the unit described above didn't go about it in the right way for a number of reasons, no doubt related to keeping costs down:
  • The coil/magnet's mechanical setup isn't as efficient as it could be.  The use of springs (or other magnets) would improve the mechanical efficiency and "spring" the moving magnet away from the end-stops rather than the mechanical energy being absorbed in the plastic/rubber bumpers at each end.
  • More efficient coil arrangement.  A series of independent coils (e.g. a number of "linear poles") stronger magnet(s), etc. might allow for more energy recovery rather than a single, large coil.
  • Resistive losses in the coil.  The current of the of the coil is dumped into the capacitor fairly inefficiently.  As noted below, even if the coil was loss-less, the capacitor's internal resistance would rob the effort of efficiency. 
  • Improved efficiency of energy recovery from the coil.  Ideally, one would use a small, switching converter to optimally take the energy from the coil and use it to charge the capacitor.  As it is, a 4-diode bridge (using 1N4001-type diodes) has a minimum "2-diode" voltage drop (of around 1.2 volts) is used, wasting a significant portion of the effort - much of it due to effective impedance mismatch between the energy source (the coil) and the load (the capacitor).
  • Better capacitor.  A standard "supercap" is used in the above flashlight.  These capacitors have fairly high internal resistance (10's of ohms, typically) which means that a fair amount of energy is actually lost when the capacitor is charged or discharged - particularly if either is attempted quickly!  In comparison, "Ultracaps" and similar have far lower internal resistance (fractions of ohms) and would work much more efficiently.  It's worth noting that two "fresh" lithium coin cells in series will output about 6.4 volts - this, into a capacitor that is rated for just 5.5 volts!
  • A switching converter to run the LED.  This could be as simple as something along the lines of the "Joule Thief."  As noted above, the LED doesn't even begin to light until 2.7-3.0 volts or so appears across the capacitor and it isn't usefully bright until there is 3.6-4.2 volts available which means that we have over "3 volts of effort" before we get any light at all!  A switching converter could not only allow the LED to be illuminated with as little as 0.8-0.9 volts across the capacitor and utilize more of its charge, but it could more efficiently and consistently power the LED over the voltage range instead of burning power in the resistor shown in the diagram above!  Practically speaking, in order for this to work one would need a better capacitor as noted above.
  • Regulating the LED's current.  As odd as it sounds, reducing the LED's current would probably help make the light a bit more useful.  As it is, an 18 ohm resistor is present - most likely to prevent the two coin cells from being exhausted as quickly, but this simple arrangement causes there to be too much LED current when the battery is fresh and, perhaps, too little when the battery is weak - or possibly when running from the capacitor alone.  A simple current regulator circuit to keep the LED current lower all of the time would help to maintain a more consistent light level under most conditions even if it were lower overall and allow the charge from either the capacitor or battery to last longer.  More ideally, a simple regulator could be incorporated into a simple circuit like the "Joule Thief" mentioned above and increase usefulness and efficiency and charge longevity all at once!
  •  Some sort of power management.  All of the above tend to conspire to reduce efficiency, but if there were some "smarts" involved better use of the available energy from the moving coil could be made.  One growing field of interest has to do with "energy harvesting" and some of the techniques and available chips to do this might be adapted to improve overall efficacy.
While doing all of the above could actually make such a device practical, it would also (significantly) add to the cost.  It is unlikely, however, that a "shake light" would ever be as "human-efficient" as a simple crank-type generator owing to the mechanical nature of this action:  Turning a crank takes a bit less effort than moving one's entire arm back and forth!

Friday, May 11, 2012

No Friendship Cruise this year...

It happens every few years:  Winter and spring conditions conspire and there's too little water flow in the Green and/or Colorado rivers at the end of May.  If there's too little water, navigation of the river can become hazardous due to slightly-submerged sandbars and rapids appearing where "flat" water would be during a "normal" year.

What's the Friendship Cruise, you might ask?

Figure 1:
On the Green River near-ish "Turk's Head".
Click on the image for a larger version.
It originally started in the 1950's as a race, the object being to get from the town of Green River, Utah to Moab, Utah via the Green and Colorado rivers.  After a few years of this, in 1963, the "Friendship Cruise" was added as a venue to allow those with power boats (such as those used for water skiing) to participate at a more leisurely race along with their families, providing access to rarely-seen portions of the landscape.  Eventually, the race itself was discontinued leaving the Cruise as the singular event occurring yearly during the Memorial Day weekend.

Unless you've been in rural, southeast Utah it's hard to appreciate the landscape:  The Green and Colorado rivers slice their way through the landscape, spending much of their time at the bottom of 1/4-1/2 mile-deep gorges surrounded by some of the least-inhabited land in the lower 48 states.  Just downstream of the confluence of the Green and Colorado rivers is Cataract Canyon, a fearsome set of rapids that has claimed quite a few lives over the years.

In a remote, desolate place and on the where the only direction that one moves without power is downstream toward dangerous rapids it's vitally important that logistics and safety be considered should someone break down or experience an injury.  Being in a remote area where telephone coverage is spotty at best at "ground level", such coverage is all but hopeless when you are thousands of feet lower than the surrounding landscape!  Even satellite phones don't work too well on many parts of the course owing to the limited view of the sky!

Figure 2:
High-efficiency HF loop antenna on a boat.  These
antennas have been used for a couple of decades
for communications on 75 meters.  They are about
3 feet (1 meter) in diameter.
Click on the image for a larger version.
Very early on Amateur Radio (Ham) operators have been involved in providing communications for this event using their skills and available communications methods to enable coverage over the entire course.  On the river itself there are a number of radio-equipped rescue boats that patrol the river, assisting in repairs, providing emergency fuel, passing messages to/from the "outside" world or, as often happens, towing boats to the nearest place where they may be pulled out of the river and onto their boat trailer.

During the cruise's heyday in the early-mid 1970's there were as many as 700 boats on the river at the same time and careful watch had to be kept on the river to assist boaters in need as well as manage who's boat trailer needed to be delivered to what location to pull it out of the water!  Since that time, the numbers have declined, but a few die-hards and adventurous newcomers still descend on Green River at the end of May - when they hold the cruise, that is!

For decades, the mainstay for communications was on the 75 meter amateur band which, during daylight hours, has an effective coverage radius of a few hundred miles.  Utah, being by itself among the western states, puts this band largely out of reach of most of the country's population centers with Salt Lake being about the only large city within daytime range.  On the boats were mounted mobile rigs with small HF antennas - both loaded verticals and high-Q tuned loops - that provided reliable coverage from anywhere along the course, no matter how deep the canyon.  At night, 75 meters "lengthened" covering large chunks of the U.S. and Canada by nightfall and "local" coverage degraded, but by the time it started getting dark almost everyone on the river had made camp or gotten to the end and pulled their boats out so very little traffic handling was generally required.

At several points along the course - one at each end and two places in the middle - were strategically-placed stations, also equipped with HF communications where river access was possible via vehicle allowing fuel trucks to replenish the boats' gas tanks as well as trailers to allow boats to be taken off the river.

75 meter HF worked quite well for the 30 or so years that it was the sole source of communications on the river, only occasionally succumbing to the odd solar flare that caused all signals on the band to "disappear" for a few hours.  In the 60's and early 70's, VHF such as 6 and 2 meters was occasionally tried, but its signals had difficulty escaping the deep river gorges and the range was limited to only a few miles up and down the river.  By the time the 80's and 90's rolled around there were a few 2 meter repeaters in the general area but their coverage on the river was extremely spotty, again since signals had difficulty escaping the deep, narrow canyons!

In the late 90's, we started to look in earnest at how VHF and UHF might be used in providing coverage of the river, knowing that we faced a significant challenge in finding locations that had any hope of catching the feeble signals emanating from the cracks in the Earth - but that story will have to wait for another day!

Hopefully, the water conditions in 2013 will be favorable for the 50th anniversary of the cruise!

Thursday, May 10, 2012

Getting the rigs ready for Field Day

In preparation for the upcoming amateur radio Field Day event near the end of June, I decided to take a look at the Utah Amateur Radio Club's rigs to see that they were up to snuff.  Having some of my own test gear at home (and being the club's president!) I gathered up the club's three HF rigs from their storage and lugged them home. The club owns two Kenwood TS-450S's and one TS-820 - the latter being an 70's/80's vintage hybrid (solid-state except for a tube driver and a pair of tube finals) that hadn't been actually used for Field Day for several years.

The first order of business was to take a look at the transmit spectrum of the TS-450's as it seemed as though at least one of them was more "hissy" than the others - that is, when it transmitted, everyone else heard a hiss - even if not on the same band.

Throwing the rig on my service monitor (which includes a spectrum analyzer) I could see that both of the TS-450's were pretty much created equally.  What surprised me, however, was the fact that from the frequency of the radio's lowpass filter (on 20 meters, this was somewhere around 19 MHz) on down to below 1.8 MHz (where the response of the final amplifier itself dropped off) there was a fairly level noise floor - approximately -34 dBm in a 60 kHz detection bandwidth.  When translated to an SSB bandwidth, this turns out to be approximately -50dBm - plenty high enough to be audible under many conditions even when the "path loss" (that is, from the transmit antenna to the other station's receive antenna) was taken into account - and the two radios don't even have to be on the same band!

The next measurement was with the built-in antenna tuner switched into the transmit path.  Interestingly, even when the tuner "matched" to the service monitor - that is, "matched" to a 50 ohm resistive load - I could see that the magnitude of the off-frequency noise decreased markedly, implying that there was still some "L" and "C" in the signal path and doing some "matching."  Typically, the amount of noise reduction on other bands was anywhere from 8 to 20 dB, depending on the transmit frequency and band, of course.

The upshot of this is that it's worth "eating" the additional loss of the antenna tuner (a bit less than 1dB) just to gain an extra 8-20dB of reduction in the "hiss" emitted by the transmitter!

One problem that this does not solve is that of in-band desense - that is, running two stations in the same band at the same time.  Practically speaking, there are only a few ways that one can minimize this problem:
  • Separation of antennas.  This is fine, if you have the room!  It's worth noting that Field Day rules actually place a limit on how large the site may be (that is, all radios and antennas must fit within a 1000 foot diameter circle) and still be counted as one station.
  • Sensible arrangement of antennas.  In North America, it's generally better to place antennas in a north-south line as one will, generally speaking, be sending signals east and/or west, putting the other antennas off the sides where the response will generally be reduce and the isolation between antennas be enhanced.  Obviously, the nature of this sort of strategy varies a bit depending on your location!
  • Selection of rigs.  Many years ago, we banned Icom IC-706's (and all variations) from our field day site as it seemed as though they did a great job in radiation tons of noise and absolutely wilted in the presence of another transmitter - even one on a different band!  While it would be nice to have a really fancy, high-dynamic range and ultra-clean rig and/or one of the old standbys that could tolerate multi-station environments (such as the venerable Drake 4 twins) we have what we have.  Compared to many others we have tried, the Kenwoods aren't really that bad...
  • Filtering.  Keeping one's emissions confined to the band on which operation is taking place is fairly easily managed with a number of off-the-shelf "transmit-through" bandpass filters, but these do nothing to keep two stations on the same band from bothering each other!  Years ago, we tried using 1/4 wave stubs, but these turned out to be a nightmare to manage - especially as the collective memory from year to year was imperfect and expertise on what worked or didn't worked was lost.  In the case of 20 meters, last year I devised a fairly simple notch-bandpass approach that worked nicely to keep the SSB and CW stations out of each other's hair - but I'll talk about that in a later entry.
After deciding that the two TS-450's were alike, I installed a CW filter in one of them and marked it appropriately so that it could be used for the CW station if needed.

Next on the list was the old TS-820.  In turning it on, I realized that my vague memory had been correct and that it did have the stock, 500 Hz CW filter in it.  After cleaning it up, spraying a few pots and switches with cleaner to get rid of the "scratchies" and tweaking the frequency display into calibration, I set about modifying it for low-voltage, positive keying.

Being an older radio it has grid-block keying which meant that -60 to -90 volts appeared across the key, making it incompatible with many modern CW keying circuits that expected a low, positive voltage across the key.  Constructing a simple circuit using 3 transistors and a bit of RFI protection, I wired it into the original key jack, tested it, and then added a label indicating that it had been modified - I'll post details on this modification in later entry...

I also tested the TS-820 to see what its transmit spectra looked like and was pleased to see what I'd expected:  The noise output was lower than that of the TS-450's (around -50dBm as compared to -34dBm for the TS-450's) and it was confined to no more than +/- 10% of the operating frequency - a testament not only to the tunable bandpass filters driver chain but also the Pi network on the tube finals - both of which effectively limit the useful bandpass of the output amplifier signal path to those frequencies near those for which the radio was tuned.

Now, for the rest of the planning of Field Day.  Stay tuned!

Wednesday, May 9, 2012

Intermittent GPS...


Ok,  I finally got sick of it happening and I decided to take down my "PBJ" (Peanut Butter Jar) GPS antenna and figure out why it was that I kept ending up with "zero" satellites in view.
Figure 1:
Homebrew GPS antenna, in use since 2003, affectionately referred to
as the "PBJ Antenna" since a glass peanut butter jar (and its
lid) are used to house the antenna.
Click on the image for a larger version.

Years ago (2003, I think) I obtained a surplus HP Z3801 GPS receiver.

Why?

Well, they became available for an affordable price (about $250, I think) and with it, I could use the GPS system to obtain a very accurate source of both time and frequency.  Of particular interest to me was that it was capable of producing a 10 MHz output that was accurate to enough to hold a clock to within a second every several hundred thousand years.

I don't really need a clock that is that accurate, but a source of stable, accurate 10 MHz was useful in testing and calibrating other frequency sources - such as the local oscillators of microwave transverters.  A year or so ago, I put a low-power small form-factor PC on this receiver to permit monitoring of its status as well as crunch away at the NOAA weather satellite images that spun by from overhead spacecraft.  Adding this computer also made it easy to provide a local NTP (Network Time Protocol) server that came in handy when operating some of the narrowband digital modes such as WSPR:  Having a local time server that I could query very frequently was helpful in keeping my operations synchronized with everyone else's...

More recently I added a Trimble Thunderbolt GPS Disciplined oscillator - a much smaller, lower-power box that did much the same as the as the old 'Z3801 - but with a really cool user interface program (more on this on a later date) and I was annoyed when, shortly after installation, I saw that both it and the Z3801 were reporting frequent dropouts of the GPS signal.

Actually, this had been going on for a while, but it seemed to happen only rarely and for a short time, but now, as the season was warming up, it seemed to be offline about as much as it was on.

Hmmm...

Taking it down, I poked, prodded and "Ohm'd", but nothing was obviously wrong.  During the poking and prodding, I might have cracked a surface-mount bypass capacitor or two (mounted "tombstone" style to the circuit-board ground plane on which the antenna's circuitry was built) so I replaced these just to be on the safe side, reflowed a few solder joints, lugged it back up onto the roof and connected it.

Fixed!

For a day or two, anyway...

After a day or so of behaving itself, it became worse than ever - and then the weather got bad for a week.

Last Saturday was a nice day and I'd just gotten back from a breakfast meeting of the Utah Microwave Group and was going to meet K7RJ in a few hours to work on his 10 GHz transverter so I went back on the roof and retrieved the antenna once again - this time, managing to do it while the receivers were reporting a loss of signal.

This time, I was "lucky" in that I noticed right away that the voltage on the output lead of the MAR-6 MMIC preamplifier was "wrong" and the bias voltage on its input lead was zero.  Using a jeweler's loupe, I stared at the connection where the MAR-6 input connection was made with the UT-141 coax from the turnstile elements and spotted a tiny flake of metal.  A few minutes of surgical unsoldering, cleaning with a straight pin and careful resoldering (to avoid the installation of another metal flake!) resulted in proper voltages in all of the right places.

Taping things back up and running back onto the roof I reinstalled the antenna and upon my return to ground level, I was gratified that the both GPS receivers now showed that they were in the process of re-synchronizing to the satellites.

Since then, everything has continued to work as it should...  I think...

Update:

As things like this turn out, after a week or so of flawless operation, the GPS antenna once again became intermittent, so I hauled it back down to the work bench.

Twice.

The second time I finally replaced the MAR-6 MMIC since I'd replaced/resoldered everything else and that seemed to fix the problem for good!

Since then, both my old HP Z3801 10 MHz Disciplined Oscillator and my "newer" Trimble Thunderbolt have been happily locked to the signals from the GPS and providing accurate, stable 10 MHz references.