Friday, August 12, 2016

00A

JeppGuide page for Stone Mountain Aiport
Twenty years ago, I lost a good friend. Well, not exactly a friend, but a place.

Stone Mountain Airport closed twenty years ago in June. 

Stone Mountain Airport was one of the older airports in Georgia. It had been in continuous operation since 1930 until it closed in 1996. It was a very special place, with lots of character. It originally had crossing grass runways in the early days. By the time I started frequenting the place in 1989, there was but one runway -- a 2800 foot stretch of asphalt oriented 170/350 degrees.

The runway had displaced thresholds at both ends -- 600 feet at the south end, and 1200 feet on the north. The displacement at the south was mainly due to tall trees 200 feet off the end. The displacement to the north was another story. Sometime in the 1980s, a fellow built a warehouse in the lot adjacent to the airport, and then immediately complained to the FAA about all of the airplanes flying over his building. (Did I mention the airport had been there since 1930?)

The FAA solved this problem by requiring pilots to fly a three degree profile and clear the building by a sufficient height, which dictated a 1200 foot displacement. This mean that takeoffs on Runway 35 or landings on Runway 17 effectively lost nearly half of the usable runway length.

Stone Mountain airport was an uncontrolled field -- meaning it did not have a control tower. For my flying buddies that learned to fly at Peachtree-DeKalb airport, Stone Mountain seemed like something out of the wild west. A scary place where only the most daring of pilots went -- a too short runway with no controllers to talk to. Frankly, those of us comfortable at Stone Mountain felt the same way about Peachtree-DeKalb -- that it was a scary place. It had jet traffic, and you had to talk to someone to get permission to taxi, take-off or land.

The FBO was in a small white building with three rooms. As you approached the door, you'd notice two white benches on either side, under an awning. These benches were a mere 100 feet from the center of the runway, so it was a great place to watch planes take off and land. Inside, there was a great big room a dilapidated sofa and several easy chairs.

At one end of the room was a huge stone fireplace. In the winter, there was always a wood fire going, as it was practically the only source of heat. Just behind the sofa was the counter, where you could pay for your fuel, buy maps or AF/Ds, or pick up an ice cream sandwich before going back outside to the white benches to critique the landings. Behind the counter was a small room that served as a classroom and office.

Landing at Stone Mountain wasn't all that terribly difficult, so long as you had reasonable control over your airspeed. The short runway left little room for excess speed, and pilots there had no qualms about going around.

Prevailing winds generally favored using runway 35, which was the longer of the two runways. Crosswinds made this more interesting. The presence of a 900 foot dome of solid rock a couple of miles away from the runway made crosswinds more common. Winds out of the west would wrap around the mountain and produce a burble on the approach to runway 35. Best technique was to crab on final and keep adjusting, as the crosswind usually disappeared as soon as you dropped below the tree line. Usually. If not, you'd kick into a slide slip just before touchdown. While it sounds nerve-wracking, it wasn't so bad once you knew what to expect.

When the winds favored runway 17, airspeed control was even more critical, as a delayed go-around faced the prospect of putting the airplane into the tall trees off the end of the runway.

Approaches were gauged with the Mark I eyeball and the "poor mans VASI." We had no proper VASI, but about the time the displaced thresholds were ordered by the FAA, a clever arrangement was set up. About 50 feet from the runway, three large boards were placed horizontally. Two were held spaced apart and painted white, while the third was further down the runway and painted orange. If you were on the three degree glideslope, the orange board would appear directly between the two white boards. Crude, perhaps, but it worked well. You could easily tell if you were too high (and thus carrying too much kinetic energy) or too low (and risked going into the trees). The front, white boards were right at the displaced threshold, too, which made it easy know where to land.

Landing at night generally favored runway 17 in any case. You'd fly over the bright parking lot of the Walmart across highway 78, and squint into the darkness for the LIRL (low-intensity runway lights) around the runway. Seriously. You'd never want to set up a landing for runway 35. You'd never see the trees on the approach end, and the lights of Walmart would prevent you from making out the runway as you got close.

Stone Mountain did have it's share of accidents -- some minor, some fatal. On one particularly windy day, I witnessed a fellow in an Ercoupe make three landings before mid-field on runway 35. The second bounce broke the nose gear, and a bunch of us had to push it off the runway. Clearly a case of pilot-induced oscillation trying to force the aircraft down.

My friend Forrest broke a beautiful Cessna 172 -- N7654G. He was out flying on a particularly blustery day, attempting to land on runway 17. He had already gone around once, and made the approach with a bit more determination. Unfortunately, he dropped it in so hard, that one wing hit the ground, then the plane rocked back the other way so hard the other wing hit. Nose gear collapsed also, but both wings clearly had a bit of extra dihedral. Forrest walked away, unhurt, other than his pride.

Summertime could be difficult, as the heat and humidity would cause the density altitude to rise. A pilot renting a 172 packed the plane very full with four adults on a summer afternoon, ended up putting the plane on the road beside the warehouse north of runway 35. His takeoff was very anemic, which he should have aborted. He was still in ground effect as he left the runway environment. While no one was hurt, it was too close.

While Stone Mountain had a few hangars, we mostly parked our planes out on the grass at tie-downs. Some were in the back forty where the old grass runway used to be. Mine was across the runway from the FBO, about 150 feet from the runway. Some folks might think this strange -- having pedestrians cross an active runway on foot. No, perfectly normal.

Yes, I'll never forget that feeling crossing the runway on foot on a crisp autumn morning, getting ready to preflight my Cessna 150D for a Saturday of flying. It would be chilly, the grass would be wet with dew, and the earth gave off a rich, wet smell.

For several years, Stone Mountain was host to a glider operation. A Cessna 305A / L-19 "Birddog" was the tow vehicle, and the pilot would waste no time after release getting back down to the ground. For the L-19, Stone Mountain seemed a copiously large airport. Glider rides were very popular over the mountain, and, in retrospect, were relatively cheap. $85 bought a ride from 5,000 feet, and I took one on my 30th birthday. It seemed over all too soon.

Stone Mountain pilots were a pretty social crowd. On July 4th, Stone Mountain Park would put on a pretty good fireworks show, and we could go up to the airport and watch. Now, we were on the wrong side of the mountain -- most of the action was in front of the carving. But we could see plenty.

In the warmer months, pilots would frequently gather for an impromptu "dawg killin'". This was a euphemism for a cookout with hotdogs and hamburgers, and plenty of aviation conversation.

I remember a couple of pilots that I haven't seen since the airport closed. There was "Jack" (not his name) who was a perpetual student pilot. You see, he'd never gotten his private pilot's license. He probably had a couple of thousand hours by the time I met him, likely most of them undocumented. He had a Cessna 172 and flew frequently -- but I never knew him to take any passengers.

There was another fellow who owned a DeHaviland Chipmunk. It was a joy to see that plane in the air, with it's inverted, in-line four-cylinder engine. It cut a handsome profile with it's unusually narrow and long nose. But we rarely saw it in the air. I generally remember this fellow sitting on one of the white benches on a beautiful Saturday, debating on whether or not to pull his airplane out of a hangar.

I do remember on fatal accident while at Stone Mountain. I arrived early one spring Saturday morning for a lesson, only to find the airport closed. An hour earlier, a Cherokee 140 had taken off on runway 17, and ended up in the trees off the end of the runway. The two occupants had perished in the impact. Two factors seemed prominent in this accident -- the aircraft was packed very full with camping gear, and might have been overloaded. The other was the wind. While the wind sock might have been favoring 17 near the ground, the winds above the tree line were clearly out of the northwest. They had made a very marginal takeoff only to encounter a tail wind above the tree line. While no flying that day, the lesson was one of reflection and study.

Whether tragedy or fun, all of it came to an end in June 1996. You see, the Atlanta Olympic Committee built the Tennis venue just a half mile from the end of runway 35. While the Olympics were in Atlanta, there would be no flying out of Stone Mountain, due to the Temporary Flight Restriction (TFR) around the Tennis venue.

Owners of the airport decided to rent out the space for parking. By June 1, all the aircraft had to be moved to other airports. They then came and removed all the runway lights, and the fencing, and put down a crush-and-run surface down for parking. At the time, their intention was to re-open after the Olympics.

Alas, it didn't happen. While closed, someone took an interest in the property and made the 30-odd owners an offer they couldn't refuse. They never re-opened.

There were rumors that someone was going to build a retirement community on the property, perhaps a shopping mall. None of that transpired. Years later, a local model-aircraft club (Stone Mountain Flyers) bought part of the property and operate model aircraft on what's left of the runway.

I drove down Bermuda road the other day. This road runs right past the airport, with about a half or quarter mile of trees in between. The south end of the airport property nearly runs into Bermuda. Years ago, there was a little spot on the road you could turn off and you'd have a clear view of the entire runway from the approach end of runway 35.

That whole area is now grown up with pine trees over 40 feet tall. You can no longer see the runway. It is a sad and ignominious end to a place where I learned to fly.

Other information and pictures, here.

Monday, May 30, 2016

Fixing the Ameritron AL-80A. Again.

If you remember from last August, I repaired my AL-80A. Well, that fix lasted little more than a month before I once again had an arc while tuning and it started acting weird. Grid meter would drift up when the amp was keyed, and would pin hard against the right stop when RF was applied.

Surprisingly, though, it was working -- only the metering seemed to be affected. Sadly, my lust for DX overcame my caution, and I occasionally used it even though the metering was weird. While the amplifier continued to work as designed, the grid current meter pounded so heavily against the right stop that eventually the needle broke off. 

Blown 1.5 ohm 3 W resistor on left.
Proper-looking spares on right.
I finally pulled the rig over to the workbench and took it apart. What I found wasn't pretty. Yes, the same 1.5 ohm 3 watt resistor had disintegrated. The metal foil had been blasted away from the resistor form. It was completely open. It was no wonder that the grid meter acted so strange -- it had no shunt!

I also found a article by Tom Rauch, W8JI on proper amplifier metering. It talked about a very simple circuit change that would likely prevent this sort of damage in the future. 

Indeed, after doing some research, I found that this protective circuit to be part of several Ameritron amplifiers, include the AL-811, AL-80B, AL-82 and AL-572. Unfortunately, it wasn't included in the AL-80A.
Small caps added across the B- rail.
Added ground lug visible on rectifier board.

No matter, very simple to add. I placed two small capacitors on the B- rail to ground, right on the capacitor board. The glitch diode took a little more doing. I already had a glitch resistor mounted to the rectifier board, and it seemed logical to place the diode there. I added a ground lug to give me a good ground connection, and placed the diode underneath the board. 

Tom recommends a 1N540x diode, but I didn't happen to have any. I did have plenty of 1N4007 diodes -- which don't offer nearly as much protection. However, I figured that some protection was better than none at all.

I still had the problem that the grid current meter had no needle. The broken needle was still in the meter face, so I used a tiny drop of superglue to re-bond it to the post. So far, it is holding, although I don't know how long that will last. 

1N4007 on bottom of rectifier board.
Note the picture has it installed backwards,
something I have since corrected.
Buttoning it all up, I thought this would be an easy victory. Well, the multi-function meter seemed to be operating correctly now, but the grid meter behavior hadn't changed. It was still pinning with the least bit of RF. Something was still not right. 

It was a few days before I had a chance to pull the amp back to the workbench. Off came the thirteen screws holding the cover. Then the eight screws holding on the front panel, plus all the knobs and indicators. Pulled the meters, and then the meter board out where I could see it.

Placing an ohmmeter across the grid current meter showed that the shunt wasn't in place, since it read about 450 ohms. The resistor itself was OK. Looking at the meter board, I found that there was a open in one of the traces. Apparently, the glitch was strong enough that part of the board acted like a fuse! A bit of solder and a piece of bare wire bridged this open.

Buttoning it up again, it once again works as it should. Now I can enjoy chasing DX without the guilt. Indeed, I worked XR0YS on Easter Island just as soon as the amplifier was repaired.

Monday, April 18, 2016

DXCC - Meeting the Challenge

Since I started uploading my logs to the ARRL Logbook of the World in November 2003, I've been working toward the DXCC Challenge. I've been carefully trying to work DX stations on multiple bands, hoping to get my current entity-band totals past the Challenge threshold of 1000.

Well, sometime this weekend, I received enough confirmations to get me past the 1000 mark. At the moment, I have 1003 entity-bands confirmed.

I guess I'll be submitting an application for the DXCC Challenge this year! That along with 30m DXCC.

UPDATE: I also notice that I have exactly 239 current entities confirmed for Mixed DXCC. This means I'm exactly 100 entities away from working all 339 current entities, or 91 away from the DXCC Honor Roll.


Saturday, April 2, 2016

DXCC - Excellent Service!

CP1FF QSL clearly shows 15m Phone.
I recently uploaded all my logbooks to ClubLog, and I was trying to reconcile my DXCC credits with those shown in LoTW. While doing this, I noticed something odd.

Back in 2009, I submitted a hybrid application for Phone DXCC using, 52 LoTW credits, and 10 paper QSLs. Among the paper QSLs was one for an SSB contact with CP1FF on 21 MHz.

I received credit for Bolivia for my SSB contact, so I didn't think much of it. However, in trying to reconcile with ClubLog, I noticed that the credit was apparently entered for 80m instead of 15m.

I've never worked CP1FF on 80m. Indeed, I have never worked Bolivia on 80m at all. Why did I have credit for it?

A quick email to the DXCC Admin sorted this out right away. She changed my credit from 80m to 15m, as it should be. Thank you!

Of course, this means I'm one more entity further away from 80m DXCC....

Saturday, January 9, 2016

Project From a Friend - HF4B

HF4B Parts, after sitting out in the weather
for about 25 years.
I had a friend call me the other day. She was licensed about 25 years ago as N4VMN, but her license has since lapsed. In any case, she had some antennas that had been sitting out at beside her house in Marietta for quite a few years now -- she wanted to know if I might know anyone who could make use of them.

Well, I'm always interested in antenna projects, and I could certainly use some smaller antennas, so I said, sure, I could use them.

She had a slightly bent Ringo Ranger, and an old Butternut HF4B. Ah, the Butternut HF4B. I had one in Stone Mountain, GA from late 1987 until 1991, when I replaced it with a Cushcraft A3S.

N4VMN lived in another part of the same subdivision back then. She gotten licensed, bought a rig, and put up this antenna on a roof tower -- and she did it all without consulting me. While I was a bit disappointed I couldn't have given her advice, I was still impressed that she managed to do it all herself.

My experience had been that the Cushcraft A3S worked way better than the HF4B, but the Butternut was a solid performer.

The HF4B is a light-weight, trap-less tribander that uses large bow-tie shaped elements and a clever matching network. It supports 10, 15 and 20m, also also works on 12m. I never could get mine to match well on 12m, but it worked OK on the other bands. Being only two elements, it didn't offer a lot of gain, but had solid front to back. On difficulty in dealing with this antenna was it was so three-dimensional, as the bow-tie supports go three feet above and below the elements. Overall, though, it is pretty small. It can be easily turned with a small TV-type rotator.

N4VMN's antenna had spent a couple of decades outside next to the house. I expected after all this time it might need some repairs. The U-bolts are all shot, and will need to be replaced. The bow-tie supports were all bent, but look repairable. All of the bow-tie wires were broken or missing. The matching network tube supports were all bent, but look repairable. One of the element tubes had filled with water at some point, froze, and split about five inches from the center insulator. It might be repaired with a clamp or two, but replacement is probably a better option. The two fiberglass insulators seem to be in OK shape, although they need to have some of the weathering sanded off and protected with a nice coat of flat black paint (as I did on the R7000).

OK, this is going to be a project, but it looks like what remains is serviceable. I could definitely use a small tribander at the Walton County QTH, or even as a South-America facing antenna in Gwinnett County. I'll have to work out a 20-25 foot support to mount it on, eventually.

PICKit3 and DIYMall Board

PICkit 3 and DIYMall programming board.
PIC16F1503 in programming position.
When I wrote the last article about the PIC, I had forgotten to take some pictures of the PICkit 3 and the DIYMall programming board.

I've include them here. The PICkit 3 is really quite nice little unit, and pretty easy to use, once you figure out the details.

The DIYMall board, which came with no separate documentation, and certainly had no documentation on any web site, appears to have comprehensive, if somewhat cryptic, documentation on the back of the board. You can see the four heavy white lines on the back, that indicate the proper positions for different types of devices.


Complete documentation on the back of the DIYMall board.
40 and 28 pin DIPs go and the end, on the 1/40 pin mark. 8, 14, 18 and 20 pin DIPs go at the 11/30 pin mark. PIC16F57 chips have a special place at the 5/36 pin mark. As does the tiny six-pin PIC10FX chips, which go in backwards at the far end the 20/21 pin mark. The three jumpers, J1, J2 and J3 need to be appropriately selected as well.

It seems unlikely that a lot of new designs would use the older PIC16F57 or PIC10FX chips, but it is nice to know it is possible.

Once you set the jumpers and drop the chip in the right place, they actually program pretty easily.

Thursday, December 31, 2015

The PIC

K9AY controller that doesn't
work.
For a year and a half, I've been working on a push-button controller for my K9AY loops. The loop remote box is pretty much as K9AY originally designed it -- two 6 volt DPDT relays, fed with 6 volt pulsating DC or AC that is coupled into the coaxial feed line. While some people used separate control lines for the relays because of hum problems, I never encountered this issue.

For years, I used a rotary switch to select the direction. Then I decided I wanted a push-button controller so I can immediately select the desired direction.

The push-button controller design was based on a 74LS175 Quad D-type flip flop and SPDT buttons. Pressing a button drives the clock line low and also raises the corresponding D input on the flip flop. Releasing the button causes the leading edge to latch the state of the button. The not-Q outputs of each flip flop drive the LED on the button, while the Q outputs feed to an VN10KN MOSFET that drives a SPST relay that supplies voltage. Six volts for NW, minus six volts for SE, six volts AC for SW, and no voltage (no relay) for NE. Simple.

Except it doesn't work.

The buttons are the problem. Like all mechanical switches, they bounce. These bounces are probably a handful of times within 2-10 ms, but that's enough to throw off the logic which switches within a handful of nanoseconds. Sometimes you press a button and nothing happens. Sometimes you press it, and more than one relay activates.

It's frustrating. The whole purpose of the push-button controller is to command the loops to go immediately to one direction, except the circuit isn't reliable.

I wanted to keep this circuit simple -- one 14-pin chip. Now it looks like I'd have to add a lot more logic to get this design to work.

As a software developer, I kept thinking -- if I only had a micro-controller, I could avoid the switch bounces with software. And I could fix other problem with the design. For example, if you accidentally pressed two switches at the same time, two LEDs would light. With software, I could make it so only the last switch press is selected -- only one direction selected at a time.

This made me wonder -- if I were going to use a micro-controller -- what would I use? I got started on my software career when I built a 6800-based computer in 1977. I was familiar with the 6802, 6801 and 6805. But these were relatively huge chips, and required a lot of support logic. What I needed as a micro-controller that would fit into a 14-pin or 16-pin chip, and allow for four digital inputs, and seven digital outputs without any support. What was available, and how much would it cost?

So, I went to mouser.com and started searching. Hey, these Microchip PIC micro-controllers seem like they would work. After all the Elecraft K2 has a bunch of them. There were also ATmel AVR chips, whatever they are. Seems to me those are used in the Arduino.

Actually, there was an abundance of these devices that might work. It got more interesting when I sorted them by price. I ended up selecting the Microchip PIC16F1503.

This is a pretty amazing device! Two kilowords of instruction memory, 128 bytes of RAM. Capable of up to 5 MIPS. Low power consumption, very flexible operating voltages. With a whole host of interesting I/O features: 12 input and 11 digital output channels, 10-bit A/D converter with eight external and three internal channels, 5-bit D/A converter, two comparators, three timers, 10-bit Pulse-Width Modulator, two configurable logic cells, and a 20-bit numerically controlled oscillator.

Of course, you can't use all of that all at the same time, but this seemed like a marvelously flexible device for all kinds of projects. The best part was the price -- 90 cents a piece. Naturally, I ordered 10 of them.

This device has plenty of power for my K9AY controller. The first step was to figure out how to use it. Microchip offers the free MPLAB X IDE software, which can be easily downloaded for Windows, Mac or Linux. The IDE alone will let you write software and run the simulator. The next question is -- how to get the program into the chips. Microchip also makes a device called the PICkit 3 -- a USB device that easily connects to PIC processors and allows for programming as well as some limited hardware debugging. There was also an end of year special, so I could get it for $36 plus shipping.

The circuitry to connect the PICkit 3 to the chips is dead simple. I looked into building a little board with a ZIF socket. However, ZIF sockets are like $10 apiece. Before I could submit my order for one, I found a little board on amazon.com from DIYMall that is exactly what I was thinking of building for less than $8.

It took me a couple of nights to figure out how to use the IDE. The PIC itself is mind-numbingly complicated. First step is to set the configuration bits, which tells the PIC things like where it's clock signal is coming from. Then you actually get to the start-up code, where you have to program the chips innards to reflect the configuration you wish to use -- which pins for I/O, and what function blocks are connected to those pins. The PIC16F1503 is complex enough that it would actually take a lot of time and code space to configure each block. But, again, you can't use all that stuff at once, so just focus on the items you need.

The configuration is done by writing to specific memory addresses. This would be easy if the chip allowed direct access to all of the data memory. However, because of the programming architecture, it really only has direct access to the first 128 bytes of memory. So, of that space, all but the first 32 bytes and last 16 bytes of that space are banked into 32 banks of memory. Interspersed in those banks are the configuration registers.

Confused yet? Well, the PIC instruction set is nothing to write home about either. There's only one accumulator (W) and no other implicit registers, other than those in low memory. The PIC16F1503 is at least a mid-range CPU, so it has some additional instructions to make things easier to program.

If you are not an assembly language programmer, you really ought to ask yourself what the heck you are doing writing micro-controller software, but there is a C compiler that can be used.

I had little problem writing a program on the simulator. Getting it into the chips was something more of an ordeal that took me about three days to figure out. I wrote a little program that takes all 6 bits of PORTC and outputs a counter on them. It increments the W register from 0 to 0 (256 times) between counts, so the results should be visible. I used a 32 kHz clock speed, so things ought to happen slowly enough to observe.

At first, I couldn't get MPLAB X to talk to the PICkit. MPLAB X seemed to know the PICKit was there, but when going to program, it just sat there, doing nothing. After digging around on the web, I found that you could reset the PICKit by holding down it's button while you plugged it into USB.

At that point, MPLAB X was now talking to the PICkit, but it still wouldn't program. The PICkit has an option to supply power for programming, but the default is not to. Once I turned the power on,  I was getting a warning that the PICkit was trying to supply 5 volts, but it was reading only 4.75 volts. Now, there's nothing on the DIYMall board other than a ZIF socket and a couple of jumpers. Setting it to 4.75 volts made the warning go away, but it couldn't find the chip.

It was about this time I started studying the DIYMall board more closely. It came with no documentation, and I couldn't find anything on-line about it either. When I turned it over, I found there were jumper indications. I moved the first jumper to the B position, which was correct for 14-pin chips.

No difference. This shouldn't be so hard!

Looking at the board some more, it turns out that the 14-pin chips aren't supposed to go in pin 1 of the ZIF socket, but way down around pin 30. There was a heavy white line on the backside of the board indicating this. That's the first time I've encountered documentation printed solely on the board itself. I figured I'd try it. Low and behold, it programmed!

Putting it in a board, it worked the first time. I've included a little video of the chip in action.

video