Amateur Radio – Page 17

Variable Power Supply

I’ve been focusing on power supplies and related equipment lately because I don’t have a lot of bench gear. On one hand, I would like to build equipment from scratch, but on the other, it would be crazy not to look at some of the building block modules available on eBay and other outlets. I could not beat these prices, even if I built just about entirely from scrap. Using modules rather than homebrewing down to the metal seems like cheating, but it not only saves time and money, but often yields better performance and miniaturization.

So, this project consists of building a bench top power supply from three modules: a switching power supply that puts out a constant voltage, a DC/DC converter, and a combined voltmeter/ammeter. The combination is based on a youtube video by GreatScott that made use of a cheap DC/DC converter based on the LTC3780 that is being sold by various vendors at a bargain price on eBay. Some of the same vendors are also selling a red and blue volt/ammeter. There are a few variations of the meter, I selected one rated for 100V and 10A and which did not require an external shunt resistor for current measurement.

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ATX Supply

Remember that ATX power supply that I fried last year? I replaced it with another mail-ordered supply and then it sat on the shelf long enough for me to get around to fixing it: a new regulator, some MOVs, a cap and the fuse, and it was ready for action — except I had no computer to install it in. I kind of doubt that I’ll build another tower form-factor computer, so I turned it into a high current bench power supply.

It has to be more than ten years since I’ve done this, and I believe the last time I didn’t even have an ATX supply. At that time, supplies needed a hefty load to get going and remain stable. I recall using a car headlight. Literally: an old-style (maybe halogen?) automotive headlight. I reviewed a couple videos on the subject to see what people were doing with more recent supplies and found one that I liked and more or less followed.

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Soft latch

I liked the circuit so much I made two of them. Here's front and back. — I liked the circuit so much I made two of them. Here’s front and back. The one on the left has an extra electrolytic cap; its addition did not affect the switching circuit at all.

Catching up on the bench back catalog: here’s a useful little module – a soft latch that isn’t finicky, works when you first plug it in, draws effectively no power when not changing states, and operates over a relatively wide range of input voltages. What’s not to like?

The basic idea is that mechanical switches, even simple toggles, are much more expensive than push buttons. It would be nice to be able to push a cheap push button and have it turn devices on and off. Some bad ways to do this would be to have the circuit twiddling its fingers, burning power, waiting for button presses – for example, having a microprocessor down stream of a voltage regulator idling until it detects a change in state on the pin connected to the push button. Sure, the microprocessor could be throttled down in some energy-saving mode and might only consume microamps, but the upstream voltage regulator would be consuming power, certainly true for linear regulators, and to a lesser extent for switchers.

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Back to the bench: 7 segment display

Three 4-digit displays: red, yellow, and green. Ew, shiny pads!

Since the SOTA genie escaped the bottle, the blog has leaned towards operation rather than bench work, but rest assured that projects have been percolating in the background. Here’s an update on a few of them: a custom LED display, a soft latch circuit, and a high-current converted ATX power supply. Let’s start with the LED Display.

For an upcoming project (actually, one that was moth-balled last June, stuck in a butter-cookie tin, and just recently again saw the light of day, followed by several days of pouring over notes and head scratching to remember where I had left off), I needed an LED display that would show voltage, amps, and power. Sure, you could figure the power out from the amps and volts, but I wanted it to change in real time to give me feedback while I make adjustments.

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SOTA W7A/WA-010: Mingus Mountain

Sorry, Amateur TV folks, you are out of luck in this park.

You would think that with a name like “Mingus”, it wouldn’t really be necessary to specify the SOTA designator — but you would be wrong, as there is also a Mount Mingus (W4T/SU-008) in the database. I’d assert that my Mingus is the One True Mingus. I don’t know if there is any technical difference whether something is named Mountain versus Mount, but I would like to think there is, and that the one I climbed was the real deal: my first ten-point summit. We just don’t have mountains like this in the Mid-Atlantic region.

I had initially missed Mount Mingus because of a peculiarity of the Arizona association’s database. Initially, the state was divided into two regions, east and west. Mingus is in the west part. Later, they when more states were added, additional regions with tighter geographic scope were created like North and South Maricopa around Phoenix. I had wondered why some mountains appeared to be missing in the regional databases. Now I know.

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SOTA: W7A/MS-065 Goat Hill

Getting to the top of Mount Suappoa wasn’t too bad, since it’s mostly a matter of following a paved road. For the same two activator points, Goat Hill was much more of a climb. As mentioned, both peaks are in South Mountain Park to the South of Phoenix. In fact, in the picture at right, you can see antennas on Suappoa.

The aptly named Summit Road winds through the park and cuts across Ranger Trail which leads up to Goat Hill. It looks like Ranger Trail is used by both hikers and those on horses, and that some begin lower down on the trail.

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SOTA W7A/MS-048 Mount Suappoa

Since I was only in Arizona for a short time on this trip, I didn’t attempt to acclimate to the local time zone, I just let me biological clock freewheel. The night before this outing, I had gone to bed at 6:30 in the evening, which seemed just fine to me. The flip side of this was then waking up around 3 am. Instead of forcing myself back to sleep, I just started my day. I got some work email out of the way and then began looking through peak information. I found two peaks that had been previously activated, seemed like reasonable climbs, and which were near each other, both in South Mountain Park.

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SOTA W7A/MS-050: The road not taken

I have a few more SOTA adventures to report, the most recent from a brief trip to Arizona. During that trip I visited three peaks, but I wanted first to write about Lookout Mountain, W7A/MS-050. I had reviewed summits on the SOTA database before the trip and thought that this peak was a good candidate, particularly since it has never been activated.

When I flew into Phoneix it was early in the day — too early to check in, so I pointed the rental car towards the mountain. I took 16th Street south of East Greenway up to a parking lot at the base of the mountain; this is the start of Trailhead #308. There is a sign there with some topographic maps and information about environmental hazards.

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SOTA W6/NC-423 (Mount Davidson)

After a week of meetings in Washington, I arrived in San Francisco for a meeting on gastrointestinal cancer that is held every year about this time. In the previous week, I had thought about where I might operate if weather were good and decided on Mount Davidson, the highest elevation within the City of San Francisco, and a SOTA peak (W6/NC-423). I got into town the day before meetings and the forecast was good, so took a bus to the park entrance. For reference, the bus stop is at the intersections of Dalewood Way and Lansdale Avenue. I have to admit that the bus did a lot of the work, as the park entrance itself it at considerable elevation. From that entrance, there is a clear trail right up to the summit. The trail was in good shape, but a bit slippery since it had rained the day before.

There is a sign near the base of the trail that specifies that the very top of the mountain is not owned by the city, but owned privately (but nonetheless is accessible by the public). I worked from a park bench in that area, throwing my end-fedz antenna over a eucalyptus tree just to the west of the bench.

I went in the afternoon, which I thought would give me the best chance of reaching the US East Coast on 20m and perhaps working regionally on 40m. It was a week day and propagation was a little down, and I ended up with about fifteen contacts, which ranged from K6EL’s booming signal from a neighboring hill out to New York. Again, contacts spread evenly between 40m and 20m, with only K6EL hearing my call on 10m. I had meant to try 2m, but left the antenna in the hotel room.

I came down the mountain when it got dark, and while it was a fun adventure to take the bus to the mountain, I dialed up an Uber car when I got to the trail head and was back in the city 20 minutes later. The QSOs have been logged into the SOTA database, but upload to LOTW will again have to await my return to Antananarivo next week.

Here’s a picture from the peak facing North. I like this picture, because I can see my operating positions from previous visits to San Francisco: Buena Vista Park and Twin Peaks.

SOTA W6/NC-432 (Chabot 2 Benchmark)

I thought I would be lucky if I had time to activate one summit on my visit to San Francisco, but morning meetings left my afternoons free, so I activated Mt Davidson (NC-423) as planned but also worked in Richardson East Benchmark (NC-407). Yesterday, thanks to a monstrous amount of snow that shut down airports on the US east coast, I found myself with an extra day in San Francisco. After reviewing maps, reports from other activators and a quick look at weather, I chose to visit NC-432, Chabot 2 Benchmark (what does that mean, benchmark? Why are all these peaks called Benchmark? Is that a west coast thing?).

One of my main criteria for choosing this peak, like the others I visited on this trip, was that it would be accessible by public transportation: I took the BART underground from near my hotel (Powell Station), green line towards Daly City, stopping at Bay Fair. From the bus terminal at that station, I caught the 89 “counter-clockwise”. The bus runs only hourly on the weekends, so I had a bit of a wait. I took the bus to the Juvenile Justice Center, about ten minutes away. I suppose you could walk, but the route crosses a major interstate (580) and there’s more walking to come, so I thought it was worth the $2.10 fare.

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