Hi - I'm Jack, a researcher with the US National Cancer Institute. I am based in Antananarivo, Madagascar. This blog is devoted to hobby items like amateur radio (my call sign: 5R8SV), electronics, computers and interactive fiction.

Solar CDX

Electronic Load

supply_and_loadIt’s been a chicken and egg race for the last couple months – I was working on power supply projects, but at the same time needed an electronic load so I could test the supplies at known current draws. I have had a working electronic load for a few months, but only got around to making it pretty and boxing it up in the last week. The design that I came up with is not very sophisticated, but it uses common parts and it seems pretty solid. The picture at right shows my recently built variable power supply working into the electronic load.

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Acer X193+ monitor repair

tagMost of my equipment had the sense to wait until after I had moved from the US to Madagascar to fail, but not this Acer Monitor. I had picked it up cheap as a bundled deal with a desktop computer in 2009 from  New Egg Computer, and it failed early in 2014. I had purchased two identical systems at that time, and the other monitor is still working without a problem.

The monitor wasn’t entirely dead – the power LED is still lit up and when power was applied, the word “Acer” would appear for about a second, and then the screen would remain black. This suggested that most of the monitor was working. Since we were packing up for the move, I thought it would be better to box up the monitor and tackle it on the other end after I had a workshop set up. A year and a half later, it came back out of the box.

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Fox and Hound

640px-Two_Vulpes_vulpes_pupsNo, not an article on QRP fox hunts (which I miss, being a bit out of range), but a construction project to make a pair of devices for tracing down wiring. The fox sends a tone down a wire and the hound sniffs around until it finds the right wire by detecting the tone. I found some commercial versions online at a reasonable price, but there isn’t much to these devices, so I figured I should be able to put them together from parts lying around. In what has to be one of the few examples of truth in advertising still to be found on the web, I came across neat circuits for these devices on neatcircuits.com.

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40m Delta Loop

590px-Pythagoras_similar_triangles.svgThe rainy season runs from about November and sometime up to March, with peak cyclone activity at the height of summer, January and February. As a preventative measure, my next door neighbor trimmed one of the trees along our property line. I had some ropes in that tree to support a G5RV and when he gave me the heads up that crews would be whacking away at limbs, I thought it best to bring down the antenna. The G5RV never really hung high enough to work well and it stretched over the house, which may have added to noise, so I didn’t mind taking it down. Last week, I put up a new full wavelength 40m delta loop as a replacement.

I went with the delta loop because there is one large pine tree at the edge of the property and I was able to shoot a line over it with a wrist rocket. The lower corners are supported with guy lines from a telephone pole and another tree to each side of my house. The antenna is fed at the middle of the base, which is just at the edge of my roof, which makes it convenient to access. I had brought back a 50m roll of heavy duty green wire from Sotabeams in the UK. I have to remark that working with this very compliant wire was a pleasure after having made wire from household wire that loves to coil in the past.

By virtue of the position of supports, the antenna slopes from bottom to top towards the south, a bit more vertical than horizontal. Since I am feeding it from the bottom, the antenna polarization should be horizontal, but I believe that the sloping should add some directivity towards the North. I had considered feeding it up one side and using a quarter-wave of 75 ohm coax to transform the expected 100-ohm feed point impedance, but it would have been awkward to support a feedpoint at that position given what I had to work with.

I initially cut the antenna to a literal full wavelength, 299.8/7.1 * 1.05, where 1.05 was the fudge factor supplied in the ARRL antenna handbook. Initially, the resonant point was 6.9 Mhz, so I shortened the antenna in a few iterations, arriving at the intended 7.1 Mhz, where there was no reactive component and the resistive component was about 65 ohms — close enough to 50 for me to be happy to feed directly with 9913F7 coax and not worry about vSWR.

From the shack, the antenna works great with no tuner across 40m, but I don’t have a lot of experience at this point with regard to how the antenna performs. It is much louder on 40m than the hex beam, but most of the time that loudness is merely more noise thanks to the environment around the station.

DXPeditions: VK0EK and FT4JA

I am not an ardent DXer, but when an entity is only on the air every couple of decades, I’m willing to give it a try. Due to it’s remote location, Heard Island fits that description. Likewise, operation from Juan de Nova is not all that common, particularly as the Scattered Islands are the subject of a territorial dispute between Madagascar and France (and perhaps the Comoros would like a piece too).

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Immediate feedback from real time logging on the VK0EK website was very appreciated. I saw a CW contact recorded as HR8SV and was able to correct it on a subsequent attempt.

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SOTA: Christ Cross, G/DC-005

No pictures of the SOTA peak, but I will add this one of the inn where we stayed just North of Exeter, the Barton Cross. Despite proximity to Exeter, it has a rural feel and was by far the best hotel that we visited in the UK.

No pictures of the SOTA peak, but I will add this one of the inn where we stayed just North of Exeter, the Barton Cross. Despite proximity to Exeter, it has a rural feel and was by far the best hotel that we visited in the UK.

After winding up some narrow country lanes, this summit is behind a metal metal gate tied shut with rope. A rutted (and at the time muddy) dirt road leads back from the gate towards a cluster of commercial antennas that are on a bit of land only marginally higher than the flat plateau around it. I did walk to that site, but decided that I would do better to work from just across the road where I had parked.

I did not have a lot of time on the way back from Exeter towards London, so I thought I would try my luck on VHF before throwing the HF antenna up over a tree branch. I scrambled up a low wall, held the radio up, and made calls on 2m FM. I got two quick responses from stations about 25 km away and they also worked me on SSB. I continued calling on 2m until I landed my four stations required to make this an official activation. Towards the end, my arm was getting tired, so I rested the bottom of FT817 on my head to the amusement of passing drivers.

I swapped in the FT817’s 6m vertical antenna and tried calling for about 10 minutes, both voice and CW (try working CW with paddles magnetically mounted on the radio which is on top of your head — it is a challenge). No 6m contacts have been logged from the peak, so I was hopeful, but it wasn’t to be.

SOTA: Garth Hill GW/SW-034

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Daughter, mast, cows, sky.

To be honest, we had hoped to visit the Dr. Who Experience while in Cardiff, but the only way I could make the travel schedule work put us there on a Tuesday, the one day of the week when the exhibition is closed. We had some time on our hands later that day because the next stop in Bristol was not that far away, so after steeping ourselves in a bit more Cardiff culture, we headed for the hills.

Garth Hill is the high point near Cardiff, and is accepted to be the subject of the movie “The Englishman Who Went Up A Hill But Came Down A Mountain“. Colm Meaney was in the movie, so even though we missed a Dr. Who connection, we managed to have a Star Trek connection. [Okay, for purposes of full geek disclosure, in fact, the movie does have a Doctor Who connection in the sense that it starred Hugh Grant, who played Dr. Who (briefly) in a parody sketch, the Curse of Fatal Death].

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SOTA: GM/SS-280, North Berwick Law

Entering North BerwickLast month, I spent about two weeks in the UK with my daughter Lara looking at universities. We put about 1800 miles on the rental car and visited schools in England, Scotland, and Wales. Originally, Scotland wasn’t on the itinerary due to time constraints, but we ended up not only visiting the University of Edinburgh, but activating a summit just north of Edinburgh in North Berwick.

Easter weekend was right in the middle of the trip, and I had picked that downtime to visit the Isle of Man. By that part of the itinerary, we had already gone north to U. Nottingham and then west to Bangor. Along the way, we routed through Macclesfield to visit SOTAbeams and picked up a ten meter fiberglass travel mast and some other kit.

From Bangor, it wasn’t too far to Liverpool to catch the ferry over the Isle of Man. Unfortunately, the ferry hit the pier in Douglas the night before our departure. When we got to the ferry terminal on Friday morning we were told that the ferry was temporarily out of commission. I spent the next half hour tapping away at my phone in the ferry terminal car park, calculating what other interest places we could reach and then booking a hotel in North Berwick. In the back of mind, I was hoping to get on the air as MM/AI4SV, but I didn’t have any SOTA peaks in mind.

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HMS Belfast – GB2RN

IMG_20160322_101315I’m just back from visiting the UK with my daughter, Lara, who will be applying to universities there this Autumn. In a two week tour, we put 1800 miles on our rental car. I had some chance to play radio along the way, but our itinerary was so packed that I’m just now putting the details on the blog. Let’s start with the visit to the HMS Belfast, which is anchored on the Thames between Tower and London Bridges.

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Variable Power Supply

boxedUpI’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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