20 August 2014

Solar lamp experiments

My family owns a solar lamp bought at the popular Swedish furniture shop. Given the amount of light it can produce, all night long, I had to take some measurements to understand how much power the same hardware could deliver to a stand-alone circuit.

What am I thinking of? Something like an off-grid sensor that stores data for large amounts of time before any human intervention.

One doubt was: does the cover influence the amount of light reaching solar panels? If so, how much?

The twin solar panel is used to charge a 1.2 V NiMH battery. I decided to measure the current flow through the battery. The experiment was carried on with the help of my daughter: connect crocodile clips, read the ammeter, put the cover on, ...

The discharge current is just above 16 mA, and the lamp with 4x 3 mm white LEDs is very bright. There is a nice step-up circuit in there. That's 19mW out. A fully charged 2000 mAh battery could keep the light on almost 100 hours.

Having never measured a live solar system, I did interesting discoveries.
Without the cover, in full sunshine and oriented right at the Sun, the circuit pushes 100 mA into the battery (120 mW). Put the cover and current goes down to 80 mA. I didn't expect those small solar panels could produce so much current! But that's the optimum condition and requires something to track the Sun: could it be energetically worth?

What happens on a cloudy day? Recharges at 5 mA without cover, down to 3.7 mA with the lamp cover. That's 6 mW instant power, a huge difference from a bright day!

Another interesting discovery about the lamp was that it keeps charging even if the switch is OFF, meaning that you can let the battery top-up when you don't need the light at night.

In the next episode. Considering a 70% charging efficiency for NiMH technology, how much power can the stand-alone device drain for prolonged use? Would it be worth to track the Sun?

14 August 2014

70 MHz progress - August 2014

Thanks to some amazing Es openings last July 2014, my 5W and Moxon beam allowed me to reach 7 DXCC (I, G, GM, ES, 9A, OH, YO) and 8 different squares.

Few more countries should be possible, even though I probably need to move the antenna to the balcony facing South to work EA and CT. Or build/use a second antenna and run a coax through the whole apartment.

Now that the Es peak is gone I can concentrate in working neighbouring squares, like JN34 and JN45. The only station I heard from JN45 is a big gun and we will arrange a JT65 QSO, possibly with the help of aircraft scatter, because 2x SSB was not successful.

09 August 2014

Arduino CW keyer - current consumption

Before boxing my new CW keyer based on K3NG work, I measured the current consumption since I have not been able to find it online. With an ATmega32U4 (a Leonardo clone) it drains 32 mA, regardless it is powered at 5V or through the supplied regulator (RAW pin). If the power save mode is enabled in the firmware, current in my specimen drops to 3 mA, but the keyer is not functional. I had hoped for lower current.

The embedded power LED could be removed to save few mA.

Conclusion: an on/off button must be installed.

02 August 2014

How to cut potentiometer shaft

I have always been very bad at finishing my projects with a proper enclosure. But something meant to stay like a CW keyer needs a good home. That's the case of my reproduction of the excellent K3NG Arduino keyer. The main challenge for me is drilling holes, and the keyer needs at least 6. I had an unused L-C tuner and its box was pre-drilled too!

When everything was almost inside I noticed something I had forgot: the long pot shaft! The knob on the very top doesn't look too nice, does it?!

No way I would take everything apart, and a quick web search revealed few methods to cut it out. The simplest solution was to use a pipe cutter: no electric tool! I passed over the requirement for a vice, crossed my fingers and started turning around:

At this point I held the lower part with pliers and snapped away the top length of plastic:

The final result is nice and I have a CW speed potentiometer, that is much more practical and immediate than "tap here n'there" methods.

Then another problem arose: the 3.5mm panel plug is too short for the box thickness and I cannot put the nut on!

28 July 2014

Painful discovery about Baofeng UV-82L

Few months ago I bought a Baofeng UV-82L so that I would have a 5W dual-band handheld, since the little UV-3R has been stuck in the car on a fixed frequency.

Seconds after paying it I realised Baofeng UV-82L does not have a DC socket for recharging or powering the unit: it works off the battery and it requires the charging base. Not so practical if you are often on the move, or you don't want to keep the base on the desk all the time.

That said, the transceiver works as expected. Being confined to "memory mode" (without power-cycling it) is not a big deal once local repeaters have been programmed. But yesterday I did a painful discovery. I was checking if a friend was still up on a mountain and I moved around the flat with the UV-82L in my pocket while doing other things. Then I heard a /P station calling on the VHF direct frequency for mountain op's and engaged a QSO with him. During a transmission I felt a mix of burning/biting in my hand holding the radio ... right there where battery contacts are located!

My palm, slightly salty-wet from Summer sweat, was draining current out of the Lithium battery pack. I haven't had time to double-check with a resistor and ammeter, but most probably there is no reverse-discharge protection diode into the battery pack. There is no fix.

Edit. I confirm, positive charging terminal is connected to the positive battery lead going to the radio. Same goes for ground terminal. At least in my BL-8L battery pack.

10 July 2014

Like a child on 70 MHz

The day after Italian HAMs were allowed to use 70 MHz band again for a few months in 2014, I reconnected my transverter and erected the dipole on the balcony. I tuned the band checking the local beacon with my ears and looking at the DX cluter with my eyes: the band was open.
All of a sudden I heard someone distant having a QSO. Disappeared. QSB was very fast. Then another voice, very strong, GM4JTJ, that came back to my 5W SSB balcony signal! Hooray!

I felt like 25 years ago, when as a child I worked my first DX'es on CB channels. I kept tuning, calling CQ, tuning, trying to ignore the female voice(s) calling me for dinner. But this time it wasn't my mother's voice, it was my youngest daughter's reminder that dinner was on the table.

I walked to the kitchen, explained that a unique event was going on, an event that happens 4-5 times a year and doesn't last long. When returning to the shack I got the familiar "don't complain if there won't be food left for ya", this time thrown at me by the older daughter.

It was a funny parent-child-parent role inversion.

In the following days I came up with a quick way to explain propagation. You must have seen Stargate movie to understand it: sporadic-E looks like a wormhole opening to some random part of the world.

Now waiting for another randomic wormhole...

08 July 2014

My Moxon beam for 70 MHz

I like the compact design of Moxon 2-element directional antennas, even if they are harder to build than a normal Yagi. Given the fact that 4 metres in Italy are allowed year-by-year, I do not want to invest in a large antenna, and I believe the gain of a Moxon should be enough to take advantage of sporadic-E openings.

Last year I had started building one and almost forgot. Then yesterday I had a pleasant surprise when I realised that everything was ready to erect the antenna and measure SWR! The only "problem" was how to hold the two wire ends pointing at each other.

Problem solved with two rubber bands cut open and secured to the wire with simple sticky tape!

The H-shaped frame is made of 20 mm PVC pipe screwed together with slightly modified Tee joints.

A huge storm was approaching, but wind was light so I could lift the antenna on the fiberglass telescopic pole on the balcony, measure lowest SWR at 66 MHz (1.6:1 at 70.2 MHz) and take the picture above.

Both local beacons were off-the-air, so I could test the extra gain.

Then the storm came and it offered a good opportunity to experiment with the camera: