29 December 2013

New handheld ordered: Baofeng UV-82L

I couldn't resist and ordered a Baofeng UV-82L VHF/UHF handy. This time I bought within European Union, so the parcel will come without passing through Customs with their unknown processing time.

Right after paying for the new RTX I realised that it is missing something I consider important: a socket for DC input. It is either powered with its own battery or nothing.

This means that I will need a second battery for prolonged activity. It also means I will have to carry the charging base around.

I hope the transceiver performance makes me forget these design flaws (IMO).

06 December 2013

Does weight matter?

Having lost my one and only BNC-to-N adapter, I had to find a replacement. The third local shop I visited (still) had them. A bit pricey, but readily available.

I had not handled too much the previous adapter (BNC-Female to N-Male), but these feel lighter. So I weighted them at 22 grams each. I have no means to evaluate their quality.

If weight is a synonim of quality, how much do your BNC-F to N-M adapters weight?

Note. These will be used for my RTLSDR receiver and in case of emergency when a proper coax is not available. If I will ever own a device with an N output, I will build a properly N-terminated coaxial cable.

04 December 2013

On the market for a new handheld

Now that the UV-3R has become my single-channel car RTX, I am missing a VHF/UHF handheld for casual use. Of course the UV-3R can be dug out of the car, but it feels so comfortable in there. So I am on the market for another RTX under the 50€ price tag (70 USD).

UV-3R. While I love that little radio, even newer versions have not improved much. Cost has been stable around 30-35€ (Far East eBay price), while I was hoping/expecting a reduction.

UV-5R. This seems a decent and widespread upgrade for an UV-3R. It costs just 2-3€ more than a UV-3R, but I really don't like its look! Except that it comes in multiple colors (yellow being a field-day favorite).

UV-B5. UV-B6. These two look much nicer than an UV-5R but they have no CE/FCC certification (AFAIK), cost more and there seem to be little support.

UV-82. This is apparently a new model. Its price falls just within my 50€ limit and available feedback online has been positive. Like B5/B6 there are still few of these around, but it should be FCC approved

The drawback of these models is that their antenna connector and speaker/mic are different from the UV-3R I already own. This means I will need a different BNC-SMA adapter. Well, this seems to be a market standard for big brands, so I won't complain much for a gained interoperability with others' equipment.

25 November 2013

Monitoring transverter output

Without a correspondant to try a QSO on the air, I had to test my 70 MHz transverter output with my own equipment.

First of all I used the RTLSDR dongle to record my output, so that I could easily play it back afterwards for a self-audio-quality check. Easily done, with the transverter transmitting into a dummy load in the shack.

Then I wanted to check for harmonics at 2x, 3x and so on: the RTLSDR tunes much higher than that. So I moved the output to the 70 MHz dipole and started calling CQ, while RTLSDR receiver was running on the computer screen. Look at what appeared:

That's the fundamental and two noticeable splatters about +/- 200 kHz away, about 30 dB below the center frequency. What the ...?!??

Checking at 140 MHz and 210 MHz the remaining signal was not too strong, spurs obviously following. If I transmitted in FM there was no splatter whatsoever, nowhere.

That's when I remembered an article by SM5BSZ about the (mis)use of ALC in the FT817 (search for "The abominable ALC"), which creates heavy splatters, especially at lowest power settings. While they are barely noticeable in the HF noise, they pop up in VHF and do annoy neighbouring stations!

So I checked the FT817 output at 144 MHz USB, 0.5 W output, and spurs were there. No surprise. My RTLSDR does not tune down to 29 MHz, my 4 m transverter IF output, but I bet the situation is not different.

Since you always have to doubt the bounty of your test equipment, and a 15 USD TV dongle should not be over estimated, I cross-checked with a true receiver: splatters are generated for real.

A quick check at 5 W output has shown that the FT817 doesn't behave acceptably better. One solution, that would improve my '817 in any case, is to change the ALC timing with a hardware mod. Otherwise I will have to drive the transverter with the IC706MKiiG, but SM5BSZ pages contain a warning about a full-power spike when PTT is pressed...

19 November 2013

Transverter PA: self-oscillation solved

Fortunately it took little effort to tame the self-oscillation in the (PA?) 10-to-4 transverter. First troubleshooting action was decoupling the DC supply to the whole transverter board. I used a PI network composed of 2x100nF, 2x1nF and one VK200-like inductor.

The inductor goes in-line with the positive voltage. Then 1nF//100nF at each side of the RF impedance.

If you land on this page for a similar problem, don't go crazy looking for the VK200 choke. Try winding as many turns as they fit on an anonymous toroidal core recovered from some switching PSU, or a molded inductor or whatever will exhibit enough inductance and low enough DC resistance. I used disk ceramic capacitors.

But it is not the end of the story. [Note to the casual reader: what follows applies to this specific transverter board]

After correcting the self-oscillation, current drain was above 40 mA. Not bad, but I had measured 24 mA.
When I connected back the transverter PTT control to Arduino, the XV went into TX. This means that the 5V from Arduino is not high enough for the transverter circuitry. I added a BJT buffer and everything went back to normal. I just needed to update the sequencer firmware.

On-the-air test to follow!

18 November 2013

Transverter boxed. PA self-oscillates

The Ukrainian 4m transverter has been installed into the final box, including IF relay and A*duino sequencer. The container is a repurposed manual KVM (Keyboard, Video, Mouse) switch and pre-drilled holes hold flanged BNCs just right. Also the VGA connector was a good a sturdy way to bring data from the FT817, pre-wired:

The smoke test did not produce actual smoke, but the current drawn is close to 1A. Considering the transverter should be in receive mode, that's not normal. Leaving it on a few seconds the Mitsubishi PA final warms up, so it is probably self-oscillating somewhere.

I have never troubleshoot a self-oscillating PA, just quickly read about it. I am thinking of two causes: either the DC supply cord is too long and lacks decoupling or the transverter board is too close to the box/ground.

13 November 2013

System Noise-Figure Analysis for Modern Radio Receivers (link)

One guy at MAXIM Integrated has published an interesting paper about System Noise-Figure Analysis for Modern Radio Receivers. There is a little math and examples of measurement on DSB and SSB receivers.

And don't forget to check their Tutorials area (linked in the page above), with other interesting writings.

All well worth a read.

12 November 2013

Transverter sequencer with Arduino

Even if not explicitly mentioned, I decided my 70 MHz transverter needs a switching sequencer. Any existing solution I could find online uses either discrete components and ICs or a microcontroller I cannot handle (PICxx series).

Given the widespread availability of Arduino derivatives, their low cost (< 10 USD) and their extreme flexibility, I preferred to go down this route. Besides, an Arduino board allows for easy firmware changes (just plug it to an USB port of a computer!) and can be programmed for CAT communication with the FT-817 and alike (FT-857, FT-897, FT-100).

The sequencer code uses a level change interrupt (on INT0) to monitor the PTT line output on the CAT port ("TX GND"). This line goes to logical low level when the PTT is pressed

Once a transition RX-to-TX is debounced and detected, the main loop switches in sequence the IF input attenuator (not needed in RX), the transverter PTT and enables RF output on the radio (pulling down the "TX INH" line). Small delays allow for each change to be applied by the involved circuitry, being the relay the slowest to react. The TX-to-RX transition reverses the sequence described above.

At startup the sequencer inhibits RF output and configures itself in RX mode.

This is not rocket science at all.

If another output is needed it is just a matter of adding few lines of code. An extension to the code should allow to switch the RTX to the IF center frequency (29.200 MHz USB in my case) as well as make sure the FT-817 RF power is the lowest possible. Then drive a status LED, monitor the transverter PA temperature, ...

05 November 2013

Transverter 29/70 TX'es fine

In a careful hurry I checked the 4 m transverter if it is suitable for SSB traffic.

Since it must be driven with 100 mW, a 7 dB attenuator was built so that FT817 500 mW would not fry the mixer stage. A "real-world" 7 dB Pi-attenuator consists of a 2W 120 ohm resistor across, 47 ohm straight, 120 ohm across. I used standard carbon resistors and a quick check with MFJ-259 reported a 1.2:1 SWR max up to 170 MHz.

With full manual switching I listened to my whisper transverted to 70 MHz on a different receiver and it sounded good.

This was the "GO" signal to start planning for a sequencer (probably embedded into one of my I-F-R-K accessories) and a suitable box: this time I will have to do the mechanical work!!

03 November 2013

Near Field Communication recycling

I have attended a speech at the local Linux Day 2013 about Mifare Ultralight NFC ("Near Field Communication") cards and implementation bugs that render the system vulnerable to some "attacks" (now fixed, too late ;-) ). They were at DEFCON 2013 too.

These cards operate at 13.56 MHz and can carry some data as well. They are being widely adopted as electronic tranportation tickets, access badges, ... Since they come with a factory programmed unique ID, some DIY recycle is possible at almost no cost.

The speaker has described the data memory map of those cards and explained how some bytes are one-time programmable: once a bit is set to "1" it cannot be returned to "0". That is how some transportation systems keep count of used/available tickets on the card. The data area remains rewritable and the unique ID cannot be changed.

Reading (writing) these NFC tags is pretty cheap (about 20 USD@2013) and can be done with a computer or an Arduino(-like) board. Of course some sort of software is needed to interact with the reader hardware and the card.

Since I am curious about this technology I have ordered a card reader/writer at least to see what kind of home applications can be tought of. A poor man's presence detection, for example, or an authorization system for you-never-know-what.

It is QRP afterall :-)

29 October 2013

Transverter 29/70, RX current consumption

I found no mention online about current draw of the Ukrainian 29/70 transverter: my specimen drains about 24 mA at 12V in reception.

More to follow, especially a TX test once I found what is a suitable heatsink: just the containing box (yet undefined) or something larger?!

If everything works, the construction of a simple sequencer will follow. Most probably based on one of my (I)FR(K) projects.

27 October 2013

Transverter 29/70 arrived and switched on

The "ten to four metres" transverter has arrived from Ukraine. The very first impression is that it is indeed SMALL! A picture-to-real comparison with the original 10-to-2 m transverter shows that coils are different, so it has somehow been retuned to 70 MHz. Look at it on a 5€ note:

First on-air test was the reception of the local beacon. I started closing the output on a 50 ohm load "just in case" (yes, I know the load shown is not able to handle more than 0.5W). Then about 4 m of RG58 going to the FT817 tuned on 29 MHz: the local beacon was coming through S7, with the dummy load as antenna! Actually, dummy load or not, it made no difference.

The transverter circuit is very very very simple (and I have spotted one error on the included diagram), but the RX chain is hot. Using the same coax length on the IC706 tuned to the beacon frequency resulted in the same signal strength. So, apart from RF leakage, it is a (good?) sign of life.

14 October 2013

Packed up RTLSDR

A local HAM agreed to compare his 23 cm transverter with the RTLSDR in order to see if the little stick can be competitive in certain situations, like a contest. So I needed to do some adjustments to my typical home setup.

First of all, his cables terminate with N connectors. I initially though of changing the short RG174 cable end into a female N, but quickly realised how weak the whole system would be considering the weight of N and in-flexibilty of thick coax. I needed to protect the dongle with a box.

I picked a metallic chocolate box I kept aside some months ago and fitted a flanged N female. While I was at it I also shortened the RG174 cable to what was strictly necessary (1 metre to 10 cm): these two actions resulted in at least a couple of dB gain (or ... "less loss"). Note that 1m of RG174 at 1300 MHz looses 1 dB.

The USB hole is not something I am proud of, but it was realised in less than 5 minutes, so it is acceptable for this experiment. If the on-the-field comparison shows RTLSDR is a decent performer I will consider soldering directly into the PCB both the USB cable and the N or BNC female head.

01 October 2013

Transverter 29/70

While searching online for parts for a 70>23 cm tripler I came across an auction for a 10m to 4m transverter board. Just the fully assembled board and an A4 sheet with instructions.

It is supposed to output 5W on 70 Megs with 150mW drive on 29 MHz. It should be all-mode. It needs a heatsink, housing, wiring, IF attenuator and RX/TX sequencer.

Looks like a good companion for the FT817. Time will tell, since I bough one of those.

Edit: (At the time writing there is one board left in Ukraine)

29 September 2013

Transmitting on 23 cm (thinking of)

After one year of SWL'ing on 23 cm I feel I would like to have a QSO up there. Besides buying a transceiver for that band, another option is a transverter. Current DB6NT catalog lists a 144 to 1296 transverter for 425€ built, or 199€ in kit (SMD). But how about a simpler solution? I came up with:
  • a Si570 generator/kit, at 60€ or so, and it requires a power amplifying chain
  • a frequency multiplier
While checking if any of my XTALs or canned oscillators would fall within 1296 MHz, it occured to me that 1296 is an integer multiple of 144 and 432 MHz. This observation led me to explore the almost forgotten world of multipliers and I met the varactor component.

A varactor is a sort of high power varicap diode which is able to return a signal tripled in frequency with a 35% efficiency, all with passive components. FM or CW only. Since I own a 30W UHF transceiver, I potentially have a 10W CW 1296 MHz transmitting chain. I think this technology has been almost forgotten, while today it would allow many amateurs to give 23 cm a try.

A quadriband transceiver will transmit on 70 cm (or at least 2m if using a 5x multiplier), and they are very popular => no additional cost.
An RTLSDR stick will provice wideband 23 cm coverage for 20 USD.
A computer is then needed as part of the receiver, but I would say most HAMs own one => no additional cost.

So, for the cost of a RTLSDR and a varactor multiplier you can be active on 23 cm (CW/WBFM). Not bad.

24 September 2013

Inside Gould 4072 DSO - bottom side

Out of curiosity (and giving a shot at troubleshooting the item), I opened the bottom lid of a Gould 4072 DSO. Top view has been studied back in 2009.

The darker board consists of analog signal processing circuitry for the two input channels, while lighter green PCB carries flat connectors and interconnections for top-side boards. Fortunately this side is not subject to forced air cooling, so it has almost no dust accumulation and its side effects.

Edit 2014-02-11: I do not own anymore the Gould 4072.

13 September 2013

Gould DSO 4072 startup sequence

Filmed mostly for future self-reference in case it breaks: the startup sequence of a working Gould 4072 DSO as seen by the "operator":

Just plain through-hole technology from 1980's.

Edit 2014-02-11: I do not own anymore the Gould 4072.

03 September 2013

Breakfast with chamois

The old road.
Woke up at 5:30 (local), had a quick breakfast, drove 30 min up to a mountain pass and started hiking.

In about 30 minutes lone walk I joined a family of chamois having breakfast. The telephoto equipment was finally put into outdoor use.
Can you count them?

They followed me as I proceeded to a nearby peak.

I got few blowing warnings to keep the distance from them. My excursion ended on a SOTA peak and two FM contacts, but I was not chasing SOTA points.

It was really nice to be part of (almost incontaminated) Nature.

Here is a link to the area of my excursion: L'Alta via dell'Assietta.

26 August 2013

Li-X charger circuitry

The RF noise and the extreme heat noticed during the very first use of this B3AC charger convinced me to have a look inside. Four screws hold the plastic case together, so it's really easy to open it up.
The PCB is a mix of through hole components and SMD parts. Near the AC socket is what looks like a switching mode power supply (SMPS). The RFI filter is not missing: it was left out on purpose since no provision is made for its components! The SMPS continues after the transformer. So far no smart charging circuit was met.

Moving to the bottom layer of the PCB, SMD parts appear and three SOIC8 chips are amongst them. The marking is easy to read: 5056. A bit of googling brings up the XA5056 datasheet from Xinna Semi. This chip is rated for 1A max current and "Mystery B3AC" exploits it for all three chips.

I tried a recharge with the box open (don't try this at home!) and measured temperature on the three 5056 and the PCB. In a minute or so IC surface was measuring 70°C (158F), which is about +40°C above room temperature. No wonder the whole thing gets hot!

XA5056 chips are configured to push 1 Amp into cells, meaning 12W (4V * 1A * 3 cells) must be dissipated somewhere. That value is configured with R2 (ref. datasheet) of 1500 ohm. I am considering of increasing it to 2000 ohm, so that charge current decreases and overall temperature doesn't go too high.

By the way, this chip looks similar to big brands product(s), even the datasheet gives clues... but I haven't found yet the equivalent.

18 July 2013

XT60 connectors

After assembling my own Li-X battery packs I realised I needed a safe way to use their energy, and finally solve my fear of inverting DC polarity of my 12V power cables.

Discussions on some mailing lists I read mentioned Anderson Power Poles and XT60 pairs. I went for the latter and ordered 20 pairs, which should be enough to wire all my polarity sensitive devices.

09 July 2013

Windows 8.1 and Bluetooth SPP

According to recorded videos from //build/ 2013 conference, Win8.1 will support (again) I/O devices. Fortunately MS offers a Win8.1 Pro preview installation ISO (lasts until January 2014), which does work on VirtualBox VM, so I could quickly test it out.

Even though I didn't spend more than 5 minutes fiddling with it, (virtualised) Win8.1 could pair with the CAT-to-BT adapter (HC-05 derivative), correctly assign two COM ports and Ham Radio Deluxe connect to the radio.

The whole process still seems a bit buggy as OS level, but at least this kind of I/O will be possible with newer computers too.

08 July 2013

Windows 8 and Bluetooth SPP

Bluetooth-to-CAT dongles for FT-817/857/897 use the Bluetooth SPP protocol ("Serial Port Profile") which does not seem to be available on MS Windows 8. At least in the preview version I have been able to try (Win8 Enterprise build 9200).

Device is found. Pairing with PIN works, a "serial-in" and "serial-out on Dev. B" device are created but no COM port is allocated on the system, therefore the serial-over-Bluetooth device is not reachable from the PC application.

Serial-over-Bluetooth HC-05 device is found and paired. But then...
Is this a Win8 limitation. Has it been solved with newer releases? Comments (moderated) are open, please write your experience if you land on this page looking for Win8/SPP information.

25 June 2013

Li-X charger, first impressions

The Li-ion/poly charger finally arrived from China. At less than 10USD shipped I expected it to get the job done and nothing more.

In 10 minutes I threw together a 3S 2200 mAh pack and started charging. Cells were highly unbalanced and had been restored from the deep sleep state with a constant voltage about one month ago. They measured something like 3.2 and 3.6V unloaded.

The "Mystery B3AC" charger reports a worrying "do not leave charging unattended". It should charge a 3S pack at 1A and 2S pack at 1.5A.

I was listening to 2m SSB when I first plugged the battery pack and a strong QRM appeared. Uh! Oh! The charger is absolutely NOT RF-friendly! (No, I haven't checked if the noise was coming through the antenna or the PSU) I looked every now and then what was happening in the shack, without monitoring the actual DC current flow. The charger temperature was high, it was smelling too. I couldn't almost keep my hand on it.

Nevertheless, about two hours after charging, first LED turned green, shortly followed by other two. Temperature returned normal.

Next step will be to power the FT817 with this 11.1V (nominal) pack while studying the charger circuit.

So far .. no fire.

19 June 2013

2m ES opening - antenna

Yesterday I didn't use a high-end antenna for my sporadic-E QSOs, not even an antenna in a good position!

When propagation helps, a big antenna is not needed. Of course I could not hear everything that was on the band, but I worked what I could hear.

Given the typical figure-8 dipole radiation pattern, I wonder if I should have installed it vertical. Original polarization is lost when the ionoshpere reflects our signals, so for ES DX-ing you don't need to match with the correspondant. "Same polarization" is true for (almost) line-of-sight contacts and, probably, tropo.

18 June 2013

2m ES opening

I was home this time! A strong sporadic E opening reached 144 MHZ today. I could hear DX traffic on the rubber duckie antenna, indoor.

How to participate, since I have no antenna?! Laying in the shack was the dipole of my homebrew VHF yagi. I quickly hanged it outside on the HF antenna fishing rod support, fired up the IC706 at 20W RF and worked two stations at 1600 and 1200 km distance (SSB).

In DX terms that counts for two squares and two DXCC entities. Probably only one of them is a new-one for me (but do I really care?).

15 June 2013

Da b0mb :)

This battery pack worries me, and I created it!

You are looking at a 4S(1P) Li-ion battery and charging electronics assembled out of parts from an hp/Compaq battery pack.

Five wires run from cells to the charger, which are used for charge balance. Since cells were already partially charged I had to be very careful not to short wires together. Next time I will solder first on the PCB side and then to the cells!

Charging at 1C (> 2 Amps) heats up cells. At one point the charging electronics was drawing 250mA into a couple of SMD transistors, which got pretty warm. I have no idea why that happened, because re-applying the power restored the charging process.

Once again charge was stopped at 4.0x V per cell, with a light unbalance. The bq2060 chip reports 80% charge, but that's probably computed from its past "experience" with other cells.

Next step will be to evaluate residual capacity, both of this 4S1P pack and the refurbished 4S2P. I don't have a costant current load so I will stick to a 12V car lamp and stop discharge at 3.2V/cell.

12 June 2013

Packing it up

Once I found out the electronics inside battery packs is a balanced charger, all was left to do was to assemble a 4S2P pack out of the 24 Li-ion cells I got. Metallic strips that keep cells together can be easily soldered, which eases the construction of a sturdy energy reserve.
My "refurbished" pack.

I opened carefully the third pack so that I could reuse at least the lower part of the case, as a container for the 4S2P battery. Working with an open pack allows you to check voltages across single (group of) cells, so they can be characterised and, in case, replaced.

Fed with 18V, "the thing" drew 1.8A for a rather long while (hours). Then it stopped at 4.0V per cell without heating. The pack now measured 16V and the charger electronics reported 100% charge even after the night at rest.

Meanwhile I located the datasheet of these cells, and they seem to be Lithium-Cobalt batteries, a technology rated for 1C discharge current (ref. "battery university" website). I hoped for better, because they might not sustain the FT817 at 5W :-) Also, the datasheet calls for protection circuitry in case cells are paralleled together, while this high brand battery pack did not carry any!

Now I need a DC lamp to discharge the pack and test a full discharge-charge cycle, to get an estimate of the residual mAh capacity.

06 June 2013

Electronics inside a laptop battery pack

Please meet the electronics inside a Li-ion laptop battery pack! There are two boards. Larger one has the smart charger IC (bq2060), five status LEDs, MOSFETs for charge control and other discrete components.

Smart charger circuitry.
The smaller connector board has 5 lines, out of which I could identify 4 and use 2: positive and negative battery pack leads, that are bidirectional (charge and discharge current flows there). Electronics on this board looks like a level converter for serial communication between the computer and the pack.

Connector board.
This setup works perfectly even without the small board, thus connecting directly to red/black thick wires between the two PCBs. I don't need the connector, nor the data communication feature: I want to recharge the pack and use its energy.

03 June 2013

That's a fully featured charger! Sort of.

My venture in recycled Lithium battery packs has now brought my attention to the electronics hidden inside those expensive energy bricks.

A positive discovery was that if the battery pack circuitry is fed enough voltage (i.e. higher than pack fully charged V), cells get charged and balanced. Even without a computer attached. Cool! This means I have a balanced charger for 4s(2p) packs. At 14.8V they are too much for the FT-817 (even 16.8V at full charge!), but some uses would eventually come up.

Further inspection of the electronics led me to the datasheet of the charger heart chip: TI's bq2060. Reading the 59 pages datasheet here-and-there, it turns out that the chip is a smart charger that knows the whole history of its companion Li-xy cells. Not only it charges and balances the pack, but it keeps it in shape during storage and offers a lot of telemetry information like remaining energy and time, number of charge cycles, ... All this is achieved with a plethora of configuration parameters stored in an attached EEPROM.
It is possible to communicate with the chip and, if it is not locked, to review vital cell information (to make it look as new), but so far I have not found someone who shared the code for Arduino or in BASCOM-AVR or C. Not worth the effort writing my own, anyway.

Now what? While I wait for the 2s/3s charger to arrive I will try out this electronic "device" and recharge a DIY-assembled 4s2p Li-ion pack out of it. At least I will be able to evaluate the actual remaining capacity of what I've got (for free).

27 May 2013

3v7 pocket heater

Everything was looking fine while trying to revive a single 3.7V Li-ion cell with my probably safe(*) method. Cell and voltage regulator were warm to touch, but it's also pretty cold in here these days (20°C in the room). When I disconnected the constant voltage source the measured voltage was 3.6V or so, showing a revived cell. My "procedure" calls for further checks of the open-circuit voltage,whenever I pass by the shack.

Thirty minutes after removing the charging current ... voltage across the cell was 0V and it was warm! Obviously it was self-discharging fast, producing heat. I moved the battery outside on a flameproof surface and let it exhaust the charge before hitting (gently!) the battery recycle bin.

(*) Feeding the cell with 4.0x Volts for 15-30 minutes while monitoring the current consumption to be (well) below 1 Ampere. This procedure should not (further) damage the cell and/or risk to set it on fire. YMMV.

21 May 2013

Anatomy of a laptop battery pack

Three packs at different stages of dismantling
After successfully reviving 7 out of 8 Li-ion cells (3.7V, 2200 mAh), while waiting for the balanced charger to arrive from China, I started working on pack #2.

In this post I will show how these three packs look like. Inside a pack there are 8 cells, in parallel 2-by-2 (marked in violet). Hidden on one side there are a lot of electronics and taped between two cells a thermocouple.

Zooming in pack internals.

In pack #2 at reachable joints I could measure some 3.6V, so perhaps these cells do not need a restoring current. Disassembling is next.

Cells from pack #1 still hold the partial charge and I am optimistic they can be turned into a set of working battery packs.... when the balanced charger will arrive.

15 May 2013

First experiences with Li-ion cells

I have been curious for a while about Lithium based rechargable batteries, and how I could get to play with them without investing too much money. Yesterday I was given three identical exhausted HP laptop batteries, marked to be 14.4V 4400 mAh, Li-ion. Not having a way to try a recharge, a disassemble was strictly necessary.

Those batteries even have 5 LEDs that show the charge level, and of course they were reported as dead. Once open I was presented a series of two elements in parallel, 4 each: 4s2p, and a lot of electronics. 
Meanwhile I had read something about these batteries at batteryuniversity dot com and I learned that:
  • to protect cells from overdischarge, then internal circuitry disables the cell, resulting in 0V across the poles; the cell can be reactivated with a charge current
  • Li-ion cells can be recharged with a constant voltage not higher than 4.20V, with a high current, even equal to C [cell's capacity], for the right amount of time
Each of my eight cells, left uncharged for an indefinite amount of time, measured 0V. So far so good. I threw together a 4.04V 2A voltage source and, while monitoring current (DVM in the picture) and voltage (analog voltmeter, not in the picture), I started charging each cell one-by-one for 30-45 minutes: in my opinion this is a safe time that does not pose the risk of (literally) blowing the cell. YMMV.

First cell went fine. After the initial 1.5A spike, it charged at 400 mA (and decreasing, 310mA on the DVM at picture time). After 45 minutes it had reached 3.8V and held it for hours with a slight decrease to 3.7V. Looks good.

Second cell was a surprise, since it initially behaved as the first but then went short circuit! Since it was unattended, I found a pretty warm regulator and cell when I checked in 10 minutes. Current was 3.5A. Maybe this cell was the faulty one in this battery pack?

Lesson learned: add a (resettable) fuse in line so that cells can be left unattended and, if they go short circuit, nothing blows or melts.

Third cell was better too. I will continue with the 45 minutes cycle to see if I can revive these cells. Having 3x8 = 24 potential Li-ion cells for free is interesting, but most important I can learn something new.

08 April 2013

23cm biquad and coax

After a long a careful theoretical planning, I moved the 23cm RX-only biquad antenna in a more permanent location, not obstructing the view out of the balcony.
Since the antenna is now closer to the coax entrance into the shack, I could shorten the cable: what a better chance to take a couple of measurements?

After fixing the antenna in place I fired up SDRsharp and tuned the local 23cm beacon. Its carrier was peaking -40dB (relative). Then I cut at least 4 metres off the coax cable (unknown 75 ohm), re-soldered the TV-plug at the shack end and measured again: carrier now peaks at -35 dB (relative). That's about 5 dB S/N improvement.

Lacking proper instrumentation I cannot certify the gain is due just to the shorter coax, or to any other factor like: impedance match (remember my antenna R+jX was never measured), better coax-to-connector(s) junction, ... In any case apparently now I have 5 more dB of RX "power" for the next 23 cm event.

I am still after a simple method to remotely turn my antenna over a 90° range (max). I have few ideas but they are mechanically too complex for my time and tools.

23 March 2013

UV-3R and external power sources

When a charged battery is inserted into an UV-3R, the radio powers up automatically. This doesn't occur when the battery is inserted, radio is OFF and the charger is plugged: the radio begins charging the battery.

The good news (for me) is that the radio (UV-3R mkI) powers up automatically also when there is no battery inserted and an external power source is supplied.

I am planning to install an UV-3R in the car to access the local UHF repeater. I don't need to change frequencies or touch the radio controls: just wear the headphone/hands-free and talk. This way I will get the radio up and running together with the car.

In order to reduce 12V of the car battery to about 4V I will use a recently acquired DC-DC switching step-down module (variable voltage, 2 amps) and throw everything into a small box under driver's or passenger's seat.

And REMEMBER: on UV-3R tip is NEGATIVE!!!

21 March 2013

New Italian prefixes

Those of you that spend time on the air will, sooner or later, notice an increase in IUnxyz stations.
While it is not a brand new prefix, since it has been used in the past for special/contest stations, "IU" has been allocated for new callsigns once the "IZ" series runs out of letters.

Greet these HAMs with a warm welcome!

26 February 2013

A container for 23cm biquad antenna

There is a bit of local activity on 23cm and the RTLSDR dongle allows me to receive that HAM band. An improvised indoor dipole brought in few interesting signals, increasing my interest for 1296 MHz. I have already built a biquad antenna, which needs a (cheap!) housing before being installed outside.

My biquad size is about 20x30x6 cm and I have had troubles locating suitable plastic containers in the kitchen department of local supermarkets.

During a visit to IKEA lower floor I spotted the SAMLA series of plastic transparent containers. The 11 litres one is large enough to host my biquad (38x28x14 cm) and it costs 1+1.75 = 2.75€ (lid+box).

The antenna will go on the internal side of the cover, which is easier to work on and cheaper in case the experiment fails. In that case the SAMLA container will be repurposed in the house.

13 February 2013

RTLUSB in VirtualBox virtual machine

Months ago I was advocating the creation and distribution of a Linux virtual machine image with pre-installed software for RTLSDR work (drivers and end user applications). The release of Zadig and SDR# for MS Windows has quickly obsoleted my idea. But how about running the whole SDR thing within a virtual machine? Would the "virtual USB" software layer be fast enough to pass through RTLSDR IQ samples?

A test within the virtual machine is quickly done with the rtl_test.exe utility distributed with RelWithDebInfo.zip file (google). My setup:
  • host computer i5 processor Win7 64bit
  • guest computer WinXP 32bit
  • R820T dongle
I have tried running rtl_test.exe at several sampling rates and always got lost bytes, even at the lowest value of 250 kSPS! And the CPU usage was not impacted at all, it remained low/idle.

My conclusion: unless you accept data loss in your RTLSDR decodes, a VirtualBox virtual machine does not guarantee enough "USB bandwidth" for successful reception within the VM itself.

28 January 2013

SDR on a netbook

Since sdr# runs fine on the 2004 laptop (Centrino CPU), I wanted to test the RTLSDR hardware on the eeePC 901 with a dual-core Atom N270 processor. That is not an hyperfast processor, but the netbook is small and it has a solid-state drive (SSD, as opposed to "spinning" hard disk or higher capacity).

First test involved using ADSBsharp to upload data to the common hub. This piece of software runs the RTLSDR dongle at 2048 Msamples/sec, and the machine was coping with the load, delivering as high as 120 decoded packets per second.

Then I tried latest sdr# development release and, despite the additional load for the display, the eeePC 901 behaved exactly as the older laptop. At 250 ksamples/s (total bandwidth of 250 kHz) there is CPU to spare.

Sure, the screen is tiny, but for a portable operation the netbook is small and solid. Note: I forced the "Super performance" mode, which apparently consists in a 5% overclock. With a reduced sample rate the CPU can be slowed down (to be tested).

21 January 2013

New RTLSDR dongle has arrived

Simply amazing. The sensitivity difference between my first RTLSDR dongle based on E4000 and today's with R820T is about 3 times, in favour of the latter. Even with the stock DVB-T antenna I could pick up more signals than the E4000 and the external GP. Then I "sacrificed" the stock antenna to use the cable with MCX connector for building an adapter to the TV plug: with the GP antenna outside I could receive airplanes as far as 300km/160nm. The ADS-B software was showing an average of >50 signals per second, against less than 10 for E4000.

So, as many others have reported, the R820T stick is more sensitive above GHz than the E4000 counterpart. I also noticed a much stronger frequency drift in the first minutes of operation, which also result in a warmer RTLSDR dongle.

Two experiments will follow:
- retry 23 cm SWL'ing during the monthly activity event
- test the ADS-B reception in a location with a 270 degrees wide horizon

14 January 2013

ADS-B ground plane antenna

This is not rocket science: dipole and ground plane are the most basic antennas you can build. And they can be good performers too! Here is a picture of the 1090 MHz GP I assembled for my ADS-B reception tests.

It is built around a panel-mount BNC socket. Each of the three solid copper wires is about 6.6 cm long and there is a 10 kohm 1/4W carbon resistor across "hot" and "cold" points to discharge static electricity right at the source.

This GP performs equally well with and without resistor, so leave it in place. This antenna is omnidirectional, and depending on its horizon it can bring up signals as far as 100 km away (E4000 tuner, airplane above 10'000 m). In this screenshot my receiver is below the ISSxyz airplane:

07 January 2013

ADSB antenna

I am not a fan of aircraft monitoring, but their ADSB 1090 MHz transmissions represent a widely available and geographically distributed beacon for testing new antennas.

My antenna test-field is the usual balcony open to N-NE.

First I tried a biquad without reflector. This is somehow bidirectional in an "8" shape. The advantage of this antenna is the intrinsic short-circuit, which avoids the problem of static electricity build-up (and frying the RTLSDR dongle).

Then I read many people suggest a collinear antenna. Projects documented online do not agree on sizes of straight elements (13 vs 19 cm) and coils (2 vs 4 cm diameter), so I opted for a simpler ground-plane: one vertical element, and 2(4) radials. All 1/4th wavelength long = 300 / 1090 / 4 = 6.8 cm (a bit less, in practice). It is short, simple to tune and easy to handle. The 1090 MHz GP antenna can be made of 1mm dia. solid copper wire, even keeping the insulation. In order to discharge static I inserted a common 10kohm 1/4W carbon resistor across antenna terminals.

Performance? They receive signals from the same distance, the GP being slightly better (but I would need a side-by-side realtime comparison) probably due to the biquad needing some form of tuning, making it a bad match outside resonance window.

Conclusion. Unless you are absolutely sure in your interest in ADSB monitoring or you have access to proper instrumentation to measure antenna impedance above 1 GHz, go for the GP antenna. According to my observations, ADSB signals propagate in line-of-sight, so look for a good, open, position: I can draw my antenna electrical horizon by looking at what/where it can receive.
Use a low-loss coax (known quality SAT-TV coax is a good choice) and keep it short: this trick will easily save those couple of dBs so hard to achieve with a different antenna without tuning instrumentation.