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After what seems like a lifetime in the attic the Cobwebb ventured outside for the Easter weekend. What a weekend as well.

I put the little antenna up on the telescopic pole about the same height and the top of the Hustler 6-btv (in the background) and spent a few minutes tuning into various stations then dashing in and out of the house to swap the feeder over between the two antennas. Several dashes later and the freezing cold east wind finally kept me in doors just as 2 VK stations appeared on the cluster. At the time I was on the vertical and paid little attention to them as experience tells me that they wouldn’t be ‘in range’ with my 100w. Especially as I was at home in the st bees dip which usually strips rf out of the ether. I tuned to their operating frequency and was met with stoney silence, as expected.

Out of curiosity I did one last switch and the first station was a real 5 & 9. A few calls later and we managed my first qso with a vk. A few minutes later I bagged my second. Within a few hours I managed 7 new countries in between walking the dog and other family stuff. I can safely say that I will be making a more rugged version of the single wire Cobwebb and retiring the vertical.

Now the bands have returned to their usual quieter state it was certainly a good weekend to be on the radio

Transceivers with a power supply of 1 and 2 Volts, how much can one achieve with that? Well, actually quite a lot according to DL2AVH, Helmut, who together with DL4ALJ, Gero, wrote two articles about that in the German QRP-Report in 2011. I am impressed by the output power, up to 200 mW with one battery cell (1.5 Volts) and 0.5 Watts with two cells.

I wrote about this in April last year where I also mentioned that the 1 Volt design from 2000 later had been corrected. Those corrections can be found in the article in QRP-Report 3/2011: “Niederspannungs-Schaltungtechnik – der 1-V- und der 2-V-transceiver” (Low voltage circuit technology – the 1 Volt and the 2 Volt transceivers). The improvements are concerned with better input filtering at 14 MHz with a quartz crystal in the front-end filter and better efficiency in the mixer and removal of an audio stage in the direct conversion receiver. This design only uses bipolar transistors and no ICs.

This is different in the newer 2 or 3 Volt transceiver for 7 MHz. Here an impressive figure of only 5 mA power consumption for the receiver is achieved. The transmitter consumes about 250 mA. Several MC1496P balanced modulator/demodulator ICs are used for the mixers in the transmitter and the superhet receiver, and for the product detector of the receiver. They seem to run quite comfortably on only 1.8 Volts as supplied by a low-droput regulator from the battery supply. The TDA7050 is used for the audio output stage. This is a low voltage audio amplifier for headphones which can operate with  a supply voltage down to 1.6 V.

The design is said to benefit from low voltage technology of mobile phones. This is the case for circuitry like that of the output stage of the transmitter which consists of a pair of BFG21W transistors. However, both of the ICs have been around for many years.

I think this was a very inspiring read, and the final comment about power consumption from the second article is interesting. They say that with two AA-batteries, the receiver will last for 285 hours, which is the same as 70 days of listening of 4 hours per day. With transmission for 10% of the time, the set of batteries will last for 4 weeks!

• Related post: Whatever happened to the 1 Volt QRP Transceivers?

One of my favorite events is the Orlando Hamcation. This year I didn’t really have a “get list” so could enjoy more time with fellow QRP ops. Our Central FL QRP Group regular Jim Diggs K4AHO helped us get a QRP Forum and Jim Stafford W4QO came in from Georgia to help bring a good session about working DXCC with QRP. Wow! Jim also did a lot of recruiting of QRP ops as he manned the QRP ARCI booth and allowed us to hang out and assist. We had quite a good turnout of QRP Ops from FL and all over the US and a few overseas members too!

  Carl AA2JZ brought some of his homebrew masterpieces and along with some QRP rigs W4QO displayed we got a lot if interests and questions on what was in the Altoids tins.

After the QRP Forum, Greg N4KGL gave us a demo of his Alex Loop and KX-3 at a nearby picnic table. The weather and bands were both cooperative and we were all impressed with the way the antenna and rig set up and operated!

Thanks to all who joined in the fun. Check out our Central FL QRP Group blog for details on our outings.

When you measure the energy out of a GSM cell phone at the moment of initiating a call, you get the picture to the right. It shows the first 15 seconds.

For the first 3.5 seconds there is the signalling between the phone and the base station. Then the connection is established, but after some time (at 4.2, 5.6, 7.5 and 9.5 seconds) one can see how the phone turns the power down, according to the commands it gets from the base station.

The first example was for the case of a strong received signal, all bars are shown in the signal strength meter. The reduction in power, preservers battery life and as a side effect the user is exposed to a smaller amount of radiation. Interestingly, one can see that after a while there is a small adjustment of the power and it is turned up a bit (at 11.5 seconds).

In other cases one can see a situation which follows the same pattern in time, except that the power stays at a high value. This second recording was done in my basement where GSM coverage is much poorer. Here the phone’s signal level indicator hardly shows any signal.

The third plot is a zoom of the previous one. Here one can see how the phone only transmits 1/8 of the time as it shares the channel with 7 other phones in a time multiplex. It is allowed to transmit every 4.6 ms and this is the reason why one often can hear a buzzing sound at 1/4.6 ms = 217 Hz in equipment which is placed close to a phone.

One also sees another frame structure, as the phone transmits 25 bursts and then breaks for one burst before continuing. Every transmission consists of 150 bits, but that is not possible to resolve with the simple setup that was used here.

The equipment was a dipole antenna and a simple diode detector:

• A half wave dipole antenna for 950 MHz has a length of 0.5*3*10⁸/950*10⁶ = 15.8 cm, thus the antenna is about 2 x 8 cm (probably not very critical). The antenna was made from stiff self-supported wires.
• There is a resistor of R=1 kohm across the antenna and then a Shottky diode which acts as a detector (A Shottky diode which handles higher than 1 GHz is needed and BAT46 was used here), and finally a 1000 pF capacitor as a filter.

The useless machine or ultimate machine originates from Claude Shannon, the scientist who figured out how to find the channel capacity in a communications system. I bought the basic machine as a kit from Solarbotics.

But then I added a few features:

• A delay circuit that makes it look more alive as it gives the impression of doing some thinking before it responds to the switch.
• Sound that varies with how open the lid is and the amount of light that hits the photosensitive resistor. It was inspired by the design of the Growl and Scream Altoids of FightCube.
• A couple of LEDs, a red one when it opens and a blue one when it closes.

The circuits were built on small pieces of veroboard and the circuit diagram can be downloaded from here. In retrospect I’m not completely happy with the sound, it could have growled and screamed even more, but then how much effort can one really justify putting into a project which is – useless – anyway?

I found this on a scrap piece of paper at the club last night. Being a bit thick and not knowing what it was for certain I asked a few people and the response was fairly consistent.

‘Its a…errr…y’know…..that you know used to do as kits for err’

Obviously I wasn’t the only one who was a little stuck. Well I don’t know what it is exactly, but I can have a few guesses – I’ll nail my colours to the mast and suggest it is a current meter of sorts. Anyone else care to join in the guesswork with more confidence? It took me long enough to find out what brass treblet tube is!

The kit building is carrying on at my garage before the cold weather comes and means that it’ll be less than appealing to go in there. This time it is a seemingly simple kit from Hans Summers, G0UPL called the Ultimate QRSS kit. Ultimate because presumably the kit does more than QRSS, however the kit is essentially a QRP (~150mW) beacon transmitter for QRSS and other modes, the attraction for me is that it also generates the tones for WSPR and as well as offering the QRP transmitter it also has the ability to generate just the audio for use with another transceiver. I was drawn to it because it offers the opportunity for a little bit of experimentation. Although things haven’t quite gone as smoothly as I’d hoped for.

The list of features for such a price is quite impressive. This is taken directly from Hans Summers’ website (http://www.hanssummers.com/qrsskitmm.html). Which is well worth a visit if not for this kit.

The kit supports the following modes:

– QRSS mode (plain on/off keyed slow CW)

– FSK/CW mode (frequency shift keyed slow CW)

– DFCW mode (dual frequency CW)

– WSPR mode (Weak Signal Propagation Reporter)

– Slow-Hellschreiber (frequency shifted slow-Hell)

– Full-speed Hellshreiber

– Half-speed ("DX") Hellshreiber

– CW (plain CW)

– Customisable FSK patterns

Other features:

– 24-character LCD + two-button user interface

– User-programmable (callsign, message, speed, FSK, mode, etc.), settings stored in EEPROM

– GPS interface, for locking the frequency in slow-speed modes

– On-chip generation of WSPR encoded message (no PC required)

– WSPR maidenhead locator can be generated from GPS-derived latitude/longitude

– Selectable “frame” size, for stacked QRSS reception

– Plain CW callsign identifier at selectable interval

– Produces 150mW RF output, or AF output for driving an SSB transceiver

– Higher output power by additional PA transistor and/or higher PA supply voltage

My 30m version has been sat on the shelf whilst the good weather (ahem!) was continuing. This came to head over the weekend when I warmed up the soldering iron and started piecing it all together. The kit took a few hours to build and I would image that a skilled builder would have it all together much quicker than I could with the excellent instructions.

Unfortunately on powering up things haven’t exactly gone according to plan. It only seems to power when it fancies it and certainly doesn’t generate the tones as you might expect although I am receiving a carrier roughly in the right area. The other small issue is that the LED doesn’t appear to do anything visual, this may be a design feature but seems a little bit odd to me.

All these faults are almost certainly a result of my work, not the kit although it didn’t help having to scratch off the solder mask from the coil connections. I think the fault finding will take longer than the building in this instance but with a bit of luck it will involve some learning and there is no harm in that.

Still where’s the fun in it working first time?