Simpler 481THz beacon TX

This afternoon I built a simpler CW/QRSS3 beacon for lightbeam experiments. Rather than use a crystal divided down in a 4060 IC I simply used my K1EL keyer IC's sidetone output to drive an IRF640 which drives the 1W LED. 10wpm CW or QRSS3 beacon message is therefore produced on an 800Hz subcarrier. The stability of the sidetone from the PIC keyer is quite sufficient for QRSS3 although not good enough for QRSS30 or 60.

Homemade 45rpm disc recording

Handmade disc recording made on a coffee tin plastic lid

Whilst clearing out a cupboard the other day I chanced upon a piece of my history in the form of a small 45rpm disc recording that an old school friend and I made in 1969. Using an old record turntable with a very large horn as the acoustic microphone we recorded me saying some words and poems onto the polypropylene lid of an old coffee jar. Shouting VERY loudly, the sound is imprinted onto the disc in just the same way old gramophone records were made back in the 1800s. The metal foil inner lids of cocoa tins were also quite good for this as I recall. Francis Wood, my school friend went the whole hog and put the record into a homemade sleeve (with suitable handwritten text) with inner cover and the disc finally inside. I did play this disc some years ago and it was still intelligible (just) but nowadays I have no 45/78rpm kit to play it on. I remember the first time we made such a disc back in 1962 how amazed I was that it worked.

Cambridge Club Talk - a good turn-out

This evening I gave my talk "VLF Amateur Radio" to the CDARC in Cambridge. The turn-out was excellent, especially considering the very cold weather here at the moment. It was -10deg C coming home in the car.  At the end of the talk there were plenty of interesting questions. It was fun to share my enthusiasm for VLF things with such an appreciative audience. Click on the link if you'd like to see a copy of the slides I used this evening.

Reliability of radio gear

Tin Whiskers on an IC contact

When I mentioned the eHam review of the KX3 on the GQRP reflector last night most of the replies focused on the reliability of complex modern electronics equipment. Some people believe that with fewer parts and SMA components reliability is higher today than in earlier times. Others, including me, were more circumspect and feel that, unless production processes are well controlled, the danger of failure is higher. There are also potential issues with leakage in small geometry ICs as well as the dreaded "tin whiskers" issue where metal dendrils can grow over time between IC balls. My own experience in mobile radio design and manufacture may have coloured my views. We got it right in the end i.e. getting production processes well honed, but you cannot take process control for granted, ever. The slightest drift in quality can spell disaster, field failures and a ruined reputation.

One thing many people agreed on was this: if you want to be sure of the reliability of your amateur radio equipment then build your own. A simple QRP transceiver, easy to make from many published designs in QRP books, should last a lifetime and will be easy to fix in the unlikely event of something going wrong. There is also nothing quite as satisfying as making contacts with something you have built. Even a simple crystal controlled TX and direct conversion receiver are likely to give FAR more satisfaction than a rig costing £1000 with all the bells and whistles. I still recall the thrill of my first ever hombrew contact across the Atlantic with 800mW CW on 15m using my little Pipit transceiver with 7 transistors total and a handful of parts. This rig was so effective that it was my main station rig for many months. Every QSO, and there were lots, meant something special.

KX3 review on eHam

http://www.eham.net/reviews/detail/10271

This is the first ever review of the Elecraft KX3 by one of the field testers using SN-0006 sample fitted with internal batteries and the optional roofing filter. The field tester was mightily impressed.

Optical cloudbounce propagation theory

Bernie G4HJW and I are interested in carrying out some "cloudbounce" tests using our 481THz optical kit and we both are none to clear about the physics of scattering of signals from water droplets and dust in clouds or the sky. However, today a new tool to help our understanding was shown to us on the UKNanowaves Yahoo Group in a posting by Barry Chambers.

The free software is available at  http://www.philiplaven.com/mieplot.htm and allows us to work out the intensity of a scattered optical signal as a function of scattering angle, droplet size and wavelength. Scattering is best when the angle of incidence is at grazing incidence and the droplet size is small. If I've understood the results correctly, aiming at the underside of a cloud at 45 degrees would result in a scattered signal some 50dB weaker than if at grazing incidence. So, depending on how far apart the 2 stations are and the angle at which the optical signal hits the underside of a cloud then signals can be quite strong or extremely weak. This is why weak signal modes like QRSS60 may be needed to work a given path by cloudbounce.

A novel QRP power source

FreeCharge 12V is a small, portable generator, similar to that used in portable hand-cranked torches. The output is regulated to give 12-14.2V DC although the product datasheet does not state the available current. I suspect it is in the low milliamps as its main use appears to be to power/charge mobile phones in an emergency.

This could make a novel power source for low power QRP transceivers as no batteries would be required, just a few seconds or minutes of cranking.  Figures given are 360 turns (approx. 3 min wind) gives 9-11 minutes of mobile phone talk time and a 60 second wind gives 2-4 minutes of talk time. Price is £19.99 and it is available from Freeplay or via Amazon UK.

The sales blurb says:

"The Freecharge 12V provides emergency power to a mobile phone, PDA, iPod, GPS receiver, or any other electronic device for which you have (or can get) a cigarette-lighter adapter. Wind its hand crank to generate electricity and put power straight into your device. Never be unable to use your mobile phone, or other important device, just because its battery has run down."

Weak signal modes compared

There has been quite a bit of debate recently about just how good certain weak signal modes are when compared against similar modes. So, ON7YD has done some research and straw polling to compare them and published the results on his wonderfully informative website. He asked people to try to decode some weak QRSS signals by eye - these were at defined S/N ratios and compared the results against OPERA at various speeds and WSPR.

Amongst his conclusions is that "Opera8, QRSS10 (or DFCW10) and WSPR should have a more or less equal performance."  This is very much as I have found from practical experience on 136kHz where QRSS3 does not perform as well as QRSS30 which is somewhat better than WSPR. So, WSPR being much the same as QRSS10 seems spot on. The advantage of WSPR is of course the internet database reporting which allows you to see where you have been received. QRSS reports depend on someone decoding the signals by eye and then manually sending you a report, which rarely happens. So, WSPR remains my favourite weak signal beaconing mode.

ON7YD's graph showing the effectiveness of various weak signal modes

472-479kHz secondary allocation

From the RSGB's website today comes the latest news from WRC-2012 about an amateur secondary allocation to replace 500kHz with something more permanent. It needs ratifying but it does now look very likely indeed to happen.

Agenda Item 1.23 – 500kHz
Progress through Committee 4 (COM4) was a little easier than expected and the frequency band 472-479kHz will be allocated to the amateur service, on a Secondary basis. This is subject to no further objections being received during the two final readings through the plenary meetings, of which the first ‘blue’ reading is expected to be during the plenary this coming Friday, late afternoon.

Free power radios

KE3IJ's always excellent website has a novel receiver circuit that derives its DC power from AC mains hum and noise it picks up on its antenna.  It uses a single 2N3904 in a regenerative circuit. Ideally the circuit would be better with a lower Vbe device i.e. a germanium transistor.

Taking this one stage further, I know from my experiments at VLF that the AC mains hum between a pair of grounded electrodes can be pretty high. There is certainly enough 50(or 60)Hz energy going free in the ground to power something useful. I keep wondering if I could get a few uWs of HF RF power from a low voltage crystal oscillator that would be enough to work some local stations on CW? My nearest station is 0.3km and the next nearest 3km. Now having a QSO using free power from my back garden would be rather fun.