100 subscribers - thank you

Just noticed that the number of people who subscribe to this blog has now reached 100 for the first time.  Many people just drop in from other links, but it is good to see that so many people actually subscribe.  I try to post things that interest me, and I hope interest you too, here.  Please let me know if the blog can be improved in any way.

Things (such as designs) that are of longer term use are added to my main website www.g3xbm.co.uk so check there too if you've not visited it.

Android and iPod WSPR

WSPR on the iPod Touch 4g

To the best of my knowledge no-one has (yet) produced apps for these devices that allow them to be used as WSPR mode terminals.  Not being a software expert (at all) I am rather surprised at this: these are now very common platforms that a wide variety of people have. The number is growing daily. How much more convenient it would be to use my little iPod Touch 4g, for example, with a simple QRP WSPR transceiver, than with a PC or laptop. Are there any technical reasons why such apps haven't appeared?

If anyone knows if this has/is being done please let me know. I am aware of WSPR watch but this is NOT a WSPR terminal, just a neat reporting app.  The picture shows what WSPR might look like on such a device - I wish!

I wrote to Joe Taylor to find out if the creator of WSPR knew of any attempts. This was his reply:

"Hi Roger,

No such effort has been attempted, to my knowledge.

   -- Joe, K1JT"

A solar peak in late 2013 and another in 2015?

Some experts at NASA are predicting some strange behaviour in the next few years with the possibility of a twin peak for cycle 24 but with one peak being this year and the other on 2015. A similar twin peak occurred in cycle 14 in the early 1900s.  See http://www.arrl.org/news/solar-cycle-24-may-have-double-peaks-says-nasa-solar-physicist.  If this happens we may have (half) decent conditions for several years yet in this current solar cycle.

Conditions in this peak really are very different from the massive peaks in the middle and late 20th century when worldwide DX was workable with ease on the higher HF bands and even 6m. OK, it is still possible to work all over the world but, believe me, it WAS a lot easier back then.

24 hours with 1mW output on 40m

Well, that was fun: a 24 hour period with my WSPR beacon running at just 1mW RF output on 40m into the Par 10/20/40 antenna at just 5m up in the garden and yet still plenty of reports from around western Europe. Best DX reports were from F6HTL (737km) and F1ING (581km) with reports from G, PA, and F.  I shall now have a try at the same power level on 10m or 20m and see how it goes. It was interesting that there were few reports last evening and overnight on 40m, possibly because my 1mW signal was being crowded out by others running "high" power like 1-2W, HI.

Some of the reports with 1mW on 40m WSPR

A WSPR beacon TX at the 1-5mW power level is feasible with just one transistor and a single balanced diode mixer and may be one of my next "just for fun" projects.

UPDATE 1700z: on 20m WSPR with 1mW output I managed just one report this afternoon from F1JRC/2 at 971km.

Chinese FT817 a step closer?

Steve G1KQH has alerted me to a new Chinese HF SSB/CW transceiver kit called the KightKit KR-10 that retails in the USA for $259.95  Although this is a kit, it is available ready made for just $30 more. That is less than $300 for a built HF QRP rig.

The rig doesn't look very pretty, in my view, and I/ve no idea about its availability in Europe including the UK.

The spec is:

• RX frequency range: 0.1 ~ 30MHz
• TX frequency range: 0.1 ~ 30MHz
• Operating Mode: SSB / CW
• Receiving sensitivity: better than 0.45uV,
• RF output power: ≥ 4.5W
• Frequency stability: better than 0.5ppm
• Operating voltage: 12.0 ~ 14.0V DC
• RX Standby Current: 0.5A
• TX current: 1.5A Max
• Dimensions: 97 x 40 x 155 (mm)

See http://www.kightradio.com/X1M-QRP-SSBCW-Transceiver-Kit_p_305.html for more details.

Now, there are clearly signs that the Chinese are coming up fast on the HF QRP transceiver front. It surely cannot be long before a Chinese company launches an FT817 competitor. They have a tall order to exceed its spec but they've had 13 years to dissect and analyse the Yaesu radio.  

1mW (0dBm) TX on 40m WSPR

Just for fun I'm having a go at QRPp WSPR on 40m. The set-up is the FT817 on 500mW going directly into a 26dB attenuator that feeds the Par 10/20/40 end-fed longwire antenna in the garden at around 5m above ground. So far, after about 10 minutes a few spots received: G3XVL at 61km being the best DX with reports also from G4IKZ and G4NRG.

Amazing NLOS 481THz reception tonight!

This morning I realised that I was 2.5 degrees out in my aim last night with my optical beacon, so this evening I repeated the over-the-horizon optical test, moving instead to a new location fully in the beam at a distance of 4.8km. The difference was astounding! Last night I was struggling to copy the signal even with a long carrier. Tonight it would probably have been audible in 10wpm CW!

Excellent NLOS 481THz copy this evening

I ran QRSS3 tonight and was rewarded with signals 20dB over the noise in 0.34Hz bandwidth when beaming just above the horizon. At higher elevations the signal was weaker. With this strength I am very confident that with QRSS3 the signal should be copyable non line-of-sight (NLOS) out to at least 10km by forward scatter and possibly much further, even with my 1W LED running at 250mA in 100mm optics.  This was an excellent result and I am now confident the RX is working very well indeed.  Cloudbounce is another mode I have yet to properly exploit. The reception tonight was as a result of clear air scattering presumably from water droplets or dust particles.

This time I made recordings which are linked from my website. These can be played back through Spectran or Spectrum Lab software and further analysed. See https://sites.google.com/site/g3xbmqrp3/vuhf/optical/481thz-nlos .

Rapidly I am learning the absolute importance of accurate aim: 2.5 degrees out last night probably reduced the signal level by around 20dB. For serious tests over longer ranges a means of very accurately aligning the TX and RX is essential. Unlike with line-of-sight where the red dot can be seen by eye usually, NLOS requires careful alignment from map features.

Successful over the horizon 481THz test at 4.6km

This evening, in the freezing cold, I attempted a non line-of-sight (NLOS) optical test using my beacon TX (1W 10mm LED at 250mA in 100mm optics) at home in the bedroom firing out through the double glazed bedroom window and my new improved receiver (SFH213 detector in 100mm optics) at a new test site 4.6km away towards Cambridge. The path is obstructed by rising ground some 10m above the TX and RX height around mid path.

481THz signal (top line) at 4.6km over the horizon tonight

This time, I used a lower TX subcarrier tone frequency of 572.3Hz and a continuous carrier transmission so that aiming would be easier (!) than with CW or QRSS3. I am pleased to report successful reception of the signal in 84mHz bandwidth using Spectran, but aim was extremely critical and the signal was not solid, probably because of  aiming issues and possibly changing sky conditions.

When I got home I checked the frequency to make absolutely sure that this was my carrier, which it was beyond any doubt. The signal was totally inaudible in the headphones and there was no sign whatsoever of the red beam in the sky. The most probable propagation was by scatter off dust particles in the atmosphere.

This was MUCH harder than I expected: I honestly expected to hear quite reasonable signals by ear, but as the plot shows, the signal was only just copyable in 84mHz. When I received my signal NLOS last year at 3.5km on a different path signals were 10dB over noise in a wider bandwidth on QRSS3.

At the moment I am still aiming the TX and RX as low as possible on the horizon, but I need to try greater elevations to see if this gives better to worse results over this sort of distance.

Another 6-10dB ERP from the Phlatlight LEDs (still to be fired up) would certainly help.

Practical Wireless (April 2013)

G3XBM in New Zealand (Abel Tasman National Park) Feb 2009

For the second month in a row I have an article in Practical Wireless. This time it is one submitted several years ago describing my operation on 70cms FM when on holiday in New Zealand in 2009. New Zealand has an excellent internet-linked repeater network that links repeaters all across the country, so one can work from the very south of South Island all the way to the top of North Island and talk to anyone on this linked network.  I found this invaluable when on holiday.

Sadly the exchange rate is not as favourable now as in 2009, but New Zealand is a wonderful place for a once in a lifetime holiday, with very friendly and welcoming people.

If you get PW, I hope you enjoy the article.

Optimised 481THz receiver

As the weather was miserable here today, I decided to work on the K3PGP derived 481THz optical receiver this morning. I wanted to ensure it was working at maximum sensitivity with subcarrier tones around 100-1500Hz. With some adjustment of the coupling capacitors and the addition of an HF roll-off capacitor on the collector of T2, the sensitivity now appears to be excellent. My test is an AF modulated red LED on the ceiling of my building shack, in almost total darkness, with the test receiver (less any lenses) on the bench about 1.5m away. If the receiver is working credibly then the tone can be heard in the headphones when the LED is barely lit. In the case of this latest receiver I cannot even see the LED lit at all in a darkened room, yet the tone is audible in the receiver. When comparing this with my previous best optical receiver there is around (guess) 6dB more sensitivity. This design uses "blog standard" components: nothing selected for low noise, and not an IC in sight. I am now waiting for some decent weather - and no snow please - to test this on my NLOS test path.