Progress on the new 481THz beacon TX

Today I made a start on the new optical QRSS3 beacon. This time, the circuit has some improvements: a continuous sub-carrier option and a choice of audio subcarrier frequency. Also, the frequencies are now derived from an HF crystal so stability will be excellent.

The part completed new 481THz QRSS3 beacon

The oscillator/divider is a 4060 IC and this is enabled by the output of a K1EL keyer IC programmed to send "XBM" in QRSS3.  The square wave output from the 4060 feeds the gate of an IRF510 FET which switches the 280000mcd, 10mm diameter, LED in 100mm optics.

A possible refinement will be to pull the crystal using the keyer output signal so that I have a continuous carrier but FSK keyed. This would mean I'd always have a signal to aim at, but with FSK QRSS3 CW on it. I'm not sure how much pull I'd get after dividing down if I just changed one of the capacitors loading the crystal. I shall have to experiment and see. Even as little as 5Hz would be enough, but that would need 50kHz shift at crystal frequency! A better way may be to key the frequency out of the 4060, so mark is, say 550Hz and space 1100Hz or vice versa. Plenty to try tomorrow.

Frustrating day at both ends of the spectrum

Today I tried two experiments. Firstly a continuation of my tests with the loop and E-field probe out in the fens on 8.977kHz and then tonight, another over-the-horizon test on 481THz.

Failure 1 at VLF: whereas in the past I've had a decent signal at my test site at Tubney Fen 3.5km from home on the loop antenna on 8.977kHz, today I could copy nothing. There was some strong interference and I thought that may have been the problem, so I moved on to a second test site 5km away where again I usually get a good signal. Again nothing. In the past this second site has given me signals so strong that I could copy 10wpm CW from home on 1kHz by earth mode. Now around the village and in nearby Swaffham Prior the signal levels were (as far as I can recall) similar to past levels, so what has changed? One theory is that the wet winter has saturated the fenland soil so conductivity is much higher, resulting in much higher attenuation at VLF.  Another possibility is some utility has changed - a change of pipe type or a re-routing of an electricity cable? My TX and RX equipment is largely the same as in previous tests.

Optical QRM on the 820Hz sub-carrier frequency

Failure 2 at 481THz: I tried a third attempt at my over-the-horizon QRSS3 reception of my signal on a 820Hz sub-carrier. This has been successful in the past. The 100mm lens TX was carefully aligned just to the right of our local windmill on "the hill" and I traveled to what should have been a direct line path (but over the horizon so the signal has to be scattered) about 3.5km away. Optical conditions looked good with clear visibility of street lights in Burwell. Well, I am pretty certain that I was able to hear my signal by ear in the headphones keying away slowly, but because of a lead failure (later fixed) and then a strong interfering signal very close to the 820Hz sub-carrier, I failed to see my signal with Spectran and make a screen capture. I think this QRM signal is related to new street lighting as panning the horizon brought up this interference on most street lights at around 3km range. The solution will be to choose a different sub-carrier tone frequency. BTW, it is fun to hear the strobe lights from aircraft: these are very strong and can be copied well off the direct path by scattering.

My next immediate priority is to change the optical beacon TX so that I can use a range of different sub-carrier frequencies all derived from an HF crystal divided down with a 4060 divider. This will also allow me to run a continuous signal which will help with alignment and I can avoid QRM by moving the HF crystal frequency if needed. I could also arrange DFCW modulation by FSK keying the HF crystal: this will allow a continuous signal for audible alignment yet be detectable with software packages like Spectran in QRSS3.

As regards the VLF earth-mode tests, for now I am going to draw these to a halt and will try again in a month or so when I hope the fen soil conductivity has reduced. If things are unchanged then I suspect that something in the utilities metalwork out in the fens has (permanently) changed.

Projects update

It is some time since I summarised my projects list and progress. This is the current "ideas list" for the coming months. As we are in the middle of a house renovation/move project over the next 3-6 months it is quite likely that my amateur building work will have to go slow.

• VLF earth-mode - optimising the E-field probe and loop antennas for mobile coverage tests
• 481THz Optical NLOS tests - testing new RX and then trying the 10dB higher powered PhlatLED TX and seeing how far over the horizon I can reach.
• WISPY 10m WSPR beacon - combining the TX and RX boards into a full WSPR/PSK31 transceiver. Separate modules made and tested but yet to combine.
• Tenbox - I still need to finish either the AM transceiver or modify the design to a DSB transceiver.
• 2m horizontal omni antenna - I need a simple horizontally polarised omni antenna for the new QTH. I'm tempted to organise a pair of stacked big-wheels with around 5dBd gain.
• Simple test equipment for the shack at the new QTH - I want to build a number of pieces of simple test gear such as a frequency counter and simple spectrum analyser 
• Rebuild of the 10m Homebase-10 halo - the wooden frame structure is showing signs of age, so a fibre-glass support may be less visible and more durable 

Now, knowing the way things work with me, I 'll wake up one morning and think of something completely different to work on. That is the fun of simple homebrew amateur radio experimentation: no-one tells you what to do, unlike when at work, and each day is one filled with opportunities.

Double or single peak for cycle 24?

At the moment the jury is still out on this. We've seen activity slide since the peak around Nov 2011 but there may be signs that the trend is upwards again leading to a second peak as has happened in a few recent sunspot cycles. This NASA video gives some insight into the thinking.

More analysis with Spectrum Lab software

Spectran is a very easy package to use but it has its limitations when analysing weak audio signals. A more powerful package is DL4YHF's  Spectrum Laboratory which is an extremely powerful piece of software. The problem is that if I've not used it for months it takes me hours to remember how to drive it. A secret is to store ".usr" configuration files so one can go back instantly to a set of settings e.g. a given frequency to analyse with a specified bandpass filter and bandwidth.

Faint line at 8.9775kHz visible at greater range (43mHz bandwidth)

Anyway, to cut a long story, this evening I set up some config files to allow me to look again at the recordings of my 8.9775kHz VLF earth-mode signals made during recent drive around tests locally. Although the original analysis was done at 180mHz bandwidth I can now replay the recordings and look in bandwidths down to 34mHz. What happens then is that signals present but too weak to see now appear above the noise floor as a faint line. The net result is that the signals can be detected in some of the "in between" locations that were not apparent from the 180mHz (wider!) bandwidth analysis.

I intend to use Spectrum Laboratory and narrow bandwidths for the over-the-horizon 481THz optical tests if Spectran proves not up to the job. However, when bandwidths are very narrow there is a time-lag before the trace appears on the screen. This is less than ideal when trying to align weak optical signals with beamwidths measured in a degree or less. What is needed is an accurate beam heading and then allow the trace to build on the screen. I don't have enough experience yet to know how much beamwidth spread a cloud or free space dust scattered optical signal gets. When looking for G4HJW's signal over the horizon in clear skies last year the alignment was quite critical, but his signal was audible in headphones so the optics could be peaked by ear before analysing with Spectran or Spectrum Lab. I had more luck with my own QRSS3 signal over the horizon on a shorter path, managing to align by eye on visible landmarks enough to see the trace on the PC and then peak it.

Mobile 8.977kHz VLF loop tests started

Today I started to do my tests on 8.977kHz using my 5W earth mode transmitter at home but using a mobile loop antenna on the car connected to my PC via a tuned preamp. The idea is to be able to drive around and measure signal levels with Spectran software whilst actually on the move.

30t 80cm loop mounted behind the car

The loop was mounted behind the car in such a way that it would detect any ground propagated signals. The loop is about 10cm off the ground.

A drive test to Swaffham Bulbeck was carried out and signals were detected more or less continuously out to 3.5km from home before they disappeared in the noise. Bandwidth used was 0.18Hz with a continuous carrier. Although coverage was as I anticipated, signal levels were not as great as when the loop was actually laid directly on the ground. At one of my usual test sites 3.5km out in the fens there was no copy with this loop arrangement yet there was a decent signal copied with the loop on the ground a few days earlier. I need to do some direct comparisons between the loop on the ground, the loop mobile mounted 10cm above the ground and with the E-field probe on the car roof. Initial indications are that the difference between the EFP and the mobile loop is probably no more that 5-6dB.

Signal received with Spectran and the mobile loop

Revised UK Frequency Allocation Chart

From the OFCOM email newsletter today:

UK Frequency Allocation Table

Ofcom has published a revised UK Frequency Allocation Table. This details how various frequency bands are used in the UK, and which bodies are responsible for planning and managing them – including frequencies assigned to individual users or installations at particular locations. It also shows the internationally agreed spectrum allocations of the International Telecommunication Union. 

The table shows frequencies below 8.3kHz are unallocated in the UK but there are some footnotes in the ITU frequency allocation table that require administrations to ensure no harmful interference to services above 9kHz and to notify other administrations about research below 9kHz.

My understanding is therefore that below 8.3kHz the UK administration "does not care" what happens as long as interference to allocated services is avoided. This is my interpretation and not a legal statement.

VLF earth-mode mystery deepens

This afternoon I did a larger coverage test with 5W  8.977kHz earth-mode, driving in several directions locally in the car with the roof mag-mounted E-field probe RX antenna and with a PC in the car monitoring the signal. I drove for several kilometres in different directions recording where the signal could, and could not, be copied. The best reception distance with the E-field probe was 3.2km.

The map shows the results. Yellow shows where I drove and red shows where there was signal present and recorded on Spectran. I have recordings of the whole trip which I will more carefully analyse later.

5W 8.977kHz earth-mode coverage using EFP RX antenna

The interesting thing is that the signal could be copied in 4 local villages (Burwell, Reach, Exning and Swaffham Prior) but there was almost zero coverage once outside of these villages. This is NOT the case when looking with a magnetic loop RX antenna, where the signal can be copied more extensively in the rural areas at even greater distances.

It would appear that the E-field signal needs to be strong above ground to be copied with the EFP and this only happens where there are buildings i.e. in the villages. It suggests I'm detecting the signal from cables or pipes in houses.In more rural areas the signal is weaker above ground and not detected, at least not with 5W TX.

Mobile on 8.97kHz VLF

Route taken from A to F (about 4km)

Today I did a fascinating experiment on 8.977kHz VLF using my 5W earth mode transmitter and a mag-mounted E-field probe and laptop running Spectran in the car. Basically I did a "drive around" test to see where the signal could and could not be copied.

Signal strength on 4km run between 2 villages

A continuous carrier was transmitted and I continuously monitored the received signal in the car. The drive was from the middle of the next village (Swaffham Prior), out through to the main road, then back along the main road to Burwell, around part of the village and then back home to the TX location. The signal was visible in Swaffham Prior at 5-10dB S/N, then disappears and returns on approaching Burwell where it is up to 40dB/S/N in 0.18Hz bandwidth. Within Burwell it is almost solid copy. The red timing ticks are every 30 seconds.

What I am detecting (I think) is the local E-field from the VLF signal in the ground, no doubt aided by local utilities. What puzzles me is why there is NO copy in between the 2 villages when there are, I think, pipes and cables in the road.

In the coming days this test is worth repeating locally in other directions and further afield. Fascinating to think a 5W VLF signal injected into the ground can be copied on a 19 inch whip on the car roof like this.

Another approach to 472kHz WSPR

An old work colleague Richard G4KPX has been doing more experiments with indoor loop antennas. Recently he has been using an indoor loop for 472kHz with an ERP of around 1mW. I just checked the WSPR database and see he has achieved some amazingly good results with 49 unique spots with best report from Sweden at over 1300km! Well done Richard.

G4KPX's WSPR results over 500km with just an indoor loop TX antenna

Optical NLOS test - next time pack everything!

This evening I set off to my Landwade location where I hoped to check the non line-of-sight (NLOS) signal level from my 481THz, red LED, QRSS3 beacon TXing from home. This time I'd carefully aligned the TX and adjusted the RX optical alignment in daylight, so everything should have been spot on.

481THz RX with iPod Touch 4g running SpectrumView

Then I realised I'd left a vital lead at home that allowed me to connect the optical RX to the laptop. Next time I need a checklist as it is a 10 mile round trip to the test site.

Instead, I tried to copy the signal using the optical RX fed into my iPod Touch with SpectrumView software, but the bandwidth was too wide to allow me to find the weak signal. I hope to repeat the test in the next week (with the laptop and Spectran set to 0.34Hz bandwidth), but this time with EVERYTHING packed for the test.

I was very annoyed with myself for forgetting this audio lead as it prevented a meaningful test being done. I also need to find a different NLOS test site that is less far to drive to but still at about the same distance (3.6km).

The limitations of my cheap tripod are also apparent: I need a much sturdier one that has a compass attached and much smoother pan and tilt.

8.97kHz earth-mode tests with mag-mounted E-field probe

Today I started some tests at 8.97kHz with my mag-mounted E-field probe (EFP) on the car roof. As usual, the transmitter was my 5W QRSS3 beacon feeding the 20m spaced earth-electrode antenna in the garden.

The logical starting point was to drive to my usual "strong" test site 1.6km from home and compare signal levels on the usual 80cm square RX loop with that on the EFP.  For reasons I have yet to understand the signal was NOT copied, even on the loop! What I did see was what looked like an FSK telemetry signal, possibly from overhead power lines close to 8.97kHz. I've never seen this before. Anyone know what it is?

8.97kHz 5W earth-mode signal at 0.4km on E-field probe

I then drove to my new QTH (due to be occupied in about 4-5 months time) which is 0.4km from the TX and sat in the car in the drive with the iPod Touch 4g running SpectrumView software connected to the EFP. The antenna was a short 19 inch whip. Signals were copied quite well (see photo showing "3" from my callsign). The bandwidth on SpectrumView cannot be narrowed enough to optimally receive QRSS3 and results would be better with the PC set to 0.34Hz bandwidth.

Tomorrow I'll have to find out why I couldn't see my earth-mode signal at the usual test site on either antenna. I'm also going to do some /M reception at 8.97kHz using the E-field probe and laptop with Spectran set to 0.34Hz or 0.17Hz bandwidth. With a continuous signal I'll be able to log the signal level as I drive around the village and nearby.

What IS amateur radio?

This is a question I keep asking myself. It clearly means different things to different people, but I am saddened by the trend to cheque book amateur radio.

In its early days the hobby was clearly about experimental radio: making receivers and transmitters that communicated over short distances, with many/most of the parts being hand-made, even down to the variable "condensers". Over the years this has changed for many (most?) amateurs and now one could be forgiven for thinking all that matters is how expensive ones new HF radio or antenna is, so one can boast about how wonderful ones station is to others on HF.

I was struck by the cost of the hobby, for some, again tonight when visiting http://www.bigskyspaces.com/w7gj/vhf.htm and looking at the massive and very expensive antenna farm at W7GI.  Now this 144MHz antenna, like many, antenna arrays at this amateur's QTH is aimed at reliable EME operation where large antenna gains help. But what I see is 16 very expensive antennas plus an equally expensive support structure, expensive coax and an expensive mast. This is just one antenna for one band. He has another very big array for 50MHz too, plus no doubt a shack full of expensive radios and linears. The rotator to turn this lot will be a very large device indeed.  Yes, successful EME operation needs big antennas and high power, but honestly is this AMATEUR radio still or semi-commercial experimentation?

I can understand why an amateur may want one 100W commercial radio as the "mainstay" radio for the shack, but I see many shacks loaded to the gunnels with very expensive radios that must have cost their owners well over £10k and in some cases well over £20k.  It amazes me how much money some amateurs must invest in their hobby. I had a decent job and a decent salary when I worked, but there is no way I, personally, could justify this sort of expense on my hobby. It's a personal view and I do not want to preach to others on how to enjoy their hobby, but I am fascinated that spending lots of money on radios seems to be the norm.

Are any readers prepared to share (in the comments) how much they spend, on average, a year on their hobby? £10, £100, £1000, £10k, £20k?  Just for the record, I reckon on about £2 a week (a couple of new HF transceivers over 12 years plus the odd accessory and components).  It is possible to really enjoy the hobby and spend less than the cost of a coffee every week.

My question is, what IS amateur radio?

472kHz earth-electrode WSPRing this evening

The 472kHz WSPR beacon has been running this evening using the 20m spaced earth electrode antenna described in my March 2013 RadCom article. A reminder that there is NOTHING in the air at all, just the wires along the grass to the earth rods.

Quite a few reports received and given already.

472kHz unique WSPR reports received so far tonight

The same earth electrode antenna will be used at the TX end of my VLF test with the mag-mount E-field probe RX tomorrow morning.

Stake out on 481THz

481THz RX on tripod with optics.

In the daylight today I went to the RX site used in last night's unsuccessful over-the-horizon (NLOS) optical beaconing test. I've now marked out on the ground (with sticks and stones!) the exact direction to aim my RX in when I return for a second try, hopefully tomorrow night.

Yesterday it was so gloomy that I could hardly work out where to aim, so this now means I can be within a few degrees accuracy on initial set-up. I've also adjusted the aim of the TX beacon optics. Visibility for Thursday night is forecast to be "very good" with cloud cover according to my Met Office app, so let's hope it works OK tomorrow.

The RX and 100mm optics are shown above. Note that the upper tripod extension (below the tilt arm) is rarely extended as the whole thing is then too wobbly. I need a more sturdy tripod. Also, the low cost gunsight scope (bought for just a few pounds off eBay) is of little use at night (too little light) but very useful in daylight.

Mag-mount E-field probe on 8.97kHz

Just as an experiment, this afternoon I modified my mag-mounted FET drain tuned E-field probe to work on 8.97kHz. The last time I rigged an E-field probe on 8.97kHz and went looking for my earth-mode signal results were very disappointing wih just a couple of places within 2km radius where the 5W beacon was copied, but tomorrow morning I'll see how well (or not) it works. To tune the FET drain to 8.97kHz I just substituted the 137kHz tuned circuit with an 83mH Toko potted coil in parallel with 4n7. Tuning is reasonably sharp. Whether the car grounding will make a big difference we'll see in the morning.

Eddystone User Group

If, like me, you owned an Eddystone communications receiver at some point in the past then you may like to look at the Eddystone User Group pages. Here you will find lots of data on old receivers, links to data sheets and service manuals and a lot else too.

In my case I owned a Mk 1 EC10 receiver similar to the one shown here. This was state of the art in the late 1960s when it sold for £48. By modern standards it is a pretty rubbish receiver.

481THz over the horizon test: no success tonight

Weather this evening was not suitable for the tests, although I did try. I set up the QRSS3 beacon pointing out of my bedroom window using the local windmill as the aiming point. This is on the top of our small hill which rises about 15m. I then drove to a spot 3.6km away over the hill to look for the signal with my sensitive RX and 100mm optics using Spectran to display the trace. Unfortunately this time the slight drizzle and murk was just too bad and no signal was copied, although I've had good results in the past at a very similar spot.

In daylight I need to recheck my beam alignment at the RX location as it was sufficiently murky to not see the local landmarks used to help aim the RX last time. Despite panning across 45 degrees of aim nothing at all was copied of my signal. I shall repeat the test in better optical conditions.

For those interested, the 1W 10mm diodes are available from http://www.ebay.co.uk/itm/350347623711.  You get 10 pieces for £9.26 with free postage and they are very BRIGHT.

481THz optical tests over the horizon tonight

This evening I am doing my first "over-the-horizon" optical test this year. The main aim is to check performance with the new receiver and to see how I get on using the iPod Touch 4g running SpectrumView software as the way of seeing the QRSS3 signal. I shall also be taking the laptop running Argo or Spectran.

Latest receiver that seems more sensitive than my older RX

The receiver circuit is the one in Practical Wireless this month by Stuart Wisher G8CYW. This is simple but works well in darkness. I've added an interface to the iPod Touch 4g (a capacitor and a resistor needed to enable the external mic input) and changed the coupling caps and op-amp gain. Using just MPF102 and 2N3904 devices the results look good. The low noise op-amp may be overkill unless one uses super low noise FET and transistor stages too.

After the tests I'll post results in the blog.

40m WSPR with 50mW - best DX spot 6505km

Reports received with 50mW on 40m

Overnight I've been WSPRing with 50mW output on 40m using the Par 10/20/40 end-fed antenna down the garden.  The FT817 set to 500mW directly feeds a Telonic 10dB rotary attenuator set to 10dB attenuation, so no chance of radiation from a coax cable. The antenna is only about 15m long and just 5m average height above the ground. Results (see above) have been very pleasing with best DX report from the USA - K9AN at 6505km.

Bug keys

Kent twin paddle key

Although not a frequent or very good CW operator, I do like to try QRP CW from time to time, usually with a straight key I've had for over 40 years. With rubber stamp QSOs on HF I can usually manage OK. The problem comes when people ragchew and I lose concentration!

Some years ago I bought a beautifully made Kent paddle key but I've hardly ever used it because I kept making mistakes. So, today I dug it out and decided to persevere with it on 40m CW. I managed a nice (unexpected) 2-way QRP QSO with Rick DK4QK who, despite my sending, managed to copy everything. Later I worked DM0E on 2-way QRP as well, using the bug. Like all things, good CW comes with practice and use. Using a paddle key should allow me to send better and faster CW with a little bit more practice on my part.

So, if you hear me calling CQ on 40, 20 or 10m in the coming days on CW, and there are plenty of mistakes and extra dots, then you'll know who it is.

20m WSPR

As the weather is totally miserable I decided to sit by the fire today instead of doing any amateur radio building. In the comfort of the lounge I am watching the spots being sent and received with 2W to the Par 10/20/40 end-fed antenna on 20m WSPR. 20m is not a band I use much, preferring 10m, although conditions on 10m have nothing like matched the conditions close to past sunspot maxima.

Some decent range spots (TX and RX) despite lackluster conditions on 20m

Exchange rate changes and ham rigs

In recent weeks the pound sterling has declined quite a bit against the US dollar and the euro. Against the dollar it has fallen from around 1.62 dollars to the pound to around 1.51 to the pound. This makes purchases of rigs like the KX3 even more expensive here in the UK.

On the other hand, the yen has weakened from 125 to the pound to around 142 to the pound.  Expect some discounting of Japanese rigs in the UK incoming months.  The latest yen exchange rate suggests a new FT817ND should be less than £500 again soon.

Which major dealer will be really public spirited and pass on their savings to us the amateur radio public?  Martin Lynch or Waters and Stanton?

A PSK31 QSO

Well, the little grandchildren have gone back home to mum and dad so the house is very quiet (and tidy!) again. This afternoon I decided to do a bit of QRP on 20m as a change. First a nice 2-way QRP QSO with Emi IZ4RDX who was running 5W (me 2.5W) and then a PSK31 QSO with Luis EA3UV. Neither contacts were great DX, but fun.  For the PSK31 QSO I decided NOT to use those pre-prepared messages and instead just keyed in what I wanted to say as the QSO went along. It felt like a real QSO, which was nice.

Tomorrow I hope to get back to the optical beacon work, but after 4 days of (lovely) little grandchildren this afternoon I just needed to "chill" as they say.  The plan is to build a beacon TX that will allow a range of subcarriers and also continuous subcarrier transmission as well as CW and QRSS beacon messages. I hope to get out "over the horizon" looking for the signal later in the week. Watch this space - literally if you are nearby, HI.

PSK31 mode

Julian G4ILO mentions his enjoyment of PSK31 on HF on his blog today.  Although I've had a fair few QSOs and some good DX with this mode over the years, I'm not a great fan of it.

Although Julian rightly says it is a very good mode that well complements CW and SSB, and it is certainly true that the PSK31 part of the bands are often busy when CW and SSB signals are absent, to me QSOs feel too formalised with exchanges that follow fairly standard formulae. Too often it feels like a PC talking to a PC. Maybe I should try next time to avoid using these pre-programmed messages and go for a normal free-form keyboard "chat" instead.

It's a while since I've tried PSK31 on HF. Maybe next week when the grandchildren go home I'll give it another go.

The ARRL reports that Varicode, as used in PSK31, has now been officially recognised by the ITU. See http://www.arrl.org/news/amateur-created-varicode-adopted-as-itu-recommendation .

More VLF activity from Germany

DJ8WX has been experimenting with a new GPS locked frequency source and is trying to put a signal out on 8.9700000kHz.  The signal has been received strongly by several stations including Paul Nicholson in Todmorden and at PA1SDB. This is the signal at PA1SDB over the last few days. Note the timescale on Peter's grabber covers several DAYS. Such is the world of amateur VLF!

Signal from DJ8WX now on 8.970000kHz (was 8.970022kHz)

Nanowave over the horizon tests - nearly ready

Original optical beacon

Just about ready now to restart my optical non line-of-sight tests again using my 481THz CW/QRSS beacon and a choice of 2 sensitive receivers. I'd intended to go out this evening but (a) the XYL needed the car to go to her choir and (b) the fog has descended!

Optical beacon capable of continuous subcarrier (choice of freqs) or QRSS/CW

SpectrumView in action - it's brilliant

The beacon design needs to change somewhat: currently I can TX either QRSS3, QRSS30 or CW at around 830Hz subcarrier, using the IRF640 fed directly from my K1EL keyer IC. However, I cannot actually send just a 830Hz tone continuously. This would actually be very useful when aligning TX and RX over a non-optical path e.g over a hill. So, when the grandchildren go home on Sunday I'll make a modified version of the beacon keyer so that I can choose a number of subcarrier frequencies, including some lower than 830Hz (detector sensitivity is greater at lower audio frequencies) and also add the option of a continuous subcarrier signal. This will involve adding a 4060 based oscillator and divider to be keyed by the K1EL keyer IC. So, it may be next Tuesday or Wednesday before I actually start testing again.

I also want to optimise the use of the iPod Touch 4g as a handheld audio spectrum analyser. I have used it for this sort of test before using an excellent package available free called SpectrumView (see screenshot) available from Oxford Wave Research. With a laptop PC, running Spectran, the problem is the brightness of the screen which emits an interfering optical signal. With a tiny iPod Touch it is much less bright and can be held in the hand. Unfortunately the bandwidth can't be screwed down as narrow as with Spectran on the PC, so there will be S/N limitations. One test will be to see how far away I can detect my beacon (about 0.5W into the LED) over the horizon using just the optical receiver and the iPod Touch.

The beauty of 481THz (red light) work is the kit is simple: everything that matters is at audio frequencies and can be built and tested with the simplest of test gear.

Trio TR2300 1W 2m FM portable

Looking on eBay today I noticed someone selling an old Trio-Kenwood TR-2300 2m FM portable.  I'd forgotten I owned one of these back in the 1980s. When it came out, it was one of the first synthesised 2m radios available.

I had it to get on 2m FM from home mainly. A small vertical dipole was erected at gutter height and with this set-up I could work well equipped stations out to around 50-60 miles.  It was actually a rather good little radio that also got used in the car on holiday in France with my French call F0HXF.

Why it was sold I cannot remember. Of course, these days you get all the functionality, and a lot more, in a tiny handheld like the VX3 and the FT817 produces more than 6dB more power on all bands and modes from 160m-70cm in a box about 30% smaller.

Incidentally with 2 days to go there have already been 31 bids, so someone must want one.

ARRL DX CW contest

Until I read about it on G4ILO's blog, I'd quite forgotten about this big contest. Rather late on Sunday afternoon and evening I decided to have a go and see what could be worked on 40 and 20m. Although I managed a few US contacts with the 2.5W QRP I do find CW contests hard work: people send SO fast and by the time I've called with my straight key they've usually already had another QSO.  I suspect many these days use keyboards and auto keyers most of the time in contests. Actually I quite enjoy the odd SSB contest as I can talk (nearly) as fast as anyone else. Even with 2.5W SSB it is surprisingly easy to make contacts in a big contest, especially late in contests when the big guns are looking for new stations to work.  Overall, I prefer experimentation, but a contest just for fun can be quite cathartic.

New 481THz receiver working well

Optical RX in small screened box attached to a 110mm drain pipe "stopper"

This morning I built my new optical detector circuit using an SFH213 photo diode, an MPF102 FET head amplifier followed by a 2N3904 amplifier and a low noise op-amp. The output is fed to either a pair of 600ohms sensitive headphones or a PC running Spectran.  The schematic was as in G8CYW's article in PW this month, although I reduced the coupling capacitors to 100n to reduce the gain at very low frequencies to help hum rejection and increased the op amp gain a few dB.  Sensitivity is several dBs better than my previous best design .

Build method is my usual copper clad board with MeSquare pads built dead bug style. The junction of the SFH213 cathode and the gate of the FET must be kept well above the ground though to reduce losses.

To test the set up I modulate a small red LED mounted on the ceiling of my building shack with a 1kHz tone. With all lights out and in near total darkness I compare the level on the audio generator that I can just hear with that of my reference optical receiver. Both the new unit and the test unit are on the bench about 1.5m away from the (just glowing) LED. If the system is working well the S/N is good with the LED barely visible by eye. There are quantitative ways of measuring the sensitivity using Spectran on a PC but this means having the PC out of the room as the display would otherwise desense the RX!

I have yet to test this when mounted in the 110mm drain pipe with 100mm lens. This gives an antenna gain of around 24-30dB. A good test will be the GB3CAM optical beacon which I can just detect with my older head at a distance of around 32km.

HF noise and 481THz experiments again

This morning I notice that most of HF, to 15m at least, has an S6 noise level here. it is making operating on HF a real pain.

Phlatlight QRO LED for 481THz over-the-horizon QRSS tests

Actually I am beginning to think about restarting the 481THz (red light beam) over-the-horizon QRSS tests again. At least at nanowaves you can see the interference! My first project will be to build a new nanowave receiver using the SFH203 detector which should be some 6-7dB more sensitive than my current detector head, which is already impressively sensitive.  Next I want to try out the QRO Phlatlight LEDs I've had for several months but not yet fired up. They should be VERY bright with 100mm lenses, so a lot of care will be needed.

Practical Wireless is currently running a series of articles on lightwave communications written by Stuart G8CYW. This should be an ideal introduction for anyone wanting to have a go at speech over light or long range data transmission (line of sight or non line of sight). Stuart has done more than anyone to encourage light beam communications.

G3XBM website

Please let me have feedback on how you find my new website layout for my main website at www.g3xbm.co.uk . In recent weeks there's been a complete overhaul of the site but I have yet to get any feedback from people who visit it, good or bad.

Please email me at address given on the website and above, or leave a comment here. To prevent spam bots you will have to copy the address into your email package manually as the address is shown as a jpg image, not a clickable link.

Finally may I apologise for the silly nonesense you have to go through to post a comment here on this blog. When I remove the web bot filter ("copy the words you see" stuff) I get loads of rubbish, so felt it was necessary to keep it, despite the hassle. Alternatively you can send me any blog comments by email and I will add them for you.

G3XBM online grabber

This evening I've been setting up my on-line grabber again so that I can monitor VLF, LF or MF activity and upload what I am receiving to the internet for others to see. The grabber is, at this stage, only on intermittently as I experiment. The plan is to have a dedicated VLF or LF receiver and PC for this purpose, so the grabber can be run almost 24/7.

The main weak signal detection is done using Argo software running on my PC connected from my RX via the SignaLink USB interface. The captured signal is then uploaded to a location in my public Dropbox which is then linked to from my webpage. So, what appears on the G3XBM online grabber page is what I am seeing with Argo. The direct link to the Dropbox image is http://dl.dropbox.com/u/15047843/g3xbm.gif .

G3XBM online grabber

OXO on 14MHz

An OXO transmitter on 14MHz

This afternoon I decided to build a 14MHz OXO transmitter. As is often the case, I like to re-use old boxes and project parts, so the FETer box was photographed for posterity, then gutting and used for the OXO transmitter. In this version I did not go for full break-in and instead used a simple changeover switch, but added a push button net function to allow me to net the VXO without the PA being keyed. A small toroid in series with the crystal allows about 15kHz VXO range around the 14.060MHz QRP frequency. I used a 2N3904 for the oscillator and 2N3906 for the keying transistor and a 2N3866 for the PA, but may change this for 4  x 2N3904s in parallel for lower cost. My output is a little low at around 500mW.

It works fine with reverse beacon reports from Iceland and Slovenia and a nice 2-way QRP QSO with IK2RGV who was running 5W.

The OXO really is a classic circuit: you just build it and it works.  Another version is on the QRPkits page.

FT817 v KX3 (part 2)

Thanks for all the many comments both here an in private emails. Basically I am looking for a good second QRP transceiver to work along side my existing 12 year old FT817 that continues to work perfectly. There are times when I'd like to WSPR on one band whilst operate CW or SSB on another. Also, the second transceiver allows me general coverage RX whilst TXing on the first unit. Since I sold my IC703 to a friend the year before last, this has not been possible.

At the moment, I am still inclined to buy an FT817ND rather than the KX3. As YO9IRF said in the earlier post and on his blog, the FT817 is close to the ideal for a portable QRP radio, even after 12 years. Although it does not match the RX performance of the KX3, it does perform remarkably well, and of course it also covers the 144 and 432MHz bands and with all modes. And it is half the price.

Email habits

As someone who gets around 50-60emails a day, sometimes more, even though I am supposed to be retired, the link below offers us all some good sound advice on how to manage emails well. A good half of the emails I get are about projects on this blog or my main websites, so it's my own fault, HI.

My PC or iPod Touch tend to be on for a lot of the day and am almost addicted to reading the emails. Usually I reply promptly but occasionally emails get filed waya having forgotten to reply, for which I make a general apology.

Anyway, here is that link:  http://zenhabits.net/e/

FT817 v KX3

People who own the Elecraft KX3 generally rate it very highly as it is a very feature rich product with  an excellent receiver. However to buy one with all the features such as the auto ATU and the internal battery box is EXPENSIVE. For the price of one fully loaded KX3 one could buy 2 well proven FT817ND transceivers.

One has to question whether the KX3 truly is worth the extra cost. Although a trail friendly radio, the KX3 does have a messy cabling interface with wires everywhere, it would appear, from both sides! By contrast, the FT817 has simple, clean interfaces and is as happy in the field, in your hands or on a desktop.  The KX3 looks functional, but hardly a thing if beauty.

I'd be interested to hear the views if others.

This video, by Jim Mullen, is the first part of 2 that compare the RX of the KX3 and FT817.

8.97kHz VLF amateur activity

DJ8WX's VLF signal received by G3ZJO (frequency is Hz)

This last week or so Uwe DJ8WX has been active again on VLF from his location near Hamburg.  Uwe was the strongest signal I ever copied on the so called "Dreamers Band" a few years ago and his signal is being well received again now. To copy these signals at 8.97kHz requires a quiet antenna location and a very stable, frequency locked receiver. You will NOT be able to hear anything and signals take hours or days to appear on the PC screen using a package like Spectrum Laboratory. Getting a very very stable receiver is actually easy as Spectrum Lab can lock onto one of the strong MSK VLF commercial signals and use this, or a GPS signal, as a very accurate reference. Much more details on the Sub-9kHz Amateur Radio pages.

Pedestrian Portable HF DXing

G3XBM operating pedestrian portable in South Devon

The latest edition of Practical Wireless carries my article on pedestrian portable HF DXing. Getting out of doors in a noise free location with a simple HF rig and using it handheld - not with a large semi-permanent antenna, but with a whip on the rig - is one of the great pleasures of QRPing. With a good location, such as a clifftop site with a slope towards the sea, DX can be worked easier than might be expected even with a few watts of SSB.  Nothing quite beats talking to a station thousands of miles away with a small radio in the hand.  A small counterpoise wire is a must to get the best results. Especially in the summer Es season when signals can be S9, this can bring a whole new dimension to the hobby. Forget that plasma TV interference and get out there in the great outdoors!  Best bands are 15m, 10m and 6m (when open).

Nice blog site with useful info

A nice Pixie transceiver and tuner on the PD7MAA blogsite

Graham G8NWC has just told me about a very nice blog site with some useful QRP information. See http://pa-11019.blogspot.co.uk/.  It is surprising how much GOOD data there is out there when you look around!