481THz (light communication) progress

This afternoon I did a bit more on the optical front. I repeated my outdoor range tests using a low-cost high brightness LED as both a baseband optical transmitter and receive detector. With around 10mA TX current into the LED I was able to copy a 1kHz tone at 20m with another high brightness LED as the detector, without any additional optics other than the LED's built-in lenses at each end.

A 100mm lens properly focussed has a gain of >24dB (nearer 30dB if correctly adjusted). Assume 24dB "antenna" gain at each end of the link and we will have 48dB system gain over the simple LEDs on their own. Based on these calculations my optical transceiver should have a range of at least 5km.  If the gain of the lens is 30dB then the range could be as great as 20km. This is without using high power LEDs as the TX or using larger Fresnel lenses which would have even higher gain.

I now have the 100mm lenses I intend to use as well as 2 gun sights bought off eBay. The next step is to buy some drain pipe to house the optics. I have still to decide whether to build fully self-contained FM transceivers (simpler) or to build the optical transceive heads with separate transverters to use with the FT817.

RF skill levels

In my professional life I interviewed many graduates aspiring to become RF engineers. Very few, in recent years, had what I would call "the knowledge". By this I mean a "gut instinct" for RF that does not come from an academic course, important though this aspect is.  Rather, this "jizz" comes by living and breathing RF through building RF things yourself, however simple. A great many 2:1 graduates in communications electronics knew almost nothing about RF, had never touched a soldering iron ever and were rejected. In all honesty I believe I could sense who would make a good RF engineer within 2 minutes of the interviews starting.

Today I received a request from a Spanish amateur who professed (more or less), "I`ve a problem. I know nothing about electronics and would be unable to build the SAQ converter on your website." He then offered to pay me to build and ship the converter to him. Surely, a radio amateur in ANY country should have learnt basic RF skills as part of his training in preparation for his licence? At the most basic level the understanding may not be deep, but how can a radio amateur really not know how to put together a basic circuit?

In the UK we have a growing, and very serious, issue with poorly educated science and engineering graduates who are simply not coming out of universities with the skills needed to start work in industry. One answer was the sandwich course in which young A-level students were accepted on a company training scheme that married "on the job" skills training with educational training, usually to HND or degree level. People spotted young, with real RF "jizz" (easily judged in interviews) usually went on to become the best engineers we had.

Sunspot peak to be over 100?

The latest NOAA sunspot predictions show cycle 24 now peaking in May 2013 at a smoothed sunspot high of exactly 100. This is UP on earlier forecasts and the actual trend since this forecast was made is still upwards, I believe at a rate faster than NOAA was predicting.

So, despite the gloomy predictions of even 6 months ago, we seem to be enjoying a decent solar cycle after all with every prospect it will be better than even current forecasts suggest. Whatever, conditions on HF will continue to be good for 5 years to come, so go and enjoy them.

Today my QRP WSPR was copied in Australia a couple of times on 10m yet again. It appears that every time I fire up it gets >16000km. I just wish a few more East Coast USA stations would  come onto 6m WSPR as this is where the excitement will be for the next  few weeks if F2 MUF reaches 50.293MHz.

Busy amateur VLF weekend

G3ZJO's reception of DK7FC on 8.97kHz

Yesterday's test by DK7FC from his fixed location was a resounding success with reception all over Europe by many stations including G3ZJO, G3WCD and G3KEV, and what is believed to be the first transatlantic reception of an amateur VLF signal by a station in the Eastern USA. Results are being checked as I write.

Stefan's ERP was later re-calculated as around 800uW. It is incredible that such a tiny VLF signal can be detected so far away. If confirmed, this certainly heralds the dawn of a new and exciting phase of VLF amateur work. With another 3-6dB ERP, worldwide amateur VLF DX is now a real possibility. Of course such VLF DX reception requires incredible frequency stability, very narrow RX filters and long signal integration times; signals are far too weak to hear.

Also, Marcus DF6NM ran a 8.97kHz test today using a kite antenna. G3ZJO received a good signal in IO92ng 20dB above the noise in 424uHz bandwidth. Marcus was also well received by many other stations across Europe.

In summary, this weekend has been a BUSY one on the Dreamer's Band.

More POWER - why??

Today I see that amateurs in New Zealand are to be allowed 1kW power in future; their limit was 500W earlier I believe. I've read something about amateurs in Eire asking to be allowed 1kW in contests and I think something similar is being requested of OFCOM here.  My simple question is why?

As an example, last evening I had a totally solid QSO on CW with KT5E in Denver, Colorado on 28.060MHz 2-way QRP with 5W each end.  My antenna was a small wire halo. Like many people, I have worked well over 100 countries with QRP on CW, PSK31 and SSB and always with simple wire antennas like dipoles, never a beam.

When more power is used it just creates more splatter, and more unnecessary QRM. OK there are times when 100W rather than 5W would make QSOs much easier with fewer repeats. But do people really need to run 1kW? OK you may blast a signal through the pile-up, but do you go to bed at night with any more satisfaction than someone working DX with a few watts or even milliwatts? I very much doubt it. Power is about egos, pure and simple.

28MHz WSPR with 50mW

50mW WSPR Reports 28MHz

It really is too easy now on 28MHz! In just a few minutes, these were the reports when using just 50mW to my small halo antenna. Some reports suggest 1mW would have been enough. I need to build a bigger attenuator.

CB interference to the 28MHz band

Interference from CBers on the 28-29.7MHz band is getting worse. I guess they've been there a long time now but with good conditions their presence is more evident. Doesn't seem to cause problems with CW and WSPR operation though. The availability of rigs covering 26-30MHz capable of being easily switched from CB coverage to 10m coverage must be one of the problems and to CB operators the wide open spaces must be attractive. Use it or lose it.

More 481THz lightbeam progress

670nm receive head and converter to 80m

Today I did some further light beam experiments, this time using a 25kHz modulation signal on the light beam and receiving the signal on my FT817 with this head/converter unit above. It consists of a BPW34 photo-detector feeding a cascode FET/transistor stage into an emitter follower and SBL1 mixer to convert the signal to around 3.584MHz. With a current into the TX LED of just 10uA (a very dim glow from the red LED) the signal was 20dB S/N in 0.67Hz bandwidth on Spectran at a distance of 25cms without optics. If my calculations are correct, this means a range of around 100m could be obtained even with this miniscule power if 100mm lenses were added at each end to give some 27dB gain at each end. Using the same TX LED at 10mA (1000 times the current) then the range is already in the many km region, and this is without using power LEDs. This is encouraging progress. Tomorrow I want to repeat the test with the same LED as the TX as the detector.

80m FETer outing

This evening I came on 80m to listen for G6ALB who was taking part in the valve QRP day. Using my  18mW output FETer transceiver (18 parts total) I was able to hear almost all of the stations active around 3.56MHz using QRP.  G6ALB was worked (599 each way, but we are only 3km apart). I had forgotten how effective this little transceiver was and it was a pleasure to use it once again.

481THz (light) - first test results

Today I carried out my first optical communications tests since 1966. I built a small "baseband" (i.e. not on a sub-carrier based) optical transmitter producing a tone at around 800Hz feeding a standard low cost high brightness red LED at around 10mA current. The LED has a small built-in lens which produces a beam of around 20 degrees.

For the receiver I built the first stage of the optical head described in the RadCom articles (March-May 2011) using an identical  red LED (reverse biased) as the detector. I also tried a BPW34 detector, but it was not that different. This was followed by a couple common emitter transistor stages using my ubiquitous 2N3904s feeding a crystal earpiece. With the TX "beacon" running from a 9V battery and aiming out of my garage I walked across the road with the receiver and a 4 inch magnifying glass. Across the road, at about 25m range, this produced a quite respectable signal as long as the magnifying glass was focussed onto the RX LED. This was all a bit "Heath-Robinson" as I had to hold everything in my hand and move things around to get it spot on. There was quite a bit of interference from the street lights nearby.

I have no idea how much "antenna" gain there is in the built-in lens on the TX LED (a few dB?) or with the magnifying glass on the RX but with this set-up correctly aligned I would think 100m range is certainly possible.  This is just the beginning of a series of tests, but I am already happy that the optical head is sensitive and that good, well aligned optics will be essential to get decent distances. More TX power is easily available by using a power LED.

Next stages are:

• A better beacon TX capable of operating at higher power on both baseband and subcarrier frequencies.
• Putting the optical head into a screened enclosure, even if a temporary one.
• Starting to think about optics. Using the same LED on both RX and TX will save on optics as just one set is needed at each end of the link.

137kHz transverter picture

137kHz transverter with FT817 and SignaLink USB in the background

Thought people might like to see the current version of the 137kHz transverter used for WSPR transceive. The heatsinks are total overkill as they barely get warm when producing over 20W RF into the loop antenna. I am regularly getting reports from a couple of stations 250km away. M0BMU (69km) and G0WCB (101km) are reporting the WSPR signals almost all the time. It works but needs boxing, when I get time.

A local 478THz (red light) beacon !

Map showing coverage of the 471 THz optical beacon GB3CAM

Guess what - I've just discovered that not only is there a decent level of optical comms activity in my area, but there is also an active 478THz beacon beaming (almost) in my direction from the Wyton site near Huntingdon, location of the GB3CAM beacons on 10GHz and 24GHz. The beacon is a narrow beamwidth (5 degrees wide) signal which is FSK keyed between 1 and 15kHz allowing both baseband and hetrodyne optical receivers to be used. The beacon was designed by Bernie G4HJW. The distance from the beacon to my local /P high spots in the beam would be around 30km, so this will be an ideal test for the optics and receiver, when built.

Google Sites website design

My wife sings in a local choir called the Cambridgeshire Choral Society. They have had a website for some years but it had not been regularly maintained, so I was asked to create this new one. This I have just done using Google Sites. Although I'm no website expert, Google Sites allows quite a credible website to be created without knowledge of HTML coding. I am quite pleased with the result and hope it encourages a few more people to attend the concerts and join the choir.

Their next major concert is in Ely Cathedral in March 2012 when they will be singing Elgar's famous "Dream of Gerontius" which is a wonderful choral work. They are also singing Britten's "St Nicolas" in late January 2012.

In the next few months I hope to tidy up my QRP website and give it a refreshed look.

IC703 Sold

For around 6-7 years I've owned and used an IC703 10W QRP radio as part of my station. Although I have worked all over the planet with it on SSB and CW, it had not been used anything like as much as the FT817, so I decided to "de-clutter"and sell it.  It was bought by a local friend who hasn't got any HF SSB/CW gear apart from a homebrew rig for 20m.  I had thought of trading it in, so offered him the rig at the trade-in value. If he doesn't get hours of fun and enjoyment from it, especially on 10m at the moment, I'd be very surprised. You see very few of these transceivers available on the second hand market, I guess because owners hang on to them.

UKNanowaves Group

G0EHV's lightbeam kit (from the UKNanowaves group photos)

Today I joined the UKNanowaves Group which is dedicated to optical communications.  There is a lot of useful information on this group in the postings and in the files and photos sections. Reading the membership list I noticed several local amateurs interested in optical comms, so when I get my equipment for 481THz working credibly I will have a good chance of some QSOs locally.

Today some of my optical comms electronics parts arrived so I hope to start experimenting with these on the bench shortly. Most gear built for 481THz is simple and homebrew. Apart from designs using transverters to HF or VHF, all kit is in the 0-40kHz frequency range, so easily engineered with simple test equipment. Perhaps, like VLF and LF, this is partly why it appeals to me.

137.5kHz transverter desense - fixed

This afternoon I fixed the problem with RX desense by adding a relay to switch the RF input and to turn off the PA supply when not on TX. It has fixed the RX sensitivity issue and added about 10-15dB to RX sensitivity using the transverter. PA0A was about 30dB S/N on QRSS and DK7FC about 20dB S/N on QRSS. M0PPP is now a better signal with me too on WSPR. The TX is still running at 500uW ERP and GW0EZY is copying me in mid-Wales OK (251km) this evening on 137.5kHz WSPR.

137kHz Transverter RX Desense

When testing my transverter on the bench today I noticed the receiver was being desensitised by the undriven TX strip. I don't switch the TX part off when on RX, I just don't apply 10MHz drive into it. There must be some source of low level noise from these stages when on RX as the desense is around 10-20dB. Despite this I am still able to copy M0PPP at 182km pretty consistently these days on 137.5kHz WSPR. I need to fix this problem before this project is boxed and "finished". When the TX strip is powered down the sensitivity is very good indeed.

The 481THz Band

My tests on 137kHz WSPR are now all but completed and I do not intend to take this work any further now I've "got the measure" of what is possible. I shall put the transverter in a box after a tidy up and use it periodically over the winter.

Now I am about to start something new: 481THz band communications! This is 623nm red light for the uninitiated. This evening I've made a start by ordering some suitable components to allow benchwork to start next week. My initial tests will be low powered beaconing with a portable receiver walking down the road. Assuming this is promising, I'll then refine the kit and organise optics to give some "antenna gain" to allow much greater range.

There are a lot of resources on the internet about light beam communication, especially using high power LEDs and there was an excellent series of inspiring articles about this in the March-May RadCom this year.

10m Chirpy Measurements

Last week G6ALB made a copy of my Chirpy 14 component transceiver for 28MHz CW. Andrew had access to some better calibrated test equipment and carried out some RF power and sensitivity measurements both on his version and on my second original unit - the first was just a rat's nest on the bench.

Both on my version and G6ALB's version the measured RF power out was in excess of 200mW, which is around 2-3dB more than I had crudely measured. The RX sensitivity on both was such that below -100dBm (around 2uV) was audible in our earpieces in a quiet room. Backwave carrier on TX was rather too high at around -10dBm. Second harmonic was also only around -6dB, so a low pass filter is really a necessity apart from casual short tests.

It does seem that the simple design is reproducible and its performance not at all bad for something this simple. The only major shortcoming is the chirp.

Ten WSPR reports now on 137.5kHz

This evening G3WCB (101km) reported my 137.5kHz WSPR signal for the first time bringing my total number of reports on this more difficult band up to 10. My ERP is currently around 500-600uW, although I hope to run the transverter PA from around 20V tomorrow which should increase the ERP by around 3dB.

These are the reporters so far:

G6ALB
G3WCD
M0FMT
G3XIZ (46km)
G3XVL (69km)
M0BMU (69km)
G3WCB (101km)
G3YXM (148km)
M0PPP (182km)
GW0EZY (251km)

137kHz WSPR - big SUCCESS at last!

After yesterday's disappointments today has been a whole lot better on 137.5kHz with my best WSPR DX report ever and a report from my second DXCC country on the band.  First several reports from GW0EZY in mid-Wales (251km) and then one from M0PPP in the north of England (off the side of my TX loop too - 182km) who I heard last night for the first time.  I've copied him several times tonight as well as PA3EGO. The transverter now puts out about 20W, but the ERP is still only around 200uW based on the loop current and enclosed area. I'm tempted to put it in a box at last as I now know this system is capable of decent range on a good night like tonight.

Struggling on 137kHz - time to move on?

Today I did some changes to my 137kHz transverter and put it on the air this evening for about 4 hours sending and receiving 137.5kHz WSPR. Power from the PA is now around 20W and the ERP must be around 200uW.  I was really quite hopeful that, with enough stations active on WSPR tonight, I might get a few reports.  The band was indeed quite busy with a few stations like G0KTN and G3WCB who have regularly copied my 500kHz WSPR on the band and looking.  What a disappointment! Not only did I get not a single report, but I was unable to copy any of the active TX stations like F5WK or M0PPP. The latter was visible as a trace but not strong enough to decode.

Without increasing the power another 6dB at least to around 80W and improving the antenna considerably I am now of the opinion that, QRSS30 apart, 137kHz is not going to be a success. My feeling is I need at least 20-30dB better system performance (TX power and antenna efficiency that is) to even start to approach the level of reports I manage on 500kHz. So, do I try just that bit more or do I throw in the QRP towel on this band? I don't want to run lots of power and I don't want to erect a monster antenna: I was hoping my unobtrusive loop would have done me as well as it did on 500kHz, but clearly not.

I am beginning to think that this really IS a band where you need lots of power to make a success of things.

UPDATE: Just as I finished writing this I manage to decode M0PPP twice at 182km.
2252 -27 -0.5   0.137562  1 M0PPP IO93 17

Simple VLF Receiver

SM6LKM's excellent PC based VLF receiver

In testing my Chirpy 10m transceiver, I used the simple PC based VLF receiver by SM6LKM as a bolt-on SDR. This little VLF receiver works very well as a stand-alone VLF receiver that tunes the 0-22kHz frequency range. Simply by sliding the cursor to any frequency it produces an audible signal just as you would get by tuning a conventional receiver.  Bandwidths are adjustable down to around 300Hz. For my video showing this in action listening to VLF signals (via my loop and small preamp) see http://www.youtube.com/watch?v=TDxRhQYg7lQ. With the SM6LKM VLF receiver you can clearly hear the Omega beacons around 11-14kHz, SAQ when transmitting on 17.2kHz, and various MSK military signals around 18-22kHz. It has also proved useful when carrying out earth-mode (through the ground) VLF communication tests.

A good night on 500kHz WSPR

Not bad for 2mW ERP on 500kHz and a smallish wire loop antenna!

Very good activity levels again this evening on 500kHz WSPR with 13 unique stations reporting my signal in 6 countries. Best DX report was from OH1LSQ at 1733km, the first time this season.

I really must make an effort to get the 137kHz WSPR activity stirring. Maybe if I can get my ERP up this next week I'll swap over to that band for a few nights and see what turns up. Mind you, the WSPR activity on 137kHz is very low currently with most people using QRSS beaconing.

The "Chirpy" 14 parts QRP 10m transceiver video

This is a short video showing "Chirpy" (XBM10-2), my 14 component 28MHz CW transceiver. More details can be found at my website http://sites.google.com/site/g3xbmqrp/Home/xbm10_2.  Best DX is still IT9QAU/QRP but I am hoping for further soon. This is a simple project and, as with all very simple radio projects, it is a compromise between cost, complexity and performance. Nonetheless it DOES work remarkably well for something so simple. AM breakthrough is almost non-existent too, which was a bonus. Couple the audio into a PC rather than a crystal earpiece and  as a bonus you have an SDR receiver capable of copying from about 28.040-28.080kHz. Why the name Chirpy will be evident when you hear the keying!

Elecraft KX3 or FT817 successor?

For some time now we've been expecting the successor to the FT817 to appear on the market as the current offering is now over 10 years old, with just a minor update in this period. Sunspots are rising fast now and I'd expect Yaesu-Vertex to release this within 6 months or miss a big window of opportunity.  The potential sales volumes are very large indeed as a large part of the amateur community owns an FT817 and would aspire to upgrade.

One wonders how Yaesu-Vertex is viewing the Elecraft KX3 and whether any changes to their new product will be made as a result of the KX3 pre-release data. The KX3 does look impressive but its form factor may not appeal to many. It also looks very "square" and Elecrafty! Although it can be used handheld, I understand you have to plug in a local microphone for example - a bit clunky for true handheld portable use, although you need an external mic with the FT817.

It is widely assumed that an FT817 successor will have a Li-Ion battery pack (2hr charge), built-in wide range auto ATU, good DSP features and possibly 70MHz coverage. The form factor is unlikely to be very much different from the current model, but with more inside.

Does anyone have any inside knowledge of Yaesu's release plans? If they don't get a move on the KX3 will steal the show. The KX3 is due to be released at the end of 2011 and order placement is starting very soon.

500kHz humming tonight

WSPR reception at G3XBM tonight - busy on 500kHz!

This evening the 500kHz band is VERY busy with lots of stations on WSPR.  At the moment there are over 20 active stations with 7 stations TXing.  EI0CF and G4WGT are being copied in Russia at over 2500km despite low ERPs.  My own 2mW ERP signal managed to be detected by GM4SLV (896km) and by many others in the UK and Holland.

Another 10m QRP transceiver built

Yesterday I built another simple 10m CW QRP transceiver. This is similar to the Tenner on my website with some improvements. This time the power out is QRO (well 600mW!) and the receiver a direct conversion one built around an SBL1 with passive LP audio filter and 3 stages of audio gain. The VXO, run from a regulated 5V supply, uses a fundamental 28.060MHz crystal which pulls from 28.040-28.070MHz with a sensible RX-TX offset (happens automatically) of around 800-1000Hz. Chirp is better than the simple XBM10-2 as the VXO is better regulated and the PA is a separate stage. Yesterday I worked RZ3QZ before the RX was finished and got reports on the reverse beacon network from W3OA. This morning a full 2-way QSO with UR5IDU (him 579 me 549).

UPDATE 1520z Nov 5th: This rig is working very well with 7 two-way QSOs on 10m CW in the log already since 1140z today. There is a Russian contest and the band is busy with Russian stations. Reports are all 599 of course but no repeats needed so far.

Chirpy (XBM10-2) improvements

28MHz "Chirpy" Transceiver with tuned antenna match

In the last day I  have made some changes to my ultra-simple CW transceiver for 28MHz. Power output now is around 120mW (was 60mW) and the RX sensitivity about 3-4dB better. Both changes are a result of better matching the tank of the oscillator/mixer to 50 ohms using a tuned circuit with a suitable tap rather than a 100uH choke. At the moment the component count is 14 total (excluding crystal earpiece and key). although this could be reduced to 12 if a suitable single component inductor/capacitor with link winding was substituted for the only tuned circuit. The receiver is working and I copied an SV station and K1TG on 28MHz just now. The TX still chirps though. Now I am looking for some further 2-way QSOs (3 so far with best DX IT9QAU/QRP at 1414kms).