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!

Simple antenna current meter

https://sites.google.com/site/arvidevans/LED_Antenna_Current_Indicator.png

Just spotted this on the web. Looks like a useful idea to indicate antenna current and could not be simpler.

Simple pleasures

Today for a change, and whilst waiting for the family and grandchildren to arrive for half term holiday, I simply went on 20 and 15m and just operated using the 2.5W pep SSB from the FT817.  No great DX, with the best contact being OY, but a few nice enjoyable contacts in the log. The speech processor certainly helps.

It is tempting now to build a multi-band VXO controlled QRP CW transmitter to use with the FT817 (on receive) as it is a while since I operated QRP CW on 40 and 20m. With the EF-10/20/40 antenna now up it is an ideal time to do this and enjoy the simple pleasures of operating QRP on the HF bands again. In my mind I think a 2N3904 VXO and buffer followed by an IRF510 PA at around 2-3W.

Par EF-10/20/40 Antenna and a comparison

This afternoon I decided to take down my 10m halo for a while and replace it with a lower antenna: the LNR Precision (was Par) EF-10/20/40 end fed wire antenna, which I've owned for some years but not used recently. As it suggests, it covers 10, 20 and 40m with a very low SWR, although it is a reasonable match on several other HF bands too.

See http://www.hamradio.me/antennas/lnr-precision-ef-102040mkii-test-data.html for an analysis of this antenna.  The antenna works very well and on 40 and 20m WSPR I was getting plenty of spots with 500mW to 5W.

Photo on http://www.hamradio.me website of the Par antenna

On 40m I did a comparison between the horizontal EF antenna and the earth-electrode antenna. A series of transmissions was made with each antenna in turn, then I compared WSPR spot S/N received from a number of stations.

The conclusion is the earth-electrode antenna is around 9-16dB down on the EF antenna on 40m, so averaging about 2.5 S-points down. The test is not too accurate as conditions change, the earth-electrode and EF have some directivity and the reports sample size was small.

Grandchildren time and new projects

We've all 4 grandchildren coming to stay at different times over the next couple of weeks. As usual, this means that amateur radio activity will decrease somewhat as the upstairs shack gets used as a real bedroom again. It will still be possible to run WSPR on LF and MF and some of the HF bands from time-to-time, but not in the evenings.

Whilst this "interlude" is going on, it will be a good time to take stock and think of the next projects. The early part of 2013 has seen a burst of activity related to the earth-electrode antenna and the ferrite rod TX antenna, neither of which was planned. I also did some more work on a 136kHz transverter Several projects, including the 136kHz transverter, are still unfinished:

Tenbox 10m AM transceiver
Although most of this has been breadboarded and is working, it still has to be boxed and properly documented. I quite fancy a PCB for this simple design and that needs to be created.

471THz over-the-horizon tests
My PhlatLED very high power LEDs have yet to be switched on and I still have to build a more sensitive detector.

De-cluttering and Test equipment
With a move to a new QTH later this summer I really ought to think about de-cluttering and sell some lesser-used radio equipment. At the same time I could do with building some more pieces of simple test equipment such as a proper QRP power meter, a resistive SWR bridge, a better ATU, and a very basic spectrum analyser.

Other projects
There is a list as long as my arm of other projects I'd like to tackle, but it takes me all my time to do the ones I do! 

IC7100 Sneak Preview Video

There is a short YouTube video clip from ICOM America describing the IC7100 with a look at the various connections on the head and main unit. The thing that impressed me was just how small this transceiver is. It looked larger in the earlier pictures. The IC7100 is likely to be on sale in the UK in late spring at around £1700-1800 without the D-star option. Not cheap, but a lot of radio.

The specification of the IC7100 is available here.

Hard to believe this is without a conventional antenna

As 40m went rather quiet, I QSYed to 80m WSPR on the earth-electrode antenna this evening. The log below is from just one single 2 minute transmission with 2W.

12 spots in one 2min burst this evening with 20m spaced earth-electrode antenna

Earth-electrode antenna on 40m

This evening I have been trying my stealth antenna (20m separated earth-electrodes, wire in the grass!) on 40m again and getting plenty of WSPR spots. I did try to match it on 160m earlier but couldn't get it below about 3:1 using the Elecraft T1 auto-ATU. Spots from 6 countries in an hour (LA, DL, F, EI, GM, G) with strongest reports from Cornwall (-3dB S/N) which is in the line of the wires/loop.

WSPR spots received using 20m spaced earth-electrode antenna with NOTHING in the air.
 

Earlier today I had a visit from Ted G4NUA, so I showed him my 137kHz antenna, "Where is it?" he said. Exactly - the wire runs back to the house from the far earth rod IN the grass and it is all but invisible!

Earth-electrode antenna on 80m

This evening I have been using the 20m baseline earth-electrode antenna on 80m. From the shack (upstairs) there is a 20m coax down to the back of the garage where it picks up the earth electrode wires. On 160m the match is poor but on 80m a near perfect 1:1 match, so no radiation from the coax.

On receive there are plenty of signals visible and decoding on WSPR and on TX it seems to be getting out pretty well with 1W RF from the FT817.  I am not sure of the ERP on 80m, certainly higher than on 630m (472kHz), but it does appear to be quite effective.

Tomorrow evening I'll match the earth-electrode antenna with the Elecraft T1 auto-ATU and see how it performs on 160m. I'll put the ATU right at the earth-electrode end of the coax so that we'll see the radiation from the earth-electrodes and not the feeder.

10m WSPR

10m WSPR reports late this afternoon

This afternoon, whilst updating my website, I put on the 10m WSPR beacon. All was very quiet for the first hour or so and I was about to switch it off. Then I looked and saw a heap of stateside spots had appeared. This is the beauty of WSPR: you can get on with other things and use it to see when the band opens up. It will become especiallyuseful on 10m when the peak (such as it is) is over and we are looking at quiet conditions on 10m again. At least with WSPR there will be a much clearer picture of the openings that do occur.

137kHz E-field probe on my website

This afternoon I put a new page on my www.g3xbm.co.uk website describing the 137kHz E-field probe antenna used in my recent "drive around" tests in the local area out to 25km. You may recall I put my 6uW ERP QRSS3 beacon on and went out into the Cambridge countryside trying to see how strong it was in various locations.

The whole unit is fixed to a car mag-mount antenna and works very well indeed.

OFCOM licence exempt loopholes

Still trying to see if there are any loopholes that would allow me to legally carry out radiated tests between 40-80kHz as mentioned in earlier posts.

Currently I'm pondering an OFCOM document called IR 2030 - UK Interface Requirements 2030 Licence Exempt Short Range Devices .  This document seems to offer some hope by adopting the licence exemptions applicable to short range devices such as metal detectors and induction communications systems. For example, for metal detectors, it says,  

"That part of an induction system designed or adapted to produce:- (a) a controlled magnetic field; and (b) a predetermined recognisable signal when operating within that magnetic field" 

in the frequency range 9 - 148.5 kHz the emission level is [not greater than] 70 dBμA/m at 6 m. My maths is not good, but this is 3.15mA/m which sounds quite a lot. Some other specifications allow 72dBuA/m at 10m, which is considerably more. It seems I need to read a copy of document EN 300 330-2 which describes the rules and test methods. Although these rules are designed for systems that use induction field communications, the unknown is how much signal that meets these requirements might be radiated and detectable with sensitive kit in the far field?

Incidentally, it is surprising how many non-amateur frequencies can be used legally with (useful) QRPp power levels in the MF, HF, VHF range, no doubt with some type approval stipulation or at least CE declarations being required on the equipment. With WSPR or similar weak signal modulation systems, some most interesting experiments could be carried out in unusual parts of the LF, MF, HF and VHF spectrum, apparently without a licence being needed, as long as the emissions limits are met.

OFCOM ..."no you can't" again at LF

This afternoon I got another email from OFCOM. Although my requests have been passed upwards for other more empowered people to consider, it is effectively a refusal of permission to carry out experimental research for short periods even at 10uW EIRP on clear spot frequencies in the LF spectrum between 40 and 80kHz without getting a £50 Non Operational (T&D) Licence, which I am not prepared to do.

Thank you Mark VK6WV

Amateur radio has some very kind and generous people still.

In the post today I received a letter from Australia quite unexpectedly. In it were a number of 480kHz ceramic resonators that Mark VK6WV had sent me, as a gift, for me to try in a 472kHz transmitter. Mark, many thanks!  This was a very nice surprise in the best spirit of amateur radio. I shall indeed use these to build a little 472kHz tunable CW transmitter. I'll also try using these in an RF stage of a receiver for the 472kHz band.

This is not the first time I have been on the receiving end of generous fellow amateurs and it is so lovely to know that there are kind people about who simply want to give and to share. Mark didn't even give me an email address that I could use to thank him, so I am doing so here via the blog.

Wonderful! You made my day Mark.

137kHz 30-40W TX transverter schematic

As promised, here is the schematic of the current 30-40W TX transverter for 137kHz. I have used a 10MHz crystal but a lower local oscillator frequency would be slightly better from a stability viewpoint when using narrowband modes like QRSS30 or WSP15. One choice is to use a low cost 1.843kHz crystal mixing with the driver transmitter's output at 1.979kHz. When a stable external LO source is possible e.g. a GPS disciplined oscillator, remove C7 and feed the LO into the double balanced mixer. Although an SBL-1 mixer was used an alternative, available from eBay is the ADE-1. As balance is not super critical, a home made double balanced mixer would also be possible.

For PA heatsink I just used a couple of small TO220 heatsinks in the prototype. With optimal PA matching into 50 ohms there is little heat from the PA device. A larger heatsink could prevent overheating when the antenna is mismatched. My output network was optimised for my slightly higher than 50 ohms output load presented by my earth electrode antenna.

ERP is around 30uW with my earth-electrode antenna.

Some may prefer to use capacitive coupling into the FET gate. If TR3 failed open circuit, the gate voltage would rise leading to the IRF640 failing. Hasn't been a problem so far though.

A dialogue with OFCOM

At last, and only 3 months late, OFCOM have renewed my NoV for 8.7-9.1kHz VLF operation.

Currently I am "in negotiation" with OFCOM on another matter mentioned a few days ago.

In the next few months I want to do some QRPp radiated tests with the earth-electrode antennas at some frequencies between 9kHz and 137kHz. Ideally this would be around 35-45kHz and 70-80kHz, where I can find a quiet spot without any activity from primary users like the Ministry of Defence.  With QRSS, continuous carrier or WSPR and with an EIRP of around 10uW it should be interesting. Tests on 137kHz suggest this power is enough to see a radiated signal out to at least 25km locally with an E-field probe on the car, which would allow me to check coverage and polar plot. On the lower frequencies this may be limited to just 5-10km, but that would be OK.

But, OFCOM say they will not grant me licence-exempt permission to operate in this part of the spectrum, even at the miniscule powers and bandwidth (uWs and a few Hz).

They say they would HAVE to consult with the primary users and this would take months. They suggest instead I apply for a Non Operational (Test and Development) Licence, but does that not need primary user approval too?  Problem is this licence costs £50 a year, which sounds like total overkill when the risk of me interfering with anyone is about as likely as me winning the lottery or landing on the moon when I jump.

Now, I could just go ahead and do the tests anyway knowing I will not cause anyone a problem.  Really this is not the way it should be and anyway I'd like to publish the results later. Hardly possible if I don't do things with OFCOM's approval.  I am hoping that the good people at OFCOM will see that this is worthwhile amateur research, it won't cause ANY issues and they will soon say, "go ahead on the strict understanding that if you cause any harmful interference to primary users you close down immediately, but at that power, no licence needed."   I have written back to OFCOM again this evening making this case and we'll what transpires. I also suggested issuing me a one-off NoV, but they say they won't!

Many of you will be saying, "why not just do it". If the powers that be really cannot see sense, then maybe I may have no other option.

Website working again

The main www.g3xbm.co.uk website is now working properly. I contacted my domain providers last night who confirmed they'd updated some systems that screwed up web forwarding. If you spot any more problems, typos or link errors please let me know.

Currently I am drawing out the schematic of my 30W 137kHz TX transverter. This should be on the website tomorrow. Still deciding whether to box it, and add the RX preamp section, or stop at this stage.