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.

Simple low cost test equipment

There was an interesting post in the last day on the GQRP Yahoo group asking about portable workbenches that led on to talk about test equipment. This got me thinking about simple pieces of test equipment and what one needs to do basic QRP design work.

In my own case the most useful pieces of kit are (1) a signal generator, (2) an inductance/capacitance meter, (3) an oscilloscope,(4) a basic power meter, (5) a wide coverage all mode RX, (6) a multimeter. I keep thinking about building a dead basic spectrum analyser too. Test probes too of course. Also a good lot of cables with BNC plugs one end and croc clips on the other.

Just wondering what other people use? Certainly for HF QRP work only very basic test gear is needed, which is why I enjoy it so much.

In a way it is a little surprising that no-one sells a low cost "all in one" test box for amateurs with many of the above in one unit. A bit like a CB test box?

Not the best of weeks

Well, apart from the excitement over the ferrite rod on TX, this has not been a too brilliant week.

As you saw in the last post, my website domain name provider seems to have messed up web forwarding thereby screwing up the G3XBM website, for now at least. This is annoying as it has also caused issues on the www.cambschoral.org.uk website that I set up and maintain for the Cambridgeshire Choral Society.  And then there is 137kHz where a week of trying has netted me spots from just 4 unique reporters. Even the effort to get WSPR15 working was all but scuppered by the 4Hz drift over 15 minutes in the FT817.

In the grand scheme of things none of this much matters. Perhaps next week will be more fruitful, HI. In the meantime, I'm watching TV and having a whisky!

Website woes

In the last few days I've done a major overhaul of my main website www.g3xbm.co.uk . All was working fine, but for some reason the web forwarding is not working correctly. Landing on the www.g3xbm.co.uk site you should automatically be forwarded to https://sites.google.com/site/g3xbmqrp3/ which is where the site is now located on Google Sites. So far so good, and this happens, although the address bar, which should change to the new site address based on how I've got my forwarding set up does not. Not only that, but clicking any images does NOT bring up larger, clearer images as it should although this works fine when you start with https://sites.google.com/site/g3xbmqrp3/ . So, I think it is a problem with the web forwarding, which I will try to fix.

In the meantime, you may want to go directly to https://sites.google.com/site/g3xbmqrp3/ if you want to explore the revised site.

First WSPR15 transmission decoded successfully

After a LOT of effort, G8HUH managed to decode my WSPR15 transmission on 137.607kHz at 1815 this evening. Even with a very low (1.7MHz) LO, the drift was still 4Hz in the 15 minute TX period, mainly due to the FT817 I think. At only -32dB S/N decode this was actually not as good a result as with WSPR2 over the 250km path. Short of force cooling the FT817 or using a rig with a TCXO reference, there is nothing more I can do.

My WSPR15 transmissions were also copied and decoded by G4FFC and G4FEV.

CONCLUSION: WSPR15 is a much more tricky mode to use successfully unless the transmission is very stable. This is the screenshot Tom G8HUH sent me.

30uW ERP 137.607kHz WSPR15 signal received by G8HUH 

137.5kHz WSPR15 tests

Using a very stable external signal generator as my 10.0000MHz LO 5dBm injection, I'm now in a position to try WSPR15 with a stable signal. After a quick frequency check with WSPR2 I propose to switch to WSPR15 with its greatly improved weak signal capability for this evening and overnight. WSPR15 activity takes place in the 25Hz slot just above the WSPR2 activity.

Please let me have any reports.

The first WSPR15 transmission will occur at 1600gmt.

Update: Tom G8HUH reported an upward drift of 5Hz during the 15 minute TX burst, so I've moved the LO to 1.7000MHz and the FT817 to 1.836kHz. Drift (all due to the FT817) is now 1Hz. Awaiting decodes. 

137.5kHz ...it's getting repetitive

Well, I've had the 137.5kHz WSPR2 beacon running for about 18 hours now, almost continuously on a 25% TX cycle. I've tried to drum up reporters by posting on the WSPRnet chat page, RSGB LF Yahoo Group and the LF Blacksheep reflector, plus a few direct emails to stations likely to copy my signal.

Consistent 137.5kHz WSPR spots from G8HUH at 250km, but no others!

All I've managed are the very consistent reports from good old G8HUH at 250km. The signal is obviously spanning this distance without any issues so why no others reporting?

Later I am going to replace the 10MHz LO in my transverter with the stable source from my synthesised signal generator and have a go tonight at WSPR15 (15 minutes TX periods) and see if that gets me a few more reports. It should be several dB more sensitive. If that fails to get anywhere, then I am calling it a day on 137kHz. In terms of returns for effort, this is not good value.

Internet Time Servers

For WSPR, and probably quite a few other programmes, it is important to have your PC's clock accurate to within a second or so. With WSPR, if you are more than a few seconds out the software will be unable to correctly decode signals. There are several internet time servers around which sync the PC clock to very accurate time standards around the word.

The one I use is http://www.worldtimeserver.com/atomic-clock/ . This allows you to download a program called atomic.exe which syncs your PC clock at an interval you choose to an internet time server. It is a great help to keep an old PC in time for WSPR. Without this my old Dell Inspiron would be all over the place with time. Once installed there is nothing to do as long as you have an internet connection.

Going QRT on 137kHz

Another evening on 137.5kHz WSPR and reports again from G8HUH at 250km,  BUT FROM NO-ONE ELSE. I really don't want to run higher power or erect a big antenna. To be honest it is not worth the effort continuing on this mode on this band as there are too few monitoring stations. At the moment I am not inclined to box and finish the transverter. Instead, I think I'll try something else. Not sure what but the potential and unfinished project list is huge.

Ferrite Rod TX on 10MHz WSPR

This morning I tried the ferrite rod antenna on 10MHz WSPR TX for an hour. As before, I mounted the ferrite rod VERTICALLY on the wooden desk with all other antennas disconnected -  the only other antennas are a VHF colinear and a 10m halo, and both of these are around 10m away from the shack. Quite a respectable number of spots we obtained with 2.5W from the FT817.

So far I have not managed to get the ferrite rod antenna to match on 14MHz. It may be the losses in the ferrite are starting to impact performance?

I am still unclear how this tiny TX antenna is working: the assumption is a combination of a small amount of radiation off the H-field (ferrite rod coil) loop and some E-field radiation off the coiled vertical section above the tuned part. Then there is still the possibility that it is just acting as an efficient coupler into the house wiring that is doing the real radiation. Whatever, it puts a signal around Europe and occupies a volume with the tuning cap of just 15cm x 10cm x 5cm on the wooden shack table.

More Ferrite Rod TX experiments

Vertical orientation today - good results on 40m WSPR TX

This morning I tried to get a few more WSPR reports on 7MHz using my small ferrite rod antenna. I managed a few only, then after about 20 minutes I decided to try again with the ferrite VERTICAL on the desk. Don't ask me why I did this, but then I started getting a large number of spots!

Now, all other antennas were disconnected and I tried this arrangement in several places around the room and ALL got decent spots. Maybe what I have here is a bit of a hybrid. If you look at the diagram there are about 80turns on the rod beyond the parallel tuned circuit that I assumed was the magnetic loop doing the radiating. Then again you can consider the parallel tuned circuit as a base loading for the 80t short vertical above it. Tuning C1 will bring the whole system to resonance and a low SWR can be found by adjusting the tap point, which turned out to be best very close to the bottom, about 1 turn up. There is no earth connection. I make no claims as to how this works. Some suggest it is just an elaborate coupler into the house wiring, but the very sharp tuning makes me think this is not likely. Also, if this was the case then surely moving it around in the room would make a big difference? Below are the spots for a few hours on 40m.

WSPR spots with the antenna above on 40m today

However it works, it manages to do pretty well. Now I do not believe in "snake oil" antennas, and make no claims for this one: a small ferrite rod will radiate something (H-field). Add a ferrite loaded vertical as well (an E-field antenna) and that will radiate too. What happens in the far field goodness only knows!

When the weather is better I will take the whole kit into the back garden well away from the house and repeat. If it is working without coupling into the house wires (as I think is the case) then results should be comparable. If spots disappear then it will have turned out to be a very good random wire coupler, HI.

73 Magazine back-issues on-line

http://mikeyancey.com/73mag/listauthor.php? is a searchable list of articles from the old 73 Magazine. I was pointed to it by Leon Heller for an article by Richard Q Marris, G2BZQ about ferrite rod transmitting antennas. Mike Yancey's site has some other useful stuff too, so worth a more general look.

Requests to share xbmqrp website

Friends, PLEASE, bookmark my main website correctly. Don't bookmark my pages where they are actually located (Google Sites) as these may change, as they did yesterday when I did a major site update.

So to access my main website go to, and bookmark:

www.g3xbm.co.uk

Dry eyes and RF?

Testing the ferrite rod antenna on TX this evening (with lots of RF within a metre of me) I'm noticing something I used to get when testing VHF RF PAs years ago in my design days: dry eyes. I assume this is an effect of RF on the body.  Apart from being madder than ever (!) I cannot say RF exposure has done me any noticable harm, but wonder if others have noticed this dry eyes effect?

Although the evidence in general is not strong, there was strong correlation back in my Pye Telecom days between those working on the design of high powered HF/VHF/UHF PA devices and those fathering girls. Maybe there was some subtle damage to sperm with exposure to high RF that made girl pregnancies more likely to succeed? Co-incidence?

A lot more controlled tests are needed, but with the widespread exposure to Wi-Fi and mobile phones it won't be too long before we find out more. So far the evidence is not at all conclusive but you do wonder whether, like smoking, we'll look back in 50 years time and say, did they really all use mobile phones and Wi-fi devices?

More Ferrite Rod TX DXing

This evening I fired up the FT817 and the small 15mm diameter ferrite rod tuned with a 365pF air-spaced variable and have been spotted on WSPR even further away. This time a couple of spots from Norway, the best being LA9JO 2096km away. As someone pointed out, I may be coupling into local wiring and this might help, but the ferrite rod behaves just like a loop with good directivity and matching just as you would expect i.e. a very low impedance tap point is needed for a good match and tuning is extremely sharp. Personally I believe the radiation is all coming from the ferrite rod and nowhere else.

WSPR reports with a ferrite rod TX antenna on 40m (5W into rod)

TXing with a ferrite rod antenna on 7MHz

Just for fun this morning I tried WSPRing on 7MHz using JUST a ferrite rod wound coil and a 365pF tuning capacitor as a tiny loop antenna sitting on the desk. All other antennas and grounds were disconnected fully. I used one of the low tap positions to find a 1:1 SWR position and put the FT817 on 2.5W (3 blobs). The rod did not get warm. The wire used is around 0.5mm enamelled copper with around 60 turns, tapped at every few turns at the cold end.

The ERP was very small, although I have not yet measured it. To my total amazement, I got an immediate -24dB S/N WSPR report from OZ7IT in Denmark at 853km. Just proves how incredible WSPR is and what a powerful tool it is for simple experiments like this.

Ferrite rod TX antenna on 7MHz WSPR - it worked!

OFCOM licence exemption

Martin G8JNJ has brought to my attention a little known, to me at least, OFCOM concession that appears to allow licence exempt operation under certain conditions in many, if not all, parts of the radio spectrum for research and development purposes.

Although OFCOM will grant Non Operational Licences (these were once known as Test and Development Licences) and charge you £50 a year for the privilege (!)  to test new equipment or carry out specific research, they do NOT require a licence if emissions measured at a specified distance are below certain levels (supressed radiation conditions). See http://licensing.ofcom.org.uk/binaries/spectrum/non-operational-tech-licence/ofw357nonopguide.pdf for some guidance notes on this.

My own interest is to research earth-electrode antennas in the frequency range between 8.97kHz (where I already have done some tests) and 137kHz (where I have also tested this antenna structure). Using WSPR and other weak signal techniques, quite a lot of useful work can be done with low uW EIRP levels. It would be interesting to see how such an antenna structure behaves at say, ~40kHz and 73kHz. It may just be possible to do tests at moderate ranges (in the far field) without a licence. Now wouldn't that be interesting?

Lack of WSPR2 activity on 137kHz

Having run WSPR2 now for a couple of days on 137.5kHz, I have still only received reports from 2 different stations, although I have had LOTS of their reports, suggesting my signal is consistently reaching 250km. My signal is clearly visible to at least this distance, but without people looking I cannot be sure how much further can be expected with the earth-electrode antenna and 30uW ERP.

Although I will box up the new 137kHz transverter and tick the "finished" box I am disappointed that there is not more activity. Most LF/MF people are exploring the new 472kHz band, so interest in Europe for 137kHz is not high apart from DK7FC who is putting out a massive signal that is being copied in both North and South America.

So, what next?  My mind is beginning to think of my new QTH in the village, which we expect to move to in the summer.  What antennas can I put up without upsetting the neighbours? What will the noise floor be like? How much better will VHF/UHF coverage be from the top of our little "hill"?

Main G3XBM website facelift

Revised G3XBM main website

This week I have been doing some housekeeping on my main website www.g3xbm.co.uk .  At the moment the content is much the same as before, although some old pages have not been recreated.  Hopefully the new site layout will be easier to navigate using the sidebar menu. Please let me have any feedback or errors that you spot with links or content. Over the coming weeks I hope to add further new content.

If you bookmark the site please bookmark www.g3xbm.co.uk and NOT the page it automatically redirects too. You will no longer be able to reach the old site and I do not propose to grant individual access permission to the archived old site. Already I have had several requests for access to the old pages.

My new WSPR DX record on 137.5kHz

Having run the 137.5kHz transverter with WSPR-15 (15 minute on periods) overnight - around 30uW from the earth-electrode antenna - I wasn't too hopeful about my chances with WSPR-2 this morning. WSPR-15 failed because of the thermal drift in the 15 minute on period I think.

Anyway I put the TX on WSPR-2 on 137.5khz this morning and let it run. After a couple of hours with no success I was VERY pleased to see I had been spotted several times by G8HUH at 250km. My previous record a year or so ago was just 148km (G3YXM) so this is considerably further and entirely in line with my predictions based on the QRSS3 beacon results.

WSPRing again on 137.5kHz

Today I built a breadboard version of my transverter for 137kHz and now I have it running WSPR-2 for the evening.

RF power from the IRF640 transverter PA is around 30-40W (depending on the PA voltage) and the ERP should be around 25-30uW using the earth-electrode antenna.  At present, the transverter is only on 20% duty cycle TX and I have still to add the RX preamp and switching.

My recent 137.766kHz QRSS3 tests using a measured just 6.6uW ERP from the earth-electrode antenna have now concluded.  Best reports were G3WCB (101km), G3XDV (61km) and G4FEV (56.7km).

G3XBM just detectable on G3WCB's trace at 101km

Stronger signal with G3XDV at 61km

Similar signal at G4FEV at 56.7km

Judging by the QRSS3 results with 6dB lower ERP than my WSPR signal, I think reports out to >100km should certainly be possible as long as people are looking.  WSPR2 is able to detect at about the same level as QRSS10, so overall I have around 11dB more "system gain" (5dB QRSS3 to WSPR, 6dB ERP improvement).

Oscar 6 and 7 satellites

Way back in the 1970s I took my first steps into amateur space communications by listening to the SSB and CW signals coming down from the new (then!) Oscar 6 and Oscar 7 satellites as they passed over. Equipment was an HB9CV antenna in the loft, a 2m-80m homebrew converter feeding a Codar T28 receiver. It was crude, but it worked fine. The same set-up worked well for monitoring 2m CW and SSB terrestrial activity as well.

Using my "osculator" - a map with the satellite paths and an overlay showing when the satellite would be in range on the various paths I could predict when signals would first appear from the south and disappear in the north.

Best passes were ones over the mid Atlantic when , for around 10-15 minutes, sometimes less, US and Canadian stations would appear at the top of the 2m band. It was very exciting at the time. If I recall correctly HB9HB was a beacon near the top of the band and that could be copied too via the satellites.

Although I had one satellite QSO years later with a 10m-15m transponder on one of the later Oscars, I never did get into it on TX.  In the Southgate News today I read that Oscar 7 is still good for DX QSOs even though it is now 37 years old. Whatever happened to the Phase III satellites in geosynchronous orbit like Oscar 40? Did that fail to work?

You can see where the satellite is now at various websites allowing tracking. For example http://www.n2yo.com/?s=7530 .

137.766kHz ERP - now measured at 6.6uW

So, today I repeated my field measurements to establish the ERP of my 8W 137.766kHz beacon feeding my earth-electrode antenna. This time I did the measurement correctly. Here's how.

1. Travel 2km from the home QTH with E-field probe, FT817 and PC running Spectran.
2. Choose a location in the best direction for the "loop in the ground" so the measured signal strength is close to the maximum possible i.e. not off the sides of the loop.
3. Set up FT817 so the RF gain is adjustable and turned well back and the AGC is inactive.
4. Tune in my LF beacon and adjust the RF gain to the lowest possible detection level.
5. Measure the S/N of my signal with Spectran and note reading.
6. Retune to DCF39 (138.830kHz) and, without adjusting the RF gain at all, measure the S/N with Spectran.
7. Repeat these measurements 5 times.
8. Calculate the difference in dB between my signal and DCF39 (in my case 41.3dB)
9. Using the assumption that DCF39 has a field strength of 1mV/m, work out my own field strength (in my case 9uV/m)
10. Using the formula ERP = (E^2 * d^2)/49 work out the ERP.

Answer? My measured ERP on 137.766kHz is 6.6uW

Caveats:

1. If DCF39 is not approx 1mV/m then the ERP needs to be adjusted up or down proportionally.
2. Measurement error is +/- 2dB.
3. The ERP is the figure measured in close to the best direction. Off the sides of the loop the ERP will be much lower.

Conclusions:

1. Stations able to detect the QRSS3 signal at any distance are doing well as the signal is very weak indeed.
2. Using my proposed WSPR transverter at 32W, for example as a reasonable target output, would give me 6dB more ERP at around 25uW.
3. Based on results with QRSS3, I should be able to be copied using WSPR-2 at up to 100km on ground wave. At night with sky wave, considerably further is possible. 
4. Using WSPR-15 and 32W my ground wave range should be up to around 200km, possibly a little more. 

The QRSS3 beacon is still running over the weekend and more reports would be welcomed

SMA version of the G3XBM 472kHz transverter

In an email,  John G4BAO tells me he has built an SMA version of my 472kHz transverter. At present, he is getting 5W RF out using standard SMA parts and a different FET.  If you wish to enquire about this version please contact John and NOT me!

G4BAO's SMA version of the G3XBM 472kHz transverter

Amateur activity on VLF in the last few days

Several amateurs in Europe have reported strong signals on 8970.022Hz VLF, a frequency used in the past by DJ8WX near Hamburg. It is some months since there has been any amateur "dreamers band" activity, so this is very welcome. This is the signal as seem in the Czech Republic on the OK2BVG grabber. Note the timescale on the grabber picture. It is necessary to watch the signal for very many hours to see the signal appear. Hence, very stable transmissions are needed, and a receiving system that is able to hold to a few uHz for hours and hours on end. Just listening on VLF and you will have ZERO chance of detecting such signals.
Amateur VLF reception is usually a "whole new ballgame" compared with listening for the strong MSF signals sending to submarines which are very strong.

VLF amateur signal, believed to be DJ8WX yesterday seen on Lubos, OK2BVG's grabber

My ERP on 137.766kHz is.......

Thanks to G4FEV, I've just realised that I made a fundamental mistake measuring my field strength, forgetting to turn off the AGC when taking the measurements of my signal relative to DCF39. Whereas my initial measurements indicated the ERP was in the low mW region, in reality my signal is much, much weaker. For example, G4FEV reckons my signal is some 70-80dB weaker than DCF39 where he is, if not more! So, tomorrow I shall have to try the test again and see if I can get a sensible figure with AGC turned OFF.

G3XDV's screenshot of my QRSS3 LF signal this afternoon.

Mike G3XDV (61km) has just sent me a very comprehensive report with 178 screenshots of my QRPp signal over the last 30 hours. Copy was remarkably good considering everything. Again, I am amazed how well this works.

G4FEV reports my QRSS3 LF signal at 56.7km

Path between G4FEV and G3XBM

This afternoon I was out and about with my E-field probe checking signal levels of my little 137.766kHz QRPp QRSS3 beacon at various locations around the Cambridge area. The furthermost point I tried was near Comberton, 21.5km WSW of the home QTH in Burwell. I have taken a lot of measurements, including the level of DCF39 at the same locations so that later I can work out my field strength and thence ERP.

G4FEV's screen shot of my QRPp QRSS3 137.766kHz beacon at 56.7km

When I arrived home I had an email from Dave G4FEV 56.7km due west of me to say he had copied my signal and had sent a good clear screenshot. Signals with Dave looked quite good, suggesting the signal due west may be stronger than signals in the Cambridge direction (SW - WSW). The earth-electrode antenna has directivity but, aside from a zero copy at one location orthogonal to the "loop" I have still to work out exactly which directions have the strongest signals. Based on the above I think it is close to W-E.

Disappointment on 137.766kHz

Despite running my QRP LF beacon for over 2 days continuously I have received no successful reports. A couple of people looked without success, but at least they tried. I am leaving it running QRSS3 today as I want to do some further reception tests this afternoon and measure my ERP by taking actual field strength measurements out to about 15km from home. Let's hope I get a few positive reports as the signal should be detectable out to at least 60km.

Checking my 137.766kHz ERP by measuring field strength

Well, today has been a bit of a disappointment: my QRP QRSS3 beacon has been running for over a day on 137.766kHz and, apart from my own highly successful reception tests out to around 8km (as far as I went in the best direction) not a single station has reported seeing it  ....yet.

Tomorrow, I am going to do one more experiment using the QRSS beacon: knowing the field strength of DCF39 on 138.830kHz, a commercial station in Germany, is around 1mV/m here in the south of the UK in daytime, I want to measure the S/N of this station about 5km from home using the mag-mounted E-field probe. Then, at the very same spot, I will measure the S/N of my beacon with the same bandwidth settings and RX kit.

Based on these two measurements, I should be able to work out the ERP of my beacon to an order of magnitude and probably to within +/-3dB. The field strength of my own signal can be worked out just by comparing the S/N with that of DCF39.  Knowing the field strength and the distance from the home QTH, I can work out the ERP needed to produce this.

Any guesses what ERP I am using? I'll tell you the answer tomorrow!

New 137kHz Transverter thoughts

IRF640 FET

This evening, I've ordered a reasonable sized heatsink to use with the new 137kHz transverter. I am aiming for a power from the transverter of at least 30W and want to be sure that with mismatch the PA is able to survive quite hard abuse. The IRF640 looks a good choice for the PA, maybe a pair, as it is rated at a high voltage (200V) and high current (18A) so I can run the PA from a 30V (or even 50V) supply to get more out. Even with 30W RF, the ERP will still be in very low milliwatts.

As I want to ensure the 10MHz LO signal is very stable so I can use it with WSPR-15 and QRSS30 modes, I may put this in a separate insulated enclosure and pipe the injection signal in via coax.

What I am most concerned about is the lack of activity on the 137kHz band: the last time I gave it a go with WSPR the biggest issue was the very few people actually monitoring WSPR on the band. At the moment, the new 472kHz band is very much the focus of attention with up to 50 WSPR users monitoring and/or TXing on any evening. On 137kHz however the number of WSPR users is often just 3 in the world with no-one on in Europe at all.

Still, I am convinced that with WSPR-15 I should be able to reach near Europe even with my 20m earth-electrode antenna if I can get the power up to around 30W from the transverter. It may even be possible, just, with WSPR-2.This is worth a go, before getting back onto other projects ...like finishing off the Tenbox transceiver!

Lightning across Europe

Lightning map of Europe http://www.blitzortung.org/Webpages/index.php?lang=en

Sometimes it is useful to know where there are lightning strikes taking place across Europe: for example, there are some theories linking sporadic-E propagation to a secondary effect of lightning, although I forgot where I read this. Also, it is useful to know how noisy the VLF and LF bands are likely to be as a result of sferics from such strikes.

Well, http://www.blitzortung.org/Webpages/index.php?lang=en gives a map showing this data.

Homebrew RF Circuit Design Ideas website

HA5KHC's useful website

Wandering around looking for 50W PA designs for 137kHz this afternoon,  I chanced on a website that I don't remember seeing before by HA5KHC. It consists of a HUGE list of very useful links to other websites arranged by design topic (transceivers, receivers,  etc).   It is a massive list of useful links that I could spend days trawling through for ideas and inspiration.  It was quite flattering to see a couple of my designs linked.

Unfortunately there is nowhere on the page with a contact address for the website owner, although I expect HA5KHC's details will be on QRZ.com.

UPDATE:  Adrian YO5PBG said:

"I believe it is a mirror of the original site... of Iiulian - YO3DAC/VA3IUL - http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm" 

New frequency for LF QRSS3 beacon : 137.766kHz

Using the strong German commercial station DCF39 on 138.830kHz (it is S9+ with me) as an accurate frequency reference, I have checked the frequency of my QRSS3 QRP beacon and it is running higher up the band than I thought due to the way the crystal is loaded. 

Frequency to look is 137.766kHz   +/- . It should be within 1Hz of this frequency. 

Reports and screenshots (looking now in the right place) would be very much appreciated. I shall leave the beacon running all today at QRSS3 speed.

137kHz E-field probe mag-mount

Tiny E-field probe on the car roof on mag-mount

This is the schematic of my simple mag-mount based E-field probe for 137kHz reception in the car. I use a low cost MPF102 FET and a low cost 2N3904 transistor. Performance seems to be totally adequate, detecting my very low ERP QRSS3 beacon as I drive around the local area up to around 10km (yet to test at greater range) from home. The whole unit is attached at the base of a 15cm whip on a mag-mount stuck on the centre of the car roof. The coax from the EFP connects into an FT817 with the IPO button ON - this makes the sensitivity better on 137kHz, a tip worth knowing.