31 Aug 2011

What is my ERP currently on 137kHz WSPR?

Based on some measurements and calculations using the improved ATU (see photo) today, this is my calculation:

Measured antenna current in the TX loop = 2.13A
Area enclosed by the loop = 80 sq m
P = (I^2 x A^2)/(205 x 10^6) at 137kHz   (see p101 of "LF Today" book available from RSGB)
where P = ERP,  I = current in amps and A = loop area in sq m

P = (2.13 x 2.13 x 80 x 80)/(205 x 10^6) = 141uW

This is not a lot (but more than ever before) and this is before I start on the "ERP improvement" programme.

137/500kHz ERP improvements

Today I made a start on improving my ERP on 137kHz and 500kHz.

Firstly, I've bought a pile of Wima 1000V polypropylene capacitors from Farnell. With these I have now made a new ATU to match my TX loop (breadboard only ATU so far) which will allow me to run some 6-10dB more power into the loop without the ATU components overheating and failing. My old switched capacitor array was an old school capacitance decade box and this was marginal with tuning changing as caps heated up!

Secondly, I am going to change the MOSFET PA design to increase the 137kHz power from around 7W RF to about 30W. This should be worth around 6-8dB. I plan to do something similar on 500kHz too.

Finally, I've got some more wire to allow me to double the thickness of my TX loop. This will be done later and will be worth 2-3dB as long as I alter the 3C90 ATU (step down) matching transformer.

In all, these changes will give me up to 10-13dB more ERP and, with some luck will allow me to get more reports on QRSS and WSPR. It will take some weeks to implement these, but by late October my range should improve on both bands.

30 Aug 2011

VLF NoVs to be extended

OFCOM has confirmed that the UK NoVs to operate in the 8.7-9.1kHz VLF band will be extended later this year if holders request this.  Discussions with the Met Office have confirmed no problems have been observed with operation in this band. This is good news. Currently there are, I believe, 4 VLF NoV holders in the UK: G3XIZ, G3XBM, G4WGT and G7NKS.

WSPR database issues

Some people in the UK, including me, have been unable to find wsprnet.org today. After working perfectly overnight the site just disappeared and via Virgin Media and just some other ISPs it isn't available currently. For others it works OK. This isn't the same as the recent overload issues: something has changed at their end or in the way the site connects to the internet. Hopefully all will be resolved soon or I'll have to resort to CW more often!

A useful site to check connections is http://www.downforeveryoneorjustme.com/# which allows you to check if a site has really disappeared or not. According to this, wsprnet.org is still there, so I assume it is a routing issue.

Shortly before the link was lost I was getting VK8AW well on 10m WSPR. Guess I'll have to wait now to see if my 5W WSPR signals made it to Australia this morning.....

UPDATE: 1415BST - it's back.

29 Aug 2011

US politicians and science - are their politician brain dead?

As the USA starts its next election campaign I'm seriously worried that the country is likely to end up being run by a brain dead, ignorant and downright dangerous politician from the fundamentalist, anti-global warming, anti-science, isolationist brigade. See this article from the New York Times kindly sent to me by Michael AA1TJ.  Although this is about republicans, there are as many democrats with equally stupid views. It seems you have to be stupid in all things (apart from making money) to make the grade over there.  Seriously, we are talking about the nation that is supposed to show the world a moral lead, to champion policies to safeguard the planet.

American citizens, please use your head when selecting you future politicians as it matters very much.

10 unique reports on 500kHz

Stations copying me on 500kHz WSPR
Last evening's WSPR outing on 500kHz was very successful considering this is August. 10 different stations managed to receive and decode my 1mW ERP signal with best DX report from EI0CF at 602km. Best seen here was GM4SLV in Shetland at 896km. This just using a thin wire vertical loop (80 sq m area) around the garden with the lowest side running along the fence in the foliage!

28 Aug 2011

Back on 500kHz WSPR

This afternoon John GM4SLV informed me he was restarting tests on 500kHz WSPR from way up in the Shetland Islands with about 150mW ERP.  So, I've fired up my own 500kHz WSPR system in the hope of copying him later this evening. So far I have had spots of my own 1mW ERP signal from several stations with best DX so far being PA3ABK at 306km, but nothing seen (yet) from John. I'm hoping a few more stations will appear too.

26 Aug 2011


Just discovered Google also do a "shorten your URL" feature too. Go to http://goo.gl/ to try it out. I knew about tinyurl but only just noticed the Google equivalent. As with other shortened URLs, some security systems may recommend avoiding such links.

25 Aug 2011

Bitsbox - an excellent UK component supplier

Just a couple of days ago I placed an order with Bitsbox, a UK component supplier for a variety of components needed in my upcoming VLF/LF experiments. Today, by first class post, the order arrived. Bitsbox charge a fixed £1.50 first class post charge which is very reasonable. The service and value for money are truly excellent. Their website is www.bitsbox.co.uk  and they stock a wide range of useful parts.  If you've not used them before, and I had not, I can highly recommend them.

24 Aug 2011

Heathkit kits again?

The Southgate amateur news page carries a story that Heathkit may be about to start the production of kits again after a break of many years. This would be excellent news. Heathkit used to produce world class kits that were in a class of their own with first class instructions. Let us hope they decide to restart amateur radio kits as well in due course. In the amateur radio field Elecraft are the nearest.

23 Aug 2011


With the autumn season not too far off I am turning my thoughts to 500kHz and 136kHz again. This weekend I hope to return to 500kHz WSPR as GM4SLV is testing his new 500kHz antenna and ATU. After that it will be my turn to improve the ERP on 136kHz with a new PA, ATU and antenna.

21 Aug 2011

Antenna folklore

From the LF-reflector and very true.
Antenna engineers use to say about design goal limits of antennas:


Pick any two (meaning you can't have all three...).

73   Clemens   DL4RAJ

Inter-G 10m DX with 5W WSPR

In the last 24 hours, as well as some excellent long distance DX, I've been surprised by the 10m reports from stations within the UK. For example G4CUI in IO93 and G6BHS in IO81, both around 170km. These are not one-offs as exchanges with G4CUI are common at almost any time. I must keep a record of all the QTH locator squares I get reports from on 10m and 6m WSPR from within the UK. WSPR is an excellent mode for "sniffing out" openings.

20 Aug 2011

Chile on 10m WSPR

Just exchanged WSPR reports with XQ6FOD in Chile at 12285km on 10m this evening at 2054z. At first I thought this was a bogus report but checking on QRZ.com the call is genuine. I think this was Es linking into some TEP F2 propagation as I was getting good reports from Spain.

Good Es DX on 10m

This afternoon I put my WSPR beacon on 10m for a while and was surprised how wide open the band was. Strong Es signals from across Europe and N.Africa plus a couple of excellent reports from R9SA in LO71 square at 3661km to the east. I'm wondering if the band will open up across the Atlantic today. Even with 500mW I was getting very good reports. Reports from OY1OF suggest even 500uW would be enough for a report.

14 Aug 2011

Best results yet on 8.76kHz earth mode

8.76kHz earth mode signal in 45mHz BW at 6km
This morning I slightly changed my VLF low input impedance tuned preamp by increasing the tuned circuit Q and gain of the first stage by around 6dB. After lunch I did a test at 6km from home to see what effect this had on the S/N of my 5W beacon. In a 45mHz bandwidth (previously 11mHz) I was getting a signal around 18dB S/N using Spectrum Lab on my 80cm square loop on the ground. With an earth electrode antenna the signal was marginally weaker and the noise level higher.

My signal is the steady carrier (with a 2min ID break) at 8.7605kHz. The large wobbly line is interference, but who or what is the signal at 8.754kHz? This is rock steady and appears to key on and off every 5 minutes. It looks like some sort of control signal, or is someone else near Cambridge testing?

13 Aug 2011

Rural Suffolk - England at its best

We are blessed with a wonderful variety of scenery and plenty of still quiet rural countryside to enjoy despite our cities being crowded. This afternoon my wife and I enjoyed a ride through rural Suffolk in East Anglia where we stopped at a number of delightful small churches.  There is a lot to be grateful for in an English summer with a gentle breeze, warm sunshine and the sound of swallows, woodpeckers and bees overhead.

Wispy WSPRs

Overnight I was looking for MS propagated WSPR signals on 10m. There were a few early morning decodes as well as plenty of evidence of MS bursts which were too short and too Doppler shifted to permit successful WSPR decoding.

12 Aug 2011

Perseid meteor shower

Overnight tonight the Perseid meteor shower will peak with some dazzling displays in the early hours of Saturday morning if the sky is clear. With luck, MS conditions will be good on 10m, 6m, 4m and 2m with some long bursts. Not sure what band(s) to monitor but may see what can be heard/seen on JT6m on 6m.

11 Aug 2011

Inside a QRPer's brain

G3XBM's brain!
Today I had my brain scanned for scientific research. For several years I've volunteered as a guinea pig at the Centre for Speech, Language and the Brain at Cambridge University.  It involves doing the occasional language test and about once a year having an fMRI scan whilst doing some task involving language. The university has its own MRI unit for medical research. The whole MRI thing is painless and is actually rather relaxing, especially when they are doing a full scan and the machine is vibrating which is like having a massage. If anything untoward is seen in the scans they inform your doctor, which is good. Let's hope that it looks OK. Certainly it looks much like the one I had done a few years ago.

The purpose of the research is to better understand how the brain functions and they hope this will help with people recovering from strokes.  It must be so rewarding to be working in this field either as a PhD student or as a post-doc researcher.

10 Aug 2011

6km DX on 17.52kHz earth mode

My 5W QRP signal at 17.52kHz is clearly visible at 6km
Last evening I continued the earth mode tests at 17.52kHz by going out to the test site 6km from home and looking for the signal with a variety of antennas in QRSS3 and with an interrupted long carrier transmission.

No copy was achieved using QRSS3 and Spectran. However, using a continuous carrier with a 2 minute ID break I got extremely good copy (about 6dB S/N) with Spectrum Lab in 37mHz bandwidth with the horizontal 30t loop but no copy on the earth electrode antenna parallel to the road. Moving the loop 10m away from the road resulted in no copy, as did mounting the loop vertically or a few metres above the ground.

It would appear that at 17.52kHz it is easier to detect the signal at distance with a loop than with an earth electrode antenna whereas at 1.095 and 8.760kHz either scheme works. Perhaps someone who understands the theory will be able to explain this.

My next test is to repeat these tests at 137kHz to see to what extent 137kHz is aided locally by utilities assisted earth mode. At the test site 6km away I can see how strong the signal is with tight coupling into the ground at the roadside, and with an E-field probe some distance away from the road.

9 Aug 2011

3.6km with 17.52kHz earth mode

This morning I did an initial test at 17.52kHz using my 5W QRSS3 TX and earth electrode TX "antenna".  A test at 3.5km from home showed the signal ~20dB over noise (0.73Hz BW QRSS3) using the 30t loop on the ground and with a 1t loop (about 20m sq) laying in the road (see attached Spectran screenshot). Signals were also copied with the earth electrodes parallel to the road but weaker than on the loop. They were also copied weaker still with the RX earth electrodes strung across the road. Signals are definitely coming through the ground/utilities with no evidence of any radiated signal and they are every bit as strong (or stronger) than at 8.76 or 1.095kHz.  However, at another test site 4km from home where I usually manage to copy 8.76kHz QRSS3 reasonably well there was no sign of my 17.52kHz signal either with the 30t loop or the earth electrode antenna. No idea why.

Later today I may try the 17.52kHz test at my 6km distant test site with a long duration carrier, although I suspect I may copy it in QRSS3, which I'll try first. I may also try a test using my 80m sq vertical loop as the antenna at the TX end, although I don't expect any great range by pure induction.

8 Aug 2011

1.095kHz earth mode test at 6km

1.095kHz earth mode signal at 6km
Today I repeated the earth mode (through the ground) "long carrier" test of 17.7.11 this time at 1.095kHz rather than 8.760kHz. The same test location was used in the fens not far from the River Cam. This is now a very long way from home! As before, I got my wife to cut the carrier for periods of 1 or 2 minutes to positively identify my signal. I need to automate this so she can continue to do the gardening.  4 different receiving antenna arrangements were tested, using my low impedance MPF102 tuned preamp into the PC:

(a) an earth electrode pair parallel with the road,
(b) an earth electrode pair diagonally across the road,
(c) a single turn loop in the road, and
(d) a 30t 80cm diameter loop at the edge of the road. 

Best results were with (a) and (d). With (b) there was no detectable signal.  At 1.095kHz the signal was again around 10dB S/N in 11mHz bandwidth on (a) and (d) and marginally weaker on (c). This is a similar result to 8.76kHz although I was expecting the signal to be stronger at this lower frequency.  I'm now tempted to do an earth mode test at a higher frequency, possibly 17.52kHz which I can still see with Spectran and Spectrum Laboratory and I can derive with my 4060 divider circuit. Using earth mode I believe I'll still be legal as very little radiated signal can be present. The image shows the signal with the RX earth electrodes parallel to the road, i.e. set-up (a), at a distance of 6km from the home QTH where the TX was running 5W into 20m spaced earth electrodes.

7 Aug 2011

Using Spectran to listen to HF CW

Usually free Spectran software is used here to see VLF signals when doing my earth mode tests. However it also makes a very useful add-on to the FT817 as an adjustable width audio filter. Select the NDB settings and then use the filters (adjustable edges with right and left mouse buttons) with the menu on the left set to "BandPass". It is useful on SSB and on CW and allows the bandwidths to be screwed right down to as low as need be. There is also a CW peak function which puts a narrow filter around 800Hz.

Internet data usage measurement?

Although my ISP doesn't appear to set limits on the amount of data I download, can anyone tell me how I can measure the amount of data I am actually downloading each day or each week?

The financial crisis - living beyond our means?

The financial problems that have become apparent since 2008 can be put down to individuals and nations living beyond their means. How can the US government continue with an exponentially increasing debt? Why do people crank up huge credit card bills when they have no likelihood of ever paying them off? Why do many wealthy individuals in places like Greece make tax avoidance a way of life?

What happens next is hard to figure out but we are in for a period of pain and readjustment. Just maybe the outcome, eventually, will be a good and fair one but I can't help thinking we are entering troubled times where the threat of violent revolution is not far away.  This is a time when moderate people with good judgement need to make the voice of reason clearly heard.

HF noise levels

It is sad how much the noise floor has risen at my QTH in the last few years. Listening on 160 and 80m is now almost impossible on a vertical because of the wideband noise that obliterates the band to an S8-9 level. The noise is there right through to above 17m. Thankfully 10m with the horizontal halo is still pretty clear. Apart from my experiments at VLF and LF I am now tempted to move back to the VHF/UHF bands for serious operation.

4 Aug 2011

VLF beacon transmitter schematic

G3XBM's VLF 5W Earth Mode Beacon
This is the schematic of my TDA2003 5W ULF/VLF beacon transmitter used in recent earth mode tests. The frequency is derived from a 4.48MHz crystal that is divided down to either 8.760 or 1.095kHz using a 4060 IC. This is keyed in either 10wpm CW, QRSS3 or QRSS30 with a K1EL beacon keyer IC. The output of the TDA2003 is matched to the resistance presented by two earth electrodes using a tapped toroid transformer. Best DX is now 6km across the fenland near me.

2 Aug 2011

Braintree LF/VLF talk slides

The slides from my LF/VLF talk at the Braintree and District Amateur Radio Society on Monday August 1st 2011 are now available on-line. BADARS is a small but active radio club in Essex and I was given a very warm welcome by the members.