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).