Earth-mode at 1kHz and 18kHz today

As a follow-up to my recent tests at 8.97kHz, today I repeated the QRSS3 earth-mode (through the ground) tests with my latest receiving equipment but this time at around 18kHz and 1.1kHz.  TXing at 18kHz is legal as there is no appreciable radiation. As before, the TX was 5W into earth electrodes 20m apart back at home. I wanted to see how signal levels varied compared with 8.97kHz at my 3 usual test sites out to 6km distance from home.

Results were interesting: although signals were copied at 1.6km and 3.6km on both test frequencies, nothing at all was copied at 6km, where very good signals were copied on 8.97kHz a few weeks ago. Ground conductivity and weather conditions were identical on both test days: dry for the last several days, so conductivity likely to be lower than when the fen soil is saturated.

I have no real idea why 8.97kHz should appear to be a "sweet spot" in frequency. It is possible that other frequencies lower than 8.97kHz and higher than 1.1kHz may be even better. In all cases the RX loop was resonated and positioned on the ground varied for best signal.

1.12kHz earth-mode signal at 1.6km

17.952kHz earth-mode signal at 1.6km

1.12kHz earth-mode signal at 3.6km

17.952kHz earth-mode signal at 3.6km (note MSK signals close by)

Low costs SSB "Pixie" from Argentina

Pedro LU7HZ has sent me an update on work in Argentina on a low cost approach to an HF QRP SSB transceiver using very few parts. Basically they are using simple electronics coupled with an SDR approach to the modulation and demodulation process.  My own approach would be the fully low tech approach (for a CW/DSB rig) but Pedro's approach is innovative and worth watching. I hope he produces kits or, at the least, documentation to allow others to duplicate the idea as it comes to fruition.

Roger,

This is a project we've been working together with Willoh (LW3DYL) which fits partially into your quest for an extremely low cost and easy to build rig ("UKP 20 decent HF...") although not using the low tech approach but the other way around.

The design is still being debugged and more simplifications will be attempted (such as a more simpler TR/RX switch and eliminate the 7474 based quadrature filter replacing it by an RC approach. The net result should be a one IC and 4 transistors design plus PA final.

The design uses an USB power source (out of an inexpensive cell phone switching power supply or straight out of the USB port at the PC) having 0.5W with it; more like 1W with +12V.

Main software platform will be a modified version of KGKSDR. Main use should be CW or SSB although no reason why not to use it with PSK or FreeDV or WSPR.

Should fit on a (small) pocket.

http://lu7hz.blogspot.com.ar/

Main limitation so far is available time from the builders to devote to the project.

73 de Pedro LU7HZ

Dr. Pedro E. Colla
Va.Belgrano-Ciudad de Cordoba
Cordoba- Argentina

"La vida no es esperar a que pase la tormenta, es aprender a bailar bajo la lluvia". Anonimo

Finningley optical transceiver progress

In the last couple of days, armed with my wife's close-up reading glasses, a magnifying glass, tweezers and a fine tipped soldering iron, I have been doing the SMA build of G4HJW's "Finningley" optical transceiver kit, designed to be used with 100mm optics (drain pipe and Poundland lenses!).

The G4HJW designed optical transceiver

Bernie's instructions were first class with all the SMA parts for the receiver and the transmitter being organised sequentially with a clear layout diagram showing where each part has to be placed. It seems to have gone together very well with no snags, although I have still to add a few discrete parts including the LED and the PIN photodiode before testing can start. All being well, I should be able to start testing on Sunday as I am tied up with our church fete tomorrow.

Efficient electrically short antennas

Way back in my early professional life I was responsible for the design and implementation of a tiny 70cm antenna that had to fit inside the Pye PF8 UHF handportable transceiver. The mechanical design team had left virtually no space for the plate antenna we had intended, so yours truly had to come up with a solution that both fitted and worked efficiently. I managed it by changing the plate antenna to a skeleton plate antenna. In the end it worked very well but the tuning was VERY sharp. Reference here should be made the Wheeler and the Chu limit that defines the bandwidth that an efficient electrically short antenna can achieve.

Basically the thing to remember is this: the smaller the antenna is the higher the Q, and the narrower the bandwidth is, for efficient operation. This is why magnetic loops can work well if designed with a very very high unloaded Q and why they have a very narrow bandwidth if working efficiently. It also explains why a short loaded antenna will have a narrower bandwidth if working efficiently.  Dr Underhill has argued that a small magnetic loop actually violates the Chu limit.

There is a good analysis of small antennas at http://www.m0rzf.talktalk.net/RobCentral/E.S.Antenna.html which goes into some of the maths and looks at various electrically small antennas. Some are "snake oil" of course, but some well designed ones do work with the caveat of narrow bandwidth e.g. well designed magnetic loops.

What is the interest in all this for me today? Well, I am still thinking about HF operation at the new QTH and how to meet my goals of a small, low visual impact antenna, that works well. One thing in my favour is I tend to operate on quite small parts of the HF bands e.g. around the WSPR/PSK frequencies or around the QRP frequencies. As long as I am  prepared to stay close to certain frequencies like 28.1246MHz I should be able to design a very small efficient antenna. I already know that a magentic loop antenna works very well indeed and would certainly meet my goals.

Gardening at the new QTH

This evening I've been busy laying some additional turf in the back garden at our new (soon) QTH. About 5sq m of additional lawn was laid with about the same again to be added in the coming weeks. The bundalow is still a bit of a mess with lots of building work ongoing. The new back garden is around 70 feet wide, so an end-fed 1/4 wave for 80m should be possible. Tomorrow evening I hope to plant a new tree in the lawn to provide some screening from the neighbours.  There is a lot of gardening to do to get the place looking as we would like, but it is coming on OK.

I am still deciding what to do about amateur radio and antennas at the new QTH. I dislike large and unsightly antennas, so whatever I do it is likely to be something stealth like. Whatever, it will be a whole new set of challenges to enjoy. At least I shall have a purpose built shack in which I can both operate and build, unlike the present QTH, with a nice view down the length of the back garden.

Incidentally I bought the turf out in the fens - much cheaper than the garden centre. It did involve driving my car into the middle of a large 100 acre field to collect it though (see RHS).

The Low Power SPRATbook.

http://www.rsgbshop.org/acatalog/

Today, my new paper logbook (yes I still use a paper logbook!) and a new book arrived from the RSGB. The book was the Low Power SPRATbook, recently published by the RSGB and edited by Steve Telenius-Lowe 9M6DXX. As I want to de-clutter and possibly clear the book shelves of my old paper SPRAT copies (I still have them on DVD), this book was ideal as it contains a very good selection of the best of SPRAT articles from 1974-2012. If you have not read SPRAT and seen the excellent articles each quarter, then I recommend this book. I challenge you to buy it and not be inspired to build something.

Perhaps I should also mention that my 14 component 80m CW transceiver is one of the articles. But don't let that put you off! The circuit works well and G3XIZ worked GM with his version (despite running only about 18mW) and was copied on Switzerland.

PY1RO on 6m CW - real DX reception!

The magic band (6m) is full of surprises. I came into the shack this evening after gardening most of the day up at our new bungalow to hear some signals on 6m WSPR. Rather than decode, I tuned down to the DX portion of the band to hear PY1RO (GG87lb Brazil) coming through at 559 on CW on 50.108MHz at a distance of 9369km. I was copying him on the V2000 vertical and my FT817 with a long lossy feeder. A few minutes later and he had faded out completely!  Although I called him a couple of times, I did not break the pile-up, not that I was really expecting to, HI. Still, it was good to hear my best DX on the band in some years.  At this time of year the propagation is more likely to be multi-hop Es rather than TEP I believe. Here is a video of PY1RO on 6m (not this occasion though).

G4HJW "Finningley" Optical Transceiver kit

The G4HJW optical transceiver kit

Bernie G4HJW is well known for his innovative work on microwaves and optical comms. Last year he designed a neat, part SMA, optical transceiver kit to build at the Finningley round table meeting. The transceiver is capable of very good results and several (around 70) have been built and used very successfully. I believe the best DX QSOs at 481THz have been over 60km using these in 100mm optics.

Exactly when I'll get my kit built I'm not sure but it will be good to have one of these available for optical line-of-sight tests in the autumn. Once assembled, I shall be looking for some 2-way optical QSOs beyond the 10km speech contact I achieved with my own kit last summer. In East Anglia, the issue is finding some hills to allow long line-of-sight paths.

Bernie is, I understand, considering putting together a further batch of these kits, which make a good introduction to nanowave communications. In addition to these electrical kits, all that is needed is a microphone, headset and some simple optics than can be built for a few pounds.

See http://www.earf.co.uk/nanotrx.htm for more details

Yaesu price drop

http://www.universal-radio.com/

In this month's Practical Wireless , received today, I notice that some of the UK dealers have reduced the price of the Yaesu FT-450D and the FT-950 radios. The FT817ND is still around £534, i.e. no drop (yet). At last, we are beginning to see some of the exchange rate savings being passed on to customers. Thank you dealers. Please may we have even more savings? The exchange rate has moved FAR more in our favour than the price changes would suggest.

Playing with a ferrite rod at VLF

Just for amusement, but with a slight hope it might work, I tried resonating a LW ferrite rod coil (about 3.5mH) at 8.97kHz to see how it might perform as a miniature portable receiving loop in my earth-mode tests.

To test other antennas and VLF preamps, I first connect my 8.97kHz 5W transmitter into a resistive dummy load and check that I can detect the signal strongly some distance away locally (about 10m away only). The emissions from the cables are such that this gives me around 30-40dB S/N on Spectran with the usual settings on my 80cm loop. Switching over to the ferrite rod RX antenna it was hard to tell if a signal was there at all.

So, that's one experiment I'll close and report as a failure. Had it worked, even 10s of dB down, it might have made a magnetic field antenna that could have been deployed mobile. You may recall I tried /M on 8.97kHz a few months ago with my 80cm loop strapped behind the car, until someone pointed out this probably would have invalidated my car insurance and I stopped.  I had vague ideas of dropping the VLF resonated ferrite rod close to the ground behind, somehow fixed from the rear bumper.

Ho hum, another idea bites the dust.