Finningley optical transceiver working fine

Although I posted this on the Nanowaves Yahoo group , I forgot to update folks reading this blog on the progress with this optical transceiver kit designed by Bernie G4HJW.

Well, at the weekend I finished building the unit and started testing it. The TX part worked first time, but the RX did not. Time to find out why!

Using logic and common sense, I carefully went through the various stages (8V regulator, later audio stages etc) and tracked the fault down to an intermittent preset SMA pot that sets the FET bias. The FET stage is the very high impedance stage that follows the PIN photodiode.

The error was entirely my fault and easily fixed by removing the part and redoing the surface mount joints. Now the full transceiver is working well (but yet to be put into 100mm optics) and the RX sensitivity is close to that with my K3PGP design RX. In the coming weeks I hope to get a transition piece to connect the transceiver "tube" to a 110mm drainpipe that houses the 100mm lens. I'll then assemble this onto a stable tripod with sighting scope and I'll be ready to look for QSOs.

http://www.earf.co.uk/optoposition.JPG

One thing that puzzled me was how having the detector diode and TX LED slightly off-centre would work. In my mind I thought that the light would not be properly focused onto the devices, so losing sensitivity. Then someone pointed out that by slightly aiming "off beam" by around 1 degree the light would fall exactly onto the position on the transceiver where the LED or PIN diode are mounted.

How much am I RADIATING at VLF?

As a matter of interest, this afternoon I worked out how much power I am actually radiating when carrying out my earth-mode tests. The main transmission mode is conduction through the soil/rocks and buried utilities, but an earth-electrode antenna will produce some very very small amount of radiation too.

The first thing is the effective area of the "loop in the ground" and based on a guestimate of 40 ohm metre soil resisitivity (could be somewhere between 10-100 ohm metres) my calculations give me an effective loop area of 600m sq at 8.97kHz - i.e. the signal current flows quite deeply into the ground.

The second figure is the current flowing in the loop (I) which I measure as 0.2A using a current transformer to sense the current.

Rrad = (31171 x Ae^2)/lambda^4 = 0.94 *10^-8

Lambda = 33km
Ae = 600 sq m
I = 0.2 amps

Rrad = 0.94 * 10^-8 ohms
ERP = I^2 x Rrad

So, plugging in the numbers:

ERP = 0.2 x 0.2 x 0.94 x 10^-8

ERP = 37nW

There may well be errors in my sums and in the assumptions made, but clearly 37nW is a tiny amount of radiated power and (almost) negligible. To get to a level where the radiated signal is detectable over 100km away, I would need to radiate around 4-8uW, i.e. several orders of magnitude more. Radiation resistance is proportional to the loop area squared so increasing the baseline by a factor of 10 increases the radiation resistance by 100 times. This could be helped with a much longer baseline (200m long rather than 20m) and increasing the power into the earth-electrode loop to 500W and elevating the loop part that feeds the far earth electrode with current. Such changes could result in a radiated power level of around 4-8uW based on the assumptions about soil/rock resistivity and skin depth. A 200m long piece of wire (e.g. along a field edge) and 500W of audio power are not that hard to envisage and a LOT easier than winding a huge loading coil and raising a kite supported antenna several hundreds of metres high.

Progress with the new shack

Today the builder has started to fit out my new shack at the bungalow with work surfaces, cupboards and shelves being put in. I have a small workbench area for the test gear and where soldering will take place and a separate desk area overlooking the garden for the QRP rigs, PCs and printer. It will be the first time in over 50 years in the hobby when I'll have had a dedicated room for my amateur radio activity. Up to now I have had to split the "working" area and the operating area with the latter doubling as a bedroom for the grandchildren. The room is not big, but it should be ideal for my needs.

VLF earth-mode "propagation" variations

In the last few weeks I have been doing QRSS3 (slow CW) tests at approximately 1kHz, 4.48kHz, 8.97kHz and 18kHz transmitting 5W into 20m spaced earth electrodes (1 electrode at the bottom of the garden and the other connection to house copper pipes) and checking signal strengths at 1.6, 3.6 and 6km away from the home QTH using my portable loop antenna, preamp and a small netbook PC running Spectran software. Propagation is by utilities assisted earth-mode i.e. the main means of signal propagation is (I believe) conduction through buried pipes and cables with the induction field at the RX point being picked up with the loop. I have also used an E-field probe to detect the E field signal at some distance.

The recent tests were to see how signal levels varied with frequency, but I am finding VERY large differences in signal level day-to-day. The 8.97kHz signal was around 10dB S/N today at 1.6km whereas it was around 20dB S/N a week or so ago. I was unable to copy a signal at 1kHz and 8.97kHz at 6km at all when I tried a few days ago yet the 8.97kHz signal was quite decent a few weeks ago at the very same spot.

Weaker 8.97kHz received signal at 1.6km today

Weak 4.485kHz received signal at 1.6km today

There will be some dBs variation depending on the exact positioning of the RX loop on the ground but the variations seem suggest something else. Today there were a lot of static crashes and I don't know if this upsets Spectran's DSP processing? The other variation could be soil conductivity: today was wet (raining) whereas the best results seem to be with dry settled conditions when the soil has dried out a bit.

Conclusions so far? Signal strengths between 1-17kHz at 6km range don't vary that much over the frequency range, but signal levels can be up to 20dB different day-to-day as a result of other (as yet not understood) variables in the system or path.

The ITER project - first realistic steps to clean nuclear fusion power?

ITER, a nuclear fusion project funded by many nations, is assembling the biggest nuclear fusion test reactor ever, in France. Due to "go nuclear" in the 2020s, this unit should produce 500MW for every 50MW put in as a result of the fusion process. Unlike nuclear fission, nuclear fusion has the potential for almost limitless nuclear energy without the radioactive waste risks associated with nuclear fission. Even with a successful project, commercial nuclear fusion reactors are unlikely until the second half of the 21st century.

A LOT is at stake here: nuclear fusion, if the technical issues are overcome, could be a saviour for the human race at a time when energy resources are likely to be in short supply at a time when demand will be at an all-time high.

Man's ingenuity is such that even the technical challenges of fusion will be overcome when the imperative is great enough. I have faith in the ability of scientists and engineers (and even in politicians) to come up with the solutions in time to help produce a better world for my children and grandchildren.  It's just a pity I shall not be around to see it.

6m WSPR

For the last 36 hours I have been using WSPR on 6m to check for openings when busy with other things. I am surprised how often CN8LI (2171km) and I exchange spots even though I have only been running 500mW into the vertical V2000 antenna. I assume this is Es, but the path seems too consistently open for Es somehow.

I am disappointed more stations in the USA and Canada are not active on 6m WSPR: with a good number of stations both sides of "the pond" active, it would be an excellent way to spot those fleeting multi-hop Es openings at any time of the day or night.

Low cost, high performance 10GHz receiver

Recently Ian G3KKD has been telling me about some remarkable results on 10GHz using an Octagon satellite LNB that is available for around £12-15 via eBay. This has a crystal controlled PLL and has good frequency accuracy, stability and phase noise. I believe the LNB outputs a signal around 600MHz which is then down converted to a suitable IF.

Using this set-up Ian can copy the 10GHz beacon GB3CAM at around 30km with just the LNB handheld in his front or back garden which is badly screened by tall trees! Using a small Sky dish, the signal is S9+60dB from a point just along the road.

Of course, with a small surplus satellite dish, a low cost TV USB dongle used as an SSB/CW RX at the LNB output frequency, this would make an excellent SDR for 10GHz with VERY low noise figure. The LNB quotes the NF as 0.1dB, which is remarkable.

With a small 10GHz FM or CW TX into a separate dish, a complete low cost 10GHz station is possible, probably for less than £50. I am sorely tempted to try this.

I have just seen Andy G4JNT's note about this http://www.g4jnt.com/PLL_LNB_Tests.pdf .

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.