Iceland's volcanic plume

The plume of volcanic ash belching from the Eyjafjallajoekull volcano, ( 1666m ), in the Katla range is visible from space. It can just be seen on an image I received yesterday, 19th April at 1215gmt, from the NOAA 19 weather satellite on 137.10MHz.
At first I had almost overlooked it, believing, because of the enormous publicity the eruption had attracted, that from the satellite's viewpoint most of western Europe would be hidden from view under the ash cloud. A further series of images captured today from NOAA 15, 18 & 19 confirm the continued presence of the plume, but show it to be diminishing.
I shall be following the progress of the ash plume/cloud from space and post additional pictures if they are more distinctive.
Iceland is at the limit of my range from here for clear satellite reception; the satellite being only just above my horizon as Iceland comes into view !

Full earth disc

Previously posted weather satellite imagery has been from satellites in low earth orbit as they pass over above my horizon for upto 15mins every 100mins or so. For full earth disc pictures I had to receive the signals from satellites much further away in the geostationary orbit; in particular satellite Meteosat 7 at 0 deg. E. Using an 80cm satellite tv dish pointing in that direction, I had no problem receiving the analogue WEFAX imagery on 1691MHz. The last time was in 2002; it doesn't seem so, but I checked. That's a long time ago. How time flies !
Recently, I have been occasionally listening for Meteosat 7's transmissions again; but heard nothing. Has the satellite re-entered, or been parked into a graveyard orbit, I wondered. No, instead it has been moved to above the Indian Ocean.
More importantly, the analogue service ceased anyway probably early in 2004. I can't receive the new higher resolution digital service from Meteosat 9, Meteosat 7's replacement at 0 deg. E, without spending some money on equipment. I might not bother.
So, if in the future I don't receive any more full earth disc pics, I have posted one from my archive from 2002, and we just have to imagine the quality and resolution of the digital pics nowadays; or use the web, but that would be too easy.

Sat pic gallery

Today's images in the visible light band which I received "off-air" from the US National Oceanographic and Atmospheric Administration, ( NOAA ), low earth orbiting weather satellites, NOAA18 & NOAA19, automatic picture transmission, ( APT ), weather facsimilie, ( WEFAX ), service.

From top to bottom:-
NOAA19, 1104gmt, downlink 137.10MHz
NOAA18, 1141gmt, downlink 137.9125MHz
NOAA19, 1246gmt, downlink 137.10MHz
NOAA18, 1323gmt, downlink 137.9125MHz

There is still some sea-ice to be seen at the northern end of the Gulf of Bothnia.
If you look carefully you may see a red cross which gives away the position of my ground station.

The changing seasons

It is interesting to follow the seasonal changes on earth from the images which I receive directly from weather satellites. The last time on 26th January, ( see post ), showed Europe from Germany eastwards under ice and snow. The images which I captured today tell a very different story.
The infra-red image I have chosen to post here was derived from the heat detected by the infra-red sensor onboard satellite NOAA18, and transmitted on 137.9125MHz at 1151gmt. Darker shades, ( black, brown, green ), represent warmer areas than lighter shades, ( blue, white ). Many Baltic countries had a fine, warm day today. I was outdoors making the most of it !

Loopy thoughts

I've been sorting through my stock of coax cables. If I join together several lengths of the same thickness of 6mm, I could make one length of 70 metres. Perhaps it will be enough to construct a reasonably effective rectangular loop antenna for transmission on the longwave 2190m band.
So let's see.
I could support it vertically from two trees in the garden 20 metres apart, with the vertical plane running N-S. The area enclosed by the loop would be 300 square metres.
After doing some quick calculations, I predict Rrad = 121 micro Ohms, and efficiency = 0.0076%, assuming rf losses = 1.6 Ohms.
In terms of efficiency it will be nearly 4dB worse than my existing longwave Marconi antenna. Another limitation is the loop's bi-directionality, ( Marconi omni-directional ); so radiation broadside ( E-W ) could be 30dB down on end-fire direction ( N-S ).
I wonder if making it will be worth the effort.
Has anyone made a longwave loop antenna of a similar size ?
If so I would be pleased to hear of your experiences with it.
I won't be buying a single 70m length of new coax just yet !

Antenna traps using coaxial cable

Traps are tuned circuits used in various types of antennas to allow multiband operation. They can be bought from commercial sources, or home-made with the advantage of low cost, ( almost nil ), and your choice of design frequency rather than the manufacturer's. Ever since I burnt out a bought trap, I have always made my own.
My preferred method is to use coaxial cable formed into a coil round plastic drain-pipe, and avoids using a high voltage capacitor as the self-capacitance of the cable tunes the coil to resonance. I have made lots in the past, several of which are currently incorporated into some of my antennas. For lowest loss traps, coax cable having the thickest inner conductor practicable should be chosen, unless the weight causes the antenna element to sag excessively.
The one I have just made is for a modification to improve my longwave antenna. It consists of 6mm diameter RG58C/U type coax cable round a 90mm diameter pipe. I easily tuned it to the precise frequency I wanted using a 'dip' oscillator, frequency meter and adjusting the spacing between the end turns of the coil. Then the turns were held in place by applying hot melt glue into the gaps.

Spring cleaning

Every year at around this time I like to clean the inside of my fan-cooled amplifiers; suck out the dust, remove dead insects and spiders, and also clean the fans themselves. Over the course of a year's use a lot of dirt gets drawn in and accumulates. Cleaning should ensure reliable operation over the next 12 months.
My 150 watt VHF amplifier for 144MHz has its top cover removed prior to undergoing this treatment. It uses the American, Eimac type 4CX250B, ceramic, external anode, tetrode tube; also shown with its ceramic chimney alongside.

Compliments always welcome

I have just received an unexpected email from Michal, a Polish radio amateur, callsign SQ7JZI, who has been monitoring my longwave transmissions recently. He wrote, " Incredible VLF signal to 137KHz, congratulations. What equipment do you use ?"
Of course I had to tell him, and encourage him to radiate his own signal. Then there will be 3 from Poland on the 2190m band.
Signals on this band are rare; still none at all from many of Poland's neighbouring countries. I hope someone from there will one day be able to change that. It would certainly add interest.

Circuits

This evening I have been transmitting on longwave, waiting for a contact partner, but none appeared, although I know that my signal was being received in Nuernberg, Germany, 745 kms away.
While waiting, I realised that until now I had never placed on my blog a circuit diagram for any of my construction projects; and yet there might be some visitors who would like to copy some of my designs.
Although the picture can be enlarged by clicking on it, whether I do this again still depends on the clarity.
Anyway, I try it at least once, with the circuit schematic of my GS31B 50MHz amplifier from 4 years ago. ( see also 25th January 2010 ).

My Russian toys

Though not dolls, there is nevertheless a progressive increase in size.
They are Russian made high power triode tubes, ( thermionic vacuum tubes, valves ), ideal for use in VHF/UHF transmitter power amplifiers, and significantly cheaper than western alternatives.
So, from L - R, the ones I have are type GI46B, GS31B and GS35B; in each case the suffix 'B' denotes tube variant suitable for forced air cooling, with or without the finned anode cooler. ( An 'A' here would mean water-cooled ).
The GS31B is a spare in case the one in my 50MHz amplifier, ( see post of 25th Jan, 7.23pm ), fails one day.
I am currently building an amplifier for 144MHz using the GS35B.
I haven't decided what to use the GI46B for yet. If I can obtain a second one, then making an amplifier for 432MHz using both tubes with their outputs combined would be an interesting construction project.

International Space Station

I was sitting in my radio room while wondering what to do next when I saw a radio contact confirmation card on the wall. Perhaps because it has been there a long time, I rarely notice it. As it may be of interest to the many visitors to my blog, I have put it here. The card shows the International Space Station, ISS, of course, and was sent to me as a memento of a conversation I had with Bill McArthur, the Mission 11 (?) commander, as the ISS passed over on 27th November 2005 at 11.00am.
I guess the ISS has grown in size since then !

Frequency synthesiser

Having decided on all the additional functions I want, ( band change, tuning step selection, PTT and output filter ), and the switches and connections that will be needed, during the last few days I have progressed further with the frequency synthesiser project from the experimental and development stage, ( see 25th January ), to the first, ( boxed ), prototype. The green, back-lit, dot-matrix liquid crystal display gives a particularly pleasing appearance. The source code still needs some refining. The inset shows new code being uploaded via the 'in-circuit serial programming' interface, ICSP.

Weather bad, longwave good

Tonight it is snowing again. The large coil is outside and connected to my antenna, but has little protection from precipitation. Although the weather is poor, radio propagation conditions on longwave tonight have been good. I have just completed a contact with Gerhard in Austria. The screen shot shows him calling me at the start. The other horizontal lines are sidebands from the LORAN-C navigational system on 100KHz. There are LORAN-C sites in coastal regions of northern Europe. We have to put up with its interference until the system is supersceded by GPS. The sound it makes is like a steam locomotive travelling at 100mph. To our advantage, however, these 'lines' give a useful indication of propagation conditions on 136KHz, and were strong and clear tonight; hence the possibility for my contact with Gerhard.
My signal was also picked up 745 kms away in Nuernberg, Germany !

Home-made PCBs

I made a printed circuit board, (PCB), today as part of the same construction project reported on 25th January. The quality achieved when making ones own boards in the kitchen at home can be remarkably high. I use silkscreen printing and photographic methods of production depending on the nature of the board. If I need a copper ground plane, (as in this case today), in order to equalise earth currents because radio-frequency signals will be present, I adopt the photographic method. If there are only to be tracks present, then the silkscreen printing method is quicker.
The picture shows the silkscreen layer, (top), for component locations, then the track pattern, (mid), and finally the etched board ready for drilling and populating. Click on the picture to enlarge it.

Modifying PC PSUs - finishing off

Recently my electronics workshop in the cellar has become just warm enough to visit to complete the modifications. Since the posting on 26th January, I have chosen to use 30 Amp Anderson Powerpole connectors for the red/black 12V output terminals; fitting a LED 'power-on' indicator and non-slip rubber feet underneath completes the work.
( Thanks Richard for donating the original. )

Friday night activity night

Yesterday evening the first activity period on longwave took place, to encourage Polish radio amateurs with longwave receiving and/or transmitting equipment to meet up "on the air". I think that in Poland only myself and one other guy can transmit on 2190m wavelength. Amateurs' antennas for this wavelength are relatively short and inefficient. So we have to transmit information slowly in a very narrow bandwidth to have any chance of being picked up. As an example, the screen capture shows how my slow morse signal, ( 4 sec dot , 12 sec dash ), was received by another Polish receiving station during this activity period.

Extreme loading coil appears in ham press

A description and picture featuring the massive loading coil I use with my Marconi antenna for 136KHz, have recently appeared in RadCom, the monthly magazine of the Radio Society of Great Britain, RSGB, December 2009, page 29. ( click on the post title to visit the RSGB web site ).
The main winding consists of about 400 turns on a 15cm diameter, 108cm long, sewer pipe and has multiple tapping points. The rotatable variometer winding inside is made from 37 turns on a 11cm diameter plastic water-pipe. The upturned plastic food container on top keeps water out.
The impedance matching network to the 50 Ohm coaxial cable feeder from the transmitter uses an ETD44 transformer core with a 9 turn primary winding and a 20 turn secondary winding. I can obtain a perfect match with this method, though occasionally there is slight detuning of the antenna system owing to environmental effects, requiring readjustment of the variometer.

Award arrives

The award that I mentioned in my last posting has just arrived by post; very colourful it is too. It will look even more impressive when framed and hanging on the wall in my radio room.

136KHz Award

PZK, the Polish national amateur radio society, has awarded me with a certificate in recognition of my achievements in longwave radio communication. And I even get a mention on the PZK web site http://www.awards.pzk.org.pl
( click on post title )

Europe in the deep freeze

I captured these images from today's early afternoon passes of the NOAA 19 weather satellite.