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.