16 Sept 2013

In hospital -bleed on the brain

At the weekend I was rushed into Addenbrookes hospital with excruciating headaches and punch drunk legs. After CAT and MRI scan they have confirmed it was a bleed on the brian from a blood vessel in the cerebellum which is being dispersed with drugs and can be treated. Service and care has been excellent at NHS Cambridge. We are lucky to have a world class hospital so close to us.

13 Sept 2013

Optical forward scatter and frequency?

Perhaps some of my readers can help me - what optical frequency is likely to be best for forward scatter off air molecules and dust particles? My tests to date have been over non line-of sight paths up to about 9km at 481THz (red light), but IR should work in daylight with filtered PIN diodes on RX, but I don't know whether infra-red frequencies scatter more easily or worse than red light?  With red light, the RX can easily be de-sensitised by bright sunlight, and this should be (?) less of an issue with filtered IR detectors, I think.

As the atmosphere scatters blue light very well (giving it a blue colour) one might expect IR to scatter less well than shorter wavelengths like visible red or ultra-violet? See http://en.wikipedia.org/wiki/Atmosphere_of_Earth .

On 472kHz again this evening and future plans

In the next few days I need to buy some more wire and coax to continue my antenna experiments. The first thing I shall be trying is the larger "in the air" TX loop for the LF and MF bands - probably 136kHz , 472kHz and 1.8MHz coverage. The lower part of the loop can be several strands of PVC covered wire or coax in parallel to reduce resistive losses but the "up in the air" part will have to be 1mm diameter to avoid sag and being visible to the neighbours. I think I should be able to increase the loop area by 50% and reduce the wire losses by about 50%, so there should be a useful increase in ERP. This could be some weeks away though.

In the meantime I am continuing to TX and RX on 472kHz WSPR with the odd shape loop I currently have running along the garden fence and back along the surface of the lawn. It works, but as I said yesterday, it is some dB below what I can achieve in my small back garden whilst maintaining low visual impact to avoid neighbour issues.

After confirming the performance with the larger loop in the coming weeks, I shall try a short Marconi vertical to compare results - better omni coverage expected, but may not be as effective as the loop in the best directions?

After that, I shall probably be returning to 481THz and infra-red frequencies for more over the horizon scatter tests. I particularly want to try some IR scatter tests in daylight as I find going out on dark nights unpleasant.

World's oldest photographs

As I have come down with a bug of some sort, feeling light-headed and with a headache, I've been sleeping a lot today and not doing too much. My 472kHz WSPR has been running periodically.

Sitting here this afternoon, I chanced on this interesting YouTube video showing the world's earliest photos. Fascinating to look at - see http://www.youtube.com/watch?v=3LkaFCa29mQ .

You may also like The World's 10 Most Mysterious Photos - see http://www.youtube.com/watch?v=E7Cd5FWMusE.

12 Sept 2013

472kHz (630m) WSPR experiment results

Comparing the loop in the air against the simple earth electrode (EE) antenna across the garden these are the results. Remember the loop could be improved by making it larger, using thicker wire and mounting it more fully vertical.

G4KPX - about 6dB better on loop
G6AVK - little difference
PA3ABK/2 - 1-3dB better on loop
G8HUH - little difference
M0PPP - copied on loop, no copy on EE
G3WCB - just copied on EE, no copy on loop

Conclusions?  Well the loop, as it currently is arranged, is a bit better than the EE antenna by a few dB, in some directions, but not amazingly so. Will try a loop up in the air more in the coming weeks and we'll compare results again.

TXing tonight with a 472kHz "in the air" loop

As the next stage in my experiments from the new QTH at LF and MF, this afternoon I converted my earth-electrode antenna into a complete "in the air" loop by removing the earth connections and joining the wires with a length of wire along the grass. The DC resistance of the loop is 0.9ohms and the enclosed area somewhere around 60-100 sq m although the loop is far from vertical and the bottom wire actually runs along the grass rather than up in the air. The measured loop current is around 0.9A and tuning very sharp with around 1.7nF in series and matched with a 3C90 step down transformer. According to my calculations of radiation resistance, the ERP should be in the 20-40mW region, considerably greater than with the earth-electrode antenna.
630m WSPR spots of G3XBM so far this evening
My first report this evening was from PA3ABK/2  at -28dB S/N but I am hopeful of a few more 472kHz spots tonight. I expect that the results with the loop will be better than with the earth-electrode system, but the loop can be further improved by raising the upper wire (bigger vertical enclosed loop area) and thickening up the lower wire to reduce resistive losses further.

I am doing things one step at a time so I can assess the difference.

UPDATE 1800z:  M0PPP has spotted me several times this evening but had failed to copy me in the last 2 weeks, so this is encouraging. Also reports from G8HUH and G6AVK.

10 Sept 2013

More 10m WSPR

With the weather miserable here today - I just managed to cut the grass before the rain set in - I went on 10m WSPR mid-afternoon to see what was doing. With 2W I got a couple of reports from 4X1RF at 3519km at -3 and 0dB S/N, which is VERY strong, but nothing else so far.

This evening, I hope to be WSPRing on 472kHz again (using the original earth-electrode arrangement still) whilst we entertain my brother and his wife. They are coming to stay for a few days. I shall be checking results periodically using my iPod Touch monitoring the WSPRnet database in between drinks and eating dinner.

POSTSCRIPT: I was just about to QSY away from 10m when I noticed I had spotted K3NAL at 5930km. At the time of writing, I seem to be the only European station copying him. Maybe I shall stay on 10m a little longer this afternoon, or perhaps try 10m PSK31 for some QSOs. 10m is another "magic band". Less so at the peak of the cycle but often open to distant places when not expected and definitely under-used in the quiet solar years.  

9 Sept 2013

472kHz - 7 unique WSPR reports so far on earth-electrode antenna

Although not working as well as I had hoped, my very simple earth-electrode antenna is getting WSPR reports. As of this evening, I have been spotted by 7 unique stations so far. Results remind me of my first efforts on 500kHz with a simple wire down the garden some years back. My ERP then was in the uW range and this may well be the sort of ERP I am actually using now currently. A better antenna IS a must!

First 10m spot from the new QTH + more on 20m

Today I ran WSPR on 10m to see what propagation was like. Although European stations further south were catching N-S openings trans-equatorial openings and even VK6, it was harder going from here in the UK and I only managed 1 spot with 2W and that was from 4X1RF - thank you.

Back on 20m it was a different story where I had a huge number of reports from places including KL7L in Alaska,  with just 500mW to the Par EF-10/20/40 antenna. 20m is always a good bet, although not one of my usual favourite bands.

As the autumn progresses I hope 10m will come back to life again. Conditions should be excellent in October and November with still decent sunspot numbers and of course the big CQWW DX contests to add to the activity levels. By autumn next year things will certainly be on the slide down to the next minimum, but the slope down is gradual and conditions can remain decent for several more years yet.

I really must get the full transceiver version of my 10m WISPY WSPR rig boxed up so I can free up the FT817 to do other things.

8 Sept 2013

Earth-electrode antenna for 472kHz in the new garden - not too brilliant

After trying a number of different orientations of earth-electrode pairs in my garden, I have come to the conclusion that this antenna structure does not work very well here in the new QTH. I am a little surprised as the earth-electrode antenna worked well just 350m away at the old QTH. Whatever orientation I try I seem to be always in the -22 to -28dB S/N region with G6AVK 78km away.

Why is it not so good? Well, the most likely answer is that the effective distance between the far and near ground rod electrodes is smaller, even with a similar physical separation. This could be because of buried water pipes and utilities criss-crossing the garden, although I wasn't aware of any, or different soil/rock conditions, although the chalk layer is about as far down here as at the old QTH and the soil is a similar alkaline sort. The fact that the 8.97kHz earth-mode results were so poor last week rather hinted at a problem that was not present at the old QTH.
I haven't quite exhausted every layout possible in  my strange shaped back garden, so there are more things to try with earth-electrodes, but it is looking like I shall have to erect a short Marconi or a fully in the air loop antenna to get better ERP on 472kHz. On my previous tests at the old QTH, a full in the air loop with 1mm diameter wire and an enclosed area of around 80m sq was around 8dB better than the earth-electrode antenna, but far more critical to tune and match because of the hi-Q. If my earth-electrode antenna is several dB down on the performance of the same structure at the old QTH then I could be expecting >10dB improvement or even more.

Half the fun is the testing and finding out what does and does not work.  The coming week we have visitors staying, so not too much time to experiment. I shall have to stick to WSPRing on 20 and 10m.