Echoes from 1940

A few weeks ago, my wife brought me a library book to read entitled Winning the Radar War by Jack Nissen(thall) and A.W. Cockerill, published by Robert Hale, London in 1987.

This book, still widely available from the likes of Abe Books for about £5, is a fascinating read of the human experience of being a developer of radar during WW2.  There is not much technical stuff at all.

A typical Chain Home Low radar station of WW2.  Image courtesy Imperial War Museum.

 

There are always several books in the queue here, and this one has taken up residence on the bathroom reading table.  So I am reading it slowly, but carefully.

A fascinating account I've just come across reads as follows (p.76 in the 1989 edition):

'However, the really interesting experience that came out of my return visit [to Rosehearty Chain Home Low radar station, Scotland, around July-August 1940] was a discovery that altered forever the erroneous belief that radio waves travelled in straight lines [the author presumably speaks of VHF; the bending of radio waves over the horizon at HF had been known for decades]...

...The straight-line theory...was shattered one evening on radar watch.

I was intrigued by strong, even massive, signals coming to our receiver when the aerial was pointed in a north-east direction.  I remember thinking it odd that I hadn't noticed them before.  When the aerial was rotated, the signals vanished, so I had the binder [antenna rotating operator] crank the aerial back to the bearing of the blips and began checking to make sure that they weren't ghost signals. 

I studied them thoughtfully, consulted a map of the Scandinavian coastline, and finally came to the only conclusion that made sense to me.

The strong response was nothing less than a long-distance echo off Hardanger Mountains in Norway, over 300 miles away.  This meant the the supposedly impossible was happening: our 1.5 metre [~200MHz] transmissions could be, and in fact were being, bent around the curvature of the earth, giving us a reflection off the Norwegian mountains.'

Well, my thoughts are that whilst this could have been a terrestrial reflection, I wonder whether, given the NE direction and summer timing, it might instead have been returns from a Es or PMSE layer?  

I will have to see if a report the author filed about this event with a Dr. Ed Bowen - a Welsh physicist who made major contributions to radar development, is still kept in an archive somewhere.

Feel that curve!

Lots of listening to 6m over the past days led to this spectacular, presumably aircraft reflection.

The step at the fourth time marker line down is where I transmitted for one cycle.  But the rest is complete.  

There is no sign of the signal reflected being anything other than entirely continuous.  Which begs the question: what signal was being reflected?  If it was FT8, surely there ought to be detectable gaps where people stop and start TX?  I also wonder how the signal reflection was so incredibly stable throughout the pass of whatever vehicle was responsible.  I'm wondering whether it could have been the ISS.  Sadly, I didn't think to record the time, and the original file has been deleted.  Ah well!

6m 'Bursts'. Ramping up to the Perseids.

Regular readers, if there are any, will remember the discussion earlier this year about unusual 'metallic bursts' of 6m signals seen when listening across the Atlantic from Wales.

In general, others I've spoken to are quite certain that these very ghostly-sounding echoes are simply meteor 'pings'.

I'm certainly no expert on the 6m band, neither am I very well-equipped for it; I have a 2-element quad, though it has achieved very good DX over the years.

What attracted me to these metallic bursts is the fact that I have never noticed them before I turned my antenna towards the US.  For many years, my antenna has been fixed towards the SSE - towards Europe.

Now, the number of sporadic meteors entering a volume of atmosphere visibile to any given observer on the ground is very high.  Settled numbers are hard to come by, but peer-reviewed papers often give a value of several thousand per day.  From work I did with the University of Bath (actually, with identical SKiYMET radars), I know that number is reasonable.  Here's an example plot of one 24 hour period, for example:

Since 2008, other studies have found a higher sporadic rate, closer to ~9,000 per day.  So, we can expect, at the very least, about 2 sporadic VHF meteor pings from any given observing location per minute, and perhaps up to 6 per minute on more recent data.  During meteor showers, the rate is obviously much higher.

SKiYMET radar at Esrange, Sweden.  (C) University of Bath/N. Mitchell.

 

Listening today, beaming Europe on an early August Saturday morning, when there are obviously a large number of 6m operators active, I can hear no metallic bursts at all.  I heard one meteor ping, which was very short-lived - just a few milliseconds long.  

Here's the map of activity this morning, together with the paltry number of receptions of my signals:

Having listened for the best part of an hour, I heard absolutely no metallic bursts at all.

There is no question that there are large numbers of meteors coming in all day, every day.  So, the obvious question to ask those who assert this phenomenon is simply meteor bursts is: why can we not hear them all the time?

Let's see how many metallic bursts we can hear on 11-13 August, as the Perseids reach their peak.  I will listen to Europe and transatlantic...

Advice for newcomers to radio

This blog was set up many moons ago, primarily to encourage newcomers into the hobby.  If I only ever encouraged one person into the hobby through this blog, that would be achievement enough for me.

Because it's a nice, sunny day, here is my very brief but very well-considered advice to newcomers this morning:

(1) Read lots of books and determine which authors are reliable or at least motivated by genuine curiosity.

(2) Spend as little time as possible - and preferably none at all - on QRZ.com; you will be lucky to find anything other than angry, racist, white old men spitting prejudice and ignorance there.

(3) Learn that the success of radio is more down to environment than equipment.  Open fields, lakes, and especially the coast, are places that yield Yagi-beating performance from 'just' simple wire verticals.

That's it for today!

 

 

One wire

If you go out portable with a radio, the ability to multiband easily and quickly is often quite an important feature for an antenna.

All my work to date has been with elevated monoband verticals, using two elevated radials.  These are, of course, extremely good antennas, cheap and easy to build and very robust.

But the radials, spanning a diameter of 10m at 14MHz, can present a trip hazard when there are a lot of people around.  Dogs also tend to walk into them, getting very confused!  Even though I have public liability insurance via EURAO, we all have to do what we reasonably can to reduce the chances of causing injury.

No radials!  At IO73rj today.

So, I got out one of my 9:1 end-fed antennas, which I bought many years ago from EARCHI.  It's the most simple antenna you can imagine, bottom fed, and needs any random length wire that isn't a half wave on any band you want to use it for.

Using a 10m pole at the beach is not easy for two reasons: (1) there are no easily-available screw-in bases for them and (2) they are very much more prone to wind than a 7m pole.

Accordingly, I limited my coastal experiment this afternoon to a 7m pole and a plastic ground screw used for rotary clothes lines.  The wire was therefore limited to about 6m.

I found this length of wire matched up easily with the internal rig ATU (Kenwood TS480SAT), on all bands 40-6m.

After about an hour of 14MHz WSPR listening, I found a median enhancement at the coast with this antenna of+6.3dB, with a range of +2dB to +14dB.  Allowing for a 2-3dB advantage in favour of the slightly inland delta I was comparing with, this comes out at a true like-for-like advantage of about 10dB.  The best enhancements were for long-haul DX (VE7AHT (+10.5db) and AE7YQ (+14dB)).

Whilst the end-fed is likely to be a few dB weaker than a monoband elevated vertical with radials, it offers performance not too different to such an antenna, with the three big advantages of being multiband, not requiring radials, and of short length.

(Thanks to AI3V, who asserts in a typical 'Trumpian' fashion that enhancements from the coast are "BS".  But not to worry,  QRZ.com swung into action to defend a white old Republican under an attack of his own making, and deleted the thread when, after repeated requests to explain why that is so, he could do no more than submit increasing levels of idiocy.)

Waveshare - Brilliant!

Well, my little problem with Waveshare 7" screen has been fixed in 24 hours!

Thanks to exemplary e-mail customer support direct from Waveshare in Shenzhen, I was told to try and reinstall a ribbon cable at the back of the screen.

The red-marked cable socket.  A lift tab above the top of the red box isn't clear or present in this image, so make sure you lift it before removing and replacing the ribbon.

If you end up with a similar , flickering, banded or non-functioning Waveshare screen, the first thing to note is how to remove and replace the ribbon.  DO NOT pull it out, although you can do this without damage, but you won't get it back in.  First, you need to lift the black hinged tab at the back.  This releases the contact clamp, and you can easily remove and replace the ribbon now.

After this, the screen worked perfectly.

For all the popular criticism of Chinese products, you would do very well to find anyone in the UK providing such rapid and helpful responses. 

Well done, Waveshare!

Beware Amazon!

As regular readers will know, I'm a big fan of the fairly cheap and very clear small LCD screens made by Waveshare, available via Amazon, amongst others.

If you use Amazon regularly, you will soon come to realise that it is not only a seller and distributor of products it stocks, but a kind of 'open air market', where Amazon provides the platform for others - pretty much anybody - to sell upon.

Amazon, being American, has a peculiar view of consumer rights such as apply in the UK.  It has a strange 'returns window', which bears no resemblance to the 'reasonable period' available for UK consumers to assess any given product's suitability and quality. 

The difference is that Amazon decide how long you have to return the item, whereas the law is more flexible; you might have much longer to assess a product under consumer law.  You also have the benefit of a legally-enforceable guarantee in the UK (one year in most cases), whereas if you buy it from China, via Amazon, no such enforcement is possible.

This is rather important, because an LCD screen costing £54 is obviously expected to function properly after just 3 months of use  - which my latest and third Waveshare screen isn't.  It's developed a serious flicker that is not seen when the same Raspberry Pi is connected to my other two Waveshare screens, so it's clearly defective.

But I'm outside Amazon's convenient 'reinterpretation' of consumer law in the UK, and they won't issue a refund until the seller - in China - approves a return.  In fairness, many big Chinese companies are enthusiastic to develop a good brand reputation, and Waveshare may well replace or refund via Amazon (in fact, they took just hours to get me to send videos of the problem to them).  But it's by no means certain with all non-UK suppliers and if everybody just goes to ground, a UK consumer is left with, in practice, no legal remedy at all.

OK, it's not the end of the world if I'm unable to get a replacement for a £54 screen.  But it's rubbish that Amazon have these compulsory selling agreements with users that effectively ride roughshod over the consumer rights of those buying products via their UK platform.

I still think Waveshare screens are very good; I was just unlucky with one out of three I have being defective. 

But please don't buy electronics items of anything other than extremely low value from Amazon, because their terms and conditions potentially leave you firmly in the cold.  A list of UK distributors, who are legally obliged to follow UK consumer rights, can be found here, and back a level on the website, for other countries, too.

Information about your rights in the UK can be found here.