Category: Sci/Tech

Radio Waves (by )

I really love learning things, and recently I've finally been removing a long-standing thorn in my side - the fact that I don't really understand radio frequency electronics and the propagation of radio waves.

I've tried to fix this a few times in the past, but the resources I'd read never seemed to quite explain the whole picture - and I couldn't see how to piece the things they explained together into one coherent understanding of the electromagnetic world; they were clearly only shedding light on little corners of a totality that still remained mysterious to me.

Well, there are still gaps in my understanding... but I've made some progress, and in the hope that I can help others struggling with the same confusions as I was, I'd like to share my way of understanding it all.

One thing that bothered me was that explanations of transmission-line behaviour seemed to flip between talking about instantaneous voltages and currents at some point in the line, sampling the analogue signal travelling down the line - or talking about an RMS average voltage or current, and thereby causing me to struggle to make sense of what they were saying. But I think I now get transmission lines to some extent (although I'm still hazy on waveguides, because I've not gotten around to looking into them yet). And I was never quite sure what the impedance of a whole transmission line really meant, regardless of its length. If I had a transmission line and put a resistor over the end of it, and hooked it up to a battery and an ammeter, I knew that the current flowing would depend on the total resistance of the line and the resistor at the end - which would depend on the length of the line, as its resistance would be in ohms per meter. So what the heck was this impedance thing about? How did impedance mismatches cause reflections?

So, here's how I think about transmission lines now. The "DC model" of hooking a battery up to one end of a line and reading the current that flows into it is, of course, perfectly true - we can set the circuit up and test it; the reason it doesn't contradict with this weird parallel world of impedances is that the DC model is a steady state model of the system. When you first connect that battery to the line, current is going to start flowing into it, crawling along at a sizeable fraction of the speed of light; but until that current has reached the end, flowed through the terminating resistor, and flowed all the way back, it can't possibly have communicated any information about the total resistance of the line and its terminating resistor... So how much current initially flows from the battery, and why? Of course, the line can be thought of as two series of tiny inductors (with resistors in series, if we assume the inductors are perfect) with tiny capacitors connecting the two conductors, due to the inherent inductance of the wire and the inherent capacitance of the gap between them; you can imagine that the current from the battery has to charge the capacitors through the inductors for the voltage/current surge to propagate down the line. But what made "impedance" really click for me was going back to the basics of Ohm's Law and seeing it as a ratio of voltage to current. At any point along that transmission line, a certain instantaneous current will be flowing - and there will be a certain instantaneous voltage between the two conductors at that point; and the voltage divided by the current is the impedance.

So, if a 12 volt voltage source is connected suddenly to a 50 ohm impedance cable, an instantaneous current of 0.24 amps (12̣̣̣̣÷50) will flow. Now, as Kirchoff's current law tells us, the currents flowing into a node must sum to zero; so with the imaginary node at any point on the transmission line connecting two halves of it, the input current must equal the output current (although some current may be lost to resistive heating or leakage, that's not relevant in this case). So what happens when there's a change in impedance at some point in the transmission line? The current must remain the same, but the impedance changes - so the voltage must change, to make Ohm's Law still hold. If my 50 ohm cable is connected to a 75 ohm cable, that 0.24 amps flows into it and changes into a voltage of 18 volts (0.24×75). Which is why high impedance transmission lines are less lossy; a transmitter putting a watt of power down such a line (with proper impedance matching) will push out a higher voltage with less current that one putting a watt of power into a low impedance line - and resistive losses in the cable are worse for higher currents.

How about the reflections when impedance changes? I'm still a little hazy on this, but I think it's something along the lines of this: imagine a point just where the impedance changes in our example of moving from a 50 ohm cable to a 75 ohm one. A current is flowing into that point, but the voltage is higher after that point than before - which is going to create a current travelling back the other way. Where I'm hazy on is how this happens at junctions where the impedance falls (is it to do with the fact that the current flows alternately backwards and forwards, so the junction is traversed by current in both directions anyway, and the phases where the current travels from low to high impedance are what create the reflections? If so, isn't that a kind of rectifying action, that will create harmonics and intermodulation? But what is the "direction" of a signal travelling along a line, anyway? If we froze the signal in time, we'd just see a sine wave of voltage and a sine wave of current along the transmission line - if we restart time, how does it "know" what direction to propagate in? Something to do with the relative phase of the voltage and current waves?) So, yeah, I've a little more to learn there.

But this model of impedance does explain a lot. I wondered why the angles of the radials of a ground-plane monopole antenna affected impedance, but now it makes sense - the end of the transmission line basically spreads out to become a dipole, or a monopole and its ground plane; the electrical field of the travelling signal has to cross a larger region of space, so it makes sense that the voltage required to do so might vary depending on the amount of space crossed. All the mysterious constants, like the fact that a dipole trimmed to 0.48 times the wavelength has an impedance of 70 ohms are really down to the electromagnetic stretchiness of space: the impedance is the voltage required to push one amp along a transmission line (a dipole antenna just being an oddly-shaped transmission line, handing the signal over to the even weirder transmission line that is free space itself), and that is a function of the permittivity and permeability of that space.

Antennas with multiple elements are confusing, but I'm not sure anybody really understands them - as far as I can tell, the design process is almost always to mock it up in a finite-element computer simulation or build a prototype and tweak the design until the desired parameters are obtained experimentally; the mutual interactions between the elements (not to mention ground, support structures, and the transmission line feeding the antenna) are just too complicated to analyse.

I really don't get why there's a near field and a far field (or that funny one inbetween that, I think, is just a mixture of the two). Does the antenna both far and near fields at once, and the near field is stronger but doesn't spread out far, so the far field is negligible when close to the antenna? Or does the antenna create a near fields, which "decays into" the far field as it spreads out? Nothing I've found seems to explain.

But, I can understand how to run a cable to a dipole or monopole antenna, manage the impedance transitions, and make it radiate efficiently. That's progress!

September Events 2018 (by )

Weds 5th - 1-2 pm Women Pioneers in Computer Science at the Museum of Gloucester by Alaric part of our Ada Lovelace Day celebrations - Cuddly Science Histories

Weds 5th - 7 pm Space Album Launch Party at the Guild Hall part of the Gloucester History Festival free but ticketed - Sarah and Jean are part of the album which celebrates local historical places and people

Sat 8th - Pride Day in Gloucester Park - stall selling art work and offering free colouring in - in the Community Tent - Gloucester

Wed 12th - 7:30 pm Book Club Talks - Ada, Ada and Ada - part of our Ada Lovelace Day 10 year special series - Cuddly Science Histories - Cheltenham Bottle of Sauce

Thurs 13th - 6-8 pm - Back To the Future Gloucester PechaKucha - part of our Ada Lovelace Day 10 yr celebrations - Cuddly Science Histories - Eastgate Viewing Camber (the ruins in the ground near Boots) - Gloucester History Festival - Gloucester

Sat 15th - 11:30 am - 3 pm Mighty Girls of the Past - Gloucester Library - kids fun day as part of the Gloucester History Festival including puppets, activities and colouring in. Ada, Aethelflead and Mary Anning are amongst some of the Mighty Girls of the past coming to join us - includes the ever popular sandpit dig (yes inside the library!) - Free and open to all ages and abilities - Cuddly Science

Later in the month there should be some poetry events but just waiting for confirmation 🙂

Rome-Christanity and the Ending of Worlds (by )

When confronted with a graph on facebook showing the "dark ages" and the ensuing arguments over weather Christianity was the savour/cause of it... I write this:

The two events were entwined - the fall of the Empire was also plagued by natural and human fed disaster which led to desperation which fuelled the new religion which in some cases caused its own disasters but also monotheism in general was on the rise - if we'd have ended up with an Abrahamic religion which ever way we turned - the world was ending and they are doomsday/death cults on the most basic of levels. The loss of information and learning oscillated between the Christians and the Vikings with both also picking up the slack at moving education forward at various points of history as well as being the book burning racists at others ie one good period in England for education was due to Christian Missionaries from Africa (before the Norman conquest). History is a many threaded rug.


This maybe why people get grumpy with me on Facebook. Obviously this is a very very simplified statement and that in general is the issue with history - everyone wants and was taught simple narratives which not only do not paint the full picture but are often twisted to agendas and that's before you look at how biased the original sources were anyway - remember history was written by the battle winners and as writing was often the preserve of priests of one variety or another they are tinged with that element plus of cause the story telling needs and until relatively recently history was seen as something that was given to you by divine inspiration - a little factoid is missing or inconvenient? Pray and get a juicer more interesting thing to put in your script. Many of the older religions ie Judaism have mechanisms to try and prevent these copying errors/mutations but even then you are looking at scripts that spent many generations as oral transitions before they were ever confirmed in script on a page.

So yeah the Roman Empire's falling - but you know it was gradual - it became too big for it's communication network - it tried having multiple leaders which started well until Constantine decided to murder the other Empire and his son - the kid was his nephew - he let his sister live. And yes he was the first Christian Emperor due to a miracle he saw on route to battle (probably a meteor breaking up before it impacted the ground - if there was anything at all - but equally it could have been something else - maybe even the divine). But it was a political move also, a lot of the wealthy in the Empire where playing with the new religion - it was hip and trendy - it had eeking out past it's oppression (just) - it was the religion of the town - pagan comes from the latin for country side as the pantheon of gods got pushed out of the cities and was considered to only be for the unenlightened.

I think it was his mother that was obsessed with the new religion and traveled to the holy lands to find the roads that Jesus trod - she in many respects is the first archaeologists we have on record and her somewhat mythical landscape is still imprinted on the area with many pilgrims still following all that she found and was told - though this was hundreds of years after Christ had actually walked those roads.

But this was only one time in the break up of the Empire - another saw the reclaiming of the Mediterranean sea as an Imperial lake and a rejuvenation of trade and art... only to be struck down by the first virulent plague out break - the Emperor survived - his wife didn't and he was fatigued and in constant pain afterwards - many blamed his wife for being a hoar (she was a dancer when he met her and fell in love).

Yet another ending saw a sop of an Emperor, who fled the city of Rome leaving his sister as a prisoner of the Goth's - yes this was the sacking of Rome by Alaric in 410 AD - there were fires so fierce that they fused gold coin and limestone pavements - it was off course a misunderstanding - climate change and war had left the Goths with no home and little food and they considered themselves to still be part of the Empire that had still been wringing taxes out of anyone and everyone they could reach. So they fled to the capital as refugees hoping for aid - the Emperor panicked and a lot of the damage was done by the Romans themselves.

This is often seen as The End and the Emperor's sister married Alaric's bother (can't remember if it was a half/step or full brother) and it seemed to be a marriage for love and not politics.

But that wasn't The end as there was Holy Roman Empire's and time periods shift and change slowly on human time scales. And things where up and down and up and down.

The end of Roman Britain is the beginning of Anglo-Saxon/Viking Britain - but it wasn't a distinct cut off it was an overlap - and one that was gradual as the Romans pulled out the tribes come and saw no resistance, warred and then settled. The Romans took their time pulling out and didn't even really all go as many of them where intermarried and actually native born by this point.

Because I have an interest in this stuff anyway and because it is relevant to my novel series I have spent my teens and adult life reading and watching and prodding at ruins (well mostly taking photographs) - not full time - not even really part time - I am not an historian or archaeologist though people keep insisting on calling me that at the moment (last night I was referred to as a "proper" medievalist when I went to speak to someone about their talk on medieval humour and art - they were worried that I would pick holes in their talk! O.o ). I have collected a kind of over view - being a geologist I tend to bring things back to the rocks and the earth systems and this is my take on it:

The plagues did a lot of damage - the plagues were caused by over crowded cities with good travel and trade interconnects - a transport networks for the disease vectors to move along. But the plagues could only get a hold of a population if and when they became malnourished as that weakens the immune system - this is the difference between it being an outbreak and it going full blow PLAGUE. Healthy individuals who are cared for have good chances of surviving even the roughest of illnesses. Weak, hungry, over crowded, tired and overworked people with little scope for cleaning, washing or just having contaminated water to begin with - they... will not recover - they will die and it will spread like wild fire.

Weather calamities muck up food production - hungry people war over resources which causes even worse resource problems as it cuts down trade - you get a sickness, starvation, war cycle - this of course results in DEATH - the four horse men are ridding out. Religion sometimes precipitated the disaster and ones that were avoidable or had the chances for some serious damage limitation where exploded into carnage (I think it was the 13th century European plague out break that saw families abandoning the sick because it was seen as a judgement from god thus increasing the death toll drastically - sick people need to be fed during the recovery period or they will die of starvation if not relapse of the illness). OF course religion at other junctures was the balm that allowed to people to care for they're stricken neighbours and to rebuild afterwards.

When proper pandemics hit with no modern medical care (possibly even with) - you have a crash in population numbers - civilisation relies on an intricate series of feedback loops that all rely on everyone doing their part of the system. If you loose a chunk of your population - you have a problem. Even 10% is going to have a huge impact - that is 1 in 10 of the farmers, the teachers, the army. You can't produce as much food, education and knowledge transfer falters and you are in a weaker position to those around you who may be having similar food issues.

So actually my conclusion in looking at history as a whole is that these turning points - the collapsing civilisations and transition appear to be connected to the weather - to climate. Whether it is an increase in drought, damp, stupid long winters that catch you expected or rising sea levels. Some of these seem to be linked to volcanic events and others to human activity ie deforestation by the meso-ammerican cultures occurred around the right time to be a factor in the mini-iceage which is thought to have been a big factor in the "dark ages" of Europe - these things are global but we often only look at the localised focal most relevant to us.

I have asked historians at talks and so on if they think this is plausible - most just look at me slightly confused so this really is just my thoughts on the subjects. I even think the witch trials and things can basically be boiled down to... something disrupted the system and people panicked. That something I think is nearly always factors beyond our control - what then happens during the disastors is very much humanities own invention... war, famine, plague loop-la-lopping around each other in diminishing loops until things have settled and are stable again. The "dark ages" is probably the last BIG one of these but it is not the only one and I don't even think it was the biggest it is just most people don't seem to realise what a wealth of very very old and advanced history there is outside of Europe.

Below the Surface (by )

Alaric discovered this amazing website Below the Surface. This is a fusion of maintaining environments, urban upkeep, archeology, social out reach and art!

Cataloguing all the finds from the river Amstel in Amsterdam during train line works they have built up an amazing image archive showing the depths and ages of the objects, you can explore this catalogue, find out things about the civil engineering around the project and create your own displays with the finds that catch your interest.

This is all free and on line - the internet is starting to have these little lovely treasure troves of sites. This was what I envisioned the Internet being used for. For me though this project is tinged with a "could have been" here in Gloucester something like this was created back in the early days of the Internet and had the scholars and volunteers and council members enthused and then... it basically got unplugged and lost (early days of the internet I did say - things were different in those call up days!).

Many museums and research institutes are also putting their photo archives on line - Below the Surface how ever is a lovely smooth and easily searchable interface which is slightly more unusual!

There are over 700, 000 finds and the time periods spanned is more than written history - it is an awesome resource!

World Refugee Day (by )

Aethelflaed Talking on World Refugee Day

Queen Aethelflaed the Puppet - Mother of England - talking about why she founded St Oswald's to a group of Scouts - she also mentions the fact that she would have been a political refugee as a child. Her father was on the run for a huge chunk of her childhood - she was probably safe living with family in a neighbouring Kingdom (the one she later ruled) but she would have been aware of what was going on and how precarious her position was.

Yesterday was World Refugee Day - a day it sickens me that we need, a day that highlights the plight and the wrong done to those in need around the world - and some of those doing the wrong are people who should be doing the protecting - people who have forgotten their own histories of persecution and fleeing in desperation. With the US lying to refugee families using rhetoric such as "you are going for a shower" to split up families - to rip children already scared and frightened from the only thing they have - their families - to use those words - that trickery... the ghosts of Auschwitz must surely stir. They are no doubt more moved than the power hungry bullies who are creating these inhumane policies.

We are all on a tiny little rock floating in space - life is so fragile, wars and war mongers create refugees - economic collapses occur due to power struggles that have nothing to do with the people who suffer - so why are they the ones punished?

And quiet frankly - it is a matter of luck and things can change so fast - you think your safe? Well so did a lot of the refugees not long ago. It could be you standing there in their place, it could be your family being torn apart.

And even if we were in an assured place - then why not help? For fear that they might use up some of our resources? One of the things I've had hurled at me over my stance on helping people is that I don't care about my children and my family - as if I am taking bread out of my own families mouths to feed the homeless/refugee. But apart from the absurdity of this - we are not struggling for food - we have done so in the past but not now and it seems to me that those with the most capacity to share are the ones that hold onto it, rigid and unrelenting.

My kids can go without ice-cream for some other kid to have a nutritious meal, my kids (though they would often argue) live in the lap of luxury - sure they have to do chores and we don't do lots of things they see their friends do - but they have food and cloths and toys and an xbox. They can go without a cinema trip to give clothing to those who need it.

From a selfish pragmatic point of view - I am protecting them - desperate people do desperate things and that leads to higher crime rates especially violent crime. A lot of the stuff I see being called a "gang", immigrant etc... problem comes down to poverty. The lesson should be that we need to care for others but people seem to take it to mean that we shut the door and well history hasn't been kind to those who did that in the second world war... but people seem to have forgotten or never known these things - those bought up in the shadow of the second world war (baby boomers) often see it as a glorious pulling together time against the damn enemy. They have often never looked at it as an actual piece of history.

I am truly scared by the uncaring, vindictive behaviour and out right hate I am seeing grow globally especially amongst the so called civilised countries ie America, Australia - Britain. But worse is the apathy and won't say that I haven't suffered from that also - so many bad things crushing down on you - demanding your attention - you kind of shut off. We don't do TV - when I go to my parents house I am horrified by the gut wrenching, emotional manipulation of the adverts that bombard most people at regular intervals through out the day - no wonder they are desensitised to it all - I'm not sure it registers as real hidden amongst all the day time dramas and things either.

Having said all this I am at a loss on how to help - a while ago now I was involved in a fundraising evening to provide clothing and things - but I became suspicious of where the money was actually going and so I am wary. If you deal with a charity and know they are doing good things - have seen what they have done - feel free to link to them in the comments.

This is an old film now but still relevant about the UN Refugee Agency.

As a writer, artist, communicator I feel it is my duty to NOT remain quiet whilst these atrocities are being performed and don't think I am being extreme here in what I am saying - the body count is mounting, and once more it is the most vulnerable who suffer - those who should most be protected.

Yes I wear my hear on my sleeve - I am a parent - I can not divide children into those to care for and those to make suffer - that is... an UNSPEAKABLE CRIME and yet I must speak it - I must highlight that that is exactly what is happening and I must fight against it. All decent people need to fight against it and too see it for what it is.

On a more positive note - many are standing and being counted - there is Harry who is in his 90's and is doing all he can.

My tweets and retweets on the matter:

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