Introducing uRlTeX

This is a nifty little micro service I came up with when I needed to embed an equation here in the blog, but could not find a simple way of doing it. On urltex.com, you can ask for an image, where the address is a LaTeX equation and the formatted image is returned. Below is an example of the Fourier transform.

 This image is obtained by embedding an image with this URL:

http://urltex.com/eq/F(%5comega) = %5Cint_{-%5cinfty}^%5cinfty f(t) e^{-i%5comega t} dt

 You can read more on the webpage. Note that the service is still experimental.

On antenna efficiency

I rarely write on my blog about things related to my professional work. There are just so many other channels where that goes. But I felt it is time to address one particular issue, that still is very poorly understood and you can read a fantastic amount of nonsense on it. And it is about antenna efficiency (I work with designing antennas and test-systems for antennas).

Antenna efficiency is really something very simple. It is a measure of how much of the power that is sent to the antenna that is actually transmitted out in the air (and since a normal antenna (without amplifiers or other fancy stuff integrated) is reciprocal, this also holds for receiving antennas). So a very simple relation can be stated:

 Where Pin is the power sent to the antenna and Pout is the power transmitted by the antenna. e is called the efficiency or total radiation efficiency of the antenna. For small antennas, such as antennas in mobile phones, IoT equipment and WLAN (WiFi) products, this is the most important metric of an antenna. You want as much power sent to the antenna to enter the air, where it has a potential to reach and receiver. e is a number between 0 and 1, 1 being the best and meaning all power sent to the antenna get radiated.

There are many other parameters that can be stated about an antenna, some only related to the electrical properties. The most common one and, which most people are aware of, is the radiation pattern. This is a function, g(theta, phi) over the sphere indicating how large part of the radiation entering the air that is radiated in a certain direction. This is usually the most important property of a large antenna. You make an antenna large so that it can be used to direct the energy in a certain direction, for example towards a geo-stationary satellite.

Now, radiation pattern play an extremely small role in wireless communication between small terminals, such as computers and WLAN router. The reason is very simple: you have no clue in which direction the router is in relation to you WLAN device. So, ignore the radiation pattern.

The radiation pattern can be combined with the efficiency according to

 

to obtain the gain. This metric compensate for a finite efficiency of the antenna and indicate how large part of the energy sent to the antenna that is radiated in a certain direction.

If the antenna is connected to a transmitter (e.g. a WLAN modem) with a certain output power, P, that can also be added to the above formula, resulting in

 

where EIRP is an abbreviation for equivalent isotropic radiated power, a fancy name for how much power is transmitted in a certain direction (theta, phi). Note that P in this equation is the same as Pin in the first equation and thus

EIPR can be of importance for small antennas in some cases. The most well know is that regulators uses EIRP for limiting power out from a device in many situations. This is sensible since it is reasonable to require that a user does not get exposed to radiation intensity above a certain level.

There is one further property that is very common to look at for a small antenna and that is the return loss. This is a measure of how much energy sent to an antenna that enters the antenna. Some of it gets reflected back and is thus not used. For a small antenna it is common that something between 10 and 90% gets reflected back. Of course, 90% reflected back is not a very good antenna, but it is not uncommon. Making good antenna solutions is hard.

The part of the power that is not reflected back enter the antenna where one of two things can happen: It either gets dissipated in the antenna structure or it gets radiated. Of these, we of course want it to be radiated. The two mechanisms of losses can be combined, and then comprise the total radiation efficiency of the antenna, as used before and one can decompose the two loss mechanisms according to

Now comes my critique. As I stated above, the total radiation efficiency is the most important property of a small antenna. the return loss, er, can be great, the antenna can have some radiation pattern you think looks cool and the gain of the antenna can be this or that. But all of this does not matter of your total radiation efficiency is poor. If does a simple search in the internet for papers on new small antennas, they always state the return loss. And very often they state the radiation pattern. But very very rarely they state the total radiation efficiency. Why. Either because they do not understand what they are doing, or they cannot measure it (since it is hard to measure properly, both in a simulation and in a measurement set-up) and thus, cannot report it. Neither of these are good reasons for not reporting it.

Or, you can read on an otherwise very well informed and good webpage on antennas things like:

"Note that there are no TRP specs, so in general you don't want the WIFI antenna to have too high of an efficiency, or the SAR and peak gain values will require a large conducted power backoff"

This is of course total nonsense! You absolutely wants to as high efficiency as possible and back off output power if you are so lucky to have too high output power (TRP is an abbreviation for total radiated power). That will save energy and by that battery live.

Corona-kommision och hycklande självkritik

Regeringen gör en pudel när Corona-kommision kritiserar, men faktum är att detta varit känner hur länge som helst. Och självklart ska vi ha en vettig äldreomsorg, men det finns ju andra områden som är lika försummade, som vanlig vård och skola. Alla regeringar har använt dom automatiska nedskärningarna för att minska på dessa områden som en konsekvens av det nyliberala trycket väst bågnar under.

Men det är nog lite lustigt att man nu säger att delade turer och osäkra anställningar ska bort när man precis tvingar fackföreningsrörelsen att släppa dessa punkter genom ett absurt lagstiftningshot som går emot allt vad svensk modell heter.

Vi måste erkänna att Sverige är inte längre ett socialistiskt land. Vi är ett ultrakapitalistiskt land som i mycket är mest extremt i världen. Vi är beredda att acceptera nationalism för att stoppa flyktingar och tillsnurrad argumentation för att kunna införa den ena nyliberala "reformen" efter den andra. Men, medborgare, se till att hålla reda på åt vilket håll de kausala pilarna går. Det är inte immigranterna som bryter ner välfärdssamhället och skapar klassklyftor med invandrare i en underklass. Det är det nedbrutna välfärdssamhället som skapar klassklyftor med invandrare i underklassen. Och det är det nog många som vill ha. Trevligt med en tjänsteklass som kan ärva oss som hade turen att födas här. Men var åtminstånde ärlig med vad vi håller på med då. Och var också beredd på vad som måste offras. En undefinansierad äldrevård i 20 år ger höga dödstal i en pandemi. Vad tror du en undervärderad skola i 20 år ger?

Omfördelningen fortsätter

Regeringen med Sossarna i spetsen fortsätter sin omfördelningspolitik där skattebetalarna ska ge till de rika. Nu med slopad uppskovsränta på vinster på bostadsförsörjning. Med någon dimmig idé om att fler ska flytta. I själva verket är det ytterligare ett sätt att gynna de rikaste. De som gjort stora vinster på den dysfunktionella svenska bostadsmarknaden.

Detta är inte vägen att gå för att bygga ett jämställt samhälle med en rättvis omfördelning. Tvärtom. Detta är ytterligare ett sätt att gynna de rikaste. Hur kan Sossarna komma undan med denna nyliberala politik gång på gång? 

Ännu ett vansinnetsförslag från högern

Det finns vidriga människor i världen som är otroligt kreativa när det kommer till att utnyttja system och medmänniskor. Som de som driver Pelekh. Men vi kan inte ge efter för ondskan och forma vår värld efter en missbrukande minoritet. Det är inte det samhälle vi ska ha. I en välfärdsstat måste man acceptera att välfärdssystemen är för breda och kommer vissa till gagn som inte e.g. var tänkta att ta del av systemet. Det är viktigare att täcka in alla som verkligen behöver det än att vara absolut säker på att inte ett öre går till någon som inte förtjänar det. Såklart ska man inte vara naiv. Låt oss genomföra det Morgan Johansson föreslår i detta fallet och i det allmänna jobba mot att finstämda våra system. Men låt oss inte ge efter för ondskan. Det är inte den värld vi vill skapa.

Interpreting the stock market

People are debating how the stock market can continue to grow during the pandemic when so many sectors are doing poorly. The answer is simple. Two things are driving the stock market development. There is one main factor driving short-term variations and another driving long-term. The short-term factor is expectations and the long term is available capital on the stock market.

Of these, the short-term is probably not very controversial and well accepted. However, the long-term driving force is interesting to think about a bit further. What can make capital available to the stock market? It is surely due to that some entry (person or corporation or government) has financial capability to invest on the stock market. This in turn, should be interpreted as this sector is doing "well" in some regard.

Now, during the pandemics, since the stock market is rising, that should be interpreted as that this very wealthy sector (that is, the entities with enough money to invest in stocks) has found the ways to manage the pandemic situation. Since we know that many people loose enormous amounts of money, it is clear where these money is going: to the financial sector. So, all that efforts governments are doing to save jobs will at the end simply boil down to redistribution from the common to the wealthiest.