Kari is building her own diode radio receiver with a little help from me and Iselin, and like Iselin, Kari wants the receiver to be beautiful. Kari will also make her own diode, so she knows that everything truly is done here and by herself, and heating copper is far easier to understand and doesn't require any 'sejd'. She knows that it requires extra pure copper for the best results, but that's really only a requirement for the power diodes I built for higher voltage rectification, not for finding a semiconducting point on heated copper. Everyone thinks it's marvellous how I produce pure copper, and that it just magically 'grows'. In the future, we will try to find some natural semiconducting crystal or mineral. There are quite a few, and Iselin has already enthusiastically tried to find one here on the island but without success. Expected since most of it is granite, so she is beginning to realise how frustrating it must have been for people before they even knew it existed and had that kind of specific use. Future elves will have it so much easier than humans did in so many ways.

  To reduce the risk of a fire, my sambos have agreed that Haera's room should have a simple combo light installed. Just a simple little white LED, but it's some light compared to needing a lantern. Haera now understands that the wind turbines are to capture the power of the wind and then I can power things with it. And that I already did that when staying on the farm outside Borgarsandr. Of course, she also now understands that the gauge by the steam boiler manometer shows how much 'sejd' is captured or stored. She's learned that the sejd is called electricity, and I can't exactly contradict her that it's not sejd, and Haera, Skirlaug and Raneigh think my Sejdmann title is so incredibly appropriate.

  I really want more and better electric light, and I'm not alone. Charred filaments, thin carbon rods and ceramic 'resistors' coated with a thin layer of carbon will work as low efficiency bulbs if we combine with really good vacuum, but it's not a priority project, mostly due to the power shortage. Short filament life will be acceptable because we will have our own manufacturing and I can design lamp parts, glass etc for easy reuse and for replaceable filaments, and thus it will be cheap even with a short lifetime. By hopefully making two or more separate filaments in a bulb, the 'lifetime' can be doubled before the bulb needs to be replaced. And although incandescent carbon is very yellow light, it is so much nicer light for indoor use than arc lamps, although arc lights are more energy efficient. A simpler form of electric candle is possible with two parallel vertical carbon rods with some insulating but vapourising-melting between. It will be like an electric candle consumed-burned downwards, where a surrounding glass tube with a vent cap on top should sufficiently attenuate UV light, at least if given some tinting.

  I wish I had some good way to really measure UV strength. I've been trying to get a relative measurement using an LED as a photodiode and using those luminescent stones. By short and fairly accurate time exposure from an arc light via a small hole in otherwise opaque shielding and in a dark room, and then increasing the distance to get correspondingly less exposure as the distance between the hole for arc light exposure and the measured value change, I have at least been able to get a rough idea of how much glass of various types and thicknesses reduces UV radiation, but I don't know if it applies to the entire UV spectrum that the arc light produce. Just what spectrum the LED and luminescent stone is sensitive to. I have also tried using temperature during long exposure, but it feels even less accurate. But some data is better than nothing.

  One disadvantage of a DC power supply is that one carbon rod is consumed much faster than other, but a bigger and thicker one might compensate. Otherwise, the 'candle' may have to be polarity switched after some use. AC voltage would solve that issue, although then there is a clear hum from the arc, but battery is DC power. A relay oscillator is not a good solution due to wear/sparking in the relay and more noise, and a DC motor connected to a AC generator is just a hassle and less energy effective. A manageable issue is ignition, as the arc must be started by shorting the carbon rods with a third carbon rod. But using a carbon rod with wooden grips as insulation is hardly advanced, and the common person is used to lighting candles in far more complicated ways. But we need to have more power available to use these electric candles. Of course using the steam engine for extra power works, and is sufficient for quite a few simultaneous arc lights or electric candles, but is hardly optimal. A far more efficient steam boiler in the basement and a generator there too, would be better for next winter, at least as a backup to other energy production that will be weather dependent. This winter have proved how 'little' wood a huge but well insulated building like Thrymheim consume to be comfortably heated by centralised steam. Using more wood to get a lot of electric light is very worth it for my sambos and staff.

  By next winter there will be much more electric power available, and thus more electric light available. However, I have thought about making a couple of arc light spotlights to be able to have powerful electric light both inside and outside if a need arises, and having a couple of arc light floodlights that illuminate the courtyard would be a good way to impress guests. Properly positioned on corners, three 270 degree illuminating arc lights can basically illuminate all around Thrymheim, and just one on the corner of the wing will light up the entire courtyard and both entrances. Although the days are getting longer, the spring equinox is still two months away, so better courtyard lighting than the lantern in the kitchen would be useful. And not much work to do or install.

  While doing other work, Iselin and I have resumed a couple of experiments. Plating with metals on different metals is one, and it is not very different from what we did with copper. Considering our experiments with gold plating and reactions, a lot of things most definitely will be gold plated, even though the surface won't be a perfect. But it is something to improve on. I suspect some sort of intermediate plating or surface treatment might help, and I also suspect nickel would be suitable. But experiments with metal plating have also involved galvanising iron, so we are trying to make a 'practical' Zinc Negative Resistance diode, ie a tunnel diode, and will try to tweak it so it becomes a simple oscillator, but there is a hell of an issue detecting when it is oscillating as the frequency can be in such a wide range. My SDR with a pickup coil as an antenna works in waterfall screen mode for higher frequencies, but it would be far better with a specific frequency measuring instrument in the future. And preferably a pure Alfheimr tech instrument.

  This is not a new issue, and given that it just need to work at relatively low frequency and to save components, we have jointly modify first one and then the other multimeter, so the multimeters get two RF modes and with built-in rotary variable capacitor and sensitivity control. It's hardly optimal, but it works and the multimeter box has physical space for it and is already a moving coil instrument with good gain, so the box gets a special antenna socket for measuring probes or antenna connection. In principle, the multimeter also becomes a Dip Oscillator and a field strength meter. Along with the Midg?rd predecessor that used a vacuum tube and was called the Grid Dip Oscillator, these instruments have been practical and important to radio technicians and hobbyist since the 1920s until the late 1990s when modern computerised instruments outcompeted them.

  The hardest part is making, calibrating and scaling all the separate measurement probes which is a pain in the arse, as I don't have a variable frequency function generator. So I have to build a simple variable oscillator out of a transistor and an LC circuit, and modify it as the need for higher frequencies comes. But apart from the lower ranges, we can use the SDR to see what the frequency is, and by mixing in a known higher frequency we can measure the lower one, and tweak until the oscillator gives an exact frequency such as 900 kHz or 5.0 MHz, and then write down what angle the multimeter/dip dial is from zero position for that probe. This is done on both instruments at the same time, and we have to keep track of which values belong to which instrument and which coils belong to which multimeter/dip meter. By using different pinouts on the probes and connecting different capacitors or shorting across them, we have finally managed to get a coverage range from about 50 kHz to 150 MHz via 9 probes that overlap a little, and we have labelled each probe with the frequency range it covers. We tried a final one that went all the way up to 450 MHz but it is unstable and there are probably too long legs on the components and so on. I am honestly impressed with how high frequency the Dip Oscillator works well at and would have been happy with 40 MHz or so. We might make a couple of more coils to extend the range some up and down, but not currently useful. With this we can measure the frequency of a tuned circuit or antenna, and also get a general measure of signal strength differences.

  Stolen from its original source, this story is not meant to be on Amazon; report any sightings.

  As expected it is too much of a problem to engrave all these scales into the small brass plate behind the dial, so that dial will keep its angular scale. Tables to convert the angle of the dial to frequency will be attached to the protective cover of the measuring instrument and the measuring probes can also fit there. A copy of the tables, updated wiring diagram etc will be stored in my office, and Kari and Iselin will each draw an updated wiring diagram to keep inside the multimeter together with a copy of the table. The LC circuits have been labelled with the exact frequency they have and stored in my workshop, so we can use them as references, and in the future there will be made significantly more and long-term stable references sealed with dry air in glass, just to have the best possible reference when my Midg?rd technology eventually stops working. The references will be used for future measuring instruments.

  Both Iselin and Kari love these projects and work, and they are practical lessons in electronics, radio knowledge and building and testing stuff. Both also love that we actually manage to build a zinc negative resistance transmitter that is picked up by the mansion's radio even though it is extremely low output power. We test by having a volunteer write down some letters, which we try to transmit and then the letters are shouted from the guards day room. Everyone we show is impressed, not least the newcomers like Gisela who are shocked at what they are being taught to understand and use. Jane is almost as shocked as everyone else and can't understand how the small wood board with some metal pieces on the table is a real radio transmitter, and what Kari built is a real radio receiver. If she had done stuff like that in the physics class in primary school, she might have found physics much more interesting. What she and I talked about during the autumn has made her change her mind about certain areas of physics and similar knowledge. So I may not be a pedagogical teacher, but I'm apparently pretty good at getting people interested in something I find interesting and know. Iselin and Kari are so damn smugly pleased that Jane is so impressed and she doesn't understand how it works.

  But they understand.

  Jane gives me a sideways bump with her bum, smile and say: "Well, I for sure support that everyone should have their own creative handy nerd, especially if they happen to travel to the Elvish Middle Ages." She smilingly goes on: "In addition to epic sex, the nerd can then also skilfully created fantastic conveniences, luxury, technology and improve the world."

  That is a nice compliment about my skills both in and out of bed, and I'll give her a similar compliment in return. "I think everyone should have a skilled creative artist as wonderful companionship when travelling to Elvish Middle Ages, and outside of bed, skills in painting and music are also very valuable."

  I'm rewarded with a sensual and hot kiss, so I guess my compliment worked.

  Pretty much by accident I've managed to use the zinc negative resistance technology to make a small amplifier function to a diode radio receiver. It is complicated because a 'zinc negative diode' or 'tunnel diode' only has two connections, i.e. the input and output signals use the same connections, unlike for example a transistor which has three connections, and where one is common and the output signal connection is separate from the input signal connection. In a tunnel diode amplifier, the output signal also affects the input signal, so it becomes more difficult to distinguish and use, and I'm simply not used to using a component like that. Using it as an oscillator it is one thing and not hard, but using it as an amplifier it is much more complicated. Fortunately, this is very primitive radio technology, and a 'narrow band' radio receiver for a particular frequency seems to be fairly easy, both because there really isn't much option to where the tunnel diode amplifier can be in the circuit, and it seems to be fairly easy to weakly amplify the narrow high frequency radio signal once the impedance and right circumstances are met. And a regenerative receiver can be very simple.

  Actually using this tech in future radios or other electronics will be a whole bunch of other problems, especially making a zinc negative resistance 'tunnel diode' as a finished component that is durable and reliable to use, if it's ever going to see use in anything more than on a lab bench. Only after solving that will I try to build amplifiers for carbon fibre microphones or ribbon microphones, although I have started working on a ribbon microphone. I expect a wide range audio signal will be a whole other issue. But maybe we can improve the performance of the diode receiver in other ways, and perhaps introduce a simple tunnel diode oscillator to receive morse code.

  I am actually keen to try a very simple PNP transistor effect of any suitable crystal with two small needles very close together. It will be so very sensitive and fiddly, and probably only manage a couple of volts before it breaks, but if the tunnel diode or transistor can give any amplified effect at all, even if it's only three or four times, then it's a proof of principle. If they can be cascaded so one amplifies to the next, then higher gains can be achieved and be really useful.

  But that's only for radio receivers and such, and doesn't solve the problem for transmitters.

  I've really started thinking about maybe giving my future military forces and ships simpler spark gap radio systems, but there will be a lot of optimisation of their operation and physical construction. With a good enough antenna and higher frequency, it might be a reasonably practical portable radio if I can achieve a useful range of a couple of kilometres in field conditions. It's certainly better to not build something so primitive as a spark gap radio, and I don't want simplest radio technology to proliferate, but it might be too valuable if I can't manage to build good enough vacuum tubes. Development of portable systems might lead to a relatively practical ship radio or for fixed installation. If spark gap systems can provide beyond the horizon range on ships then that is valuable, and it should reach much further during nights, which has its own value. It will be very interesting to see how compact and good I can make it, because historically early radios in Midg?rd were hardly optimised to be compact or for something man portable and carried around, and that certainly applies to what was actually used in Midg?rd if I go by photos I've seen. It's a tricky but interesting bunch of problems where I have to adapt and improve each part separately. With the lathe I can probably turn metal discs that are insulated and stacked for a more efficient extinguished spark gap that is compact, quieter and should give slightly longer range, but I would probably need piezo headphones to get good range. Coherer may be the primary reception method, but it will draw some power. The battery and antenna will probably be the trickiest problems for something that is carried around.

  As Kari has finished building her very own diode radio receiver, and I have my 'not pretty' tunnel diode receiver, we go for a walk outside to test the receivers.

  Kari sits where Iselin sat, and she is so happy and relieved when her radio works that she gets tears, and we can faintly hear Caecilia singing. Iselin, Bodil, Hillevi and I get to try listening to her radio.

  Next we try the other radio with the amplifier. It's trickier to handle and get it to work, but after some fiddling the sound is much clearer-louder than when bypassed. Iselin and Kari are so pleased!

  We will definitely try to make good tunnel diodes and improve our pure Alfheimr receivers, and upgrade them when possible. Once we get enough thin copper wire, Iselin and Kari will help build another spark gap transmitter so they can say they did that too, and two complete mobile systems are interesting to really test if tactical radio units are something to spend time and effort to try and develop.

  Jane's bum, knee and ankle didn't suffer any major damage from 'The Tardis incident', but to make up for it I've promised to kiss them - and other places - to make it better. I just had to tell Alith that music will have to wait another day while I helped Jane up the stairs. When Jane shows me the new leather accessories she has sewn, I get what Jane meant by; "You're turning Alfheimr to Midg?rd, but I have gone Viking and raided for treasures."

  A good blindfold, ring for the mouth and other things to compliment her existing wrist cuffs. My workshop attic with leather, metal rings, metal buckles etc have been her raid target. Her needlework is quite nicely done too with even stitches etc, so she has spent a lot of time on these. Obviously, she isn't just painting in her room.

  As desired and expected, I am forced to 'punish' her for the unauthorised raid, as well as 'reward' her for her skill in leather crafting and how much she does to make our sex life special. In this case punishment and rewarding is basically the same thing, and is nice for both of us, and she 'threatens' me with future raids. I just warn her that the workshop attic has things like mercury and acids, and to be careful with the clay pots and other things. Read the notes I've tied to the pots, although they're in Swedish or Norse. But I haven't given her permission, because then it wouldn't be a proper raid, and then I can't 'punish' her.

  https://en.wikipedia.org/wiki/Grid_dip_oscillator

  http://sparkbangbuzz.com/zinc-osc-2/zinc-osc3.htm