There has been a lot of discussion lately, much of it just plain incorrect, about the relationship between resonance and antenna efficiency. Many incorrectly claim that resonance has nothing to do with antenna efficiency at all, similarly others incorrectly claim that resonance is a direct indication of efficiency. Neither of these statements is true. The reality is that resonance does have a significant impact on how efficient your antenna is, but the relationship is highly non-linear and depends on many characteristics.
Below I have attached a chart hat plots out the total radiation resistance (R_r) vs the measured input resistance (R_in) of a dipole. Efficiency is just R_r/R_in. In other words an efficient antenna will have 100% of its resistance as radiation resistance, and R_in is **always** larger than R_r (since it is essentially ohmic resistance plus radiation resistance). When these two numbers differ significantly an antenna is inefficient. The source for the chart below is here and it gives much of the math if you want a deeper dive:
What is important to note here is that at anti-resonance we see a **huge** R_in value and a small R_r value, this means an anti-resonant antenna will have very high losses. Keep in mind the graph is very hard to read for the values <0.5 in length because the resolution isnt high. But there is significant divergence there as well. Notice at ~5/8ths wavelength antenna would exhibit very significant internal ohmic losses due to heat.
Here is the review of the Storm2 Liquid as requested (after owning for an hour or so). Not much to review really other than to make the following points.
This is a 93.5Wh portable emergency battle I just received one of the first copies of as an early kickstarter backer. It uses 8x 18650 internal Li-ion batteries.
The screen is loaded with tons of information in a very sexy high resolution display with an impressive color range. The info reported on the main screen and info screen are: Internal battery voltage and current, time running, input/output/combined current/voltage/wattage (so for example it shows what voltage the USB-c I/O are negotiated at), battery and CPU temp separately, it even tells you the internal battery voltage of each of the 4 parallel cells separately in addition to the combined battery voltage.
Not just the screen is sexy but the whole case really and you can see the 8 li-ion cells inside.
Comes with USB-C and DC-jack input ports that can also be switched to output ports. Has an additional USB-C output port and USB-A output port as well.
The DC jack acting as an output port means you can use it to charge non-USB devices and even comes with some alligator clip outputs for the DC-jack and you can easily buy standard output jack adapters to connect to any format dc jack imaginable.
Obviously the output DC jack setting lets you configure the voltage in 0.1V increments up to 25.2V, I think it handles either 3A or 5A output, need to check spec. However irf the DC-jack output is on as you adjust the voltage it updates the current out of that port in real-time which is useful.
Overall so far I cant find a single thing to complain about, this thing has all the data and features id expect and want and done as stylish as they could have hoped to do. IT is also about as small as you can get since 90% of the space is the batteries.
YAY! The Siru.box I ordered just came in. Havent used it yet but its basically a usb controlled and powered power supply. Lets you control the voltage and/or current and even has a very simple API so you can control it programatically. Not sure if/when I will have a use for this but it was cheap enough and cool enough I figured I'd snatch one up.
For this weeks #FollowFriday I am going to do a groups addition.
@Electronics - An Electronics Group
@theamazingweb - A group about interesting and novel things on the internet.
@vim - A group for everything VIM
@funny - A group for humour and memes
@mnmlsm - A group devoted to discussing unix and related topics
@calligraphy - A group devoted to sharing and discussing calligraphy & handwriting
@FreeSoftware - A group for discussing Free and Open-source software
@math - Everything math!
@dogs - A group for sharing pictures of dogs, for any reason.
@Science - A group to discuss Science topics.
@photography - A group for sharing or discussing photograph.
So its been about a month since the QOTO Moderated Groups Server came online at groups.qoto.org. It adds group capability to the fediverse with an owner capable of moderating membership in the group unlike previous group servers which were completely unmoderated and open.
We have had some amazing groups form and overall the server seems to be the most popular on the fediverse, I’m seeing more activity than the open-group servers which is great!
As such I wanted to share a list of a few groups I know of so far in case anyone is looking for a group to follow. Just follow the group as you would a user and you will be in the group and receive group posts in your timeline!
@Electronics Anyone have a suggestion on how to convert an LTSpice model to something that ngspice / oregano can handle?
I found a .asm / .asc schematic for the ULN2003 transistor array that I’d like to try out, but oregano doesn’t seem to have a way to import it.
I’m willing to try other circuit simulators as long as they have a reasonable GUI. I already tried Qucs and it seems to be worse in this regard (and buggy in general).
I wanted to share a write up I did not to long ago explaining circuit duals with a specific focus on magnetic circuits. They behave the same as an electric circuit in the sense that anything you can do with an electric circuit there is an equivalent way to do it with a magnetic circuit. A magnetic circuit is a circuit that uses the magnetic fields propagating through “wires” rather than electric fields. It’s a very cool idea and worth a read, though all the usual electric concepts are flipped, for example instead of talking about electromotive force (EMF/voltage) you would use magnetomotive force instead (MMF) as filling the same function as voltage in an electric circuit.
Let me know what you think, this tutorial was a week long effort to write.
Finished most of the #ROES prototype board. Never have I been so excited to solder something, specifically the shield. After several years of hard work putting that shield on was a trophy! Its something that has collected dust for periods too and this is the second version I went full cycle on.
For those wondering this is the RF analogy board for an advanced highly percise SWR meter with Network-analyzer like capabilities built into an #Arduino shield. It measures a radio signals forward and reverse properties and compares them including complex impedance, complex reflection coefficient, SWR and much more. with two of them and a zigbee you can even operate one at your transmitter and the other at the antenna end and get both readouts in the shack. Cool stuff!
The yellow shielded wire wasnt working so I added a very tiny red wire instead. The final product wont need this and it may introduce some issues with the prototyping, lets hope not.
If you want to see more pictures of the project, including the GUI demo running or the earlier v1 version just check out the #ROES hashtag.
Of course the one chip i needed to roast with the soldering iron repeatedly in order to fix a stubborn solder bridge is the same chip that costs 30$ each, and the last chip i solder.. FML.
Oh well assuming i didnt fry this thing its actually coming along nicely. The missing trace i had to hack in is ugly but the fact i got it soldered on at all (had to scrape away some solder mask to get to a via) is impressive. Lets hope this thing works when im all done...
FUCK! Somehow I missed a single trace when I sent my boards off to get prototyped!!! At least its not a production run, but still this is super annoying. I'll have to jump it with a wire but might cause some RFI, not happy about this at all!
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