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:

nptel.ac.in/content/storage2/c

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.

@Electronics

A wonderful site showing a few different types of radio signal **refraction**. Important to note what you are seeing here is totally different from the effects you get from HF radio frequencies and occurs with VHF and UHF as well. Its why generally line-of-sight frequencies like UHF can sometimes go some ways over the horizon.

dxinfocentre.com/propagation/t

@Science

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.

@zpartacoos @Electronics

Wooootttt after a 4 month wait since backing it on kickstarter my Storm2 Liquid finally arrived (2 of those months was shipping time). Cant wait to plat
Y with this sexy beast.

I dedicated a shelf in one of my rooms exclusively for charging all my shit, including rechargeable batteries themselves. Pretty much everything but my laptops. My desk was getting way too cluttered.

Whats your favorite rechargeable battery chemistry.

Hacked together an ultraportable HF antenna system to work well between 3.5Mhz - 200 MHz (80 meters - 2m) frequencies. Basically took a coil loaded GRA-1899T antenna with telescoping antenna, added some off-the shelf BNC adapters and did some minor hacking. To make it work I had to remove the center connector from two of the BNC adapter s(marked with an X in the diagram). Then added a short-circuit BNC connector, which connects the otherwise floating center connector from the bottom half to ground/shield enabling the counterpoise. Added two additional telescoping elements for the counterpoise and we have a complete system.

The thing I like about the approach is the modularity. For example I can remove or add normal t-connectors to change the number of counterpoises used. The setup pictured uses 2 counterpoises but it would be trivial to setup 1 to 4.

Also the short circuit connector (pictures here as the black and teal connector with the short circuit in it) can allow me to do multiple things if i want to get more complicated. For example if I want to remove the short circuit I can replace it with coils or capacitors for additional tuning. I can also leave it as is but connect an earth ground to it to improve the effectiveness of the counterpoise.

A final note, the loading coil attached to the radiating part of the antenna has a jumper with 6 different positions. This lets you manually adjust the size of the loading coil for different frequencies. Fine tuning is accomplished by changing the length of the antenna itself.

AmateurRadio ## @Science

You know you are a nerd when you by a textbook for over a hundred dollars and at twice the price just to get it new and then cant sleep the night before because your excited to get it....

@Science

Some pictures of my APRS station brought back to life. Currently being heard in Ireland, Canada, Germany, and Washington state (I'm on the opposite coast).

@Science

Sweet, just brought back up my APRS radio station transmitting on both VHF and HF frequencies. Looks like it is working great I am being heard in both Ireland and Canada on the HF side!

Can't wait to get back to coding PEAK (the APRS software I run that runs a next gen version of APRS I am developing).

aprs.fi/info/WI2ARD

@Science

You know you are getting old when you have lived through an transmitted during 2 solar cycles.

Kinda excited to see the solar cycle peak again over the next few years. Already back on the rise!

@Science

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.

@Electronics

For anyone who still has devices with old AA, AAA, C, D, or 9V type batteries in it I highly recommend you move over to the USB chargable Li-ion type of the same format.

Most of those devices dont work with traditional rechargable batteries like NiMH because the voltage is a bit lower. Even if they do work they tend to last only a short period of time because as they discharge the voltage drops even further. So your device will often die even with 70% of charge still in those batteries.

With the newer USB rechargeable Li-ion type batteries of the same form factor, however, you have a drop-in replacement that doesnt have those issues. They basically are a LI-ion battery with a built in charger but more importantly with a DC-Dc converter to keep the voltage fixed at the desired voltage (1.5V or 9V) for the entire life of the battery. So they work in any device that they can fit in and lasts a long time as they deliver 100% of their power before cutting out (at which point it drops from 1.5V directly to about 0V).

The only downside is if your device reports a battery percentage then it will report 100% battery right up until it hits 0.

Anyway I replaced all my devices with batteries like this and they last longer than regular batteries in some cases (especially with 9V)... so I am sold!

Found this in my notes from a while back. Shows how to calculate the values for a balun to match a transmission line to an antenna.

@math

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