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.



I was asked to explain the space-weather ticker I posted earlier (attached). This was my reply.


First off the are two categories of radio operation that is relevant and effected in opposite ways..

  1. space to earth
  2. earth-to-earth.

Number 2 breaks down in two ways as well that is

2a. line of sight operation, vs
2b. skywave operation.

Skywave operation is really the most relevant here, line of sight might be effected somewhat by noise floor effects from sun but that is only relevant some of the time.

Reflection Layers

There are two main factors from the sun that affect operation. One is radio interference, this would be caused by flares and ejections directed at earth. In extreme cases it can cause an EMP but thats very rare.

The other is ionizing radiation in the form of UV (a much shorter wavelength version of UV than what reaches the earth), ionized particles, solar wind and similar. This ionizes the ionosphere in a specific way that causes radio waves to be blocked and/or reflected. Basically there are two regions in the ionosphere both in whats called the F-region.. These are F1 which is at 200 km above sea level, and F2 which is at 300 km. The higher F2 layer allows for radio signals at a particular angle to be reflected, this allows radio operators to bounce their signals off this part of the sky and reach distant receivers. Since F2 is much closer to the ground this particular region actually blocks long range communication and thus significantly reduces the distance a radio signal can reach to mostly line of sight.

Usually, when the radiation is high enough, we see the F2 layer ionize first in the morning (basically when the sun is just coming up for people who live near your horizon), which makes the morning the best time to transmit. By afternoon the F1 layer is ionized by sun radiation and thus the signal is blocked again.. the reverse happens in the evening. So early and late day propagation is best. This is called gray-line propagation.

There is also E layer propagation which operates at much lower frequencies and at steeper angles. This is what is used for very short distance transmissions within the 100’s of km. This is called NVIS (Near Vertical Incidents Skywave).

Reading the screencap

Now with this said, it only works when the radiation from the sun is just right. Basically there needs to be enough radiation from the sun to actually fully ionize the layers.


SFI on the chart stands for “solar flux index” this is a measure of the quantity of ionized particles and solar wind measured. This is usually in the range of 0 - 400 with 0 - 100 being poor for propagation, 0 - 200 being marginal, and 200+ being ideal/good.


SN stands for sunspot numbers, these effect different layers selectively. sunspots reflect the intensity of the sun’s magnetic field. It ranges from about 0 to 400 as well.

Lower values here show a preference to ionize lower levels of our ionosphere. 0 to about 150 will preferentially ionize the E-region and be ideal for low frequency propagation (160m wavelength to 80M) in the NVIS configuration, so very short distance (100’s of km) propagation only which is all these low frequencies can ever do.

Higher values, above 200 means the F-regions are preferentially ionized. That means low frequencies like 160m and 80m will not propagate at all and only work line of sight (10’s of km), but higher frequencies ~20m and higher in frequency will propagate via skywave. These frequencies now can propagate 1000’s of km around the world in these conditions (assuming SFI and other factors are good).

K index

The next line is K-index just labeled K. This one is rather complicated.. it basically looks at the horizontal component of the earth’s magnetic field and how it is disturbed (which is an indirect way of measuring the solar winds and its interaction of the earth).

This doesn’t effect the ionosphere itself so much as the other measures since its only partly effected by solar winds. This is used as a measure of expected band noise and thus how high the noise floor will be. the max value is 9 and indicates significant noise. 5 is about the cutoff where geomagnetic storms are present.

The K-index is not linear and is calculated from the a-index (lowercase a, different from A-index below).


is really just another way of measuring K-index. Or to be more precise both A-index and K-index are calculated from the underlying a-index (a-index is different from A-index). The A-index is the average of the last 8 a-index, and thus has a much simpler interpretation.

Think of A-index as a long-term rolling average of the K-index in a different scale.

Generally A-index is even less linear than K-index with 0-50 being low noise and 100 - 400 being high noise.. lower is better.


304A stands for “304 Angstroms” which is the wavelength of UV light measures. Basically its the strength of UV radiation from the sun as measured from space (different than earth UV levels). the “@ SEM” part refers to the instrument on the satellite used to record it, called SEM, SOHO and EVE are other possible instruments used to get this measurement and it changes depending on the instrument available at the time.

In this case higher is better as it means more of that F-layer ionization I mentioned.below 80 is poor, 150 and up is good, 250 and up is amazing.

Ptn/Elec Flux

This is Proton and Electron flux. These have a similar effect as UV except they ionize the E-layer more so than the F-layer. So they harm long distance short wavelength propagation but improve short distance long wave-length propagation.


This is just the predicted chance of aurora. Not directly relevant for radio.

Aur Lat

This tells us the largest lattitude likely to see the aurora.

Bz and SW

This is the interplanetary (in space) magnetic field vector (B-field means magnetic field). This is the magnetic field that is incoming and striking the earth from space.

The Bz part is the intensity, the SW part is the direction in degrees. When it lines up with the earths magnetic field it strengthens it, when it doesnt it weakens it. Positive values strengthen it, negative weaken it.

other values

Everything else is self explanatory I suspect. “solar flare prob” is the percentage change of a solar flare, which we dont tend to know until just a few minutes before their ejections strike.

“MUF” stands for “Maximum Usable Frequency”. It indicates the highest frequency (shortest wavelength) that is likely to be capable of bouncing off the ionosphere (f-layer or e-layer) and therefore the highest frequency capable of skywave propagation.


So here is a question some of my EE and radio friends disagree on... Is a purely resistive matched load, like a 50 ohm dummy load, considered "resonant". In the strictest sense of the word is that a valid term here?

While it would seem odd I'm leaning towards yes, and would be the simplest example of resonance.


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 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 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 hashtag.


These components are sooooo tiny, I really hate soldering them (0402 SMT mostly). Here is one compared to the tip of a mechanical pencil to give you an idea.


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!

Man ive been at this over 2 hours now and havent even covered a square inch yet. It messes with your head how damn small these 0402 components are.



Man soldering 0402 components is brutal. I wouldnt wish this on my worst enemy... but progress is being made!

This is either a 250kW Automatic Tuner, or they take their Irish Whiskey production very seriously.



Wanted to share my prototype design for the meter with the Electronics Group.

About a month ago I sent the boards off to be printed for a prototype run and recently got them in. So V2.0 is soon to be officially released (though I may do a minor revision before printing up a large number of boards).

Attached are some screenshots of the final schematic and some renderings of what the boards will look like when its done. Its a 4 layer board though so many of the traces are internal.

You can find the files for this, which will be released as open-source, here:


I wanted to share my favorite circuit simulator to the electronics group. It isnt the most advanced and it wont replace professional tools. But its great at modeling semi-ideal components with an epic way of visualizing current and voltage that just makes it an amazing tool at getting a feeling for how circuits actually work.

Everyone should check it out and play with it, you wont regret it.

A picture of a Radio Shack circa 1950. Its a shame self-repair is virtually non existent and shops like this and radio shack themselves, are quickly disappearing. I remember when I was younger you could go there and any electronics part you could imagine. Now they cant even give away what little inventory they have.

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