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

I want to open a store called "Perfect Example". It sells large antennas for your roof that all tune up to a perfect 1:1 SWR but have 0% effiency.

ham radio operator's credo:

1. Be a jerk to everyone you meet

2. Make assumptions about how things work based on the first explanation someone gives you and never change your mind or learn anything more about it for the rest of your career in HAM radio.

3. if someone gives you advice contrary to #2 call them names and insult them until they go away

4. Never do math, numbers are a lie. As long as you can hear someone talking in your radio then your assumptions are validated.

5. Under no circumstances should you actually learn how things work. Simply quote people with credentials and insist your misunderstanding of the quoted text is the only correct one. If someone disagrees with you remember your credentials are automatically the same as the authors, so you are right.

6. Make it a point to never understand the purpose or intent of FT8 and anytime you see anyone mention it make fun of them for not being a real HAM

7. CW is the only acceptable mode of operation, everything else is contrary to the spirit of HAM radio.

8. Only people over the age of 90 are allowed to be HAM radio operators, everyone else is ruining the hobby.

9. Making a joke of any kind should be treated exactly the same as a personal insult. You now have the right to respond to the person as rude as you'd like

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

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

Woot, my Lab599 TX-500 SDR transceiver arrived today! Powered it up and tested her and she works great. Now just need to get a mobile setup together and time to test her on a trail somewhere.

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

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

@Science

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

ionosphere

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

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

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).

A-index

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

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.

Aurora

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.

@Science

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.

@Electronics

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.

jeffreyfreeman.me/an-indepth-l

@General

@Electronics

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.

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