The unphysical free-space path loss

Propagation of wave energy to distance d, 2d, 3d
 showing how the size of the surface that the energy
spreads over increases in proportion to 
d², (2d)², and (3d)²

Many places it is stated that the lower the frequency, the smaller the free space loss. 

This is very counterintuitive, because if one solves the wave equation, the amplitude of the solution is independent of frequency. The physics of the problem is that intensity just falls with distance squared according to how the surface of a sphere increases with the radius as shown in the figure.

The Friis formula used in link budgets says something else. It gives received power, Pr, as a function of transmitter power, Pt, receiver and transmitter antenna gains, Gr and Gt; wavelength, lambda, and distance, d:

Eleven and 87 year sunspot cycles

It is well known that the sunspots vary over an eleven-year cycle. As the sunspot number increases, the ionosphere is more ionized and radio propagation on the high shortwave bands from about 10 - 30 MHz. Also, the higher the sunspot number, the more likely is the appearance of Northern Lights.

Here's spectral analysis of the monthly sunspot numbers from 1750-2020. First I show Fourier based spectrogram analysis. The y-axis is frequency or inverse years and there are arrows marking 11 years as well as the Gleissberg cycle of about 87 years. Note how the 11 year cycle has split into two periods since the 50's. There is a weak subharmonic at 5.5 years also. Due to the 90 year analysis window length, the time scale ends 45 years before 2020, i.e. in 1975. 

Book rather than Blog

My blog has suffered in recent years and here is the reason. For three years now I have been writing a book entitled "Waves with Power-Law Attenuation". It is now in Springer's catalogue under classical and continuum physics and I'm also very happy that it is published in the Acoustical Society of America Press series.

The emphasis is on models for waves that experience attenuation that follows a power-law in frequency. Topic-wise it is more about mechanical than electromagnetic waves, but analogies are drawn between the two fields as many of the models are the same. Power-law models in electromagnetics are in particular useful for waves in biological tissue, which is indeed also the case for acoustic and elastic waves.

Radio Ghosts Have Haunted the Airwaves for Nearly a Century

“The starship hypothesis is a very interesting one, and the one which seems to be the most popular one on the internet,” said Sverre Holm, a professor of signal processing at the University of Oslo. “Such theories always excite our imagination, but it builds on a very poor data set. Unfortunately I believe it says more about human imagination than anything else.”

Although scientists have yet to settle on a final explanation for these mysterious echoes, Holm believes this is has less to do with a lack of scientific knowledge than a lack of willpower.

“I think that with today’s satellites and sensors, the mystery of Long Delayed Echoes (LDEs) could probably be solved,” he said. “What’s holding us back is most likely the problem is not considered important enough—it doesn’t occur often enough and doesn’t affect important enough forms of communications.”

These are excerpts from an interview in an article entitled "Radio Ghosts Have Haunted the Airwaves for Nearly a Century" on Motherboard Vice written by Daniel Oberhaus. It builds on a web page that I created some years ago after having spent days studying the archives from the 20's of professor Carl Størmer at the National Library in Oslo.

Nice, watery CW signals from Alaska

 Great circle path between Anchorage and Oslo

Here's what a transpolar signal sounds like (click here to listen) and looks like (below). This one has traveled from Anchorage, Alaska to Oslo, Norway.

The characteristic sound of a CW signal that has passed over a moderate geomagnetic disturbance (Kp = 2) isn't too hard to recognize with a little practice. There is also some static on this short recording as we had a local thunderstorm coming in with the first summer days here.

The great circle distance between the two cities (actually their two airports) is 6446 km as illustrated by GPSVisualizer. Anchorage and Oslo are about at the same latitude, 61° N and 60° N, respectively. As they are at longitudes 149° W and 10° E, there is a difference of 159 ° - almost 180 ° - and this means that the signal almost passes directly over the North Pole, although a bit hard to see on the projection used in the map.

Fantastic Conditions on 10 and 12 m

This last month has seen some of the most fantastic conditions I have ever experienced. Especially the higher bands have given world wide coverage. I haven't had that much time to operate from home, but despite this I have gotten many first. My recent verifications on the Logbook of the World testify to that.

Let's all hope it will last!

Amazing Reverse Beacon Network

I haven't called CQ for a long time on CW except in contests. Mostly I have just responded to DX calls with a super short "5nn TU" and that's it. But this Saturday I heard a presentation at the Norwegian Ham Meeting by Roland, SM6EAT about a Swedish initiative to increase CW activity. It is called Scandinavian Open CW Activity (SOCWA) and it has at present 452 members from Scandinavia in a wide sense of the word. It really got me interested in improving my CW skills.

So now I have started to call CQ SAX and have had my first long CW QSOs for years with SM and OH.

It is also amazing to look at the reverse beacon network and watch your own CQ being reported almost in real time from various Software Defined Receivers with CW Skimmers. Below is the result of the two CQs I have sent these two last days.

My first 24 hours on WSPR

My first beacon on 30 m, a free-running Ultimate QRSS kit (no GPS) has now been running for a full 24 hours using the Weak Signal Propagation Reporter (WSPR) mode. The figure comes from the WSPRnet page.

With an output power of about 150 mW to an 80 m horizontal loop it has not been possible to reach beyond Europe so far. Perhaps this will happen in the future with better conditions and/or with some more output power.

Added 26.9.2012: I made it for the first time across the Atlantic!
Timestamp           Call       MHz         SNR Drift  Grid      Pwr Reporter   RGrid      km      az
2012-09-26 00:50, LA3ZA, 10.140262, -26,   -2,   JO59fu, 0.2, WB2EEE, FN21xh, 5852, 290

Will I ever complete "Worked All States"?

Here's my map of confirmed US states as it has slowly been filling over the last 10 years. 41 states have been confirmed on CW on Logbook of the World, while 9 are still missing.

In recent years progress has been very slow so I don't see my WAS being finished any time soon. Perhaps there is some resource on the web that could assist me with arrangements for the remaining states, or even some readers in these states who would help me?

CQ DX Marathon and 2011 Activity

I just submitted data for all my radio contacts for 2011 to CQ DX Marathon. My log program is UcxLog by DL7UCX and I started by exporting the ADIF-log and then analyzing it with the recommended analysis program by AD1C.

In the process of doing the conversation I also happened to find the Contact Map tool from NS6T which generated this map from my 2000+ contacts in 2011. What it shows below it not so surprising - from my location in the south of Norway it is easiest to work Europe, Russia and the East Coast of the US, but it is nice anyway.

2011 contacts from LA3ZA, open in separate window for larger map.

My CQ DX Marathon result was 167 countries (165 real DXCC countries), 35 zones giving a total of 202 points which is a result I was very happy with. It was actually my highest country count in a single year since I got my license in 2001. Much of it must be attributed to the renewed activity of the sun last year which gave a lot of new opportunities on the 10 m band. All countries except one are CW (morse) contacts with a 100 W Elecraft K3. Antennas are a 75 m long horizontal loop for the lower bands up to and including 21 MHz, and a 5 m half wave wire vertical for 24 and 28 MHz. The length of the wire loop exceeds that for the Formula Class, so I had to submit my score in the Unlimited Class.

Now I am only looking for a software tool which can analyze my ADIF-file for US states and Russian oblasts, but so far I haven't been able to find any.

Communication with vector potential waves

Field lines (black) and potential (red) for a dipole, static field. 

In QEX July/August 2011 Robert K. Zimmerman (NP4B, VE3RKZ) had an intriguing article entitled "Transmission and Reception of Longitudinally-Polarized Momentum Waves."  What he claims is that he has communicated over a distance of 1500 m at 1296 MHz using vector potential or momentum waves.

Unlike transversal electromagnetic (TEM) waves these are longitudinal waves just like sound waves. This may seem like real magic, but if true it would allow covert communications which is undetectable with ordinary radio receivers and antennas.