Speech coding in DMR, D-STAR and System Fusion

Example of a speech signal which transitions
from an unvoiced to a voiced sound

Digital VHF and UHF communications is increasingly popular among radio amateurs using DMR, D-STAR and System Fusion. Very few radio amateurs, however, have much understanding of the signal processing required to compress a speech signal so it can be transmitted with the low bit rates available. Here is an attempt at an explanation.

My favorite faces for the Multi Face GPS Clock

Weekly progress bar with Monday as day 1
in week 9 and yearly progress bar
as of day 56 in the year.

Among the 50 different faces (or screens) now implemented on the Multi face GPS clock, it is hard to select favorites. 

So I start with the latest one that was implemented, i.e. the progress bars for week and year shown to the right. It was new in version 2.3.0 dated 2025-02-04.

A QMX+ coming together

I got an unassembled QMX+ for Christmas this year, and here are pictures of it coming together. First the winding of toroids for the low-pass filters:

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 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:

A Fourth Method of Generation and Detection of Single-Sideband Signals

Envelope Elimination and Restoration, from Kahn 1952 

There is a method for SSB generation which is now becoming popular with digital signal generation and digital output stages. This is the Envelope Elimination and Restoration method. It is receiving renewed interest among radio amateurs as it is used in the SSB implemention of e.g. the interesting QRPLabs QMX transceiver. 

In the QMX a single frequency signal is generated in the digital domain and then phase modulated (upper branch of figure). It then has a digital output stage with very high efficiency as it only switches between on and off. The output stage is amplitude modulated with the envelope signal from the lower branch.This gives a much more efficient power amplification than is possible with the three conventional methods.

The three methods

How does it compare with other methods? In 1956, Donald K. Weaver, Jr. wrote a paper with title "A Third Method of Generation and Detection of Single-Sideband Signals".

v2.2.0 Multi-Face GPS-Clock

A few new screens:

• NextEvents() - New screen showing Next Equinox/Solstice, Easter, Lunar/Solar Eclipses in sorted order, i.e. sorted after date as shown to the right
• SolarEclipse() - New screen showing solar eclipses for this year and coming years (table-based until 2030)
• Equinoxes() - New screen for time of equinoxes and solstices

Demo mode now has a choice of increase, decrease, or random next screen number (selectable in Secondary menu).

More languages selectable: {"en", "es", "fr", "de", "no", "se", "dk", "is"}. Any language with max 4 special letters in alphabet can be implemented.

Better accuracy:

• More accurate prediction of sun rise/set times
• More accurate formula for Mercury, Venus, Mars, Jupiter magnitudes in clock_z_planets.h, now follows Meeus [thanks Richard]

Now runs on Adafruit Metro Express (M0). This makes it much faster for the Hebrew calendar in particular.

And some more minor fixes, see details on Github.

Groups.io discussions for the Multi-face GPS Clock

Front panel design by W4OA. 3D print design files on github.

The new discussion group is https://groups.io/g/Multi-Face-GPS-Clock/messages.

Please sign up!

The latest version of the code is on GitHub.

Mysterious Logbook of the World DXCC Behavior

I just applied for additional credits for my DXCC status with Logbook of the World (LOTW). However some countries that I applied for, and which were awarded, are still in the "pending" category and don't seem to count.

 

It's a mystery for me that LOTW has approved of a QSO with for instance Equatorial Guinea, but it is still in the "Pending" category. 

The only reason I can see is that I happened not to select the very first QSO with Equatorial Guinea, but the second one. And then it does not seem to count.

I wonder if I somehow can select the one approved to be the one which counts towards DXCC, thus moving it from "Pending" to "Awarded"? Any clues from a reader of this blog?