De VRZA is verhuisd!

Op vrijdag 3 februari vond de eerste bijeenkomst plaats op de nieuwe locatie. Na even zoeken waar de ingang was en hoe je in de zaal kwam, hadden toch 12 leden de bijeenkomst gevonden, een mooie opkomst! Er werd klassiek geouwehoerd, zagen wat minder frequente bezoekers en zo werd het toch weer gezellig.

De QSL-kast komt ook weer op te hangen. Door wat logistieke uitdagingen is de kast wel op de nieuwe locatie aangekomen maar hangt ‘ie nog niet op, dat gaan we nog verzorgen. Dus je hoeft niet om je kaarten verlegen te zitten!

Het nieuwe adres is:

’t Volkshuis, Dennestraat 2 in Heerlen

Dus tot en met 23 januari ben je nog welkom in Treebeek!

Retro Gadgets: The CB Cell Phone

There was a time when one of the perks of having a ham radio in your car (or on your belt) was you could make phone calls using a “phone patch.” In the 1970s, calling someone from inside your parked car turned heads. Now, of course,  it is an everyday occurrence thanks to cell phones. But in 1977, cell phones were nowhere to be found. Joseph Sugarman, the well-known founder of JS&A, saw a need and wanted to fill it. So he offered the “PocketCom CB” which was billed as the “world’s smallest citizens band transceiver.” You can see the full-page ad from 1977 below.

Remember that this is from an era when ICs that could operate at 30 MHz were not the norm, so you have to temper your expectations. The little unit was 5.5 in by 1.5 in and less than an inch thick. That’s actually not bad, but you had — optimistically — 100 mW of output power. They claimed the N cell batteries would last two weeks with average use, but we imagine a lot less as soon as you start transmitting. The weight was 5 oz, but we suspect that is without the batteries.


The device had a crystal for channel 14, and you could buy another crystal to get a second channel. Given that the unit was selling for about $40 to $20, it was telling that the extra crystal cost $8. We heard that over 250,000 of these were sold. The ad copy mentions they were used on the TV show Charlie’s Angels, but we can’t picture how that happened. It also mentioned it can be used as a pager, an intercom, a telephone, or a security device.

In operation, the devices were pretty simple. The 40″ antenna, when pulled out, would make the unit a bit more cumbersome. We found a relatively recent review on the CB Gazette from someone who picked up two of these on the used market. Seemed like they did work, although they were probably no better than a kid’s walkie-talkie.

Many hams convert CBs to the 10-meter band or even the 6-meter band, and we wonder if a crystal would pull these to 10 meters. Before cell phones, people thought we needed bigger towers, more power, and more channels. Turns out, it is just the opposite.


AIOC: The Ham Radio All-In-One Cable For Audio And APRS

The Ham Radio All-in-one cable (AIOC) is a small PCB attachment for a popular series of radio transceivers which adds a USB-attached audio interface and virtual TTY port for programming and the push-to-talk function. The STM32F373 microcontroller (which, sadly is still hard to find in the usual channels) is a perfect fit for this application, with all the needed hardware resources.

With USB-C connectivity, the AIOC enumerates as a

” data-image-caption=”” data-medium-file=”″ data-large-file=”″ width=”400″ height=”326″> sound card as well as a virtual serial device, so interfacing to practically any host computer should be plug-and-play. Connection to the radio uses 12mm separation 3.5mm and 2.5mm TRS connectors, so is compatible with at least the Baofeng UV-5R but likely many other cheap transceivers that have the same physical setup.Instructions are provided to use the AIOC with Dire Wolf for easy access to APRS applications, which makes a nice out-of-the-box demo to get you going. APRS is not all about tracking things though since other applications can sit atop the APRS/AX.25 network, for example, HROT: the ham radio of things.

We’ve seen quite a few Baofeng (and related products) hacks, like this sketchy pile of wires allowing one to experiment with the guts of the radio for APRS. Of course, such cheap radio transceivers cut so many engineering corners that there are movements to ban their sale, so maybe a new batch of better radios from our friends in the East is on the horizon?

Thanks to [Hspil] for the tip!

Antenna Mount Designed For On-The-Go SDR

Software-defined radio is all the rage these days, and for good reason. It eliminates or drastically reduces the amount of otherwise pricey equipment needed to transmit or even just receive, and can pack many more features than most affordable radio setups otherwise would have. It also makes it possible to go mobile much more easily. [Rostislav Persion] uses a laptop for on-the-go SDR activities, and designed this 3D printed antenna mount to make his radio adventures much easier.

The antenna mount is a small 3D printed enclosure for his NESDR Smart Dongle with a wide base to attach to the back of his laptop lid with Velcro so it can easily be removed or attached. This allows him to run a single USB cable to the dongle and have it oriented properly for maximum antenna effectiveness without something cumbersome like a dedicated antenna stand. [Rostislav] even modeled the entire assembly so that he could run a stress analysis on it, and from that data ended up filling it with epoxy to ensure maximum lifespan with minimal wear on the components.

We definitely appreciate the simple and clean build which allows easy access to HF and higher frequencies while mobile, especially since the 3D modeling takes it a step beyond simply printing a 3D accessory and hoping for the best. There’s even an improved version on his site here. To go even one step further, though, we’ve seen the antennas themselves get designed and then 3D printed directly.

Getting To The Heart Of A Baofeng

In amateur radio circles, almost no single piece of equipment serves as more of a magnet for controversy than the humble Baofeng handheld transceiver. It’s understandable — the radio is a shining example of value engineering, with just enough parts to its job while staying just on the edge of FCC rules. And at about $25 a pop, the radios are cheap enough that experimentation is practically a requirement of ownership.

But stripped down as the Baofeng may be, it holds secrets inside that are even more tempting to play with than the radio itself. And who better than [HB9BLA], a guy who has a suspiciously familiar Swiss accent, to guide us through the RF module at the heart of the Baofeng, the SA818. For about $8 you can get one of these little marvels off AliExpress and have nearly all the important parts of a VHF or UHF radio — an SDR transceiver, a power amp, and all the glue logic to make it work.

In the video below, [Andreas] puts the SA818 module through its paces with the help of a board that pairs the module with a few accessories, like an audio amp and a low-pass RF filter. With a Raspberry Pi and a Python library to control the module, it’s a decent imitation of the functionality of a Baofeng. But that’s only the beginning. By adding a USB sound card to the Pi, the setup was able to get into every ham’s favorite packet radio system, APRS. There are a ton of other applications for the SA818 modules, some of which [Andreas] mentions at the end of the video. Pocket-sized repeaters, a ridiculously small EchoLink hotspot, and even an AllStar node in an Altoids tin.

Of course, if you want to get in on the fun, you’re going to need an amateur radio license. Don’t worry, it’s easy — we’ll help you get there.


Building A Digital Library Of Amateur Radio And Communications

For years the Internet Archive has provided the online community with a breathtaking collection of resources, out of print books, magazines, recordings, software, and any other imaginable digital asset in easily retrievable form. Now with the help of a grant from the Amateur Radio Digital Communications Foundation they are seeking to create a collection that documents amateur radio from its earliest days to the present.

The work will be multi-faceted, and include the print and digital materials we’d expect, as well as personal archives and oral histories from notable radio amateurs. For many of us this will provide a wealth of technical details and insights into taming the ionosphere, but for future historians it will be an invaluable reference on the first century of the hobby.

Amateur radio is perhaps the oldest hardware hacking pursuit of the electronic age, because certainly at the start, radio was electronics. Thus amateur radio’s long history has indirectly given us many of the things we take for granted today. Sure it has its moribund aspects, but we think if it continues to follow the growth of new technology as it has for so many years it will continue to be an exciting pursuit. We look forward to browsing this archive, and we hope to see it grow over the years.

Header image: Lescarboura, Austin C. (Austin Celestin), 1891-, No restrictions.

How to make better measurements with your oscilloscope or digitizer

Modern oscilloscopes and digitizers are getting better and better. Higher bandwidth, better vertical resolution, and longer acquisition memories. Not to mention more firmware tools for application-specific measurements. With all these advanced analysis capabilities it is sometimes hard to remember some very old and simple rules that can improve the accuracy and precision of your measurements.  Here are a few good ideas to help.

Use the full dynamic range of your instrument’s front end

Digital instruments feed their input signals to an analog-to-digital converter (ADC). The dynamic range of the ADC is related to its number of bits of resolution. The instrument matches the input signal to the ADC input voltage range using attenuators or amplifiers. If the input to the ADC is less than its input range, it reduces the total dynamic range of the ADC. This can happen when users set up multiple traces on the screen.

Some oscilloscopes and digitizers display software only offer a single display grid. If you try and display more than one signal trace at full dynamic range, the signals overlap, making it hard to view them. Most people faced with this problem reduce the vertical scaling of each channel. If you have four traces, just increase the volts per division setting by a factor of four. Each trace now occupies only a quarter of the screen and all four traces fit on the screen with no overlap. Problem solved? Not really. You just reduced the dynamic range by two bits, you made your eight-bit oscilloscope a six-bit oscilloscope. You attenuated the signal, but the internal noise of the instrument is the same, the signal-to-noise ratio is now worse by two bits.  Figure 1 shows the effect of the loss of dynamic range.

Figure 1 An example of the decrease in signal-to-noise ratio due to reducing the signal amplitude in order to fit multiple traces on a single grid.

The bottom grid shows the original signal acquired a 50mV/division. The top trace shows the trace acquired at one quarter of the full screen or 200mV/division.  If you vertically expand the attenuated trace and display it at the original 50mV/division, the vertical noise has increased significantly as you can tell from the thickening of the displayed trace. Measurements made on the attenuated trace will have increased uncertainty due to a poorer signal-to-noise ratio. This is not a problem for an oscilloscope or digitizer that has multiple grid displays, each grid displays the signal at full dynamic range and multiple signals can be compared, each in its own grid. If you don’t have access to a multiple grid oscilloscope, make sure that any measurements are made on the full amplitude signals, reserve the attenuated signal for visual comparisons only.

Improve dynamic range and measurement accuracy by eliminating noise

Use signal processing in the form of averaging or filtering to reduce noise, improve dynamic range and measurement accuracy.  Ensemble averaging, where the nth samples of each acquisition are averaged together over multiple acquisitions, reduces Gaussian noise proportional to the square root of the number of averaged signals. This can bring a low level signal out of background noise for better measurements. It does require multiple acquisitions.

For a single acquisition, you can reduce noise by bandwidth limiting the signal. The improvement of dynamic range is proportional to the square root of the bandwidth reduction. Reduce the bandwidth by a factor of four to achieve a two-to-one improvement in dynamic range. This assumes that the signal has a low bandwidth and is not affected by the bandwidth reduction. Figure 2 shows the improvement that can be achieved using either averaging or filtering.

Figure 2 Averaging multiple acquisitions or filtering a single acquisition can improve the dynamic range of the acquisition by eliminating noise.

The acquired signal is an exponentially damped sine wave. The top trace shows a raw acquisition. Note that the signal disappears into the noise about three quarters of the way across the screen. The center trace shows the average of multiple acquisitions. In the bottom trace, a Gaussian low pass filter has been applied to the acquired signal. Both averaging and filtering reduce the noise and improve the dynamic range of the measurement. The signal is clearly discernible after either type of signal processing.

Improving the accuracy of cursor measurements

Cursors are vertical and/or horizontal lines that can be moved over the oscilloscope or digitizer display to mark significant points on a waveform. Cursor readouts show the time or amplitude of the waveform at the cursor location as shown in Figure 3. The waveform is a keyed RF carrier and the horizontal relative cursors are used to measure the width of the RF burst. This is a measurement that cannot be made with the instrument’s automatic measurement parameters. The cursor horizontal readout appears in the lower right-hand corner under the timebase annotation box, it reads 8.06275 µs.

Figure 3 Horizontal relative cursors are used to measure the duration of an RF pulse burst.

Is that really the duration of the burst? The answer is no. This waveform has two million samples in the acquisition. The horizontal screen resolution is 1920 pixels. So, it’s obvious that not all the samples are shown on the screen. Instrument manufacturers apply compaction algorithms to reduce the number of displayed points. They manage to show significant points like peaks but there is still a lot that you can’t see unless you expand the display.

A more accurate way to make this measurement is the used the zoom traces to horizontally expand the waveform at the start and end of the RF burst as shown in Figure 4.

Figure 4 Using zoom traces to make more accurate placements of the cursors at the first and last sample points of the burst.

Zoom traces Z1 and Z2 horizontally expand the beginning and ending of the burst. The sample counts in the zoom traces are smaller than the screen resolution so the compaction algorithm is not used. The cursors track on the acquired signal and the zoom traces. The cursor on zoom trace Z1 (yellow trace) marks the beginning of the RF burst which starts at a zero crossing. The cursor on zoom trace Z2 (red trace) marks the end of the burst. The cursor horizontal readout shows the burst length as 8.33295 ms, a more accurate result.

Built-in measurement parameters

Oscilloscope and digitizer support software offers built-in measurement parameters. Most oscilloscopes include about twenty or more common measurement parameters like amplitude, frequency, rise time, and fall time to mention a few. Application-specific software packages can increase the number of available parameters to over a hundred. The standard parameter measurements are usually based on IEEE standard 181 which employs statistical techniques to make the measurements on pulse waveforms as shown in Figure 5.

Figure 5 IEEE Standard 181 bases pulse measurement parameters on a statistical determination of the top and base values of a measured pulse.

The amplitude values of the pulse top and base are determined by forming a histogram of the acquired samples of the waveform, this is shown as an inset on the right of the screen.  A square wave or pulse waveform will have a histogram with two distinct peaks. The average or mean values of the upper histogram peak is called the “top”. The mean of the lower valued peak is called the “base” of the waveform. Using the statistical mean of many pulse measurements suppresses the effects of waveform aberrations like noise, overshoot, and ringing. The pulse amplitude is the difference between the top and base. The maximum value of the waveform minus the top is the positive overshoot. Likewise, the difference between the waveform minimum value and the base is the negative overshoot. The pulse width is the time difference between the leading and trailing edges crossing the mid-amplitude or median between the top and base. The peak-to-peak value of the waveform is the difference between the maximum and minimum amplitudes. The transition time measurements, like rise and fall time, measure the time to transition from 90% to 10% of the pulse amplitude. If the waveform is not a pulse, the measurement engine sees that because the waveform histogram has more or less than the two peaks that define a pulse. In that case, the amplitude measurement reverts to a peak-to-peak measurement and indicates the fact that the waveform is not a pulse using a measurement status icon under the parameter readout.

In almost all cases, the measurements made using measurement parameters are far more accurate than those made using cursors. They are also made automatically saving a great deal of time.

Measurement Statistics

How do instrument measurements vary from measurement to measurement? Measurement statistics answer that question. Many instruments include statistics reporting along with the basic measurement parameters as shown in Figure 6.

Figure 6 Measurement statistics record how measurement values vary over multiple measurements showing the last value, mean, minimum, maximum, standard deviation, and total population.

Some oscilloscopes include all instance measurements. Time-related measurements, like frequency and width, report one value for each cycle of the measured waveform. If you have 100 cycles of a signal on the screen, the measurement engine adds 100 measurements for each acquisition. Amplitude-related measurements only add a single value per acquisition. You can acquire a good many measurement values over many acquisitions. Measurement statistics provide very useful views of this data. The table under the waveform display, shown expanded in the blue box, lists the last value measured in the acquisition, the mean values of all the acquired values, the minimum and maximum values of the set, the standard deviation of the set, and the total population of all the measurements. It also includes a status indicator and an iconic histogram of all the measurement values.

The amplitude measurement reports that 11,873 values are included in the statistics. The mean or average value is 237.5457 mV. The mean value is reported with a higher resolution than the last value because the mean is an averaged value. As we saw in the waveform, averaging the averaging process improves the vertical resolution of the measurement, the same thing happens if you average multiple measurements, hence the more significant figures in the mean value.

The largest value is 241.5 mV reported as the maximum, the smallest value, minimum, is 234.8mV. These values can help detect transient events that occur during the acquisitions. Other tools can plot measured values versus time to see when transient events occur and match them in time with possible sources.

The standard deviation describes the distribution of the measured values about the mean, in this case is it 826 µV. The mean and standard deviation are useful in understanding the distribution of the measured values as is the iconic histogram. The iconic histogram can be expanded to view the full-sized histogram for a more detailed analysis with its own set of histogram measurements. All of these measurement tools help understand the dynamics of the particular measurements. A knowledge of the distribution of measurements enables you to establish test limits for signals.


These tools and techniques can help improve the measurement accuracy and reliability of your instruments. Other tricks can be gleaned from manufacturer’s webinars and application notes. The more you learn about your instrument, the more accurate and reliable your measurement results will be.

Arthur Pini is a technical support specialist and electrical engineer with over 50 years of experience in electronics test and measurement.