International System of Units (SI) Checklist

Metrology is the science of measurement. The International System of Units, also called SI, consists of standards which result from meticulous negotiations among international metrologists. The purpose of the International System of Units is to communicate quantitative information clearly across languages and cultures.

This check-list summarizes the most important elements of those standards. For more detail, you may wish to download the PDF document NIST Special Publication 811, 2008 Edition, by Ambler Thompson and Barry N. Taylor: Guide for the Use of the International System of Units (SI). A relevant Wikipedia article is also useful. The Bureau International des Poids et Mesures (BIPM) also publishes useful information in French and English.

Here is a simple checklist to help you use SI correctly:

  • Except for degrees Celsius, SI units like microfarads and millivolts are always written in lower case and are almost always pluralized. (See below for exceptions to the usual pluralizing standard.) Because of their phonetics, some SI units like megahertz are written the same in singular and plural.
  • SI symbols like kHz and µV are written in lower case or UPPER CASE Latin or Greek characters or in combinations. SI symbols are the most universal parts of SI, and are never pluralized.
  • Be careful with UPPER and lower case: UPPER CASE M is the SI symbol for the mega- prefix; lower case m is the symbol for meters or metres as well as the milli- prefix; lower case Greek µ is the symbol for the micro- prefix. With the advent of computer word processors, using u as a substitute for µ is an obsolete practice. Lower-case italic m represents mass. UPPER CASE K is the SI symbol for thermodynamic temperature in kelvins and lower case k is the SI symbol for the kilo- prefix. One should not be used in place of the other.
  • With three exceptions, SI values and SI symbols are always separated with spaces and never with anything else. Those exceptions are the symbols for angular degrees, minutes and seconds. The 100 m dash and a 10 A fuse are correct expressions. It is also correct to write: The summit of 6190 m Denali in Alaska is located at 63°04’08.7”N 151°00’25.5”W.
  • When used in an adjectival sense in English, SI values and spelled-out SI units are separated with hyphens and are not pluralized: the 100-meter dash and a 10-ampere fuse are correct expressions. When accompanying values of exactly 1 or -1, SI units are not pluralized.
  • Abbreviations do not exist in SI. Instead of abbreviations like amps and secs, use SI symbols like A and s or fully spelled-out SI units like amperes and seconds. Note that the symbol for the time unit minutes is min, which is not an abbreviation, and therefore it is not pluralized and it is not followed by a period.
  • Never use SI prefixes in isolation. Avoid using expressions like 10 kilos of flour or 5 K run; use 10 kilograms of flour or 10 kg of flour or 5-kilometer run or 5 km run instead.
  • Except at the end of a sentence, an SI symbol is never followed by a dot or period. To avoid confusion, try not to end sentences with SI symbols if possible.
  • Fractional SI values are decimalized and preceded with a zero or other integers: 0.529 µm or 0.529 micrometers.
  • Since either a dot or a comma may be used in SI as a decimal marker, the comma should never be employed as a separator for long integers or long fractions. Segment values with five digits or more utilizing spaces or half spaces. Using a word-processor, create a half space by changing the font size of a regular space to about half the value of the rest of the text. The speed of light, whose symbol is italic c [see footnote 1] is 299 792 458 m/s or 299 792.458 km/s or 299.792 458 Mm/s when written in SI. The speed of light may also be written as 299 792,458 km/s or 299,792 458 Mm/s without any change in meaning.
  • SI symbols should never include suffixes. Instead of 115 VAC, write AC 115 V or 115 volts alternating current in correct SI.
  • Avoid orphaned values. Instead of 9-15 volts or 9-15 V, write 9 volts to 15 volts or 9 V to 15 V in SI.
  • SI dates are rendered with numerals in descending order. The origin of what became the International System of Units began in Paris on 1875-05-20 with an international treaty. SI time is reckoned in the 24-hour system, often with the time zone specified: 1445 UTC or 0657 EST.
  • SI standards have changed over time. Avoid obsolete expressions. The old degrees kelvin should be kelvins (symbol K). The obsolete mhos should be siemens (symbol S), which is followed by an s in both singular and plural unit forms. The old cubic centimeters unit is still commonly used in medicine, but milliliters or millilitres (symbol mL) [see footnote 2] should be used instead. The obsolete microns unit is now micrometers or micrometres (symbol µm). Multiple prefixes like µµ or micromicro- are no longer allowed in SI. Use the pico- unit prefix or the p- symbol prefix instead. An acceptable SI substitute for the obsolete parts per million (ppm), parts per billion (ppb) has not yet been developed. If international metrologists eventually agree on an SI unit and symbol for nominal-scale entities, then fractional prefixes combined with that unit or symbol will do a good job of carrying out that proportional function.

¹ Quantities to be measured and their symbols are written in italics: current and inductance are examples. Think of e=mc2 and I=E/R.

² Although lower-case l may be used as a symbol for liters of litres, that character may be mistaken for the numeral 1, so most writers prefer the upper case L for that symbol.

J. Bruce Prior, N7RR, is a special contributor to and writes from Washington, USA. Contact him at [email protected].

The Spectrum Monitor — December, 2017

Stories you’ll find in our December, 2017 issue:

The Beginning of Sports Broadcasting and Radio’s First Sportscasters
By John Schneider W9FGH

Despite its great advantage of immediacy, radio did not become a dominant news medium until the start of World War II. Throughout the 1920s and 30s, newspaper owners were successful in keeping the press news agencies from selling their services to broadcasters, and radio remained a secondary source for news. But, the reporting of sporting events was another story. Sports and radio were a made for each other like ball in glove, and the country’s broadcasters were quick to capitalize on that advantage from the industry’s earliest years. John charts the rise of sports on American radio.

The Brief and Colorful History of Private US Shortwave Giants
By Richard Fisher KI6SN

In AM radio’s ever-evolving place in broadcasting history, there was a time when U.S.-based AM stations took to the shortwaves, either as standalone broadcasters or as an extension of their AM broadcast band partners. While their popularity soared in the 1970s and ’80s, many have vanished as others carry on.

Powerhouse American shortwave stations, including WRNO, WNYW, WBCQ, KUSW and KNLS, profiled here, had (or have) a substantial worldwide following on the high frequencies. In this 21st Century, many are gone or have changed formats from, say, popular music and news to Christian oratory or other programming. Richard looks back at some of these stations.

Meter Matters: Modern vs. Vintage Meters in Radio Restoration
By Rich Post KB8TAD

What happens when you calibrate that Hickok tube tester at those 150 and 130 voltage specifications or the bias voltages ignoring the line that calls for that ancient 1000 ohms-per-volt meter and just use a digital meter like my very-expensive-when-new Fluke 87 or that bargain Harbor Freight CenTech P37772 instead? Well, the calibration for your Hickok will be off. Those modern meters have a specified sensitivity of 10 megohms. Rich warns that not all that will be off as he examines the use of various meters in vintage radio technology.

TSM Reviews: Yaesu FT-70DR
By Cory GB Sickles WA3UVV

When an item is released that offers breakthrough technology or more features and benefits than previous models, the price is typically higher. When the price of an item is higher, many tend to hesitate in buying it. Further, economy of scale eventually kicks in, allowing a manufacturer to lower prices a bit, or produce and release additional models with many of the features of the premier version. The FT-70DR (FT-70DE in Europe) is the latest dual-band portable and takes its place in the market with a substantial entry-level feature set, as well as being the most inexpensive portable produced by the “traditional” amateur radio manufacturers—all for a street price of just under $200.

Scanning America
By Dan Veeneman
Interoperability Update; Orange County, Virginia

Federal Wavelengths
By Chris Parris
Urban Area Security Initiative (UASI)

By Larry Van Horn N5FPW
Introduction to Military Monitoring: VHF Low Band—the Forgotten Military Band

Utility Planet
By Hugh Stegman NV6H
North Korea Resumes HF “Numbers” Broadcasts

Shortwave Utility Logs
Compiled by Hugh Stegman and Mike Chace-Ortiz

VHF and Above
By Joe Lynch N6CL
The Geminids and Ursids Meteor Showers

Digitally Speaking
Cory GB Sickles WA3UVV
System Fusion II

Amateur Radio Insights
By Kirk Kleinschmidt NT0Z
A Vertical in Hospice!

Radio 101
By Ken Reitz KS4ZR
AM Band DXing Circa 1964 and Now

Radio Propagation
By Tomas Hood NW7US
Heliophysics Research Reveals More About Substorm Mysteries

World of Shortwave Listening
By Rob Wagner VK3BVW
Making Shortwave Audio More Listenable

The Shortwave Listener
By Fred Waterer
2017 SW Review and New Programming

Amateur Radio Satellites
By Keith Baker KB1SF/VA3KSF
A Wealth of New Amateur Radio Satellites

The Longwave Zone
By Kevin O’Hern Carey WB2QMY
Primetime Arrives!

Adventures is Radio Restoration
By Rich Post KB8TAD
What’s an “Acoustic Labyrinth?” The Stromberg Carlson 240M

The Spectrum Monitor is available in PDF format which can be read on any desktop, laptop, iPad®, Kindle® Fire, or other device capable of opening a PDF file. Annual subscription is $24. Individual monthly issues are available for $3 each.

Ken Reitz, KS4ZR, is publisher and managing editor of The Spectrum Monitor. Contact him at [email protected].

Update: More on Olivia, the Great Compromise Mode

Some HF digital modes were designed for long-distance (DX) radio-wave propagation via the ionosphere. One such keyboard-to-keyboard digital mode is Olivia.

Friday evening, 8 December 2017, at 0200 UTC {9-DEC}, Larry, N7ZDR, called an Olivia-mode 80-Meter digital roundtable net. The following video is a snapshot of about nine minutes of on-air net operations as received at my location in Omaha, Nebraska.  My antenna is a wire run from an SEA marine autotuner mounted under the three-story-high roof’s eaves.  I live in a high-RF environment within two miles of eight high-powered broadcast antenna facilities–TV, FM, AM–as well as business and public-service transmitters.   All that RF desensitizes my receiver.  The noise floor is also affected by industrial-level man-made RF noise.

No, Olivia is not lightening-fast keyboard-to-keyboard chatting, but it can get the job done. This following video shows some real-world operation in which the very weakest signals did not decode well. However, even with the 80-Meter band (center frequency is 3585 kHz) really difficult to work with, it did well in terms of what was available for the Ham Radio Deluxe DM780 software to decode.

Example QSO in Olivia Video:

In 2005, SP9VRC, Pawel Jalocha, released to the world a mode that he developed starting in 2003 to overcome difficult radio signal propagation conditions on the shortwave (high-frequency, or HF) bands. By difficult, we are talking significant phase distortions and low signal-to-noise ratios (SNR) plus multipath propagation effects. The Olivia-modulated radio signals are decoded even when it is ten to fourteen dB below the noise floor. That means that Olivia is decoded when the amplitude of the noise is slightly over three times that of the digital signal!

Olivia decodes well under other conditions that are a complex mix of atmospheric noise, signal fading (QSB), interference (QRM), polar flutter caused by a radio signal traversing a polar path. Olivia is even capable when the signal is affected by auroral conditions (including the Sporadic-E Auroral Mode, where signals are refracted off of the highly-energized E-region in which the Aurora is active).

Currently, the only other digital modes that match or exceed Olivia in their sensitivity are some of the modes designed by Joe Taylor as implemented in the WSJT programs, including FT8, JT65A, and JT65-HF–each of which are certainly limited in usage and definitely not able to provide true conversation capabilities.  Olivia is useful for emergency communications, unlike JT65A or the newly popular FT8. One other mode is better than Olivia for keyboard-to-keyboard comms under difficult conditions: MT63. Yet, Olivia is a good compromise that delivers a lot.

Join us — not just on the HF waterfall, but by joining our email-based group at:

–> https://Groups.Io/g/olivia

or, on Facebook at:


Thanks for spreading the Olivia love!  See you on the waterfall.


Current CENTER Frequencies With 8/250 (eight tones, 250-Hz bandwidth): 

1.8269 MHz
3.5729 MHz
7.0729 MHz
10.1429 MHz
14.0729 MHz
18.1029 MHz
21.0729 MHz
24.9229 MHz
28.1229 MHz

See the pattern?

The current suggested CENTER frequency with 16/1000 or 32/1000 on 20 meters is 14.1059.

(Why the xxx…9 frequencies? Experts say that ending in a non-zero odd number is easier to remember!)

Q: What’s a ‘CENTER’ Frequency? Is That Where I Set My Radio’s Dial?

For those new to waterfalls: the CENTER frequency is the CENTER of the cursor shown by common software. The cursor is what you use to set the transceiver’s frequency on the waterfall. If your software’s waterfall shows the frequency, then you simply place the cursor so that its center is right on the center frequency listed, above. If your software is set to show OFFSET, then you might, for example, set your radio’s dial frequency to 14.0714, and place the center of your waterfall cursor to 1500 (1500 Hz). That would translate to the 14.0729 CENTER frequency.

The standard Olivia formats (shown as the number of tones/bandwidth in Hz) are 8/250, 8/500, 16/500, 8/1000, 16/1000, and 32/1000. Some even use 16/2000 for series emergency communication. The most commonly-used formats are 16/500, 8/500, and 8/250. However, the 32/1000 and 16/1000 configurations are popular in some areas of the world (Europe) and on certain bands.

These different choices in bandwidth and tone settings can cause some confusion and problems–so many formats and so many other digital modes can make it difficult to figure out which mode you are seeing and hearing. After getting used to the sound and look of Olivia in the waterfall, though, it becomes easier to identify the format when you encounter it. To aid in your detection of what mode is being used, there is a feature of many digital-mode software implementation suites: the RSID. The next video, below, is a demonstration on how to set the Reed-Solomon Identification (RSID) feature in Ham Radio Deluxe’s Digital Master 780 module (HRD DM780).

I encourage ALL operators, using any digital mode such as Olivia, to TURN ON the RSID feature as shown in this example. In Fldigi, the RSID is the TXID and RXID; make sure to Check (turn on) each, the TXID and RXID.

Please, make sure you are using the RSID (Reed Solomon Identification – RSID or TXID, RXID) option in your software. RSID transmits a short burst at the start of your transmission which identifies the mode you are using. When it does that, those amateur radio operators also using RSID while listening will be alerted by their software that you are transmitting in the specific mode (Olivia, hopefully), the settings (like 8/250), and where on the waterfall your transmission is located. This might be a popup window and/or text on the receive text panel. When the operator clicks on that, the software moves the waterfall cursor right on top of the signal and changes the mode in the software. This will help you make more contacts!

RSID Setting:

+ NOTE 1: The MixW software doesn’t have RSID features. Request it!

+ NOTE 2: A problem exists in the current paid version of HRD’s DM780: the DM780 RSID popup box that lists the frequency, mode, and configuration with a link to click, does not work. HRD support is aware of the problem. You can still use the textual version that shows up in the DECODED TEXT window, a feature of RSID that you can select in the HRD DM780 program settings. This setting ensures that the detected RSID details appear in the receive text area. If you click the RSID link that comes across the text area, DM780 will tune to the reported signal, and change to the correct settings.

Voluntary Olivia Channelization 

Since Olivia signals can be decoded even when received signals are extremely weak, (signal to noise ratio of -14db), signals strong enough to be decoded are sometimes below the noise floor and therefore impossible to search for manually. As a result, amateur radio operators have voluntarily decided upon channelization for this mode. This channelization allows even imperceptibly weak signals to be properly tuned for reception and decoding. By common convention amateur stations initiate contacts utilizing 8/250, 16/500, or 32/1000 configuration of the Olivia mode. After negotiating the initial exchange, sometimes one of the operators will suggest switching to other configurations to continue the conversation at more reliable settings, or faster when conditions allow. The following table lists the common center frequencies used in the amateur radio bands.

Olivia (CENTER) Frequencies (kHz) for Calling, Initiating QSOs

It is often best to get on standard calling frequencies with this mode because you can miss a lot of weak signals if you don’t. However, with Olivia activity on the rise AND all the other modes vying for space, a good deal of the time you can operate wherever you can find a clear spot–as close as you can to a standard calling frequency.

Note: some websites publish frequencies in this band, that are right on top of weak-signal JT65, JT9, and FT8 segmentsDO NOT QRM weak-signal QSOs!

We (active Olivia community members) suggest 8/250 as the starting settings when calling CQ on the USB frequencies designated as ‘Calling Frequencies.’ A Calling Frequency is a center frequency on which you initially call, ‘CQ CQ CQ. . .’ and then, with the agreement of the answering operator, move to a new nearby frequency, changing the number of tones and bandwidth at your discretion. Even though 8/250 is slow, the CQ call is short. But, it is narrow, to allow room for other QSOs nearby. It is also one of the best possible Olivia configurations for weak-signal decoding.

– End of Addendum –


Tomas Hood, NW7US, is a regular contributor to and writes from Nebraska, USA. Contact him at [email protected].

uBITX now on back order.

The uBITX kit as I predicted, proved so successful when it went on sale on Saturday 9th December, by Monday 11th, Asharr Farhan was telling us all on the BITX20 group, current stock of the first uBITX production run was exhausted!

Demand has just outstripped supply, by what the thinking was there was enough stock to last for 2 months?

Anyone ordering the uBITX now, will not get shipped until after at least the 25th December. This is now being flagged up when you come to order.

Did the uBITX  become more successful overnight than the ICOM IC-7300, did it sell more in it's first days of sale? Or does it say to the main three radio manufacturers, you missed a market for a plain no bells and whistles multiband radio that everyone can afford and muck into and understand?

One thing for certain Asharr Farhan has proved without a doubt that he has been the first to achieve and do this, putting into mass production a multiband rig at a price point that everyone can be part of and enjoy! I am sure as well as the uBITX there is a lot more to come from HF Signals in the future!

Well done VU2ESE!

Steve, G1KQH, is a regular contributor to and writes from England. Contact him at [email protected].

The FA-VA4 Vector Antenna Analyzer (LF-100MHz)

For some time I had been considering the purchase of the MFJ259 antenna analyzer but after a little online sleuthing, came across this little beauty, the FA-VA4 Antenna Analyzer by Funk Amateur in Germany and available through their Box73 website here.

I liked the fact that the cost of the analyzer was about half that of anything else comparable ($140 US including shipping) and that it covered the new 2200 / 630m bands!

I think many amateurs planning on building a system for either of these new bands will find the very affordable FA-VA4 a handy piece of equipment when it comes to working on their LF / MF antenna since most available SWR meters do not cover these frequencies accurately.

Delivery time was fast and everything was very well packaged. The FA-VA4 comes in partial kit form and requires only a short amount of time to put together.

The necessary assembly consists of soldering pin strip connectors, switches, AA cell holders, and the BNC connector. All of the tricky SMD components have been pre-mounted ... total assembly time was less than 60 minutes and everything fired-up nicely, without problems, thanks to the well written instruction / user manual.

Included with the kit are three BNC connectors needed to calibrate the instrument for the highest accuracy. These consist of a 'Shorted' connector, an 'Open' connector and a 50 ohm 'Load' connector (SOL). A simple three-part calibration procedure for all frequencies takes about 15 minute to complete, while the instrument calibrates itself as it scans through all frequency ranges with each connector plugged into the output. Once this task is completed, the analyzer is ready for use.

If you're like me, I think the main use will be to check out and tweak some of your HF antennas using the SWR or Z sweep function. This allows you to set a desired 'center' frequency along with a + / - sweep range and have the display draw a nice plot of your system.

Had my 630m antenna not already been tuned and matched, I would have found the analyzer to be a great help but, thanks to my 'scopematch', that antenna has already been optimised.

All menu features and data entry is via three momentary-contact push switches. Although this might initially seem awkward, it is not, and operation is pretty intuitive.

The main modes of operation are:

Single Frequency SWR  Measurement


Single Frequency Impedance Measurement


Single SWR Measurement Run


Single Run For Impedance Measurement (Resistance and Reactance)


SWR Measurement On Five Frequencies (5 Band Measurement)


As well, all of the above can be viewed in a continuous 'cycle' mode, as inputs are changed and all screens can be saved for future reference.

Additional capabilities include use in an HF Signal Generator Mode (~ 1V square wave @50 ohms), the ability to measure C and L at a given frequency, as a 'dip meter' and to measure cable resonances and determine lengths.

The complete manual may also be downloaded from their website here.

I will soon put all of my antennas to the test and see what work might need to be done to optimize them, particularly my HF half slopers, which, in spite of their great performance, have always proven a bit of a mystery when it comes to pruning them to resonance ... I rather suspect that the sloping wires are more of an impedance tuning stub than a radiator and that most radiation comes from the vertical support tower, not the sloping wire.

All-in-all, the FA-VA4 appears to offer very good value for the money and is a well built, quality test instrument. I think it will become a popular choice among hams, especially those on LF / MF. The only thing different that I would have liked, would be to have a UHF (SO 239) connector rather than a BNC on the output, since most amateurs are using these on their HF systems ... or, the inclusion of a BNC-to-UHF adapter.

If you already use this device, please feel free to add your comments below!

Steve McDonald, VE7SL, is a regular contributor to and writes from British Columbia, Canada. Contact him at [email protected].

Radio Frequency Interference From 12V-to-USB Adapters

Many small electronic devices have switching regulators in them that can generate a bunch of Radio Frequency Interference (RFI). This is not my first encounter with RFI-spewing devices. See this article about a automotive 12V-to-USB adapter giving me trouble: This Interference Seems To Follow Me Everywhere

I recently bought a couple of adapters that are physically larger than the one I wrote about. I was thinking that a larger size might allow for a little more filtering and a design that does not radiate. I was half right: one of them works pretty well, the other is an RFI Bad Boy.

Take a look at this short video where I check them out.




This is an Amazon link to the adapter that works pretty well.
Enercell® 2-Port USB CLA Car Charger


73, Bob K0NR

The post Radio Frequency Interference From 12V-to-USB Adapters appeared first on The KØNR Radio Site.

Bob Witte, KØNR, is a regular contributor to and writes from Colorado, USA. Contact him at [email protected].

ICQ Podcast Episode 255 – The Art of De-Soldering

In this episode, Colin M6BOY is joined by Martin M1MRB, Edmund Spicer M0MNG and Bill Barnes N3JIX to discuss the latest Amateur / Ham Radio news. Colin M6BOY rounds up the news in brief, and this episode’s feature is The Art of De-soldering.

We would like to thank Kevin Murphy (W8VOS) and our monthly and annual subscription donors for keeping the podcast advert free. To donate, please visit -

  • Hams Promote Hobby to western Virginia School
  • Distracted Driving in Canada
  • Are Millennials are Killing Ham Radio??
  • Older Callsigns Available from Ofcom
  • 10 Watt EME contact from Essex
  • Amateur Radio Operator to Change on International Space Station
  • Croatia gets 60m, expands 160m Access
  • German Klasse K Licence Postponed

Colin Butler, M6BOY, is the host of the ICQ Podcast, a weekly radio show about Amateur Radio. Contact him at [email protected].

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