The next CLE event will be the special Christmas holiday event and includes two challenges! CLE 226 covers any NDB north of the Arctic Circle, while CLE 227 is a 'bearing' event, with each listener chosing a particular bearing from their receiving location and seeing how many beacons can be heard from states, provinces or countries through which that bearing slices! You will have plenty of time to listen as well, since the event runs from Monday 25th December to Tuesday 2nd January.

 


For those unfamiliar with this monthly activity, a 'CLE' is a 'Co-ordinated Listening Event', as NDB DXers around the world focus their listening time (usually) on one small slice of the NDB spectrum.
 
Normally, December provides some excellent propagation but the planet continues to be bombarded with seemingly non-stop coronal hole streaming that can cause geomagnetic disturbances disruptive to MF propagation. However, often these 'disruptions' are not as dire as they first appear and MF propagation can remain robust or even be enhanced.

Listeners in Canada and the northern states as well as those in northern Europe will have a much better chance of logging the Arctic beacons. Most of these are large 'enroute' navigation markers with big antennas and plenty of erp ... they are heard very well.

A pdf list of all NDBs within the Arctic Circle can be downloaded from here.

If you are interested in building a system for the new (U.S.) 630m band, the CLE will give you the chance to test out your MF receiving capabilities and compare against what others in your area might be hearing.

When tuning for NDBs, put your receiver in the CW mode and listen for the NDB's CW identifier, repeated every few seconds. Listen for U.S. NDB identifiers approximately 1 kHz higher or lower than the published transmitted frequency since these beacons are modulated with a 1020 Hz tone approximately.

For example, 'AA' in Fargo transmits on 365 kHz and its upper sideband CW identifier is tuned at 366.025 kHz while its lower sideband CW ident can be tuned at 363.946 kHz.

Often, one sideband will be much stronger than the other so if you don't hear the first one, try listening on the other sideband.

Canadian NDBs normally have a USB tone only, usually very close to 400 Hz. They also have a long dash (keydown) following the CW identifier.

All NDBs heard in North America will be listed in the RNA database (updated daily) while those heard in Europe may be found in the REU database. Beacons heard outside of these regions will be found in the RWW database.

From CLE organizer Brian Keyte, G3SIA, comes the usual 'heads-up':

Hello all

Time to tell you about our Holiday CLEs.
Yes – we have two of them, running at the same time, something we have often done in the Christmas – New Year period.

The Early Advice for both CLEs is described here, but we shall treat them quite separately after this.

==================================
CLE226 - SANTA’S BEACONS

We'll be sharing Santa's attempts to use the NDBs north of the Arctic Circle (Latitude N67 degrees) as he navigates his weary reindeer on the last stages of their long flights back home.

Please tell us of any normal NDBs north of the Arctic Circle that you manage to log.

Days: Monday 25th December – Tuesday 2nd January
Times: Midday on 25th Dec to Midday on 2nd Jan, your local time
QRG: Normal LF/MF frequencies
Target: NDBs within the Arctic Circle, north of Latitude 67 degrees

That is similar to what we did way back in Holiday CLE059 (Christmas 2004).

There are about 130 qualifying ‘active’ NDBs currently recorded in RWW.

(You can see the old results from CLE059 in the CLE Archives Section,
http://www.ndblist.info/cledata/CLE59santa.pdf  It only ran for 24 hours after midday on Christmas Day).

We do apologise to the listeners who are too far south to hear anything. (The further north listeners often miss out in normal CLEs, especially in the summertime when there is very little sky wave propagation for them).

The Final Details for the Santa CLE, CLE226, will follow in a few days.

===================================
CLE227 - BEARINGS CLE

Like CLE226, this is also a re-run, something that was very much enjoyed over 10 years ago - as CLE092 during a weekend in early June 2007.

Days: Monday 25th December – Tuesday 2nd January
Times: Midday on 25th Dec to Midday on 2nd Jan, your local time
QRG: Normal LF/MF frequencies
Target: Up to 10 NDBs in each Radio Country in your chosen direction

You choose a line in any one direction from you. Then try to log 'normal' NDBs in each of the radio countries crossed by that line - not more than 10 NDBs from each country.
Your line can be at any bearing of your choice - e.g. 123 degrees but NOT including the opposite direction (303 degrees).

Preferably use a Great Circle map to choose your line and to see which radio countries it cuts (a country is included if any part of it is crossed).

Remember that each USA and Australian State and each Canadian Province is a separate Radio Country. See http://www.ndblist.info/ndbinfo/countrylist.pdf

(If your line crosses the sea, any platforms roughly in that direction would also qualify as a radio country for the CLE).

The event will give you an opportunity to plan your own tactics. You could:

Try out a directional aerial
Include a favourite country or countries
Listen for NDBs which mostly have your favourite offset
Concentrate either on DX or more local reception
Exclude signals from the direction of your worst QRN
- any or all of those things, and more.

The aim is not to try and include as many countries or as many NDBs as possible, though you could do that if you wanted to!

TO CHOOSE YOUR BEARING, for non-dx loggings you could use an ordinary map (Mercator projection), especially if your location is near to its middle.

Better would be a Great Circle map centred on your location - you should find that https://ns6t.net/azimuth/azimuth.html is good and very easy to download and use. Just put in your location (e.g. Locator), choose a distance and click on ‘Create Map’. It misses out smaller countries, but reference also to a ‘normal’ map should cater for that.

Perhaps ideal would be Google Earth if you can download that (it is a powerful program for lots of purposes). Click on its Ruler icon and draw a line with the mouse. It tells you distance and Bearing ('Heading'). (Feel free to tell us about any other suitable Great Circle programs)

I can highly recommend the ns6t map generator as it produces a very nice great circle map, shown below for my location on Mayne Island.

courtesy: https://ns6t.net/azimuth/azimuth.html

I have yet to decide which bearing I will choose but 81 degrees looks promising from here as it cuts across BC, Alberta, Saskatchewan, Manitoba and Ontario while catching the northern edges of Minnesota and North Dakota.

(If you wish you could use any one remote receiver for your loggings,
stating the location and owner – and with their permission if required.
A remote listener may NOT also use another receiver, local or remote,
to make further loggings for the same CLE.

These listening events serve several purposes. They:

• determine, worldwide, which beacons are actually in service and on-the-air so the online database can be kept up-to-date

• determine, worldwide, which beacons are out-of-service or have gone silent since the last CLE covering this range

• will indicate the state of propagation conditions at the various participant locations

• will give you an indication of how well your LF/MF receiving system is working

• give participants a fun yet challenging activity to keep their listening skills honed

Final details can be found at the NDB List website, and worldwide results, for every participant, will be posted there a few days after the event. If you are a member of the ndblist Group, results will also be e-mailed and posted there.

The very active Yahoo ndblist Group is a great place to learn more about the 'Art of NDB DXing' or to meet other listeners in your region. There is a lot of good information available there and new members are always very welcome. As well, you can follow the results of other CLE participants from night to night as propagation is always an active topic of discussion.

You need not be an ndblist member to participate in the CLEs and all reports, no matter how small, are of much value to the organizers. 

'First-time' logs are always VERY welcome!

Reports may be sent to the ndblist or e-mailed to either myself or CLE co-ordinator, Brian Keyte (G3SIA), whose address appears above.

Please ... give the Holiday CLE a try ... then let us know what NDB's can be heard from your location! Your report can then be added to the worldwide database to help keep it up-to-date.

Have fun and Happy Holidays to everyone.
Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

Our Amateur Radio and the Maker Community post defined our stance that the future of ham radio is in experimentation and learning. This post builds upon that cornerstone article by outlining why you should even bother getting an amateur radio license. I won’t make points around the ability to talk around the world or independence from infrastructure that are often touted as benefits of ham radio. Instead, I will highlight why as a hardware designer and a software developer having your amateur radio license is a ticket to designing more interesting, useful, and complex projects.

The Federal Communications Commission provided US citizens with an amazing opportunity to experiment with and develop innovative technology when creating Part 97. You should take advantage of this opportunity. Let’s take a closer look at it!

Part 97, Part 15, and Part 18 (ISM)

We’ve seen these terms thrown around with little explanation. Often, they are taken at face value when you come across a transceiver on Adafruit or Sparkfun. In-reality there are very specific reasons a radio may be one or the other and in most-cases not requiring a license is preferred by manufacturers. That’s why Adafruit and Sparkfun do not focus on selling ham radio transceivers. We on the other-hand tailor to radio amateurs. FaradayRF specifies right on our Starter Pack that you must be a licensed radio amateur to use Faraday.

Licensed Versus Unlicensed Spectrum Use

Before we dive into the regulations lets take a moment to talk about the use-cases of each type of radio. We should be careful to directly compare radios such as Faraday which require an individual license against radios such as the Sparkfun RFM69 Breakout as they are aimed at very different use-cases.

Unlicensed radios operating under Part 15 let you do essentially whatever you want as long as you don’t change the manufactured device. There is no requirement to identify who you are and you can encrypt all your communications. Broadcasting is even allowed. Projects looking to connect to WiFi or Cellular networks will absolutely want to be encrypted so they should use these radios. However, as a hardware designer and software developer you’re not allowed to modify the radio or run higher power. Additionally, you’re at the whim of politics and interpretation as seen in the FCC firmware lock-down saga which is still a problem but has been alleviated because some manufacturers are taking a small stand.

Licensed radios operating under Part 97 on the contrary allow you to modify the hardware, firmware, and software to your hearts content. Most operating modes on most bands even allow you to push out 1500W to the antenna (not including antenna gain!) which is honestly just crazy amounts of power. Since most amateur bands give radio amateurs primary or at least privileged use of RF spectrum other users have to accept if you interfere and radio amateurs can also legally challenge interference against unlicensed users if necessary. There are many cases where this power has been helpful and one of the most notable cases is the ARRL and Broadband over Power Lines clash.

While you cannot encrypt your communications the debate is out whether authentication is legal. Exploring authentication will prove to be a fun endeavor in the near future for ham radio. With the lack of encryption the amateur radio community has a completely different feel to it since they want to communicate with each other. Generally, you don’t want your neighbors on your WiFi router but with ham radio we actually want them to join in most of the time. This helps create a community of experimenters that I’m proud to have been a part of since 2004!

Being able to hack at your hardware, firmware, and software just because you passed the easiest amateur radio test to get your technician class ticket makes the effort worth it. Projects like Faraday encourage open communication, open experimentation, and active collaboration on projects that are higher power and longer range than most unlicensed offerings. Next we will explore the differences between the radio services but remember that your amateur radio license doesn’t stop you from using unlicensed radios. It gives you all the privileges aimed at experimentation which I’ve outlined and lasts a lifetime with simple renewals once every 10 years. It’s worth it.

ISM and Part 15 is the Same Thing Right?

No! This is a really easy mistake to make. The Part 18 Industrial, Scientific, and Medical (ISM) band radios are not allowed to be used for telecommunications. See §18.107(c) which defines ISM equipment as “Equipment or appliances designed to generate and use locally RF energy for industrial, scientific, medical, domestic or similar purposes, excluding applications in the field of telecommunication“. The ISM bands provide areas of RF spectrum where unlicensed transmissions can occur that are often dirty, broadband, and sporadic. If you’re going to have these types of transmitters emit RF and they generally only need to transmit then grouping them together makes sense.

FCC Part 15 addresses the telecommunications gap for unlicensed use. Part §15.1(a) classifies what types of devices fall under it “This part sets out the regulations under which an intentional, unintentional, or incidental radiator may be operated without an individual license“. The last part about operating without an individual license is the most important statement. If you do not assume the operator is technically skilled enough to understand proper operation then it’s up to the manufacture to make sure the electronics are compliant as marketed and shipped to the consumer. This makes sense due to the FCC having no ability to determine whether you’re skilled enough to operate legally as a general consumer.

Part 15 Radios Using the ISM Bands

Many wireless solutions for makers and experimenters often operate in the ISM bands. This falls under Part §15.247which defines operation on 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz. These bands are three really popular ISM bands with the latter two best known for IEEE 802.11 WiFi use. Even the CC430F6137 used in Faraday is aimed directly at operating under Part 15 on the 902-928 MHz ISM band, that’s why we chose it! There is also a very good reason for manufacturers using ISM bands for unlicensed communications under §15.247. Most Part 18 users who can file complaints against part §15.247 devices do not even attempt to receive in the ISM band. In other words, the lights are on but no one is home.

ISM use is generally used for one-way transmissions such as microwave ovens, medical heating therapy, and IC wafer manufacturing (creating plasma with RF). Most CFL lightbulbs are Part 18 due to the RF energy needed to excite the mercury vapor inside them! Therefore any Part §15.247 radio transmitting on these bands is extremely unlikely to cause any noticeable interference to an ISM device. Secondly, when you as an experimenter use these radios and modify them (however legal that actually is) it will be much more likely that any interference which results will go unnoticed.

So What About Amateur Radio?

The FCC Part 97 rules define what Amateur Radio is. Amateur radio is justified in §97.1 using five points, of which the fourth is our favorite “Expansion of the existing reservoir within the amateur radio service of trained operators, technicians, and electronics experts“. This right here is why we love amateur radio! One of the founding principles of the hobby was to spur innovation.

I will highlight why as a hardware designer and software developer having your amateur radio license is a ticket to design more interesting, useful, and complex projects

You need not look much further before finding §97.103 which clearly states “The station licensee is responsible for the proper operation of the station in accordance with the FCC Rules“. Unlike general consumers the FCC trusts you, a licensed radio amateur, as being capable of properly operating your station. In the more than 100 years of ham radio this expectation of trust and self-regulation has worked out far better than one would initially assume.

So far we’ve only showed you why earning the FCC’s trust is beneficial. Now we will show you what that trust gets you! That’s where §97.303 comes in. Faraday operates on the 33 cm ham band (902-928MHz) as a Part 97 device. More importantly §97.303(b) and §97.303(e) define how we as radio amateurs can use the 33 cm band.

(b) Amateur stations transmitting in the 70 cm band, the 33 cm band, the 23 cm band, the 9 cm band, the 5 cm band, the 3 cm band, or the 24.05-24.25 GHz segment must not cause harmful interference to, and must accept interference from, stations authorized by the United States Government in the radiolocation service.

(e) Amateur stations receiving in the 33 cm band, the 2400-2450 MHz segment, the 5.725-5.875 GHz segment, the 1.2 cm band, the 2.5 mm band, or the 244-246 GHz segment must accept interference from industrial, scientific, and medical (ISM) equipment.

As a maker interested in amateur radio these are profound opportunities. You are allowed to transmit unless you cause interference to the “United States Government in the radiolocation service” and you must receive interference from ISM band devices since we are secondary users of this band. As I stated earlier you are not allowed to interfere with ISM devices but since almost no ISM devices have receivers, interfering would prove very difficult to do in practice.

The requirement not to interfere with the United States Government sounds scary but KB9MWR has a great web-page talking about just what these uses are. In summary, you have little chance of actually being required to stop transmitting due to interfering with government radiolocation services. This leaves the requirement of accepting ISM interference as the only real downside to using the ISM band for ham applications. As long as you are OK with some extra RF noise the 33cm band is wide open for ham radio.

The ISM Bands are Junk!

So, ISM bands are largely relegated to “junk” use and radio amateurs must accept interference from ISM devices when using them. This doesn’t mean you have to stop using them when interfered with, it means you have no legal ability to complain about an ISM device bugging you. This is true for Part 15 devices as well and yet we use ISM bands for communications all the time with WiFi on 2.4 GHz and 5 GHz. Most garage door openers, wireless headphones, and baby monitors use ISM bands as well. For example, sometimes our microwaves cause WiFi to slow down but most of the time we never notice.

Amateurs have often denounced the 33 cm band (902-928MHz) as junk due to the noise heard on it. This however is antiquated advice. Digital transmissions are much less susceptible to observation of noise than analog transmissions. Using 33 cm for FM voice maybe be irritating but digital users may never notice the noise.

This is why Faraday is pushing the use of 33 cm for hams. Combined with the incredible privileges of a ham radio license, Faraday is set to be revolutionary for the 33 cm ham band. We want you to start experimenting, start learning, and start using amateur privileges on the 33 cm ham band.

Go Earn Your Amateur Radio License… Now!

We’ve convinced you that being a radio amateur is pretty badass. We know it is, too. As a designer or programmer you will find it easy to “earn your ticket” with a little study. The opportunities to work on interesting projects with increased functionality, range, and reliability are a few of many reasons an amateur radio license kicks-ass. Using your Part 97 license gives you the right to build more powerful, more complex, and more useful projects than possible using unlicensed radios.

To use Faraday or any other amateur radio transceiver on the 33 cm band you only need a Technician class license in the United States. This is the easiest license to get and requires no Morse Code skills. The AmateurRadio subreddit has an awesome wiki page on what you need to do to become licensed. Check it out, get your license, and push the boundaries of RF experimentation with us.

We are excited to see you get licensed! If we’ve convinced you to get your license please let us know. We’d also love to hear your thoughts on the benefits and drawbacks to using ISM, Part 15, and Part 97 devices here in the United States. Leave us your thoughts in a comment below!

We are simply conversing about published documentation regarding ISM, Part 15, and Part 97 regulations and are not lawyers! Do not take this article as legal advice.

Bryce Salmi, KB1LQC, co-founder of FaradayRF, is a Professional Electrical Engineer designing and building avionics for rockets and spacecraft during the day and developing the future of digital amateur radio experimentation by night. Contact him at [email protected].

Amateur Radio Weekly is curated by Cale Mooth K4HCK. Sign up free to receive ham radio's most relevant news, projects, technology and events by e-mail each week at http://www.hamweekly.com.

The latest blog post by Sterling Coffey (N0SSC), Millennials Are Killing Ham Radio, dives into a topic we’ve brought up continually here at FaradayRF. That topic is the future of amateur radio. We’ve known Sterling for a long time and this post comes as no surprise to us. He’s an ardent supporter of FaradayRF and even gave an impromptu lightning talk about our project at the 2017 TAPR/DCC.

Being a millennial myself, I barely remember not having a computer in the house and when we did have a computer there was at least dial-up Internet to go with it. By the time I was in high school most of us had cell phones and in 2007 when I graduated high school the iPhone changed the world. To put it bluntly, mainstream ham radio has always been behind the curve of mainstream technology for as long as I can remember. Rather than being deterred, people such as Sterling, my brother Brent, and myself have taken on the optimistic view that we can reinvent amateur radio.

Here’s how…

Millennials are Savvy

Growing up with computers and the Internet makes us a bit naive about technology. If we think it can be done then we can probably figure out how do it. This is a great trait because no one can tell us it’s not possible. Just because it wasn’t possible before doesn’t meant I can’t do it now. We didn’t grow up designing computers from scratch. We grew up piecing graphics cards, hard drives, and motherboards together while figuring out how to boot Linux (all before Ubuntu!). That’s made us savvy with technology. Some of us can design computers, but a heck of a lot more can cobble them together and apply them to something interesting. That’s progress.

Millennials are Efficient

Building upon our savviness, I’d argue that millennials are efficient too. In fact, today’s fast-paced world means few have interest in becoming licensed to slow down and ragchew over HF. Love it or hate it that’s a strong trait I’ve observed. It’s trivial to contact almost anyone anywhere in the world if there is an Internet connection. It’s a hard sell to put ham radio in any other context beyond emergencies, contesting, and being something like sailing.

Using the resources available to us we can iterate quickly without reinventing the wheel. Building projects starts at proof of concept which involves wiring premade circuit boards together and applying some software glue. We know that building upon others work is faster. We grew up with open source and that’s changed our perception of what a project is. It’s efficient to take what works now and build something better. Some will enjoy building 40 meter CW transmitters but many more will find value in much more relevant technology applied to amateur radio. There are likely more millennials interested in working at the application layer than at the transistor layer of a radio.

Millennials are a Step Ahead

Readers of our blog as well as the massively popular Hackaday blog will note that open source electronic design software such as KiCad and manufacturers such as Oshpark give millennials a leg up versus prior generations. For less than $20 and two weeks of time one can order a four-layer circuit board that has good performance through 1GHz. This is insane compared to just 20 years ago!

The tools available to millennials allows them to experiment and iterate at speeds unseen before in amateur radio. This allowed projects such as FaradayRF and HackRF to quickly iterate hardware with minimal investment. Additionally, SMT components are the standard for most hobbyists these days. While 0402 components may be annoying, some of us are hand soldering 0201 components (dust) and 0603 or larger are a breeze. Hardware is getting much cheaper. Hardware is practical.

Millennials are not Patient

A blessing and curse of growing up as a millennial is that we’re not very patient. We went from dial-up Internet to broadband cable in a decade as kids. We went from no-frill cell-phones to having a smartphone that provided high speed Internet in our pockets in half a decade. Finally, we’ve seen smartphones nearly replace the need for desktop/laptop computers in another half a decade after that. Technology moves fast, and we expect that. Ham radio isn’t an exception to these forces. I’d call this progress and we need to keep up.

It’s our Time

The attitudes, savviness, and naive view of what couldn’t be done in the past can provide the driving force in ham radio. It could also drive its disappearance into irrelevance. Millennials are now in their 20’s and 30’s. Among us are the Steve and Woz’s of our generation building Apple or the Bill Gates starting Microsoft. Among us are the people ready to take what we’ve learned growing up and see the opportunity to build a better version of tomorrow. Millennials are poised to define a new paradigm for the hobby. I say we should welcome it.

What do you think about millennials driving the future of ham radio? We’d love to keep this discussion moving forward. It’s an exciting time to be a radio amateur. We’re on the cusp of becoming forever a retro activity or catapulting into an era of fast-paced advancement. Let us know what your thoughts are in the comments section below!

Bryce Salmi, KB1LQC, co-founder of FaradayRF, is a Professional Electrical Engineer designing and building avionics for rockets and spacecraft during the day and developing the future of digital amateur radio experimentation by night. Contact him at [email protected].

Our good buddy and co-host-on-hiatus Rich, KD0RG, is supplementing our vacation with some content for your ear holes! This is the first installment of his series, BSD in the Ham Shack. We're sure it's great. Have a listen!

73 de The LHS Crew

Russ Woodman, K5TUX, co-hosts the Linux in the Ham Shack podcast which is available for download in both MP3 and OGG audio format. Contact him at [email protected].

Much to my surprise the price has still to fall, although there are “cracks”: some are now offering the rig with free gifts.

Personally, I can wait. It is a good rig, but to my mind, the dealers have had a very good time and very good profits.

Now is the time to drop the price. Sub £1000 (~$1,300) please – soon.

Roger Lapthorn, G3XBM, is a regular contributor to AmateurRadio.com and writes from Cambridge, England.

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 AmateurRadio.com and writes from Washington, USA. Contact him at [email protected].