Friday, April 20, 2018

Modifying A Switching Power Supply Into A Variable Power Supply (A May Communicator Preview)


An Inexpensive Project To Power Your Amateur Radio (Or Other) Gear

By Daniel Romila VE7LCG

I was faced with a problem that many radio amateurs have: Getting a power supply capable of fulfilling my needs today and for the reasonable future. I decided that switching technology is the way to go, and that 12 Volts is my main voltage requirement. Regarding power, I was limited by my budget, because the more current a power supply can deliver, the more money I would have had to spend. I established 42 Amps would be enough, and that means 500 Watt capacity.

The above moment of decision was in 2016. So, now – in 2018 – I can tell you about the results of my selection of power supply and the modifications I made.

Whenever I was looking at eBay, Amazon and the Chinese websites (aliexpress.com, banggood.com, gearbest.com, etc), I was searching for 12V at 42A. 




The size of such a brick, at 12V and 42A is 115 x 215 x 46 (mm). The current price  around $38 CAD - about $29 US (shipping and taxes included).

I modified the circuit somewhat and replaced the trimmer resistor with a linear potentiometer. That extends the voltage range from the original 9 – 14 Volts to 4.5 – 15 Volts. Here is the result:


I successfully used this power supply for my Kenwood 7950 HF transceiver. I had very short power wires, so I put the power supply on top of the transceiver, on its speaker, because I used headphones... and there was no noise. I also used it for various audio experiments with operational amplifiers installed on a breadboard at around 30 cm from the switching power supply.

It ran cool, and despite my tries, I was not able to make this power supply run hot under various heavy loads. Under maximum power of a little less than 150 Watts. The fan starts to rotate automatically and it is silent.

A comparable digital power supply made for Amateur Radio would cost well over $150 CDN so this is a budget solution.

The full article will be featured in the
May SARC Communicator (available here May 1st).




International Marconi Day - This Saturday




A 24-hour Amateur Radio Event


Amateur radios, point-to-point contacts, high-frequency transfers, a mysterious yet attractive prize for the most connected stations… All of this sounds like the beginning of a quirky B-movie. In reality, it is the essence of International Marconi Day, a 24-hour amateur radio event which celebrates the career of Italian wireless communications pioneer Guglielmo Marconi. 

Fitting with ‘The Rest Of The Story’ featured in the April 2018 Communicator, the event is held annually on the Saturday closest to to Marconi's birthday on 25 April 1874.  This year the contest runs on Saturday April 21st, operating hours are 0000 UTC to 2400 UTC (5pm Pacific time).

To commemorate the Nobel laureate’s achievements, fans use HF radio to make direct point-to-point contact between stations, relying on the same technology Marconi developed and utilized in his time. Although nowadays the Internet is the medium of choice for global communications, the idea behind International Marconi Day is to keep the spirit of invention alive. The event also provides an exciting throwback to the days when a connected planet Earth was but a bold dream and only a few exceptional people, such as Marconi, saw the value in it.



The organizers issue a very nice certificate for contacting 15 of 60 or more stations at significant sites around the globe related to Marconi's work.


At the time of writing, there are over sixty stations registered for the event. The full list, throughout Europe and North America is available at http://gx4crc.com/imd-stations/ 



Full details of the award and participating stations are available on the website gx4crc.com


Sunday, April 15, 2018

World Amateur Radio Day


The following information is courtesy of the

International Amateur Radio Union

Every April 18, Radio Amateurs worldwide take to the airwaves in celebration of World Amateur Radio Day (WARD). It was on that day in 1925 that the International Amateur Radio Union (IARU) was formed in Paris. Amateur Radio experimenters were the first to discover that the short wave spectrum — far from being a wasteland — could support worldwide propagation. In the rush to use these shorter wavelengths, Amateur Radio was “in grave danger of being pushed aside,” the IARU’s history has noted. Amateur Radio pioneers met in Paris in 1925 and created the IARU to support Amateur Radio worldwide.
Just two years later, at the International Radiotelegraph Conference, Amateur Radio gained the allocations still recognized today — 160, 80, 40, 20, and 10 metres. Since its founding, the IARU has worked tirelessly to defend and expand the frequency allocations for Amateur Radio. Thanks to the support of enlightened administrations in every part of the globe, Radio Amateurs are now able to experiment and communicate in frequency bands strategically located throughout the radio spectrum. From the 25 countries that formed the IARU in 1925, the IARU has grown to include 160 member-societies in three regions. IARU Region 1 includes Europe, Africa, the Middle East, and Northern Asia. Region 2 covers the Americas, and Region 3 is comprised of Australia, New Zealand, the Pacific island nations, and most of Asia. The International Telecommunication Union (ITU) has recognized the IARU as representing the interests of Amateur Radio.
Today, Amateur Radio is more popular than ever, with over 3,000,000 licensed operators!
World Amateur Radio Day is the day when IARU Member-Societies can show our capabilities to the public and enjoy global friendship with other Amateurs worldwide.

IARU has provided a poster for World Amateur Radio Day. Any club may download it and use it to promote WARD in their area. The poster comes in two sizes: 61cm x 91cm and a small (A4) flyer.

Groups should promote their WARD activity on social media by using the hash tag #WorldAmateurRadioDay on Twitter and Facebook. The IARU will list all WARD activities on the webpage. To have your WARD activity listed, send an email to IARU Secretary David Sumner, K1ZZ.

April 18 is the day for all of Amateur Radio to celebrate and tell the world about the science we can help teach, the community service we can provide and the fun we have.

We hope you will join in the fun and education that is World Amateur Radio Day!

For more information and to download a poster please visit the World Amateur Radio Day webpage at http://www.iaru.org/world-amateur-radio-day.html

Source: The International Amateur Radio Union


Alan Griffin
RAC MarCom Director

Thursday, April 12, 2018

Construct A $10 Dummy Load


A Communicator Reprise... October 2011


"I made this here dummy load and can’t figure out why I’m getting a 25:1 SWR!!”  “Got such great deal on this 100 watt 51 ohm resistor off of eBay and though it would make a great dummy load for the HF rig,” he beamed as handed me the homebrew project.  Did a nice job putting it into an aluminum project box, with both a UHF [SO-239] and a BNC connector...  


But of course the first giveaway was the aluminum encased resistor, the second was that it was 100watts in a relatively small package… When we hooked it up to the MiniVNA, and saw how it reacted to a sweep from 1 to 180 MHz., I could see then that it wasn’t your garden variety resistor, it was a wire-wound resistor – usually encased in an aluminum heatsink and a fraction of the size of a carbon composite resistor.  And boys and girls, what do we know about something that’s wound like a coil – an inductor?  Yessiree Bob… it’s an inductor. With enough wire to act like a proper load somewhere in the lower AM broadcast band.  So the closer to 1 KHz or DC, the better the SWR. So when he put 14.100 MHz into it, no wonder he measured 25:1!!  Of course the eBay seller didn’t say it was wire-wound and if you hadn’t seen one before, it just looked like a nice bright and shiny deal at $5.65.So, we chucked that experiment in the cylindrical file and proceeded to make him an inexpensive dummy load.


[Note: 3” discs would have been better in retrospect]
Here is what you need.  A paint can... you can buy new [and empty] for $1.36 at the local paint store.  A single hole SO-239 [$1], a piece of solid copper wire, two 2½” copper discs [in the photo] one has the drilling pattern already glued onto it and, twenty  5-Watt 1000 ohm carbon resistors.  Ceramic will do too… about $8 landed. 

The discs I cut from a piece of thin PCB, the resistors from eBay after I verified with the seller that they were not wire wound.  
After drilling the 22 holes in the discs and soldering all 20 resistors into place, one disc becomes the braid or shield side, the ground of the SO-239 and the piece of bare copper wire #10 or #12 bare copper goes from the centre pin on the connector to the disc on the bottom [of the photo].



The resistors were 5 watts, so 20 times 5 = 100 watts.
It gets hot enough in 30 seconds that you would not
be able to hold onto it for long.


What you have when finished  is 1000 divided by 20 or 50 ohms. But these are 5% resistors, and I didn’t ask for 20 hand measured resistors, so of course they were not all 1000 ohms or higher. All it takes is one to be 5% low and it brings the whole array down below 50 ohms. This one here measured 49.6 ohms. 


Close enough for its purpose.  Yes, this does present a small degree of capacitance and inductance – the discs do that, but it’s not enough to cause a problem.  







Hooked up to the MiniVNA and it was rather decent!  Not for 6 meters or higher, this was definitely a 1.8 to 30 MHz dummy load for under $10 in parts and about 2 hours of labour.  














The SWR didn’t change when put in the can with 1 litre of pure mineral oil from the drug store.  You could have used it as a dry load, but the oil makes it usable for minutes, rather than seconds and the paint can does reduce the RF radiated by roughly 60db.




As we can see from the sweep below, from 1.8 to 30 Mhz. the Impedance [green line] is pretty darn close to the 50 ohm reference line all across the entire HF band. The SWR 1.02:1 at 160 metres and about 1.26:1 at 30 MHz.  OK, not a perfect dummy load, but it costs less than $20, you can make it all at home and it does the job of giving your transceiver a non-radiating load for testing. The fancier commercial ones have LCR circuits incorporated in the array to compensate for the inductance and capacitance of the device – in other words, they doctor the load to get that perfect 1:1 across the band.











You can see  above, from 50 to 55MHZ, the SWR is about 1.3:1 across the six meter band, 
so it could be used if you needed to.  But by the time you get to the 2 meter band, it’s above 1.6:1 and not a good load. Thus commercial products tend to get more expensive at higher frequencies because you have to make them differently with higher tolerances, higher or more precise engineering and a few more parts to null out any inductive or capacitive reactance.

Next, the sweep below, from 1 MHz. to 180 MHz. is actually a good representation of most HF Cantennas, MFJ and other ‘non-VHF’ dummy loads.  The green line represents the impedance of the load.  From 1 to 21 Mhz. it’s pretty good at staying near 50 ohms and with an SWR of less than 1.1:1. But as you can see by the time it climbs out of the 30 Mhz section, the impedance drops and the SWR climbs, so by the time it reached 180Mhz., the limit of my MiniVNA,  it’s almost 2:1 with an impedance closer to 30 than 50 ohms.




This is mainly due to the construction of the dummy load, the 5% resistors soldered between two copper discs act somewhat like a capacitor, with the inductive reactance of lead lengths and 1¼ inches of #12 wire from the centre pin of the SO-239 and the lower disc, going through the centre of the discs, which must have some inductive quality. So not a perfectly symmetrical or resonant device, but as you have seen perfectly “HAM” in nature and quite adequate for the few times you need to test at full power without annoying others on the air.







CQ CQ CQ

Modifying A Switching Power Supply Into A Variable Power Supply (A May Communicator Preview)

An Inexpensive Project To Power Your Amateur Radio (Or Other) Gear By Daniel Romila VE7LCG I was faced with a problem that many radio ...

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