AmateurRadio.com

I’ve noticed a few spirited discussions regarding modifying computer power supplies for use with Amateur Radio equipment. On the surface it seems as though they supply the perfect solution: Inexpensive, high current, regulated 12V DC supplies for a fraction of the cost of specialized amateur equipment. Is it really is as straight forward as lopping off a molex connector and replacing it with an Anderson Powerpole?

By design PC power supplies are designed to output a fairly well regulated 3.3V & 5V to the PC motherboard and 12V to the motherboard, fans and hard-drive motors. Modern units are typically rated anywhere from 75W to 1200W which should be a measurement of the output power available from all the 3.3, 5 and 12 volts. Since this isn’t a lab grade power supply you can expect marketing hyperbole has perhaps inflated the power output figures.

Back when my job was to build PCs I had an issue with a server not being able to start its complete complement of disk drives. When I opened the case I found a 300W desktop supply board had been used in place of the 800W board … sometimes you don’t even get what you pay for!

Before you convert your first PC power supply there are two issues that may, or may not, cause a problem depending on your unit.

The first is load regulation or the ability of the power supply to maintain its rated voltage under load. If the output voltage drops too far your rig will shutdown, distort or fail to provide its rated output power.

The second issue is due to the high frequency switching circuits used in switch mode supplies. Depending on the individual power supply there can be adequate to no filtering to prevent radio frequency interference being broadcast to your receiver. Toroids on the input and output lines can help to reduce interference.

Because of construction differences between models and even between batch numbers for the same model you can never be certain how the power supply you purchase, or recycle, will perform. For the most part people’s experiences have been positive but I have heard of power supplies that were unusable because of RF interference or such poor load regulation that the 12V rail dropped to 11V under load.

Without a motherboard presenting a load and supplying the power-on signal there are a few changes that need to be made to the power supply. Modern power supplies will not enable the 12V output unless the power-on wire is grounded and a load should be placed on the 5V line to help with regulation. Additionally there is usually an adjustment that can be used to raise the voltage above 12V

The following links detail the steps required to convert a PC supply for use with amateur radio equipment. Whether this represents a good investment of your time will depend on your desire to do-it-yourself and the quality of the power supply you begin with. I’ve heard strong opinions either way but I’ll just say that, if luck favors you, you’ll save some money and learn a few new skills in this exercise.

Computer Power Supply Converted for Ham Use

CONVERTING COMPUTER POWER SUPPLIES (Advanced with theory)

Converting Computer Power Supplies to stabilized 13.8 V DC 20 A

I’m off and running with the online ARRL course on Emergency Communications! Already I’m learning new things. Take VOAD’s, for instance — I’d never heard of them in my life, but now, thanks to this course, I’m signed up to attend the 2012 MNVOAD Training Conference.

What is a VOAD? VOAD stands for “Voluntary Organizations Active in Disaster.” The first VOAD (and still the main VOAD) was NVOAD (National VOAD), born in 1970:

Hurricane Camille led to the formation of NVOAD. After Hurricane Camille, it became clear that voluntary agencies were responding to the needs of disaster victims in a fragmented, uncoordinated manner. Representatives from several voluntary agencies began to meet on a regular basis to share their respective activities, concerns, and frustrations in disaster response. On July 15, 1970, representatives from seven voluntary agencies came together in Washington, D.C. to form NVOAD. (FEMA course IS-288, “The Role of Voluntary Agencies in Emergency Management,” 2-11)

Those first seven agencies were the American Red Cross, Christian Reformed World Relief Committee, Mennonite Disaster Service, National Catholic Disaster Relief Committee, Seventh Day Adventists, Society of St. Vincent De Paul and Southern Baptist Disaster Relief. Now there are nearly 50 agencies involved, including the ARRL:

The mission of NVOAD is to foster more effective service to people affected by disasters. NVOAD, itself, does not deliver disaster response and recovery services. NVOAD coordinates planning efforts by many voluntary organizations responding to disaster. Member organizations provide more effective service and less duplication by getting together before disasters strike. Once disasters occur, NVOAD or an affiliated state VOAD encourages members and other voluntary agencies to convene on site. This cooperative effort has proven to be the most effective way for a wide variety of volunteers and organizations to work together in a crisis. (4-9)

The state VOAD movement began five years after NVOAD was born:

Not long after the development of NVOAD, State and regional VOAD organizations were created to ensure an effective response to disasters at the State and local levels. The first State VOAD was formed in 1975. The VOAD movement initially grew without much order and without official sanction or direction from NVOAD. However, in 1988 NVOAD developed formal procedures for chartering State and local VOAD members. At this time, there are chartered State VOAD organizations in almost all the U.S. states and territories, and there are a growing number of local VOADs. (4-13)

The Minnesota VOAD has 37 member organizations, including the ARRL — and this year, RACES/ARES is taking center stage at the 2012 MNVOAD Training Conference on Saturday, March 24. The keynote speaker is Peter Angelos, KCØKRI:

9:00-10:00 Keystone Session – Pagami Creek Fire Response – Peter Angelos

The Lake County Emergency Management response to the Pagami Creek Fire (September 2011) and the role Lake County RACES/ARES played is a good example to illustrate effective and successful use of affiliated volunteer organizations in incident management. This presentation will outline a brief description of the incident, the specific support that RACES/ARES provided for logistical and situational communication, and most importantly–the organizational practices and principles that lead to success.

I’m looking forward to hearing what Mr. Angelos has to say about how RACES/ARES helped fight the Pagami Creek Fire.

But perhaps even more valuable for me will be the rest of the training day, which has nothing to do with Amateur Radio. After all, the whole point of VOAD is to learn how to work with one another efficiently and effectively when the time comes!

I attended the Greater Houston Hamfest and as I walked past the tables of equipment I wondered if interest in vacuum tube equipment was starting to wane. Compared to the last few years the prices of collector quality gear had held steady but parts and restorable gear seemed to be going for less.  I’d like to know your thoughts if you’ve noticed trends one way or the other.

I was happy to pick up a EICO Model 625 tube tester for $15. It is in good condition and appears to work well. The roll of settings for each tube is in good condition and a little searching on the internet supplied settings for older tubes like the number 78 in the picture below.

EICO Model 625 Tube Tester with a number 78 tube

The EICO 625 is not a top of the line tester but it does basic tests and will let you know if a tube is functioning and an idea of the life left in it. It was sold in kit form for $34.95 in 1958 which is roughly equivalent to $274 in 2012.

Inside the EICO 625 from diyaudioprojects.com

The EICO 625 is fairly unique in having its own 6H6 diode tube to rectify the 30V filament voltage. It provides DC for the neon short-indicator bulb. If the tube is suspected of having a short then there is a fairly comprehensive series of tests than can be administered to isolate shorted elements.

EICO Model 625 circuit diagram

Well, I finally have had time to sit down and put together part three of the DIY Magnetic Loop Antenna, sorry it has taken so long!

This post will cover building and coupling the loop to your transceiver. After reading through posts one and two you should have a good idea of the parts you’ll use and the physical dimensions of the main loop.

DIY Magnetic Loop Antenna – Part 1
DIY Magnetic Loop Antenna – Part 2

Most magnetic loops have the capacitor at the top of the main loop and the gamma match or matching loop at the bottom, this arrangement avoids running the feed-line through the center of the antenna.

You can assemble the main loop from continuous copper tube or from eight straight sections and 45 degree joiners. Make sure you have a blow torch or propane torch to solder the joints as you’ll need more heat than a soldering iron can supply. Whichever way you decide to build the main loop make sure that all joints are soldered or clamped as securely as possible, you want the lowest resistance possible to avoid your output power turning into heat. Other materials can be used for the main loop such as aluminium or low loss coax but copper pipe is easy to work, has low resistivity and available from just about every hardware store.

To construct the frame of the antenna you can use PVC pipe. It is a cheap and relatively sturdy building material and is available in a range of thicknesses, just about any hardware store will stock a wide selection of fittings. It insulates well and can be glued once you are sure your project is in its final form.

Once the main loop is constructed you’ll need to connect your capacitor to the two ends of the pipe at the top of the loop. Depending on the capacitor you may want to solder tags to the ends of the loop so they will be easier to attach. Copper pipe is a great conductor of heat and takes a lot to heat up and solder while it is not advisable to apply the same amount of heat to your capacitor.
It is also a good idea to attach the capacitor to a solid support so that the connections are not under strain.
The main loop and the capacitor forms the resonant circuit of the magnetic loop antenna.

To couple the main loop to your transceiver and match the expected 50 Ohms impedance you can use one of two methods. Probably the easiest is to use is a loop of insulated wire 1/5 the circumference of the main loop. The smaller loop is placed at the bottom of the main loop and can be shifted around to provide the best match. If you have an antenna analyzer you’ll be able to set it to the desired frequency, tune the variable capacitor for resonance and then move the small matching loop around till you have achieved close to 1:1 SWR. If you don’t have an antenna analyzer you can tune the capacitor for the greatest received noise and then on low power tweak the capacitor and move the coupling loop around for best SWR. Do NOT touch the loop while it is transmitting, use a wood or plastic rod to make adjustments as there are high voltages and intense RF fields near the loop.
An alternative to the coupling loop is the gamma match. The shield of the coax feed cable is connected to the base of the main loop while the inner conductor is connected to a point approximately 1/5 of the circumference around the loop. Its a good idea to use stiff wire (large gauge) for the gamma match as it can be critical of the position and orientation and once you have it in the right position you won’t want to move it again.

It would be preferable to have the ability to remotely tune the loop. A motor with a reduction gear could be used to move the variable capacitor but because the point of resonance is very narrow there should be a way of slowing the motor down. A simple control circuit using variable pulse width modulation could be used to slow the motor down while still retaining enough torque to move the capacitor. Whatever method is used to move the capacitor it should be well insulated from the other components of the antenna. Several thousand volts are generated on the MLA and care should be taken to ensure they don’t find their way onto control leads and back into the shack. Control leads should also be wrapped around toriod inductors as they leave the near field of the antenna to reduce the possibility of RF travelling along them.

With a SWR bridge and microcontroller you could build a fully automatic tuner that swept through the range of the tuning capacitor when the SWR rose above a defined limit indicating that the transmit frequency had changed.

With a little creativity and knowledge you could have an impressive MLA the equal of multi-thousand dollar military style units.

Hopefully this has given you some ideas for constructing your own loop antenna. Regardless of if you go top-of-the-line and buy a vacuum variable or build for economy and QRP you’ll have a compact, useful and unique antenna.

How many of you ham radio operators are also classical musicians? (I’m using “classical” loosely here, the way NPR does — not merely referring to the classical period per se, but broadly referring to all music of higher artistic expression.) I’ve always been intrigued by this kind of simultaneous development of artistic ability and scientific/technical ability. I’ve long heard that the two complement one another nicely, e.g. I’ve heard that musicians make better programmers.

Rehearsal of Exultate Festival Choir and Orchestra (Kristi Brackett, Photographer)

Right now I’m working hard with the Exultate Festival Choir and Orchestra to get ready for an upcoming performance of The Messiah by George Frideric Handel. Ham Radio has taken a back seat in my life during this seven-week project (as well it should, if we have our priorities straight). Yesterday’s rehearsal in the Twin Cities was exhilarating, and once again proved that the 2 1/2 hour drive to get there is definitely worth it. Dr. Tom Rossin is an outstanding conductor, and the choir is so good I have to pinch myself sometimes to see if my place there in the bass section isn’t just a dream. (If any of you happen to be in the Twin Cities on the weekend of March 9-11 and would like to hear The Messiah in its entirety, send me an email and I’ll email you a coupon that will get you two tickets for the price of one.)

Music was part of my life as a boy before I became a ham, but it didn’t blossom until 13 years ago at the age of 31. That was when my brother Tom (NØBSY) got me involved in a cappella shape-note singing from The Sacred Harp. This taught me how to sing parts; without it I could never have gotten into choral singing the way I have. My first choral work was with Exultate, singing Bach’s Mass in B-Minor, followed by Brahms’ German Requiem (in Rutter’s English translation). Since then I’ve been involved in a small choir here in the church, too. All of this has been a huge surprise to me. Up until I was 31 years old I was afraid to sing in front of other people, and I couldn’t sing parts if my life depended on it! So if any of you think you can’t sing, think twice — you might be surprised at what has been lying dormant in those vocal chords of yours, just waiting for the proper nudge to burst forth into beautiful song.

I see Tyler Pattison, N7TFP, is not only an accomplished ham radio operator but an accomplished musician. Along with his excellent tutorials for ham radio operators, Tyler has also posted a video of his performance of Charles-Marie Widor’s Toccata in F from Symphony No. 5. In this video you can see the organ from Tyler’s perspective, not only as a musician but as an electrical engineer. He is bringing both sides of his brain to bear upon the magnificent task of rebuilding and upgrading this organ — and then making beautiful music on it.

How many others like Tyler and myself are out there? If you are a musician and an amateur radio operator, what do you think? Has one influenced the other in your life? How?

Anyone looking at my blog could be forgiven for thinking that I had dropped off the face of the earth for a while, has nothing been happening in my world?

Well, the answer is that a LOT has been happening and all at once. My daytime job has become busier and there have been several non-radio projects at home that needed to be completed. All this has kept me away from Amateur Radio blogging even though I have spent more time on the computer than usual.

In between projects I did manage to stumble across this video of Rear Admiral Grace Hopper explaining just how “long” a nano-second is and what it looks like. This has relevance to radio as we’re usually well aware of frequency and wavelength but don’t usually spend too long thinking about speed.

My family sure was nice to me on my birthday this past Wednesday! One of the gifts I received was something I’ve wanted, but I couldn’t bring myself to cough up the cash for it: the 2012 edition of The ARRL Handbook for Radio Communications, graciously given to me by my daughter. Since the most recent copy on my shelves was several decades old, I was glad to get my hands on it.

I can see why this is a required textbook for the classes my friend Scott has been taking. He is a Signalman with BNSF Railway and periodically travels to Kansas City for training (no pun intended). The ARRL Handbook is a great resource for more than just ham radio operators. It is well-written and comprehensive — so comprehensive that I felt like an ignoramus as I paged through it on my birthday! I may have my Amateur Extra Class, but now I see more clearly than ever how little I really know.

But don’t let that scare you away from this book, Technicians. There’s still plenty in this book that you will find accessible, and anyhow we’re never going to learn if we don’t push ourselves.

One thing that isn’t covered in this book is the topic of operating procedures. But I can see why this topic has been relegated to a book of its own. The ARRL Handbook is quite a hefty tome as it is.

As with most of the ARRL library, you’ll find this book cheaper over at Amazon.