Showing posts with label homemade. Show all posts
Showing posts with label homemade. Show all posts

Sunday, December 1, 2013

Where to find the $20 Software Defined Radio?

A while back I wrote a blog post about the availability of $20 software defined VHF/UHF radios in the form of re-purposed USB digital television dongles.

Now-days, with the improvements in software and documentation, the hardest part is finding the right dongle. What you order from EBay, and what you receive, can be two different things and only some of the dongles are suitable for use as VHF/UHF software defined radios.

So, I was pleased to see that at least one hobbyist electronics supplier has sought out and supplies a suitable device for SDR at a fair price :
Adafruit has available the USB dongle and "antenna" suitable for experimentation for $22.50, not far from the EBay (direct from China) price.

Click here to go directly to the product page: Software Defined Radio Receiver USB Stick - RTL2832 w/R820T

No, I didn't receive a free evaluation unit and I don't work for Adafruit ... I'm just glad to see these useful devices available from a local company with an increased chance of you "Getting what you paid for."

Adafruit also helpfully stock the adapter cables to convert the less common MCX antenna connector into the much more common BNC connector: MCX Jack to BNC RF Cable Adapter

Monday, July 9, 2012

The $20 Software Defined Radio

Introduction:

Despite my interest in boat-anchors I do find myself peeking 'over the wall' from time to time and taking a look at new and emerging technologies. After several demonstrations from friends I had become convinced of the incredible potential of software defined radios and even found thinking about owning one ... one day.

Perhaps the best known SDR in amateur radio circles are the FLEX rigs from FlexRadio. I had the chance to see a FLEX-3000 in use during Winter Field Day 2011 and had to admit that, barring the lack of knobs & dials, it was a very impressive rig!

One thing stopped me from running out and buying one straight away was the cost and perhaps the notion that once the new had worn off I would regret the significant outlay required to own the blue box. So, I shelved the idea of owning an SDR and found other things to occupy my time.

This changed when a post on www.reddit.com/r/amateurradio/ mentioned an unmodified digital TV receiving USB device that had been used as a software defined receiver in the 60MHz - 1.7GHz range. The best part was the cost, around $20 for most examples of this kind of device. Finally software & commodity hardware had come together to deliver useful receiver that everyone can afford.

The nuts and bolts:

There are specific parts required to put together your own $20 SDR but I will document what I used to get mine running and hopefully you can follow along.

Hardware: The device that I used was a Ezcap EZTV668 DVB-T Digital TV USB 2.0 Dongle purchased from DealExtreme. The part was shipped from Asia and I gather from reading else ware that DealExtreme is a middleman and not the actual supplier. Be prepared to wait a while if ordering from this supplier, my Ezcap took about 3 weeks to arrive but I have heard that a month or more is not uncommon.

The upside is that shipping is free and your purchase involves 0% tax, this really IS a $20 SDR.

This particular DVB-T dongle uses the RTL2832U chip which is required for use as an SDR, other dongles with this chip may work but if it does not have the RTL chip it will NOT work currently.

Software (Linux) : After poor results with the software running on MS Windows I moved across to Linux and got it working well there. I can't point you to a single howto for this because I used several different guides and tried a few things before it started working. The most helpful, and probably all you really need, are the build-gnuradio script which gets hardware support and gnu-radio running and the "Getting Started With RTL-SDR" page by Tom Nardi which covers installing Gqrx. All the software used is in development and requires familiarity with the command line to install and use at the moment.

Software (Windows) : I had another shot at getting the MS Windows software running and stumbled across the excellent website http://rtlsdr.org. Rtlsdr.org mentions using a new version of SDR# software which worked very well! 
I would recommend following the instructions under the Windows Software section, this had me up and running in a matter of minutes. Follow the instructions EXACTLY, I made life hard on myself by not paying attention to details and I think was responsible for my earlier issues.

Going further - Antenna : The stock antenna that is supplied with the Ezcap EZTV668 is sufficient for testing but you'll want to add something a bit more substantial for regular use. You may even want to remove the existing (hard to find) antenna connector from the board and install a standard connector and a less flimsy metal casing. This will help with RF shielding and temperature stability. 
If you are going to use a larger antenna, especially an outside antenna, you'll want to check to make sure a protection diode has been fitted to the input. The Ezcap EZTV668 is a very inexpensive device and others have found units in which the protection diode was not fitted to save costs.

Going further - 160M - 6M ? : I've just seen an interesting blog post titled FunCube Upconverter where the author, George Smart, has built a converter allowing the reception of 160M - 6M using the FunCube dongle. The FunCube is functionally the same as the RTL dongles available for $20. For any home brewers out there this could be a great project as George has included all the details including schematics and board artwork required to build the converter.


Update : Thanks to a link from Neil W2NDG to an EBay sale I've been able to track down a pre-assembled HF up-converter on this page : New HF Converter Kit for the SDR Fun Cube Dongle The price seems to be 45 euros, or about $55 US.

I've had a lot of fun using the $20 SDR to listen to AM aircraft traffic, local repeaters, emergency services and amazingly good quality broadcast FM stereo programming. Its easy to see, with an SDR, just how wide a radio broadcaster is transmitting and move your filter bandwidth to match.

Hopefully this is just the beginning of inexpensive SDR hardware that the radio community can re-purpose and re-engineer. 

Tuesday, March 27, 2012

Now I understand - Measuring capacitance with a micro-controller

The excellent article by Rajendra Bhatt explains not only how capacitance can be measured but also how a micro-controller can be interfaced to an analog circuit to create a useful piece of test equipment.


Capacitance meter by Rajendra Bhatt
I found the explanation of the RC time constant method of measurement as interesting as the micro-processor project itself and congratulate Raj on demonstrating a practical and workable real-life example of what can normally be a dry textbook subject.

Click here : http://embedded-lab.com/blog/?p=4400 to read the article which includes everything you need to duplicate his project. 

The page is part of the excellent http://embedded-lab.com/ web site which is well worth a look. I know it is going in my bookmarks and RSS feed.

Wednesday, March 21, 2012

Ham Radio and Mesh Networks

Lately I've been fascinated by the capabilities of mesh networks. The ability to quickly create ad-hock computer networks could be an invaluable resource for amateur radio operators in general and particularly for emergency communications (EMCOM)

Linksys WRT54GL Router
The particular device and software I have been experimenting with is the Linksys WRT54G router and HSMM-MESH firmware from http://hsmm-mesh.org/.

Installing the HSMM-MESH firmware changes the way the Linksys router functions and allows it to automatically connect to other HSMM routers in a mesh network. No special configuration is required after setting your callsign. All TCP/IP configuration is pre-configured, even down to automatically assigning addresses to connecting clients.

Mesh Network Diagram
Mesh networks are highly fault tolerant. Every router in the network is aware of every other router and has the ability to move network packets through from one unit to another provided there is a link, or chain of linked routers, between them.
In the diagram to the right each router is represented by a numbered circle. If router number 6 were to fail then network packets that needed to move between router 1 and 7 would travel through routers 2 & 3 or 5 & 10 until 6 was repaired. All this happens automatically and quickly enough so that there is no disruption to the traffic.

Anything you can access on a normal computer network can be made to work on a mesh network. Some of the services that have been demonstrated include email, voice over IP (VOIP), video conferencing, file sharing, web servers & groupware applications.

With simple modified antennas the modest output power from the WRT54G (100 to 200mW) can be used to reach distances of many miles or tens of miles with directional antennas. Mounting the router on a mast in a sealed enclosure can reduce losses from long cable runs while running off 12V power makes them compatible with ham radio power sources including solar and wind power.

The example to the left is from NG5V located on hsmm-mesh.org and consists of an omni-directional external antenna and a lawn sprinkler controller box from a popular home improvement store.

Did you know that ... Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.

I hope to acquire a few more WRT54G routers and put together a mesh network in the Katy TX area as a resource for experimentation and education in an area not normally touched upon by regular amateur radio operators. Who knows what the future holds & it behooves us to investigate this technology and bend it to our own needs.

The Amateur is Progressive ... He keeps his station abreast of science. It is well built and efficient. His operating practice is above reproach.

Sunday, March 11, 2012

PC power supplies for Amateur Radio equipment?

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

Monday, March 5, 2012

DIY Magnetic Loop Antenna - Part 3

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.

Wednesday, February 8, 2012

The Power of Making

A brilliant video detailing the power of making through a triptych of views into the workshops of makers.


A three screen film installation for the Power Of Making exhibition. A collaboration between the V&A and the Crafts Council, this exhibition presents 100 crafted objects in a cabinet of curiosities that explores traditional and time-honoured ways of making, as well as innovations taking place around the world.

Visit the Victoria and Albert Museum at http://www.vam.ac.uk/

Friday, February 3, 2012

Winter Field Day 30 - 10 Meter Loop

This is a very rough diagram of the magnetic loop antenna I built for Winter Field Day. The tuning capacitor is a military surplus 150mmf (150pf) air variable with a worm and wheel drive. It also has a anti-backlash mechanism for very fine control.
The main loop is made of 1/4 inch annealed copper tube 8.51 feet long. Half inch pipe would have been better but quarter inch was easier to work .. and it was what I had. Both ends of the loop terminate at the tuning capacitor with soldered connections for the lowest loss possible.
The coupling loop has a circumference that is 1/5 that of the main loop. In this case it is 1.7 feet. It is located opposite the tuning capacitor and can be moved or squashed slightly to adjust for best SWR.
The one improvement that immediately comes to mind would be to terminate the connection to the coupling loop in a SO-239 connector rather than the short length of coax I used.

I have plans for remote tuning and automatic tuning but it remains to be seen if I can get the time & resources to bring those to completion.
A short length of heavy wire is used to connect one side of the tuning capacitor to the loop, the other was bolted and soldered to the body of the capacitor. As the tuning cap had been sitting for several decades a shot of Deoxit restored the connection between sliding contacts after I noticed that tuning was erratic while using an antenna analyser.
The supports for the loop are made from the ham's best friends : white pvc pipe and zip ties. Holes were drilled to keep parts from moving.

Wednesday, February 1, 2012

Incredible materials : Ultra dense plastic - Malleable at just 150F

Ham radio folk have been home brewing, inventing and crafting before most Makers were a gleam in their parents eye but that doesn't mean we can't learn from those industrious Maker guys. One area that is receiving more and more attention has been new and innovative construction materials.
Most of us are familiar with the concept of cutting a plastic chopping block up to make insulators but what would you do if you needed to create a molded part or something more complex? Injection molding is expensive for one off parts and anything more complex than drilling a hole also requires a substantial investment in machinery.
A new material that goes by several names (Shapelock, InstaMorph) is malleable at just 150 degrees Fahrenheit (66 degrees centigrade) and cools to an ultra-dense plastic similar to nylon.
It can be molded with your hands when heated and machined with low speed tools when cool.  I couldn't find specific details but I imagine it has similar dialectic properties to nylon which would make it suitable for a wide range of radio and electronic applications. Perhaps you'll be the first to add this material to your arsenal of home brewing tools?
Check out the demo below which shows how easy this material is to mold using simple tools or just your hands. You can get Polycaprolactone under several different brand names such as Friendly Plastic, InstaMorph or Shapelock from a number of different suppliers or search for it on Amazon.

Monday, January 30, 2012

Twittering Morse Key - Tworsekey


I'm certainly not the first to theorize that if there is a greater than zero probability of something happening then you'll find it happening on the Internet. So it was when I stumbled across this home brew creation of Martin Kaltenbrunner. Martin has created a Morse code key that decodes whatever you hammer out and sends it to a Twitter account, thus neatly bridging more than 160 years of history while ranking fairly high on the, "But why?" scale. I have no idea why Martin created the Tworsekey but you have to admit that it looks great and I wouldn't mind having one siting on my desk.


Sunday, January 29, 2012

Winter Field Day and a Magnetic Loop Antenna

Last Field Day I spent a fair bit of time taking photographs and video which made for an entertaining record of the event when uploaded to YouTube. This time I was determined to do something more in tune with the Field Day theme and actually get my hands dirty ... or possibly burnt, cut or crushed (Physical coordination not being my strong point). Fortunately I only sustained one small scrape in the course of constructing a magnetic loop antenna for the 30 - 10 meter bands (A frequency range can be measured in meters since wavelength is directly proportional to frequency, a frequency of 7.49 million cycles per second has a wavelength of 40 meters at the speed of light). I had finished the antenna construction Saturday evening but the 20M band had fallen silent as ionospheric conditions favored the longer wavelength bands like 40M ... which the antenna didn't cover.

On Sunday morning the 20M band opened up again and I was able to make contacts all over the US using 10 - 25W. If you stop to think how far the light from a 25W light-bulb can reach it puts the fact that I could talk all over the US, using the same amount of power, into perspective!
My loop antenna is a simple resonant circuit: Consisting of a loop of copper connected to a variable capacitor. A smaller matching loop inductively links the transceiver to the larger copper loop so the radio see the right load.

The devil is in the details of course but I'll save a discussion of theory and construction for another post. There was a fair amount of interest in the loop as other folk also live in similar antenna restricted neighborhoods and are prohibited from putting up large antennas for the HF bands. Another ham brought out a very fine commercial loop antenna with a flexible loop that could be packed into a netbook sized bag. Such an antenna could be just the thing for trekking with a radio and operating in the great outdoors.
Seems I didn't learn my lesson with cheap coax ... The short piece that connects the wire matching loop to the longer cable run was a piece of RadioShack brand with a PL-259 connector conveniently attached. As I started started to transmit I noticed the SWR (Reflected power ratio) start to rise the longer I transmitted. As soon as I stopped for a moment it quickly dropped so I knew that whatever was getting upset had to have a fairly small thermal mass ... it wasn't the tuning capacitor for sure! I'll have to swap out the short piece of coax for a SO-239 socket and run my good coax directly to the antenna. While I was testing and making a few field day contacts I kept the power level low which kept the SWR under control.


Tonya added her baked creations to the Field Day menu and I suspect we may have beaten last years time in consuming everything apart from one slice of apple pie which lasted until Sunday morning. We were extremely well fed with delicious food thanks to many contributions with special thanks to Mike N5TGL and his wife who hosted the event and tolerated our impromptu lectures and animated discussions of ham radio miscellany for the two days of Winter Field Day.
The Society for the Preservation of Amateur Radio is the organizing body that schedules this event for the last full weekend each January. The object of the event is familiar to most Amateur Radio operators: set up emergency-style communications and make as many contacts as possible during the 24 hour period. The rules encourage as many contacts on as many bands and modes as possible, because during a real emergency, the most important factor is the ability to communicate, regardless of band, mode or distance.

Wednesday, January 18, 2012

Remarkable relay computer - The TIM-8

Computers don't really make very impressive noises now-days. Hard drives whir and cooling fans exhale white noise, you might detect the quite chatter of disk access or the groan of a failing fan but that is about it.

Rewind a few tens of years and computers used to make really impressive noises that matched their impressive size. A virtual symphony of noise told you that things were really happening in there, things that could probably take a finger off it you happened to stick it in the wrong place!

1955 computer engineer. Popular Mechanics in 1949 confidently declared: "Computers of the future may weigh no more than 1.5 tons"
Every now and then someone gets the urge to recreate a piece of history, a computer that makes the right kind of noises along with other essential prerequisites like blinkenlights and a paper tape reader.

The latest creation I have seen was built by Rory Mangles and christened TIM-8. It is the 8th in a series of increasingly complex and refined builds the last of which qualifies as a complete computer with input/output and processing abilities.

The TIM-8 8-bit relay computer using on 152 relays.
Check out the YouTube video below for an example of TIM-8 executing a program from papertape.

Monday, January 16, 2012

Homebrew Hero - Homemade NBTV video recording system in 1974

What do you do in 1974 if you are 20 years old and want to send video to other Amateur Radio operators?

An off-the-shelf home-video camera was the equivalent of $8000 USD (if you could find one) and the circuitry required to transform the high bandwidth signal into one that could be transmitted on AM would have been prohibitively complex.

Believe it or not the only solution was to build your own narrow band video camera! These creations followed on from narrow band television work done in the 1930's and took advantage of advances in materials and solid state technology.

The camera used by VK3AML (Chris Long) in the video below was a Flying Spot Scanner camera which required a completely darkened room and used a spot of light that scanned the scene. The reflected light was picked up by a photomultiplier tube and recorded as a frequency modulated audio tone on tape or broadcast via radio.

We're fortunate to have some of the original video preserved from 1974 since the audio and video signals had been recorded onto open-reel tape.


The 30 line television system developed by John Logie Baird in the 1930s allowed home experimenters to build their own equipment, a practice which still exists today through the Narrow-bandwidth Television Association. Relatively few narrow-band TV signals are transmitted nowadays so most amateur radio operators are unaware of this special interest group.

The video below shows some of the actives and projects that members of the Narrow Band Television Association have been involved in and gives some historical background on this interesting field.



Chas (WA1JFD) from the Antique Radio forums mentions that at approximately the same time other amateur radio operators such as Donald Mara (WA1PLT) were experimenting with Slow Scan Television (SSTV). SSTV sent higher resolution pictures at a slower frame rate, typically taking 8 seconds to send a complete image. Below is a picture of some of the first commercial SSTV equipment that was made available to US hams.

Robot 70 (monitor) & 80 (camera) SSTV system introduced in 1970
I wasn't able to find exact prices for SSTV equipment like the ROBOT 70 & 80 but period articles seem to indicate you wouldn't get much change from $1000 in 1970 for a complete SSTV station. This is equal to around $5000 USD today.

Friday, January 13, 2012

An oscilloscope clock - Recycling vintage equipment without destroying it.

As a fan of vintage electronics, and vintage technology in general,  I love to see things being re-used rather than being dumped in the trash. This has the very desirable effect of preventing sometimes toxic chemicals from being released into the environment and reduces the demand for new parts that can also involve toxic chemicals during their manufacture.

The only downside to this recycling is that frequently the original function of the equipment is lost so I was pleased to see this creation from Bob Alexander. He has combined one of the oldest types of test equipment with some of the newest microprocessor based devices to bring us a Oscilloscope Clock that still functions as an oscillloscope!

Heathkit oscilloscope with AVR Oscilloscope Clock module
Bob ran into some problems while installing the AVR Oscilloscope Clock Module but was able to invert the horizontal output from the clock module before feeding it into the scope. To read about his build in detail have a look at : An Oscilloscope From the Trash

A small modification to the rear panel to allow setting the clock and switching between clock and scope.
Check the video below for a demonstration of the Sparkfun AVR Oscilloscope Clock Module in action on a significantly newer oscilloscope.

Thursday, January 5, 2012

Winter Field Day and generators

With Winter Field Day coming up some radio operators may be running your stations using gas/petrol generators. While you can just drop the generator down outside and start it up you really should, for safety, have a ground rod set into the earth.
Although the system below does have a ground rod placed in the earth I'll leave it to you to discovery why it is not going to be very effective ...

Not the right way to ground a generator system, "A" for effort though.

Cheap accessories can damage your expensive electronics

The power supply below looks just like a normal Canon power supply, right down to the correct model number and style. If you dig deeper, or just try and use this power supply, you start to notice things aren't exactly what they appear to be.


It seems as though there are some great deals to be had on Ebay for electronic accessories but like the saying goes, "You get what you pay for!".
Giorgos discovered the difference when his Canon camera started behaving strangely and was fortunate enough to have the experience and the test equipment to show just how poorly his bargain power supply performed.
So, before you buy a cheap power supply or battery charger for your cell phone, camera or iDevice, check out the video below and decide for yourself if its really worth saving a few dollars.

Monday, January 2, 2012

Deathrays and the garage home-brewer

In days past home-brewers would often be at the forefront of new and developing technologies. Apple Computer got their start in a suburban garage, Marie Curie refined radium in little more than a garden shed and the founders of Hewlett Packard worked out of a home garage in Palo Alto.

Unfortunately we moved away from encouraging kids to "tinker" in the garage and instead we've supplied ready made entertainment in the way of game consoles, demographically targeted TV and an endless series of extra-curricula activities ... all ultimately aimed at preventing boredom and keeping kids busy.

To see some impressive tinkering, take a look at this great build from Teravolt.org. Its certainly something that could be dangerous if used incorrectly but the assumption that something is unsafe unless proved otherwise and the knowledge to know the difference is sometimes better that relying on a commercial manufacturer's assurance that everything is ok ... because sometimes it isn't.

X-Ray Machine from Teravolt.org
I don't think well raised kids will take to the streets in rampaging mobs if they are allowed to become 'bored' and I think there is the possibility that through their inventiveness they will discover and create things we haven't even imagined. Given the tools, basic education & a measure of respect we could see more garage pioneers in the coming years. While I understand the value of robot kits and 'following directions' I am more enthusiastic about the Maker movement and the great selection of micro-controllers and electronic building blocks they have created.

Looking through a hard-drive using the Teravolt.org X-Ray source

Saturday, December 31, 2011

New video from ARRL : The DIY Magic of Amateur Radio

From the ARRL:
ARRL's new video, "The DIY Magic of Amateur Radio," is an 8-minute video that follows some of the innovative, imaginative and fun ways "hams" use radio technology in new and creative ways. The presentation is directed toward the DIY (do it yourself) movement, which is inspiring a new generation of creators, hackers and innovators. The message should be helpful for existing members to shape the ways they understand and talk about ham radio.


Tuesday, December 27, 2011

What we can learn from a Mexican drug cartel.

The AP carried the following article detailing an extensive, low cost & flexible radio repeater system employed by a Mexican drug cartel to coordinate their operations. The system seems to exceed the sophistication of regular amateur radio linked repeaters while improving on independence from grid power. America's ham radio community has the required technology, know-how and government support to upgrade our repeater systems ... what is stopping us from pushing the technology further?

Mexico's cartels build own national radio system



MEXICO CITY (AP) — When convoys of soldiers or federal police move through the scrubland of northern Mexico, the Zetas drug cartel knows they are coming.
The alert goes out from a taxi driver or a street vendor, equipped with a high-end handheld radio and paid to work as a lookout known as a "halcon," or hawk.
The radio signal travels deep into the arid countryside, hours by foot from the nearest road. There, the 8-foot-tall (2-meter-tall) dark-green branches of the rockrose bush conceal a radio tower painted to match. A cable buried in the dirt draws power from a solar panel. A signal-boosting repeater relays the message along a network of powerful antennas and other repeaters that stretch hundreds of miles (kilometers) across Mexico, a shadow communications system allowing the cartel to coordinate drug deliveries, kidnapping, extortion and other crimes with the immediacy and precision of a modern military or law-enforcement agency.
The Mexican army and marines have begun attacking the system, seizing hundreds of pieces of communications equipment in at least three operations since September that offer a firsthand look at a surprisingly far-ranging and sophisticated infrastructure.
Current and former U.S. law-enforcement officials say the equipment, ranging from professional-grade towers to handheld radios, was part of a single network that until recently extended from the U.S. border down eastern Mexico's Gulf coast and into Guatemala.
The network allowed Zetas operatives to conduct encrypted conversations without depending on the official cellphone network, which is relatively easy for authorities to tap into, and in many cases does not reach deep into the Mexican countryside.
"They're doing what any sensible military unit would do," said Robert Killebrew, a retired U.S. Army colonel who has studied the Mexican drug cartels for the Center for a New American Security, a Washington think tank. "They're branching out into as many forms of communications as possible."
The Mexican army said on Dec. 4 that it had seized a total of at least 167 antennas, 155 repeaters, 166 power sources, 71 pieces of computer equipment and 1,446 radios. The equipment has been taken down in several cities in the Gulf coast state of Veracruz and the northern states of Nuevo Leon, Coahuila, San Luis Potosi and Tamaulipas.
The network was built around 2006 by the Gulf cartel, a narcotics-trafficking gang that employed a group of enforcers known as the Zetas, who had defected from Mexican army special forces. The Zetas split from the Gulf cartel in 2010 and have since become one of the nation's most dominant drug cartels, with profitable sidelines in kidnapping, extortion and human trafficking.
The network's mastermind was Jose Luis Del Toro Estrada, a communications expert known as Tecnico who pleaded guilty to conspiracy to distribute cocaine in federal court in Houston, Texas, two years ago.
Using millions of dollars worth of legally available equipment, Del Toro established the system in most of Mexico's 31 states and parts of northern Guatemala under the orders of the top leaders in the Gulf cartel and the Zetas. The Gulf cartel boss in each drug-smuggling territory, or plaza, was responsible for buying towers and repeaters as well as equipping his underlings with radios, according to Del Toro's plea agreement.
Del Toro employed communications specialists to maintain and run the system and research new technology, according to the agreement.
Mexican authorities, however, presented a different picture of the cartel radio infrastructure, saying it was less monolithic than the one described by U.S. authorities. A Mexican military official denied that the army and navy have been targeting one network that covered the entire Gulf coast. The operations had been focused on a series of smaller, local systems that were not connected to each other due to technical limitations, he said.
"It's not a single network," the official told The Associated Press on condition of anonymity due to the sensitivity of the topic. "They use it to act locally."
In recent years, reporters traveling with the Mexican military have heard cartels using radio equipment to broadcast threats on soldiers' frequencies. The military official told the AP that the signals are now encrypted, but cartels are still trying to break in.
At least until recently, the cartel's system was controlled by computers that enabled complex control of the radio signals, allowing the cartel to direct its communications to specific radios while bypassing others, according to Grupo Savant, an intelligence and security consulting firm in Washington that has firsthand knowledge of Mexico's cartel operations.
The radio system appears to be a "low-cost, highly extendable and maintainable network" that shows the Zetas' sophistication, said Gordon Housworth, managing director of Intellectual Capital Group, LLC, a risk- and technology-consulting firm that has studied the structure and operations of Mexican cartels and criminal groups.
Other Mexican criminal organizations maintain similar radio networks, including the Sinaloa cartel, based in the Pacific coast state of the same name, and the Barrios Azteca street gang, which operates in Ciudad Juarez, across from El Paso, Texas, a U.S. law-enforcement official said. The Zetas' system is the largest, however, the official said, speaking on condition of anonymity because of the sensitivity of the topic.
The Mexican raids are "a deliberate attempt to disrupt the business cycle of the cartels," said one former law-enforcement official with direct knowledge of the network. "By going after command and communications you disrupt control."
Law-enforcement officials and independent analysts described the operations against the Zetas' communications system as significant short-term victories in the fight against the cartel.
"The seizures show that the organization is scrambling," said Steven Dudley, co-director of InSight, a group that analyzes and investigates organized crime in Latin America.
The longer-term impact is unclear. The cartel has had little difficulty in replacing radio gear and other equipment seized in smaller operations in recent years. And contacts among the highest-ranking Zetas operatives tend to take place in highly encrypted communications over the Internet, according to Grupo Savant.
Certainly, cartel radio equipment is a near-ubiquitous presence for Mexicans living along the front lines of the drug war.
In the state of Tamaulipas, across the border from eastern Texas, many antennas are concealed in the foliage of the rockrose, an invasive shrub that has spread across much of the state's open land.
Even from a few feet (meters) away it's nearly impossible to see the towers or their power cables.
In Nuevo Laredo, the Zetas' first stronghold, antennas sprout from rooftops and empty lots. One soldier told the AP that even when authorities took down an antenna there, it was swiftly replaced.
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Associated Press writers E. Eduardo Castillo in Mexico City and Efrain Klerigan in Victoria, Tamaulipas, contributed to this report.

Thursday, December 22, 2011

Coil Winding using the Gingery Coil Winder

Anyone who has seen the video below from KC9KEP will probably be wondering where he got the coil winder used to make those high Q coils with universal windings.


The design itself is based on the Morris Register Company (MoReCo) Coilmaster and modified for home brewing by Dave Gingery. His excellent book is available from lindsaybks.com and provides plans that use parts and tools commonly available in the home workshop.

Gingery coil winder by KC9KEP
Another resource for coil winders is a page from K5BCQ that shows the original Coilmaster, a different home brew plan and a large volume of useful information.
A vintage text is also available which covers inductor (coil) design in significant detail and should be downloaded by anyone who REALLY wants to know what they are doing. It is available here.