10 000 visitors and counting

Two years after I first published my SteppIr BigIR Mrk III dissection / review page , the web counter is at 10 000 visitors (only unique IPs). It is a small aniversary and makes it worth all of the effort to create the web page! Enjoy!

It's a boy!

For lack of better words - the happiest day in my life! Today, Jan 28, 2010 at 4:26 Eastern Time my first harmonic - Vichren Andrey-Endri Stoev was born! He is 9 lbs 3 oz and 21 inches in length. Absolutely a MIT (or Cal Tech - have not decided yet who is going to have the honour ;-)) material - one can tell from first sight! (His crib is furnished with the basics - netbook, shortwave transceiver and CW trainer). Mother and baby are doing very well!

BulbDial Clock

The idea about an "Indoor Sundial Clock" is not a new one. There are many patent applications filed over the years (some dating back to 70s), describing such devices. It is one of those "how come I didn't think of this" type of ideas - simple yet brilliant. David Friedman of ironicsans.com described such device with a nice illustration (he might have come to this idea independently from the other inventors or not, but he is one of the first with a nice visual instead of the boring wording in patent applications). That's how the name of this clock came about - The Bulb Dial Clock. It was only natural, this idea to be picked up by Evil Mad Science and turned into a really nice kit. The kit is based on the Arduino platform, using Atmel AVR controller (ATmega168). When I saw the kit, I knew I had to have it - such a brilliant idea as a very well executed project = a must-have cool gadget!
I ordered the kit from Evil Mad Scientist as soon as it was made available.

The kit quality is simply superb. Extremely high quality PCBs and components! Everything is absolutely "top-notch", including the nice laser-cut enclosure (available in a few different styles). All components are sorted by type in labeled plastic bags and packed very well. Included in the kit are a few spare parts - LEDs and mounting hardware. The manual is not provided with the kit - it is available for download and it can be printed. A few words about the manual - probably the best kit manual I've seen lately (maybe even over-done) and it beats Heathkit! The kit is designed for beginners and the manual even includes a section on soldering. If you never held soldering iron, you should be still OK - just follow the instructions.

The build is straightforward. The most tedious part is installing and aligning the 72 LEDs located on 3 PCBs. This is the main BLUE PCB - it includes 30 blue LEDs for the "seconds hand" as well as the AVR controller and most of the components. The clock has 2 seconds and 2 minutes resolution - in other words - the "seconds" hand moves every 2 seconds and the "minutes" hand - every 2 minutes. This is actually not too bad - imagine dealing with 132 LEDs for full resolution - it would be crazy ! When LEDs are switched on, it can be done with "fading" which gives a nice smooth "analog feel" and makes up for the 2 seconds resolution (it actually interpolates the "in between" state)

There is a connector for accessing and re-programming the ATmega chip. I wish they had provided a socket for the IC in the kit. I felt that it is much safer to play with the firmware if the PIC was socketed, so I added a socket. There is also a provision for an on-board IC voltage regulator should one decides to use non-standard power supply. The design is very simple - ATmega168 chip, crystal oscillator (20ppm), a few current limiting resistors, 3 buttons and a charlieplexed matrix of LEDs. The source code for the firmware is open and the schematics are freely available for download - all in the spirit of the Arduino platform.

This picture shows the main board with the nice "bulbdial" face installed on stand-offs. There is machined gnomon in the center which casts the "shadow hands" The GREEN PCB is for the "minutes" hand and it has 30 green LEDs. The picture also shows the special laser-cut "LED leads forming tool" . All LEDs need to be pointed downward and aligned to produce nice centered hot-spot. There is an alignment mode in the firmware to assist this task. One should gently bend the LEDs. Sometimes it is necessary one of the solder joints of the LED to be heated with the soldering iron, while aligning the LED body in order to reduce the mechanical stress.

This the last of the 3 PCBs - the "hour hand" RED PCB. It has 12 red color LEDs.

The little circular board in the center of the picture is the optional ChronoDot. This board contains a high-accuracy real-time clock (RTC) based on the DS3231 chip. This option improves a lot the accuracy of the Bulbdial clock - without it the clock will drift aprox. +/- 2 min per month. With the ChronoDot, the clock will be accurate to +/- 2 minutes per year. This high accuracy is achieved by the built-in 2ppm Temperature Compensated Crystal Oscillator (TCXO) inside the RTC chip. The ATmega firmware will automatically detect if the ChronoDot is installed and will start using it instead of the software timers. One added benefit of the ChronoDot is the 3V Lithium battery on the back of the PCB (not visible)- it is good for up to 8 years and keeps the time even when the clock is powered down.

This is the completed PCB assembly. The LEDs of each board must be aligned before the next board is added to the stack. Power supply adapter is provided with the kit. The clock can also be powered with the optional programming cable (USB-TTL-5V) but only if the power supply is not connected. There is no ON/OFF switch. The Z (sleep) button is on the bottom side which is not the most convenient place - I wish the buttons were more accessible.

All 3 boards are inter-connected with 10 zero-ohm resistors (jumpers) and held together with threaded stand-offs and stainless steel hardware.

There are 4 modes of operation - Time Displaying Mode, Time Setting Mode, Alignment Mode and Optional Configuration Mode. The modes are selected by pressing and holding combinations of buttons. Once the clock is powered, it goes into Time Displaying Mode. In this mode the Z button is Sleep ( it turns off the display) and "+" and "-" control the brightness level.

There are a few different case styles offered with the kit. The case by itself is an optional item. The enclosure is made of laser-cut acrylic for the front and back faceplates and thin, flexible plastic elements for the sides to create the classic "mantle clock" look.

If all LEDs are properly aligned, the gnomon in the center will cast nice centered shadows in the LED's hot-spots. Because of the height of each LED ring above the face plane and the angle of the LEDs, each of the three shadows has different length much like the hands of a real clock. The kit that I got is with RGB LEDs but it is also offered in a "monochrome version" using only white LEDs for yet another style.

I just couldn't resist the "geeky" look with transparent front plate to show off the internal construction. IMHO it looks very cool, with a futuristic "tech feel"!

There are 7 user-adjustable brightness levels and even a "white balance mode", where the brightness of each color can be adjusted separately. At the highest brightness level the clock could almost serve as a night light. All of the configuration variables are stored in the ATmega's eeprom space. There is also a user-selectable "rear-projection mode" where the movement is reversed (CCW) in order to be viewed through the back if the clock is equipped with a semi-transparent face.

The Bulbidal clock is a fun project and the resulting clock is just beautiful to look at.

A very exciting day!

Today, I got the chance to personally meet and chat with the person who is responsible for my career as a computer engineer - the co-founder of Apple Inc. and the engineer who designed the famous Apple I, ][ and III - Steve Wozniak! The guy is practically a legend! Back in the early 80s when I was teenager, I had a poster of him on my wall. Applesoft Basic was my very first programming language! My second one - Assembler for MOS 6502. The first computer hardware I designed was for Apple II. Currently, Steve is the Chief Scientist of Fusion-IO - company creating a revolution in the data storage technology utilizing nano-flash memory. Today, they announced their partnership with IBM as their ioMemory technology will be used in IBM's family of System X servers.

It was only fair to show Steve how the Future meets the Past as I handed him my Apple II CFFA project card - a SSD (Solid State Drive) based on CF card for the Apple II family. This project was developed by Richard Dreher - a firmware engineer at Cray Inc.

This is my CFFA 2.0 card - I have 90% of my entire collection of vintage Apple II software on the CF Card! (yes! games too - who can live without a weekly game of Pac-Man or Space Invaders). The CFFA (Compact Flash For Apple) supports directly ProDos and GS OS partitions and also supports DOS 3.3 volumes via Dos Master.

Well, the card is now officially "Woz" certified! :-) Steve was very impressed with this piece of hardware (tnx Rich!!) but couldn't resist asking me the question - "Why do you guys, do this? What is it about the Apple II?" My answer was - "I hoped that you'll be one of the few who can understand it, Steve".

My collection of Apple IIgs computers - the bottom one is a ROM03 machine. The top one - ROM01, Limited "Woz" edition and now *Ultra* Limited edition with the real signature of the Master!

The "Owner's guide" for my Apple IIgs signed in the spirit of "Apple II Forever" :-)

N2PK VNA - LLC calibration standard

The RF-IV sensor is very useful for performing measurments of high-Q devices. To improve the accuracy of such measurments, an extra calibration step is required - LLC or Low-Loss Capacitor calibration. It "provides reference of impedance with an accurate 90 degree phase angle in place of the 50 Ohm LOAD standard". A good read about the RF-IV method is this Agilent document. There is also a very informative application note from Agilent about High-Q measurements. MyVNA software allows for this calibration step since ver. 0.47. LLC calibration requires a special calibration standard - capacitor with very low ESR and very high Q (>10 000). Paul, N2PK recommends the use of a few loads which are "impedance of -j50 at the center of frequency range and maybe a 4:1 freq range - i.e. from Fc/2 to 2*Fc" or 3, 10 and 30 MHz for example. "Another option is to use a cap that has about the same reactance as an inductor whose Q is to be measured".
MyVNA software has a built-in model for the ATC 100B series (Porcelain Superchip Multi-layer) capacitors by American Technical Ceramics . These capacitors are ultra-stable, low ESR, High Q and low noise, specifically designed for microwave use. The accuaracy of the capacitance value is not extremely critical since the software allows you to enter the frequency at which the cap is expected to have -j50 impedance and correction can be made there. I followed Paul's example and made 3 calibration standards centered at frequencies close to 3, 10 and 30 Mhz using standard values available by ATC. The construction technique for the standards is exactly the same as the one I used to prepare my other BNC calibration standards (described here).

This picture shows the "30 Mhz LLC standard", using two 47 pF (tolerance 2%) ATC 100B capacitors in parallel for a total value of 94 pF (the impedance is -j50 at proximately 33.85 MHz).

N2PK VNA - RF-IV Sensor

Finding an enclosure for the RF-IV sensor turned out to be a real challenge. As I mentioned before, because of the size and connector locations of the RF-IV PCB, there are not that many off-the-shelf boxes that were a good fit. I wanted a box that will allow me to install the sensor directly on the VNA's BNC ports (2" apart) and with enough height to install the corresponding bulkhead connectors. I was almost ready to go the CNC machine route and fabricate the enclosure out of a solid block of aluminum. I wanted the sensor enclosure to be compact since it is supported only on the two BNC connectors. After some more searching though, the Bud Industries CN-5701 box (Digikey p/n 377-1512-ND) seemed to be a possible candidate. I still had to use a vertical mill machine to remove the little PCB slots on the inside of the aluminum box and make the walls nice and smooth.

This picture shows the box with a bushing for the control cable and the 3 bulkhead female SMA connectors. These connectors require a D-hole to prevent unwanted rotation. Initially, I was going to install male BNC connectors but decided in favour of the SMAs. They require less mounting hardware and I can always use adapters to BNC or N type connectors. In addition, the enclosure is small and installing regular 4 screws bulkhead connectors will prove to be a headache.

On the inside I installed two L-shaped supports / rails (formed out of tin-plated brass sheet) to create a "bed" for the PCB and solderable ground connection for the SMAs.

On the bottom of the box I placed a piece of FR4 fiberglass PCB material (I etched completely both copper layers using a mixture Hydrogen Peroxide and Hydrochloric Acid (1:2))

This board serves as an insulator and also acts as a spacer in order to raise the PCB from the bottom of the box and bring it closer to the bulkhead connectors. The two L-shaped tin-plated side rails go on the top of the fiberglass spacer board holding it into place. The RF-IV PCB goes on top of these rails.

The RF-IV PCB is installed in the aluminum enclosure. Small ferrite toroid is used for RFI suppression on the control / power lines. The RF DET SMA is connected to the PCB using a short piece of UT-085 semi-rigid coax. Small pieces of silver-plated jumper wires (in teflon sleeves) are connecting the PCB RF ports (RF DDS and DUT) to the bulkhead SMA connectors on the box. I was trying to keep them as short as possible. Unfortunately, with this enclosure I can't use RA PCB mount SMAs.The outer edge of the PCB's ground plane is soldered directly to the tin-plated brass sides (the L-shaped side rails on each enclosure side with SMA connectors installed)

I used tin-plated brass screens to create the internal RF shielding. It is important that there is a good RF screening between the RF DDS and DUT ports. Each sampling transformer has its own screened compartment. The L-shaped plates on the two sides with the RF connectors helped a lot with mounting the screens - I just soldered the RF shield elements to the sides.

This picture shows that the internal screening is raised about 1-2 mm from the PCB, allowing good clearance from the components and signal traces.

Picture of the completed RF I/V sensor. This is the side up for Detector 1 use but it can be used with either detector - exactly the same way the reflection bridge is used: just flipping the box and installing it on Detector 2 port (the reverse side of the box is marked for Detector 2)

N2PK VNA - Accessory Connector

The VNA software can control different accessories - like the S-Parameter setup or the RF-IV sensor. This means that some extra control signals and power have to be available thru an Accessory Connector. There are no available pins on the DB-25 connector and in addition it is not a good idea to have power supplied there anyway.
The Accessory Connector should be at least 6 pins if an S-parameter setup will be connected. I am not planing to build one at this point, so I need a connector with only 3-4 pins for the power and control signals to the RF-IV sensor. Most people are using the Mini-DIN connectors (like the ones used for the PS/2 keyboard or mouse) but I am not really fond of these connectors - this type connector does not provide very secure connection and can be easily pulled apart.
The connector I ended up using is HR10 (Hirose Electric) Digikey P/N HR1568-ND (female, panel mount) and HR1558-ND (male, plug). This is a much better connector than the Mini-DIN. It is available in 4 pin and 6 pin configurations, it is small and has a very nice locking mechanism.
It is not cheap by any means - a pair (male-female) will set you back almost $30 but it is very high-quality product (nice looking too).

The Accessory Connector installed on the back panel of my VNA. I am using only 3 out of the 4 pins. Maybe one day I'll make a new silk-screen for the panel and will mark the connector appropriately. The dust cap is Digikey P/N HR345-ND.

N2PK VNA - USB to Parallel interface

I am pretty happy with the Parallel port interface - it doesn't require any drivers and works just fine, but for portable applications using my netbook, i have no choice but to use USB interface. My netbook doesn't have PCMCIA slot or parallel interface so the only option is USB. A standard off-the-shelf USB to Parallel port for printer interface won't work. These converters are designed for printers use only and they don't have 100% parallel port support. Fortunately, Dave G8KBB designed a very nice interface based on the Cypress FX2 (EZ-USB) USB micro-controller (CY7C68013A).
For my project I used PCB from WB6DHW. His interface is a nearly identical clone of the G8KBB interface. To be honest, I am less than impressed with the PCB layout done by WB6DHW and I was almost ready to design my own board (G8KBB board is much better but his PCBs are not readily available). At the end of the day tho, I got the bare board from WB6DHW because of its low price - fabricating my own board was going to cost a lot more and wasnt worth it just for a single piece. All components are from DigiKey, including the Cypress chip and the Hammond die-cast aluminum enclosure housing the interface.

I had to modify (mill) the PCB in order to fit it in the enclosure. The PCB is raised on stand-offs since the Mini-B USB connector along with some other parts is on the bottom side. I prefer to have the much sturdier and more reliable USB - B version of the connector but there wasn't an easy way to modify this board. The Cypress FX2LP chip is in a package with fine pitch leads but it wasn't that difficult to solder it pin-by-pin under sufficient magnification. There was no need to install any of the other connectors - I just soldered the wires directly to the board. The enclosure is a tight fit and if I had the connectors installed it would have been dificult to manage the wires inside. The most time-consuming part in this project is wiring the board to the cable and the female DB25 connector according to the schematics and the table provided by Dave G8KBB.

This is the complete interface. It is rugged yet compact - the only delicate part to worry about is the Mini-B connector. The initial setup is a bit complicated - a Vendor ID and Product ID must be written in the EEPROM in order for the USB micro-controller to properly report the interface in Windows. To accomplish this task, a step-by-step procedure and a piece of configuration software are published on Dave's, G8KBB web site. First, special drivers are installed in Windows to get access to the Cypress FX2 chip and the EEPROM address space. Then, using "USB Configure" (by G8KBB), the appropriate IDs are programmed in the EEPROM according to the hardware in use - version of the interface/VNA and current demand (in case the USB is used also to power the VNA). This setup is one time deal - afterwards the interface is used with its regualar USB drivers.

N2PK VNA - RF-IV sensor PCB

I've completed the PCB for the RF-IV sensor. Now I have to come up with an enclosure. In addition, I have to install a mini-DIN connector on the VNA's rear panel with power and control signal for the RF-IV sensor.

The PCB is very simple and easy to work with. A thing to note is the slightly awkward placement of the RF connectors - it is needed to achieve certain level of port-to-port isolation. There are two transformers, one (on the left) takes the Current sample, the other (on the right) the Voltage sample - this part of the circuit is almost the same as in Larry's N8LP coupler for the LP-100. The DUT is connected to the RF DDS of the VNA thru the current transformer. The RF switches (Peregrine PE4220 ) are controlled by the software and switch the signal path of the samples to the RF DET input of the VNA. While the VNA takes a sample of the current (I), the voltage (V) transformer is terminated with 50 ohm load and vice versa. There is an on-board 3.3V voltage regulator supplying power to the RF IC switches. Only one detector is used in the VNA in this configuration which improves the stability and accuracy of the measurements as both -the I and the V samples are measured by the same detector alternatively at a high frequency. The control signal to switch between the samples is generated by the software and in this case is just looped thru the VNA.

Winding and installing the transformers is a bit tricky because of their construction and small size. One of the winding is done with very fine (AWG #36) wire. In addition, the current transformer (shown on the picture) has a grounded electrostatic shield between the primary and the secondary. Both transformers are attached to the board with tin-plated brass strips bent into U-shape. The strips provide RF screening and stress-relief at the same time.

VNA plots of my SteppIR BigIR

I posted a number of plots of my SteppIR BigIR Mrk III /w 80m coil on my antenna site.
All plots were generated with the myVNA software. Calibration of the VNA was performed at the far end of the 100ft feedline to tune-out the transformation effects of the transmission line.
The scan was done while the antenna was tuned for minimum SWR on the 20m band.
The graphs can be seen here