Pic-A-Star, the saga continues

Having decided to house the transceiver in the chassis frame of an old Tektronix  model 620 CRT monitor, and to use the Pic-N-Mix DDS unit as the control processor I needed to figure out how to fit that circuit into the confines of the frame.  I had obtained a bare board from Glenn, VK3PE, which had both the Pick-n-Mix and Status board circuitry on it, but the board was too wide to fit in the available space in the chassis frame, nor could it be cut into two pieces to do so.  So I ended up using Peter’s design as re-implemented by G6AK.

The Tektronix 620 monitor was a 6″ CRT XY monitor, the one I had no longer functioned and was deemed unrepairable due to critical parts no longer being available (at a reasonable price).  The chassis frame measured about 8″ wide by 5″ high and was about 17″ deep.  It consisted of machined front and rear panel frames mounted between 4 extruded aluminum rails.  The top, bottom, and side covers slid into slots in the rails.  My unit was an OEM model, which came without the covers, feet, or handle, and was intended to be built into the OEM’s product.  I had obtained the monitor from a former employer as dumpster salvage.  As the frame is deeper than I’ll need, I plan on cutting the four rails down, probably to a depth of between 12-15″, the actual length to be determined once I’ve built all of the necessary transceiver modules and test fit them into the available space.

PanelFront.JPGAfter removing the CRT bezel and the controls from the 620 front panel, I made a new panel insert to replace the bezel, and a dress plate for the control portion of the panel.  I wanted the various jacks and the audio gain control on the left hand side, so I’m using the 620 panel mounted upside down from the way it was originally built.  I etched the two PnM boards from the artwork by G6AK, and trimmed the boards down by about 3/4″ removed from the side where the home brew optical encoder was.  I’ll be using an available encoder unit from Oak-Grigsby.   The layout is a bit different from the way G3XJP intended it, I have the keypad and status board on the lower right hand side of the display instead of to the left of it, and the encoder knob underneath the display instead of to the right of it.  I’ve combined the functions of the four VFO indicator LEDs into two by using dual color LEDs, and I’ve added a dual color LED to indicate ‘Best IP3 mode’ and ‘Attenuator on’ functions in the place of one of the VFO LEDs.  The other vacated LED position will now be the DSP LED.  I had a large 12 segment, three color bar graph LED display in the junque box, it was mounted above the display and wired to the status board in place of the called for 1.8mm LEDs.  Since this display required more drive current than the PIC could probably handle, I added a small perf board containing 12 PN2222 transistors for the extra drivers.

PanelBack.JPGHere you can see the back side placement of the parts, minus the PnM boards.

PnMdisplay.JPGThe Pic-n-Mix display board designed by G6AK

PnMmain.JPGAnd the Pic-n-Mix processor board.
I added a second LM7805 regulator on the reverse side of the board, underneath the one on top to power the DDS circuit.  In this photo the LM7808 regulator for the Butler oscillator has not yet been installed, nor has the oscillator.  (The DIP IC’s also have yet to be socketed). I plan on using an On-Semi 340mhz LVPCEL oscillator to drive the DDS.  I got this part a few years back, it looks like it isn’t made anymore by On-Semi, but there are other similar parts still available in the same 5x7mm package.

These photos show work in progress, I still need to finish wiring up the front panel boards together, and then test/debug the Pic-n-Mix.

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Tools

Building your own radio equipment requires tools for soldering, and physical construction.  Everyone has their own preferences, I’ll discuss what I’m currently using.  I’ve collected quite the assortment of tools over the years, buying something new usually when the need for it arose with a new project.  Some of my tools have been in my possession for over 40 years or more now, a testament to how good things used to be made back then.

Soldering tools have changed quite a bit in the last 40 years.  Way before my time soldering irons were huge things, sometimes heated by a gas torch.  The heavy iron tip had to hold heat in to allow moving the tool from the torch stand to the work.  These things were used for soldering sheet metal, not electronics!  Smaller, electric powered versions of these ancient tools made in sizes of as much as 100 watts down to maybe 30 watts were common.  These early soldering irons took a long time to heat up, and were rather inefficient.

Then the soldering gun came along.  Rather than using a nichrome element to heat up the tip of the iron, the soldering gun had a directly heated tip made of heavy gauge copper.  It was heated by passing a low voltage, high amperage current though it, supplied by a step down transformer with a single turn secondary.  I still have the Weller Jr. 100 watt soldering gun that my father bought for himself, and then gave to me when I was in my teens.  Weller is still around today, and still makes similar soldering guns, but they’ve redesigned the clamps holding the tip to the gun.  The new clamps are cheaper to make, but the old system using heavy nuts instead of small set screws worked better.  Every time I find an old style Weller gun at a garage sale or ham flea market, I’ll buy it.

Soldering guns were fine for the point to point chassis wiring used on tube type equipment, but when printed circuit construction came along something less powerful was called for.  Lower powered soldering irons, sometimes called soldering pencils, were developed.  The latest generation having electronic temperature controls are referred to as soldering stations.  For surface mount work a hot air gun is used to heat the solder paste that is first applied to the board.  The hot air gun is required where a soldering iron cannot get to the small pads often underneath the parts.  There are two types of hot air guns, one has the variable speed blower built into the hand held tool, the other has an external air supply connected to the tool via a flexible hose.  Both kinds work equally well.   Special soldering stations, often called ‘rework stations’ combine a hot air soldering tool and a soldering pencil with separate controls for each.

I have both a Weller WES51 soldering station, and a ZENY 862D hot air rework station.  The latter is a Chinese made tool with a hot air gun (blower inside the handheld tool) and a soldering pencil.  The unit came with various sized hot air nozzles and soldering iron tips.  Both of these tools work reasonably well.

Also required are an assortment of hand tools to cut and bend wire leads, and to hold SMD parts while soldering.  I have several different wire cutters, including a flush cutter to snip excess leads close to the circuit board.  Various sizes of needle nose pliers, and tweezers, the latter for SMD work.  I also have a special cutter for #30 gauge wire wrap wire.  Wire wrapping was once a common method of wiring up a prototype circuit using special sockets with long square posts.  A wire wrap gun tightly twisted the end of a wire lead around the socket post actually making a better connection that soldering.  Parts in SMD, and dirt cheap printed circuit fabs in China have made wire wrapping go the way of the Dodo bird.  Wire wrapping wire is still made, it’s an idea gauge for bodge connections on circuit boards, for patching design mistakes in prototypes.

If you make your own circuit boards for one off projects you’ll need a way to drill out the board for through hole parts.  While they do sell drill bits made for this with standard 1/8″ shafts, I’ve found the kind usually available on Ebay from China to be quite fragile, often lasting for only a few holes.  OTOH, you can buy a set of wire drill bits #61 – #80 that will work as well, and seem to hold up.  Also  Harbor Freight  has a pack of miniature drills in sizes from 0.5mm to 3mm .   The four smallest sizes in this set will cover most through hole parts, and the larger sizes will find use as well.  At $4 it’s a bargain.

Drilling circuit boards with these tiny wire bits requires a drill press, and a high speed drill motor.  A Dremel moto tool with an adjustable chuck (instead of the standard single diameter clamp), mounted in the Dremel drill press is the ideal tool for this work.
I’ve also used a “standard” workbench drill press set on its highest speed (about 3100 rpm).  While not as fast as the Dremel  (which can get to 10000 rpm!) it does work.  Since the usual Jacob’s chuck supplied with these tools won’t clamp down on any bit less than 1/16″,  I obtained a small pin vise with a 1/4″ handle, and sawed off the end of the handle.  This is used to hold the desired drill bit (#61-#80) and is then chucked in the drill press.   The drill press in question is the Harbor Freight 8″ Central Machinery model.  It has a nice attached work light on a gooseneck mount.  I’ve replaced the supplied bulb with a screw in LED lamp.  It’s not a very powerful drill, but works well for this purpose, and for general drilling into aluminum or soft wood.
I also have Harbor Freight’s 29 piece Titanium drill set.  They work well into soft wood and metal.  As with any stuff from HF, wait till there is a good coupon sale before buying major tools. (Sign up on their website for coupons) I’ve seen the 8″ drill press for as low as $50, and the drill set for $10.

 

PC boards, Pic-A-Star

Having previously posted about building the Pic-a-Star transceiver, and making my own PC boards, I thought I’d show you a work in progress.  The two photos are of the band pass filter board.  Originally, the design used through hole capacitors and slug tuned inductors in the filters, however the Toko coils used are no longer available (except as hard to find NOS), although some builders have salvaged usable ones from old CB sets and rewound them.  I plan on using Toroids and trimmer caps, mounting these on daughter cards which will then be soldered to the BPF board instead of the Toko coils.

P1010502.JPG

This photo shows the ‘track’ side of the board with parts for the first two banks of filters mounted.  This board will perform the switching operation between filter banks, the actual filter parts to be mounted on daughter cards on the other side of this board.

P1010503.JPG

And this is the back side of the board.  Not much here; ground plane, pads where the daughter cards connect, and two bus lines for input and output.

The board was made using the process previously described using G3XJP’s artwork from the picastar project.  The ‘tin’ plating on the board is just a very thin layer of solder applied to the board with a soldering iron (paste flux rubbed on the board first).  This will help keep the copper foil from becoming tarnished.  Wish I had thought of doing that on the first boards I made!

 

DIY Printed Circuit Boards

I made most of the printed circuit boards for the Pic-a-Star myself.  I did get a few of them from Glenn, VK3PE, but the really hard ones to make, I did myself.  The artwork for these boards were downloaded from the project group, so I didn’t design the boards myself, I only fabricated them.  The process for doing this is what I’ll describe here.

The boards were made using the toner transfer process.  This involves printing the artwork with a laser printer onto a medium that allows heat transferring the printer toner onto a blank copper clad PC board.  There are several ways this can be done.  Glossy magazine paper can be used as a transfer medium (the print on the paper won’t be a problem, though it can be difficult to see the outline of the laser printed image on top of the magazine print sometimes).  Others have used various brands of glossy ink jet photo paper as a transfer medium.  I have good results with the Techniks ‘press and peel’ transfer sheets, available from AllElectronics.com .

The toner transfer process is simple enough.  Print the artwork onto the transfer medium with the printer set to a dark setting (but not so dark as to smear the image).  Make sure that the artwork is a mirror image of what is actually required.  You may have to use an editor such as Micro Soft Word, or Libre Office Draw to print the image, first using the editor to ‘flip’ the artwork from left to right.  In the case of the PicaStar artwork, the image files were already reversed, and ready to be printed.

The circuit boards must be cut to size, and cleaned to perfection.  There are many techniques that may be used to cut the PC board to size.  Common tin snips work, but can slightly deform the edges of the board.  You might need to cut them a bit over sized and then file the edges straight.  Wear a dust mask when filing fiberglass PC boards, the dust is an asbestos like health hazard.  I recently discovered a neat way to cut PC board easily.  First score the board where it is to be cut using a Stanley knife.  Use a metal straight edge to guide the knife blade, and make several light passes with the knife until you have cut all the way through the copper.  Score the board on both sides.  Now you can just snap the board cleanly along the score.  I used a Harbor Freight bending brake to snap the board.

Use a fine grade of steel wool with a bit of kitchen scouring powder (Ajax, Comet, Bon Ami) and water to get the copper surface of the blank board clean.  Dry the board, and then use some rubbing alcohol or paint thinner to remove your finger prints from the surface of the copper.  Now cover the boards with paper toweling until ready to use.  Cut out the desired image from the transfer sheet and place it on top of the board so it lines up.  Use a hot clothes iron to press the image onto the board.  Use downward pressure rather than an ‘ironing’ motion.  You may need to experiment to find just how long you need to keep the iron pressed down on the transfer to get it set.  Too much pressure may cause the image to ‘bleed’, closing up the traces.  Not enough pressure and parts of the image won’t transfer.  Allow the board to cool back down to room temperature before attempting to peel the transfer sheet off.  If you are using the ‘press and peel’ sheets you can attempt a second pressing if you see an incomplete transfer when you peel up a corner.  If you are using the magazine or photo paper you’ll have to run the board under warm running water to soak off the last of the paper, as it usually peels off in layers.  Soaking the board in soapy water might help.

Now for the etching.  If you are trying to make double sided boards (two artworks, one per side) we will do the entire process twice.  Two toner transfers, and two etchant runs.  Spray the other side of the board with some spray paint to protect it while you etch the current side.  Ferric Chloride is the time honored chemical used to etch PC boards, but I’ve discovered a better way.  I use a solution of Hydrogen peroxide and Muriatic acid (2 parts H2O2, 1 part Muriatic acid, pour the acid into the peroxide when diluting).  Muriatic acid is a specific dilution of Hydrochloric (HCl) sold by swimming pool supply houses for PH adjustment.  Etch the boards in a glass baking dish (some plastic containers may work too, if the plastic turns milky white from the acid it’s the wrong kind!).  Slowly rock the container to agitate the etchant to speed up the process.  The nice thing about using the HCL-H2O2 solution is that it is clear, you can watch the copper disappear and stop the process when done.

After the etching is done, rinse the board in cold water to remove all traces of the acid bath.  Now drill out the board where required.  If you are making a double sided board, you can just drill a few holes in the corners of the board.  Remove the spray paint from the back of the board (double sided), and clean it like you did the first time.  Repeat the toner transfer for the second side, use the holes to align the back side image with the front, perhaps using pins.  Again apply the hot iron and transfer the image.  Spray the front of the board with the spray paint to protect it, etch, rinse etc.  Remove the spray paint from the front side, drill out all of the holes, and clean off what remains of the toner.

The final work is to clean up the board.  You’ll probably find some traces that didn’t completely etch out, resulting in shorts between them.  Remove these with a sharp hobby knife.  You may also need to repair any traces that are open with fine wire and solder, but wait to do this until you are soldering your parts on the board.

To protect the copper from oxidizing we can ‘tin’ it.  There are chemical solutions for doing this, but we can just use solder.  Wipe the board with a paste flux, and then apply a very thin layer of solder to all the copper.  I use a flat soldering iron tip for this.  Apply a bit of solder to the iron tip and then wipe the board with it.  A small amount of solder will spread over a large amount of the board surface before you need to add more to the iron tip (if you have first applied the flux to the board.)  Done right, you won’t create any solder bridges, even between very close traces, the solder will tend to stick only to the fluxed copper surfaces.

Double sided boards require ‘vias’, ie plated through holes to connect traces on one side of the board with the other.  For DIY boards, we just use jumpers, which can be the leads of our parts soldered to both sides of the board.  The PicaStar artwork used both methods, the parts placement artwork showed which holes had to be soldered on both sides.  This included some IC sockets.  Augat sockets are raised off the surface of the board by individual pin sockets, they can be soldered from the top if there is enough spacing between them and other parts to get the tip of the soldering iron in.

 

 

The Pic-a-Star project

joined the Pic-a-Star Yahoo group about 8 years ago with the intent of building one of these rigs.  The ‘Star is a DSP transceiver designed by G3XJP, and was first written up in the RSGB Radcom magazine around 2003.  Picastar has been called a software defined radio, but is such only from the final IF stage onwards.   In this regards, its design is similar to many ‘IF DSP’ radios from Icom, Kenwood, and Yaesu.  It’s a dual conversion scheme with a first IF (as designed) of 10.7mhz and a second IF of 15khz.  Users can pick a different first IF frequency (8-9 mhz usually) to suit available roofing filters by swapping out a crystal in the second conversion oscillator and changing some software constants in the DDS unit that provides the first conversion injection.

The project was under continuous development until sometime around 2009.  The project was supported until recently on the Yahoo Picaproject users group, but Peter has pulled down all of the software and hardware design files from the group sometime last year, effectively shutting down his support and involvement in the it.  With many of the parts (especially the DSP processor and the codec chip) reaching end of life, there are few new builders of this rig.  The design might be long in the tooth hardware wise, but a new improved DSP software set was developed about two years ago.  (I wasn’t able to help beta test this as my unit wasn’t finished.  Now with Peter pulling the plug, I don’t know if I can obtain this new software.  The original DSP code from ten years ago is still functional however.)

Originally, building the Picastar required the builder to etch and drill his own printed circuit boards, however VK3PE has designed several different sets of professionally manufactured blank boards which he has made available on a dead cost basis with G3XJP’s permission.  I have built my own boards for both the DSP (three pcb’s) and the IF from Peter’s artwork.

As designed by Peter, the rig is controlled from his Pic-n-mix DDS unit which was also described in Radcom.  The entire article for this was reprinted by Analog Devices as an AP note for their AD9850 DDS chip.  Peter’s UI using the Picnmix controls EVERYTHING in the rig from a standard 12 key ‘telephone’ keypad and a rotary encoder.  The rotary encoder is used to tune the DDS vfo, but it is also used to vary dozens of parameters such as AF and RF gain, keyer speed, vox settings, etc.  Which of these parameters is being adjusted is selected by multiple presses on the keypad.  Some settings can be made using only the keypad via direct numerical entry.  Everything is displayed by a single six digit seven segment LED readout.

While fully functional, this bare bones UI is extremely unconventional, and requires memorizing numerous key press combinations, or constant use of a ‘cheat sheet’ reference to control the radio.  Many builders of the Picastar have opted to use a related project, the TRXAVR controller.  This AVR based DDS unit also has a keypad and a rotary controller, but makes use of an LCD display to present the UI.  Various graphical and textual LCDs can be used, along with a touch screen display.  Multiple additional rotary encoders can be added, each one dedicated to a single parameter.  The front panel of a TRXAVR equipped ‘Star will more closely resemble the usual ‘store bought’ rig then the home brew design of G3XJP, though it will have the same performance factors.

I originally planned on using the TRXAVR controller with a 192×64 graphical LCD display.  This would have required my modifying the code for the 128×64 graphical LCD to make use of the wider display.  However there was a problem, the TRXAVR design makes use of a PC based program called Hobcat to configure and load the Star software and parameter files.  Hobcat is a Windows program based on the Delphi Pascal runtime system.  It won’t run natively on Linux (it might work via WINE though).  Peter’s Picnmix code is also configured via a PC utility, but he wrote his in Quick Basic.  At least I can run QB natively on Linux via dosbox.  TRXAVR is quite a bit more complex than the Picnmix, both in hardware and software.  Using it would have required more work in customizing the software to my liking, as well as finding a solution to the problem of getting Hobcat to run on Linux.  (I could have run a copy of Windows under a VM on Linux, or used a dual boot setup).

For various reasons (including the mental roadblock of the TRXAVR vs Picnmix), I set the STAR project aside for several years.  I had also got involved with 3D printing, designing and building my own 3D printer.  Now that that project has reached a point where only software updates are necessary, I dug the completed Star DSP and IF assembly out of storage.  I was able to re-verify that the DSP module still works, and was finally able to ‘smoke test’ the IF assembly.  I injected a 10.7mhz signal from my GDO into the IF input, and heard the beat note from the DSP board through an external stereo amplifier and speakers.   The next step will be to build the front end BPF and bilateral mixer modules, then I’ll have a working receiver.  The transmit portion comes after that requiring a power amplifier chain and a LPF, along with the necessary TX/RX switching.

I’ve also decided that Peter’s PNM DDS unit will be used as the front panel.  It may be a bit too bare bones for my liking, but it will be a quick way to get the radio working.  I can always build something else later, reverse engineering the DSP API while using the PNM to control the rig.

dspboards_back

dspboards_front

As I mentioned earlier, I etched and drilled the boards for the DSP and IF units myself.  Toner transfer was used for the resist, printed from an HP laser jet printer onto special iron on transfer sheets.  Above are photos of the boards after etching and drilling, before any parts were mounted.  Some additional cleanup with a hobby knife was required before soldering after I checked the traces for shorts and opens.

SONY DSC

Here is a photo of the DSP motherboard and the processor board after soldering the parts on.

IF_DSP

Finally on the right is the DSP motherboard with both the processor and codec board added, and on the left is the assembled IF board.  The DSP board was later mounted with spacers under the IF board, and the two were interconnected via shielded wire.  Several of the trimmer resistors on the IF board have been changed out since the photo was taken.

High Pressure Sodium security lamps

The familiar yellow-orange glow of outdoor high pressure sodium lighting have been around for about a half a century now.  HPS street lamps replaced the harsh blue-white Mercury Vapor HID bulbs that had previously replaced high power incandescent lamps before them.  Each advancement in lighting technology was more efficient than the one before, as well as offering longer bulb life, and better illumination.

Some people have thought that the poor color rendition of the Sodium lamps was a step backwards from the Mercury vapor lamps, and indeed Mercury lamps are still in use in industrial settings.  However, the Sodium bulbs have an often overlooked benefit, their warmer color does not havoc our circadian rhythm as the blueish Mercury light does, which can induce sleepiness during prolonged exposure during long nighttime road trips.

Today, LEDs have been replacing the HPS HID lamps when cities install new streetlights or upgrade older equipment.  Replacement parts are still available for the older HPS lamps, in many cases bulb replacement, and fixture repair are still less expensive than out right replacement of the equipment with newer LED lamps.  While the LED equipment is more efficient than the HPS, the difference is actually small, so the savings in cost to operate would take years to recoup.

When my wife and I moved into our house nearly twenty years ago, I installed a HPS HID barn lamp over the entrance to our garage where it lights up our driveway.  During that time I’ve replaced the bulb only three times, even though it burns all night, 365 days a year.  That’s an average life of 5-6 years per bulb.  I’ve also had to replace the igniter twice.  That’s a small circuit that performs the same function as the old fluorescent lamp starter, sending a pulse of high voltage to spark the bulb into conduction when power is applied.  The original igniter lasted over 15 years, the first replacement, barely 2.  Cheap, replacement parts from China.

When the lamp failed to start again a few days ago, I broke down and ordered a new LED fixture.  I did a post mortem on the HPS fixture, and it seems that this time the photo cell has failed, not the igniter, as I had assumed.  If I’d known that, I might have ordered a new sensor as the repair could be done without removing the fixture from the house.  Still, the new LED lamp should last me 20 years, if the 50000 hour life expectancy is correct, even if I have to replace its photo sensor some time.

Maintenance of HPS lamps is easy, so if you have one of these fixtures you might chose to keep them going.  The bulbs will give off less light as they age, but the process is so slow that your eyes won’t notice it.  The dead give away for a bulb that needs replacement, is it blinking on and off every few minutes.  The bulb starts off with a blueish color as the Mercury vapor starting gas fires on lamp start.  As the bulb heats up the Sodium starts to conduct, adding its yellow-orange light to the mix.  However, when the bulb ages, the vapor pressure inside the lamp falls off, and the Sodium stops conducting as the temperature inside the lamp rises.  When the bulb cools enough the igniter fires again, and the lamp restarts, for the cycle to begin again.  If the bulb isn’t replaced, eventually the igniter will self destruct from over work.

The ballast is a large transformer, or inductor inside the fixture that limits the current flow into the bulb.  It must be rated for the correct wattage to match the bulb.  This current limiter is necessary because a HID bulb appears as a negative resistance.  Ballasts rarely burn out, to test one you can screw an incandescent lamp into the socket in place of the HID bulb, and cover the photo sensor with some black electrical tape.  If the bulb lights, the ballast is good.  If not, you’ll have to check the sensor to be sure that that ballast is gone.

The photo sensor operates backwards from what you’d think.  The photo cell controls the current to a relay.  When light hits the cell its resistance is low and the relay pulls in.  The relay is a Normally CLOSED type, meaning that when the relay pulls in, the circuit is OPEN.  When the photo cell is in the dark, the relay drops out, CLOSING the circuit.  You can hear the relay operate, it will make a very faint click as it opens and closes.  My failed photo sensor would pull in the relay when I powered up the fixture in daylight, but the relay would not drop out when the photo cell was covered.  If I had powered up the lamp in darkness the light would come on, and it would go out when the photocell saw light, but it would not come back on again the next time it was dark.  The relay got stuck whenever it pulled it.

If the ballast, bulb, and photo sensor check out, but the fixture won’t start, you have a bad igniter.  Replacement units are housed in a sealed module with three wires.  Note how the original was wired in before removing it and re-wire the new one the same way.  A wiring diagram should be printed on the module.  Be sure to obtain an igniter sized for your bulb wattage.

I’ll probably get a replacement photo sensor and keep my original HPS HID lamp as a spare.  Somehow the old American made hardware seems more trustworthy than its modern tech, made in China replacement.  We’ll see.

Linux

Unless you’ve been hiding under a rock, you’ve probably heard that Microsoft won’t be supporting Windows 7 home, (what many of you may be running on your PC right now) by the end of this year (drop dead date is 1/14/2020).  So if that’s what you’re running you’ve got till then to decide how you’re going to upgrade your computer.

The obvious choice, and the one that Microsoft recommends is Windows 10.  What happened to Windows 8 and 9?  Well W8 was the successor to W7, and there was a W8.1 as well.  However, it wasn’t until what would have been W8.2 that M$ finally managed to get things right.  Their marketing department decided to cut their losses and just release the respun operating system as Windows 10.  They leapfrogged over Windows 9, to avoid confusion with the Windows 9x family of releases.  Guess they didn’t want to be accused of polishing a turd twice.

Not that Windows 10 has a clean reputation either.  The operating system was caught performing upgrades without the user’s consent, and M$ even managed to ship a broken upgrade that crashed users computers.  Then there are the privacy violations with W10 phoning home to Redmond with the users personal data, you know to better provide you with a great experience (like to sell you shit).  Eventually, the word got out as how to disable most of this stuff, but not before a lot of users got really pissed off.
Then there is the not so secret fact that Microsoft desires to eventually stop selling Windows and rent it.  So you’ll be paying them an annual fee for the privilege of running the latest Windows, like it or not.

So, are you ready to upgrade to Windows 10?  Perhaps you’re thinking of giving M$ the finger and will buy a Mac?  Really?  I won’t go into all the stuff that Apple has done to their once wonderful computer, but let’s just say they’ve been keeping up with their buddies in Redmond.  When you buy your Mac, make sure you specify all the memory and disk space you’ll ever need because you can’t upgrade the machine.  Everything is soldered in place, CPU, memory, solid state disks (no more rotating disks in Mac books).  You can’t even open the computer anyway, they are glued together.  When your battery goes bad, you’ll have to replace the whole laptop, or have it permanently tethered to its power brick.

There is another option though, and you already know what I’m going to tell you.  Upgrade to a Linux operating system (a BSD operating system is another choice, but we won’t go there for now).

Technically, Linux isn’t an operating system, it’s just the kernel of one.  The Linux kernel contains the system smarts that enable a computer to run multiple programs at once (actually switching between them in rapid succession).  It manages memory usage, disk files, and hardware drivers.  What the kernel doesn’t provide is the user interface (either graphical or command line), start up and shut down logic, and all of the system applications that control and configure everything.

Operating systems which are called ‘Linux’ are called distributions, and there are hundreds of different ones.  Since almost all of them make use of the same basic kernel (with various custom mods) along with a standard set of system apps from the GNU project, almost every application written for ‘Linux’ can run an all of these distributions.  The difference between these systems is the presentation layer to the user, that is what the desktop screens look like, the key shortcut mappings, and the choices of what programs were included with the installation.

Short history:  The Linux kernel was developed by Linus Torvalds in 1994 as a college project.  He wanted to create a Unix like system with all original code.   While Linus was the original author and maintainer of Linux, the kernel is now maintained by an army of on-line supporters, with Torvalds still having the final say over things.
Meanwhile, another computer hacker (not to be confused with the ‘black hats’ that try to break into systems) named Richard Stallman set out to build an entire Unix like operating system.  Stallman started by creating open source versions of every system program that was part of Unix, including the compilers, linkers, and C libraries needed to build other programs.  Eventually, he had everything he needed, except a kernel.  Stallman’s most famous program is probably the Emacs editor, a real Swiss army knife that can not only edit, but even play games, debug other programs, and serve as a user interface shell.  This set of programs is called the GNU system, which when combined with the Linux kernel, finally provided the goal of a totally free (both as in beer and as in speech) Unix like operating system.

Eventually, the Linux kernel was adopted for use in systems other than Unix like computers.  Android phones use the Linux kernel.  Chromebooks use the Linux kernel.  The Tivo video recorder uses it.  Lots of gizmos with embedded computer systems make use of the Linux kernel (lots also use Windows, have you ever seen the ‘blue screen of death’ on an electronic billboard?).  Billboard BSoD

But you say, can I run the same programs I am now using on Windows with Linux?  Maybe.  The Firefox and Chrome browsers have Linux versions.  Many other Windows programs can be installed under Linux using the Wine utility.  There is a commercial utility that you can buy that will enable Microsoft office and many other programs to be used.  crossover   There are also many opensource free programs that perform the same functions as many of the Windows programs you are now using.  The Libreoffice suite, for example, is a complete office package that can replace the Microsoft one.  It will even read and write MS office files (not 100% perfectly, some formatting differences exist, but it’s very very close).  The Gimp image editing program does the same job as photoshop, some say it’s even better, but you will have to learn how to use it.  The steam gaming platform supports many windows games on Linux. ( steam )
Finally, there are lots of Linux specific apps for Ham Radio, and many of the Amateur radio Windows apps will run on Linux via wine.

So how do you install Linux?  Download an ISO (DVD/CDROM) image for one of the distributions, copy the file to a DVD-R disk or a USB flash drive, set your computer to boot from the media (usually Del, F2, or  F12 during boot up).  This might involve a setting in the bios.  Then once the image loads, follow the directions.  You might want to print the installation manual on the distribution’s web site first.

Which distribution?  The two I’d recommend first would be any of the   Ubuntu or  Linux Mint  flavors.   Both of these are based on the Debian distro, one that has been around almost as long as Linux itself.  (Debian is a rock solid OS, but it’s really not for beginners.) With Ubuntu you have the choice of the  Gnome, LXDE, XFCE, MATA or KDE  desktop environments (Ubuntu, Lubuntu, Xubuntu, Ubuntu-Mate, Kubuntu).  Linux Mint supports the Cinnamon, MATE, and XFCE DE’s.   I’d recommend either Cinnamon or KDE for the most Window’s like experience, though all of the above are good choices.  Ubuntu with the Gnome desktop is the most unusual of them all.  While Gnome’s workflow is excellent, you really have to re-learn how to navigate the system all over again.  Installing the Cairo-Dock (Mac like program launcher) might help you keep your sanity when transitioning to Gnome.

I’ve been running Linux on my own computer since 1996.  I’ve switched distributions a few times.  I’ve used Debian, Red Hat, Slackware, and Gentoo before settling on Ubuntu and then Linux Mint.  (Now that Linux Mint has abandoned their KDE version, I’ll probably go back to Ubuntu-Kubuntu).
I’ve only scratched the surface here, and I’ll probably re-visit the subject in another post.

Building a Transceiver, more thoughts

recently ran into a few videos on YouTube featuring the Collins KWM-380, and the Heathkit SB-104A transceivers.  Both of these radios are contemporary, the years in which they were made overlap.  However there is QUITE a HUGE difference in the price of these rigs, the Heathkit being nearly an order of magnitude less expensive than the Collins.

Both rigs have quite simple front panels with few controls (compared to today’s rigs!).  Both have an analog S-Meter that also monitors other parameters during transmit, and seven segment frequency displays without an analog dial.

The SB-102 reads out the operating frequency to the nearest 100 hz by use of a frequency counter.  It computes the on the air frequency from the sum and difference of the crystal HFO frequency in the first conversion, the second conversion VFO frequency, and the carrier oscillator-bfo frequencies.  The displays use neon plasma type devices.  It is not easily possible to add WARC band coverage to the SB-104 (it might be possible to give up some of the 10 meter band positions and make some major modifications to add different crystals and band pass filters on these positions.  The 12 meter band would be the easiest to add, and perhaps the 15mhz WWV position could be modified to work on 17 meters.)

The KWM-380 shows its operating frequency to the nearest 10 hz on red 0.56″ seven segment  LED displays.  A PLL frequency synthesizer is used in the first conversion, and digital logic (micro-processor) is used to control the PLL and displays.  The KWM-380 did not have a band switch, this was done by using a tuning rate of 1 mhz / step.  As the KWM-380 was a feature reduced version of government radio, it was possible for Collins to add transmit ability on the WARC bands to the radio via a firmware update.  Owners of these radios were able to also add the 60 meter band many years later!

The Heathkit transceiver uses much the same conversion scheme as the earlier members of the SB10x family, a variable first IF centered on 8.5 mhz, and a second IF at 3.3 mhz.  Two different crystal filters in the second IF provide bandwidths of 2.1khz, or 400khz.

The KWM-380 up-converts to a first IF of 39mhz, and then down to a second IF of 455khz.  A third conversion is made to 6.255 mhz., and a final conversion back to 455khz.  Several 6.255 mhz crystal filters with different bandwidths may be selected.  The purpose of the final two conversions is to move the bandwidth of the 6.255 mhz filter in reference to the the carrier oscillator frequency.  This allows for removing the influence of a close by signal, at the expense of an non optimal placement of the bfo signal.   It should be pointed out that many of the later Japanese radios offered this ‘passband’ tuning feature, along with a notch filter AND a variable bandwidth feature.

I’m giving some though to some kind of ‘old school’ approach to a transceiver design that would look something like a cross between these two rigs, at least from the front panel.  I like the idea of large LED’s for the frequency display (either 0.6″ or 0.8″ in size, I have some of both).  I’d use an AD995x series DDS instead of a VFO or PLL, which would give better performance than either the Heath LMO or the Collins synthesizer.  I have some 9mhz crystal filters and also some 455khz Collins filters in the parts bin, so a variable bandwidth IF setup is planned for.  I don’t know if I’d use a 45mhz first IF (which would allow for general coverage on receive) or use the 9mhz IF as the first conversion.  Both could be included and switched in as desired.  I have two different cabinets I could use, a large (almost relay rack sized) one, and a smaller box (that’s still a bit larger than many current Japanese transceivers).  I could fit the rig, speaker, and power supply in the larger box, but I’m partial to the smaller one.

 

 

You can’t work ’em if you can’t hear ’em

You can have a modern transceiver with a good sensitive receiver that won’t turn turtle under the pressure of strong signals connected to a good antenna, but the signal still has to make it from the rig to your ears (unless you’re running some digital mode).

Speakers

Some of today’s transceivers throw in a small downward (or upward) firing speaker.  These mostly sound rather tinny with some buzzing (how bad depends on where you’ve set the radio down on your operating position).  The built in speaker is better than nothing, and will probably even be just fine for a rag chew with a strong local on a quiet band.  However you won’t want to use it for serious DXing, or in a contest.

Yeasu, Kenwood, Icom, and Elecraft offer matching speakers for their transceivers, which solves the problem of having a front facing speaker.  Hopefully, these speakers are designed acoustically correct to avoid unwanted internal resonances, and to fully cover the frequency range of the human voice necessary for communication (about 300hz to 3000hz).  Expect to pay between $100-$300 for such a speaker.

You can, of course, get a very good communications quality speaker for a lot less by buying something originally intended for another purpose.  I have a small Optimus (Ratshack) speaker that nearly matches my IC-746, and it does a good job.  The shack made a few different small two way book shelf hifi speakers that make decent communication speakers.

You can also build your own.   Let me tell you more than what you probably wanted to hear (unless you are into building speakers).   What you need to find is a suitable driver (raw speaker), and then build a correct sized box to house it in.  Since the frequency response required is one octave from 300hz to 3000hz, a mid-woofer or mid range driver of about 3.5″ to 5.5″ in diameter will suit our needs perfectly.  It has to be a fairly efficient driver because most transceiver will have an audio output power range somewhere around 1.5 to 3 watts of power.  This isn’t as limiting as it sounds, since we aren’t going to fill an auditorium or even a living room with sound, just a semi-circle of space, about an arm’s length in diameter.  Several sources of such drivers come to mind, ranging from the auto sound after market, and drivers made for musical instrument practice amps.

One thing to look out for in selecting a driver, is the cone surround.  This is the flexible band that connects the edge of the cone to the driver frame.  Foam, rubber, treated cloth, and pleated paper are the most common materials used here.
Avoid foam based surrounds like the plague.  They have a half-life of about two years or so before they start to fall apart in a pile of dust.  Your mileage will vary on this, but if you live in a warm-humid climate you are in prime foam rot land.  (I threw out two different sets of expensive tower speakers that had their woofers and mid-range drivers develop this cancer).
Rubber surrounds are vastly superior to foam, and will probably last forever.  I have a pair of home made speakers in my media room that are over 25 years old, their rubber surround drivers are still going strong.
Treated cloth surrounds were once very popular in wide range speakers (woofers with a ‘wizzer’ cone for mid-tweeter range).  They will also last forever.  Finally pleated paper.  This is just the edge of the cone.  During manufacture, the outer inch of so of the cone is soaked in water (maybe with some other solvent) and is compressed between two halves of a mold that form the pleats.  Some heat is applied and when the paper dries the pleating is permanent.  Drivers for PA systems and musical instrument amps are built this way.

In order to know how large a box you need to build for a speaker, you need to know the driver’s Thiele-Small parameters.  These are the acoustic specifications for the driver.  We need be concerned with only three of these.   Rs (or Fs) is the drivers free air resonant frequency.  This must be lower than the lowest note we must reproduce.  So for our case, it must be below 300hz.   Qts is the total Q of the driver.  It will determine the shape of the high frequency cutoff of the driver.  Different types of speaker enclosures require different ranges of driver Qts.  Finally there is Vas.  This parameter gives us the effective volume of the driver cone.  The speaker enclosure must have a larger internal volume than the Vas, how much larger depends on the enclosure type, and desired response.

The common types of speaker boxes are sealed, ported, and infinite.   The sealed box enclosure is the easiest to design and build.  I won’t discuss the math here, there are plenty of websites that have on line calculators for working out suitable designs.  Drivers for sealed box enclosures usually have a Qts from 0.33 to 0.55.  The box itself is usually designed for a Q of 0.707 (Butterworth  LP response).
Ported boxes have an opening in either the front or the back via a tube (PVC pipe) inside the box.  The box is ‘tuned’ by adjusting the length and diameter of this pipe.  Ported boxes do not have rational cutoff response curve (I’m referring to the math here), but there are several design equation sets that are commonly used.  At the low end the speaker impedance drops suddenly like a rock, and a high pass filter is usually employed to protect the driver from excessive movement.  Drivers with lower Qts values are suitable for ported enclosures.
At the high end of driver Qts ranges (0.707 and higher) we have the infinite baffle design.  The ideal infinite baffle is an infinitely sized board with the driver mounted in the middle.   Open back cabinets, car doors and rear decks approximate what is required here.  Those old time, tube era transceivers had such open backed matching speakers.

Headphones

Even the best speaker isn’t going to cut the mustard during weak signal conditions in the middle of a DX pileup during a contest.  You know, when the guy you REALLY need to hear is being stepped on by the QROO crowd.  What you need are a pair of CANS!

Communications headphones used to be rather uncomfortable things.  That’s probably where the radio slang term ‘cans’ came from, they felt like a pair of tin cans clamped to your ears.   High impedance, magnetic headphones go back to the days of Marconi.  They have a thin flexible iron or steel diaphragm that is pulled by a magnet.  A coil wound with many turns of very fine wire surrounds the permanent magnet.  The weak radio signals drive this coil, which adds to, or subtracts from the magnetic field, causing the diaphragm to flex and move the air next to the ear, thus producing sound.  There is a variation in the construction of this type of headphone where a lever arm is attached to a smaller diaphragm inside of the earpiece.  This lever arm transmits the movements to a thin mica diaphragm that generates to sound.  This type of headphone (Baldwin) is based on the structure of the human ear.  Magnetic headsets were made with impedance values (with both earpieces wired in series) somewhere between 2000 to 5000 ohms, with 2000 and 3000 ohm values being common.   Early magnetic headphones used individual ‘tip’ plugs and jacks for connection to the circuit, but even the first available commercial communications receivers were set up for the now common phone plug and jack system.
During WWII, most communications headphones were magnetic types, but these had to be ruggedized.  Extreme sensitivity was no longer a requirement as the radio equipment had plenty of internal audio gain.  These headsets usually were built to a 500 ohm impedance, a standard that carries over today in the aviation industry.

Amateur radio equipment from the pre-war era, usually had receivers set up to drive medium to high impedance headphones.  By the 1960’s, during the AM to SSB switch over, lower impedance headsets became common.  I’ve looked back at the specs on old Drake, Collins, and Heathkit rigs.  Only Heathkit continued to require the 2000 ohm headset impedance on their SB line receivers and transceivers, the others had switched to speaker level impedance headphones.  Perhaps the adoption of hifi headsets in the shack was the thing driving the lower impedance of today’s headphone jacks.  BUT, they are still mostly wired as monaural jacks.  BTW, hifi headsets are not magnetic drivers, they are dynamic drivers, having actual pint-sized speakers in each earpiece.

If there is one place where a communication quality headphone has to keep outside noise from interfering with the operator, it is in the cockpit of an airplane.  Technology changes slowly in aviation, and bits of the past are ingrained in newer tech.  Many standards have been inherited from the military, the 3/16″ diameter tip/ring microphone plug for example.  (The only maker of amateur radio gear to use that style of microphone connector was Collins, probably due to their involvement in avionics.  BTW the sleeve is ground, the tip is PTT, and the ring is the microphone).

Back in the late 70’s, I started taking flying lessons in Cessna 150’s.  Rather than use the flying schools crappy headsets with the plane’s hand held microphone, I bought myself a  David Clark H10-30 headset.  This time proven unit is still available today, though with an improved microphone.  It’s a medium impedance headset (around 300 ohm, with a series volume control).  While I haven’t flown in years now, I’ve kept the headset for use with my ham gear.  Even though there is quite the impedance miss-match, most transceivers will still drive it, and I can always use an output transformer ripped from an old transistor radio wired ‘backwards’ to step up the impedance if necessary.  The microphone is an amplifier dynamic type that requires power supplied by the radio to operate.  Like most aviation microphones, it’s designed to work in a carbon microphone circuit.  These noise canceling microphones have a frequency response that matches the human voice range of 300hz to 3000hz.  They won’t sound hifi, but they will cut through the crap.
Most transceivers today provide a 5 to 12 volt power pin on their microphone jacks to power electret units.  I made an inline adapter to power the microphone through a 470 ohm resistor from this power source,   Audio is then coupled to the microphone input via a 10uf capacitor back to the rig with a 10k pot in between.

There is nothing like a pair of well made (for the purpose) headphones for bringing the weak signals right to your ears.  Your radio may have the latest in DSP audio processing (perhaps done at the IF frequency), but the best DSP filter for separating a weak voice out from a crowd of others is still that lump of gray matter between your ears.  But you have to provide your brain with the entire input, as directly as possible.

David Clark makes a whole line of aviation headsets over a wide price range.  They still sell parts for anything they ever made.  I recently ordered new padding and filters for mine that had been turning to dust over time.
There are other brand names in the market today, but I’m happy that this “made in the USA” supplier is still going strong.

Using a weird surplus LED bar graph

The photo I posted in my previous post of a home made project box for a future QRP transceiver project showed what looked like a bar graph meter above the LCD frequency readout.  Most of the common LED bar graph displays have 10 vertical rectangle segments and can be driven by a the popular LM3914 series chips.  These parts can handle such displays directly and are available in linear, log, and VU processing versions of the signal to display.  They can also be expanded by cascading additional drivers and displays to up to 100 segments of common anode displays.

Buried in my junkbox were several Toshiba GL-112T9 LED displays that I got for a few bucks at a past ham flea market.  These are 12 segment displays with horizontal rectangular segments.  There are four green, four yellow and four red segments.  They are not common anode displays however.  Two of the green LEDs and two of the red LEDs are wired in series with a connection to both ends and the common middle.  The four yellow LEDs are wired in two series connected groups.  The end result is that the display has only 20 pins instead of the 24 that would otherwise be required.  Needless to say that this makes it incompatible with the LM3914 drivers.

The obvious solution to the problem (if I wanted to use these bargain bar graph displays) was to make a custom driver using a micro controller such as the Arduino.  I designed such a driver using an atmega16 chip in a 40 pin dip package.  This part is overkill, the required code will fit in only 4K of flash and only 13 I/O lines are required (one being an analog input), so an atmega48 would work fine.  However, I already had several of the atmega16’s in the junkbox, so that’s what I used.

BargraphHere you can see the result.  There are 12 current limiting resistors, and 4 diodes.  The micro controller lights from 1 to 12 of the LED’s depending on the voltage input to the A/D converter.  When both of a pair of series connected diodes are to be driven, only one of the two lines are pulled low.  The common line to the two LEDs is driven through a diode to prevent back flow from the micro controller which outputs a high level (5v) when a segment is off (the anodes of the display all go to +5 volts).

Here is a link to the code:  Bargraph (Github).
The code is licensed under the GPL v3.0, so you can make free use of it for your own projects under the terms of that license.  If you want to port it to a smaller AVR controller the only thing that will possibly need to be done is to modify the some of the register and/or bit names as Atmel has moved things around from the older atmega16 to the atmega48, atmega88, atmega168, and atmega328 processors (the ones used in the Arduino).

To keep things quiet (from an RF point of view) the processor is put to sleep while the A/D converter is running.  The converter is put into the auto-run mode, so it does not have to be restarted after finishing each conversion.  The A/D converter interrupts the CPU after each conversion, which wakes the CPU up from sleep.  At this point the result of the A/D reading is converted into a bar graph display, and the correct LED’s are driven.  The CPU then goes back to sleep, waiting for the next display cycle.
I used the atmega16’s built in 1 mhz RC clock, it’s more than fast enough for this application, the slower speed clock makes less rf noise, and it eliminates the cost of a crystal.

The nice thing about this approach is that I can modify the processing of the input signal to display in linear voltage, “S” units, Log or Vu scales.  There are unused I/O pins so I can even have the processor switch display modes on the fly by adding code to monitor the extra pins, using them as a function switch.  Right now the display is purely linear.  The LED’s light up from green, to yellow, to red, but you could wire the bar graph up in the other direction if you think that makes more sense for your application.