Posts Tagged ‘re-purpose’

Converting the HP ESP120 Power Supply

August 23rd, 2015

Quick notes on converting the HP ES120 2950-watt blade server power supply to run “48-volt” amateur radio amplifiers.  The power supply I have has a slightly different in configuration from the one described by W8ZN on the K8GP site.


I picked up the power supply on good terms at Dayton some years ago and finally managed to get around to hooking it up after I put two 240-volt, 20-amp circuits in my shack this spring/summer.  I used a molded air conditioner extension cord with the female end cut off to attach it to the wall.  Hot-ground-hot is the wiring on the AC input side.  On the output, there is a jumper block and two pairs of blade connectors, with one pair being positive and the other negative, strapped together.  In the middle of the output there is a jumper block.


Here is where the steps differ from the W8ZN steps:  instead of shorting two pairs of pins together, this power supply requires three in a line to be shorted together.  It’s visible in the photo below, I think.  The center row.


I’m getting 51.4 volts unloaded.  Load will be described in the future as it comes to be…

Signal and Noise

August 4th, 2014

“One man’s signal is another man’s noise,” began Dr. Kudeki as he derived incoherent scatter radar theory from Nyquist’s noise theorem in ECE458.  I think of that statement often, whether it be QRM on the ham bands or sifting through the pocket litter of web users looking for their consumption preferences.

This morning, I admired just such an example of signal and noise while watching the NOAA Doppler weather radar.  Undesired targets of a radar that return echoes are termed “clutter” in the radar parlance and one simplistic way of eliminating clutter, especially when you expect the desired scatterers (“targets”) to move, is to assume that all of the stationary returns are clutter.  In the weather radar, we get clutter from all sorts of stationary things like trees, hills, and buildings.  Of course, what causes the clutter to move?

You see, it was one of those humid August mornings when a ham’s mind wanders to…tropospheric ducting.  Yes, indeed the clutter returns were moving, intensifying before and after sunrise.  I was fixated on this and watched the loop over and over again before noticing an even more interesting bit of clutter!


Beginning at 0958 UT on 4 August 2014, there is a small ring forming out over the Elk River area.  The ring, which is indicated by the downward-pointing vertical arrows, expanded over the next >40 minutes.  I was puzzled and watched the loop over and over.  I considered and discarded a number of theories before resorting to Google.  Apparently, it’s very likely a flock of birds.  Sure enough, the epicenter of the ring is Elk Neck State Park.  Fascinating.

The slanted arrows in the figure above indicates the ground clutter that I was originally noticing as a signature of tropo ducting, obviously now of secondary interest in this sequence of images!

Epilogue:  I sent these frames to my father, who is an avid observer of the natural world.  He passed them along to two friends back home who are birders.  At press time, one reported that he had learned of these “bird circles” from Greg Miller, another birder from the area who got famous as one of the subjects of the book (and movie of the same title) The Big Year.  I haven’t read/seen it, but I guess they went to Adak, which has a special place in my heart.  Anyhow, it’s a funny small and interesting world in which we live.


SoftRock Ensemble RXTX IF modification

November 12th, 2011

This is a pretty simple modification that converts a SoftRock Ensemble RXTX SDR RF interface board from “common-IF” (RX and TX share the same antenna port) to “split-IF” (RX and TX have separate ports).  Split-IF is the standard for high-performance transverters on the 50-, (70-), 144-, 222-, and 432-MHz amateur bands.

So, I had a look at the RXTX schematics (here, here, and here) and considered the following options for where to break the RX and TX portions of radio:

The purple dots were the first option.  Unfortunately, these locations on the actual printed circuit board were not easily accessible to miniature coax and this process would involve significant surgery to perform and restore the modification.  The second alternative I considered was the red Xs…jumpering over the BS170 PA transistors.  By this time, I was looking for a way to avoid butchering the original circuit too much.  So, I elected for option three, which was to install a second T/R switch at the antenna jack (golden circle).  This had at least two advantages, the first of which was being minimally invasive.  The big advantage, though, is that the radio could be operated at its design output and run through a fixed or step attenuator on the TX side to the transverter.  This meant that I would be assured of having a reasonably clean signal to work with if I configured the radio correctly.  It also meant that I could operate the radio as designed if I simply disabled the the second T/R switch and connected the antenna to the default port.

So, here is the modification that I came up with using parts I had in my junk box.  KB9YIG ships the Ensemble RXTX with a couple of spare BS170 FETs that can be used in place of the 2N7000.  I just had a lot of 2N7000s and thought I’d save the BS170s in case I ever burnt one in the RXTX.

The interface to the transverter is through a DB9 connector.  PTT for this transverter is +12 volts (as done with the TS-930S) on pin 6.  Pin 1 is ground.  Pins 2 and 3 are shorted together in the transverter cable connector to enable the modification in the SoftRock.  The right portion of the schematic with the relay driver and Omron G6Y relay is based on the T/R switch from W1GHZ’s “Multiband Transverters for the Rover” that I decided not use on the microwaves when I found a cheap source of SMA coaxial relays.  An I2C decoder would be great to put band data on the other pins to select a transverter (or transverter cascade for the microwaves).

The whole mess works great from a switching standpoint.  When I key the PTT on Rocky or PowerSDR, it switches the TX line and keys the transverter.  I’m a little ambivalent about the quality of transmitted signal that’s actually coming out.  I think it’s good enough if you live in a sparsely-populated area, but I have a lot of VHF neighbors that I’d rather not upset.  So, I need to do some more testing on this—a lot of it is getting the RXTX and PowerSDR configured correctly.  It appears that the I/Q channels are flipped on my sound card (Audigy 2 ZS) between transmit and receive.  I don’t know if that’s a wiring error in my breakout box or whether it’s normal.  Spectra to come at some point…

Eliminating CRTs

October 9th, 2011

Ever since I replaced my primary station computer (a decision that may be reversed soon—details in a later post), I desired to replace the remaining 19-inch Dell Trinitron CRT monitor with something lighter and smaller.  Mom and Dad were in town a few weeks ago on a much-needed vacation and we went to the National Air and Space Museum’s Udvar-Hazy facility near Dulles Airport.  This is only a few miles from one of the best used computer shops in the DC area—CedarPC.

CedarPC is nice because they’ll sell you “damaged” stuff at a discount if you don’t care about the damage.  I inquired about a 24-inch flat panel I had seen on the web site, but they could not find it.  They did find me a nice 20-inch flat panel that was just missing the stand and the price was right.  The missing stand was no big deal because I wanted to mount the monitor on an arm so I could bring it closer to the HF end of the station desk, tuck it in at the VHF end, or even swivel it out over the couch to watch a DVD.  Sold.

Monitor arms are generally expensive…at least 2-3 times what I paid for the monitor itself, often more.  So, I went to trusty eBay and found something designed for mounting televisions for $15 including shipping.  This did require some modification of the monitor housing and liberal application of wide washers to reinforce the plastic in the housing.  But, it was done with all junkbox screws and washers.

The Rupture 2011

May 22nd, 2011

Thanks to some quick thinking on Sarah’s part, I was able to attend the Hamvention (Saturday only—the day that the sewer backed-up and “ruptured”…spewing nasty water down through the fleamarket) for the first time in a few years.  This is a recap from my perspective.

  1. Attendance was down.  The fleamarket was shrinking.
  2. There were a lot of lookers but few buyers in the fleamarket.  Predict that the fleamarket will shrink further next year.
  3. There were still good deals to be found in the fleamarket—I picked up some LMR-600, a WA2AAU 2304-MHz amp (unmodified 1900-MHz PCS amp), a Rohn 45G rotator plate, some 20-GHz rated SMA relays, and some miscellaneous parts.  And, I passed on a few good deals as well.
  4. I saw a lot more young people than I remember from past years.  Or maybe I’m just getting older and the population of hams younger than me is growing on account of that.
  5. Hamabouts (and their drivers) were not so obnoxious as prior years.
  6. Hara Arena may be a dump (K1LT told me the story—don’t know if it’s true—that during the Rolling Stones first U.S. tour, they had been booked at Hara, but refused to play when they saw the facility); but, it’s perfect for the riff-raff who show up for the Hamvention.
  7. In the end, the Hamvention (like ham radio itself) is about the people you know and meet.  I had fabulous eyeball QSOs  with guys from almost all phases of my ham career (except the early years from 1993-2000).  The VHF/UHF weak signal crowd is a pretty amazing bunch of hams.  I had a great time getting to know some of them in the fleamarket.

Marrying the TI-85 and the DJ-580T

April 13th, 2011

The May issue of QST arrived in the mail today and an article about building a “fox” for hidden-transmitter hunting was included.  That brought back memories of a teenage project of mine that I had once thought of writing up for QST, but now just makes a good story for the blog.

The first (and only) handheld radio I’ve owned is an Alinco DJ-580T.  Like most HTs of a certain age, it has provision for an external (“speaker”) microphone.  The microphone input is a sub-miniature (3/32-inch, “2.5 mm”) stereo phone plug.  As a high school student, one of my passions was tinkering with a graphing calculator—the venerable Texas Instruments TI-85—do kids these days even use this stuff or have they gone the way of slide rules and nomograms?  The TI-85 offered the provision to link to a computer or another calculator through a similar sub-miniature stereo phone plug.

Well, one afternoon in probably 1997, I was sitting with the DJ-580T in one hand and the TI-85 in the other…and it hit me…I wonder if I can use the the TI-85 to drive the DJ-580T microphone input?

A few preliminaries are now in order.  Thanks to a helpful (and still operational, albeit now with a CMS and the attendant spam) web site called, a few friends and I had learned to load our TI-85s with third-party binary machine code programs with considerably faster execution times than the built-in scripting language.  This allowed us to play relatively powerful video games surreptitiously on a school-sanctioned platform…a tactic that worked well until the English teacher wisened up to the fact that the five students with their calculators out were not typing essays on them.  Not satisfied to just play games—although I did set a very high score in Tetris during Spanish class—I sought to harness the power of the Z80 microprocessor in the TI-85 for myself.  Recall that this was before widely-available and inexpensive microcontroller development systems like the PIC, Arduino, and AVR.

I gathered the tools and eventually managed to write some fairly sophisticated (given my utter lack of formal training in computing) software in Z80 assembly language, including a crude clone of Space Invaders and a crude adventure game I called “Kashmir.”  Maybe some screenshots or stories about them will come later.

But, for the story at hand, I learned how to manipulate the link port.  Fortunately, the sleeve was ground on both the TI-85 and the DJ-580T.  So, it was just a matter of tip and ring—one was audio and the other was PTT on the radio, and both were settable on the TI-85 for some kind of two-wire communication link.  So, I reasoned that I could write up a bit of assembly code that would key the PTT by pulling it low, then toggle the audio line back and forth at 500 Hz or so to generate a rough audio tone.  It worked!

This was an expensive, although trivially so since I had the hardware, way to build a hidden transmitter.  So, I modified the software to send my callsign in Morse code (using a look-up table) and stuffed the whole thing in a cigar box.  It was good fun for a few of us teenage boys.

And, for the interested, I found the original source code, which is sadly not well commented or dated.  But, it does have my old callsign (AA8UP) listed by the lookup table.

A short vertical for 160 meters

January 9th, 2011

160 meters, Topband, …the names conjure all sorts of visions of grandeur, enigmatic propagation modes, and big antennas in the minds of hams everywhere.  Since I have lived on suburban lots for the past five and a half years and in an apartment for two years before that, it has been the better part of a decade since I’ve had my own permanent 160-meter antenna system at my “home” station.  (Despite this, I did manage to get 160-meter WAS from NO9Z’s station and if my Rhode Island and Delaware contacts ever upload to LoTW, I’ll request the certificate from ARRL.)

So, the story at hand.  Just before the November Sweepstakes contest, I put up a secondary 80-meter antenna—the open-wire fed dipole I used at K8GU/9.  Its performance was underwhelming and the vertical seemed to play just fine.  But, I got busy and just left it up in the trees.  Somewhere in the annals of the Blog, I may or may not have described this antenna, which was designed to also operate on 160 by shorting the feeder and feeding the whole mess against ground.  I never used this functionality because I had to lay radials on top of the patio and that was a pain to take them up and put them down.

The North American QSO Party was this weekend and I’ve been participating in the NCCC Sprint Ladder, both of which include 160 meters.  Around about last Thursday, after the NS Ladder, I decided it might be fun to have 160 for the NSL and NAQP.  So, I ducked out of the office early on Friday afternoon and set about stripping the old tuning network from the K8GU/9 incarnation of the antenna.

We have a lot of AM broadcast stations in the DC area.  And, because of that, antenna analyzers are not always too useful on the low bands.  So, knowing already that the antenna was near self-resonance after my K8GU/9 efforts, the first thing I did was just hook the antenna up to a TS-930 and give it a 5-10 watts fed against my nearby 80-meter vertical’s radial field.  Sure enough, the VSWR was about 3 at 1.999 MHz and off-scale at 1.801 MHz.  So, I inserted the loading coil from the old matching box.  The coil is just #14 THHN solid wire in approximately the optimum-Q configuration of diameter to length and wound on a cardboard shipping tube.  (As is clear from the photograph, it’s not really pretty nor the lowest-loss possible.  But, it was great for what I had on-hand.)

The coil has four taps on it.  I clipped the fourth tap, shorting the bottom half of the inductor and did the VSWR sweep, finding a dip at 1.950 MHz or so.  Each successive tap brought the minimum lower and lower.  With no taps clipped, it was tuned to the bottom of the band.  I got lucky (erm, did a lot of tweaking at the previous QTH).

The best news of all of this is that there is enough RF actually being radiated (not just as heat, either!) to make some contacts!  Further good news is that even though the antenna is between three and five feet from my 80-meter vertical, with the W3NQN filters, I can operate SO2R on both bands simultaneously.  Of course, the RX noise level may just be hiding the trash.  I haven’t tried the K9AY because I had that portion of the station torn-up during the conversion of all my DC accessories to PowerPoles and the preamp popped a fuse in my RigRunner when I plugged it back in.

The bottom line is that it’s not a full-sized 4-square, but it gets me on 160 from my lot in a way that’s compatible with my operating style.

VHF/UHF firepower

September 16th, 2010

As if I don’t have enough projects already, I recently obtained these two surplus FAA AM-6155 amplifiers on, as usual, very attractive terms.  I don’t have the equipment to properly test them at this point.  But, that is coming.  The FAA specified these to do 50 watts continuous duty AM.  With modification, they will do about 300-400 clean watts with 10 watts of drive on 144, 222, and 432 MHz.  Once I get the first two working (on 222 and 432), I plan to find two more of them and use them on 50 and 144 MHz.  For 50 MHz, I plan to remove the VHF/UHF cavity and components and install an RF deck using the same Amperex DX393 or Eimac 8930 tube.  Comments and ideas welcome.  They’re a lot cheaper than bricks!  One of my units appears to be at least partially converted already, but I’ve only had it open for a few minutes with my brother Seth, who got all of the mechanical aptitude in the family.

Note:  Thanks to WY3X for catching my error on the tube type.  He also notes that 300 watts would be a conservative maximum on 432.  I plan to run the amps with very low drive after tuning so I can compete in the ARRL’s low power category at 100 watts on 222 and 432.

Homebrew Fire Ring

October 3rd, 2009
Homebrew Fire Ring

Homebrew Fire Ring

At our last place in Urbana, we had our “space” in the back yard, sort of an outdoor living room.  The new house lacked that until recently.  We obtained a rusty old truck tire rim from some of my not-too-distant kin in the tire business.  I picked-up a rust-buster abrasive head for my angle grinder and went to work on the rust and caked-on road/tire grime.   Some degreaser and a rag helped get most of the rest of the grime out.  Then, I painted it with flat black grill paint for a classy rust-free look.

Total cost: about $10 plus three hours’ time to finish the rim.  The neighbors probably think we’re rednecks.  But, who cares?  We had the first of hopefully many pleasant fires tonight.  Besides, how many chimenea owners had the pleasure of busting rust off of a 35-pound hunk of steel?

Interesting trivia:  In the past three posts (inclusive) with photographs, the on-going projects are pictured.  That is, in the workbench photo, the antenna mast and rotor control box are shown in the lower left portion of the image.  In the rotor photo, the unfinished fire ring is under the rotor.  Then, this post has the finished fire ring. The beat goes on…

Resume of a Master Dumpster Diver: the Early Years

February 21st, 2009


With transition imminent in our lives, I have begun packing up some of my things that I don’t use much right now. It’ll save some time and headaches when we finally figure out where we’re going and begin the moving process. Coincidentally, my good friend Matt recently moved cross-country and elected to dispatch the majority of his tinkering resources via Craigslist. You see, Matt and I share a common vice: we are master dumpster divers.

I was reminded of this reality as I have been trying to center myself with respect to what’s important in life last week week. I have a lot of stuff, frankly, an embarassing amount of stuff. And, although I use a surprising amount of it, I really don’t need it. But, this post is about collecting the stuff, not getting rid of it. I’ll save that for a later post.

As I began sifting through some of the goodies tonight, a confluence of thoughts began to swirl in my head. I’ve had resumes and vitae on my mind for quite a few months now since I’ve been looking for employment (if you hire engineers or scientists, particularly for RF/signal processing/remote sensing/upper atmospheric/space research and development, I’m your man). And, I was poking through the rubble of my home “office,” which is actually my office, hamshack, and workshop, plus Sarah’s desk and books and the place that Sarah and I cram stuff into when company comes. Suddenly, it hit me: my entire resume can be read through my collection of odds and ends.

Dumpster diving, to borrow the analogy from Nelson Muntz, is like “kicking butt” in the sense that it might not involve any kicking at all. Likewise, you have to get to the stuff before it gets to the dumpster. This is the first rule of dumpster diving: Know who to ask, how to ask, and when to ask. The second rule is don’t get greedy. I learned both of these rules at a tender young age.

You see, the house I lived in between the ages of three and nine was next to the Village of Millersburg’s street department garage. Of course, this was a great boon for a child of my age to see all of the equipment and workers coming and going. Mom and Dad may remember this story differently; but, this is my recollection.

Although I was fascinated by all aspects of construction work, the one thing that I obsessed over more than anything else was signage. Some kids are experts on dinosaurs, I was fascinated by road signs. I coveted the road sign poster on the wall at the BMV. Mom had inquired about obtaining one for me to no avail. The other thing I coveted was a road sign or two of my own. A friend had a stop sign in his room; but, I was looking for something more exotic, maybe a yield sign. My poor mother worked some connection she had at the Street Department to get a discarded sign. She told me that we could go down to the sign depot and pick one out in the morning, which was probably a mistake.

I rose particularly early the next morning and, after locating the sign depot, collected a few signs for myself. When you’re a kid, street signs don’t look big and heavy on their posts. But, when you get up close, they rival your personal geometry. So, I left a trail of signs I couldn’t carry back up to the house. I don’t remember the details of what happened next, other than that we had to return all of the signs and get “approved” ones. I hope somebody thought it was funny; goodness knows I learned a lesson that day about the difference between dumpster diving and theft of city property.

A few years later, Mom had an antique dealer come through the barn behind the house and the signs caught his eye. She let him have them for a song. I was incensed at the time, although in retrospect, it was probably better to not profit too much on them.

The basement of the Inventor’s Hall of Fame once hosted an area where kids could dismantle old hardware. We were fortunate to visit when some racks of AT&T Long Lines hardware had been recently donated. I think I carried a half-dozen plastic sacks of relays, waveguide, transistors, meters, and other assemblies out of there that day. Although I have sifted through most of that by now, the juiciest pieces still remain in my inventory, ready for use. I still don’t think that the docents knew what hit them when the budding master dumpster diver rolled in.

Although I dabbled off and on in the barter of used electronics and such in high school, the dumpster diving began in earnest again in college, where I met guys who weren’t afraid to actually climb into real dumpsters to fish things out. Those were good times. Most of the stuff we pulled out of the dumpsters was building materials, which we used to spruce up our living spaces. Blocks from a demolished (the Young Building of Philosophy and Relgion, a grievous sin against architecture and HVAC) academic building allowed us to put an “upper deck” couch behind the regular couch in our apartment for stadium seating. This was great for watching movies, or at least watching my roommates play Mario Kart 64 with their pharmacy notes on their laps…right.

One of the other great successes was DuddiNet and the Tower of Power. I dragged an 8-foot relay rack (rescued from the scrap heap at a summer job) into my dorm room and filled it full of computers and networking equipment. I asked the university IT people if they had any leftover rolls of CAT5 cable and they gave me as much as I wanted. We pulled our own network in the dorm. At that time, the dorms were 10baseT with hubs. So, it was a real bottleneck if you wanted to move some data (use your imagination here) around. We put in a private switched 100baseT network that connected four rooms on two floors.

In more recent years, I’ve scored some terrific stuff just by paying attention when spaces are being cleaned-up. For instance, that’s how I got my HP vector voltmeter and my oscilloscope. And, indirectly, through Dad, it’s how I got some more Greenlee punches and a set of metal-marking stamps. Anyhow, in order to protect “sources and methods,” I’ll decline from disclosing too many details about my more recent activities…I haven’t swiped anything from a forbidden dumpster, though. Promise.

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