Posts Tagged ‘re-purpose’

Converting the HP ESP120 Power Supply

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

“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

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

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

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

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.

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