Amateur Radio


Licensed since 1960

Here at KX4OM the main interests are restoring and operating vintage equipment, building stuff, QRP and straight key CW. You can contact me by email via this spam-free link: Contact me

Site last updated on October 11, 2016.


Technical Solutions


Here are some projects that I am working on:

Updated April 2, 2016

My build of the 8640jr, designed by Wes Hayward, W7ZOI. I've actually completed it, but I haven't gotten around to adding info and photos to the site. As the name implies, it is an RF generator that is based on the Hewlett-Packard HP-8640 signal generator, in that it uses a wide-range oscillator that is digitally divided down to lower frequency ranges. It works really well. I built it in a scrapped PC power supply case,my new favorite form factor.

I've been working on this next project for quite a while, and it is now (October 2016) in the calibration and testing stage. It is the Poor Ham's Scalar Network Analyzer (PHSNA). This wonderful suite of test equipment is detailed on the PHSNA Yahoo group. The PHSNA consists of a measurement module, the log power meter, and a controllable signal generator, which I'll call the SNA module. The version I built uses a Windows PC as the control and display. If you are looking at something that can perform many of the functions of a spectrum analyzer or VNA, but at much lower cost, this PHSNA, along with it's companion measurement receiver could be for you. If you already have built a log power meter (see below, in my Completed Projects section), you are one step ahead. My 2002 homebrew log power meter works with the SNA, but I built the new LPM using the project PC board into a larger enclosure, with all components shielded in a sealed copper-clad RF proof internal box. The new LPM includes a very nice Weston 50 uA meter that I've had on hand for several years. I made a new scale for the meter which reads directly in dBm (Jim Tonne's free Meter Basic program.) The external box for the log power meter is a PC power supply enclosure. The SNA unit, separate from the LPM is stack of boards including an Arduino Uno 3 clone (China), an AD9850 module (China) and the SNA board itself (NI5B and crew.) The SNA module is enclosed in an aluminum box identical to the one used for my original homebrew LPM. The measurement receiver is built in a slightly smaller aluminum box of the same type. The measurement receiver provides more functionality over that provided by the basic PHSNA; an external RF source signal is mixed with a local oscillator signal provided by the SNA module, controlled by the Arduino. A 6-pole crystal filter removes unwanted mixing products. The output RF is sent to the log power meter. Many thanks to Jim, NI5B, Jerry, W5JH and Nick, WA5BDU for their design work and testing.

My never-ending work on my HW-101 is in a holding pattern until I complete the PHSNA. I have a problem with the SSB filter, USB and LSB crystal oscillators, or both. USB sounds "high"and "hissy" compared to LSB. I use it for CW mainly, but it ought to made to work right in all modes. I've fiddled with trimmer and padder caps on both the crystals, cut pads in the circuit to do so, measured with a counter, all to no avail. I'll be able to sweep the xtal filter, and also determine the exact chatracteristics of the 2 crystals with the PHSNA.

I've done an interesting mod to the HW-101 (No holes, completely reversible!) to allow use of the rig as a receiver-only setup with a separate transmitter and an external T/R relay. It mutes by not just disconnecting the input from the T/R relay, but by cutting off the receiver stages ala the SB-301 dircuit. I did actually create a new hole on the back panel, but it is identical to the 2nd spare jack on the SB-series transceivers, right down to the same orientation of the hole, and labeling it as "Spare 2" with the same font. I mounted a toggle switch in the RCA-jack-size hole, with the newly-installed RCA jack pushed aside, internally, which disables the transmit function of the rig and cuts off the receiver when the transmitter (boatanchor, or whatever; MOPA, MOSFET/BJT transistor XMTR) actuates the external T/R relay. It also turns on a series pair of red LEDs with a dropping resistor from the 12 VAC connection to the S-meter lamp (through a rectifier diode.) I said, "transmit is disabled;" not exactly. Switching to Tune, attempting to PTT, or any other likely scenario will not make the rig transmit. However, should the former sailor (me) plug in the CW key to this "receiver", turn the switch to CW, and key the rig with the J-38, it will transmit. The red LEDs shining in the S-meter window alert me not to do exactly that. That, and red-tagging the hole with a wood plug where the key is normally plugged in. As far as I'm concerned, the rig is "sailor-proof." The edited schematic has the modifications, and it is kept under the rig, with detailed reversal instructions to make it stock. About a 45 minute job.

Here are some projects that I have completed:

Front View of the Log Power Meter

Updated April 2, 2016

A Log Power Meter, designed by Wes Hayward, W7ZOI and Bob Larkin, W7PUA (June 2001 QST; article available as a Members Only download). See my step-by-step photos and description here. This device allows direct measurement of signals of over 20 mW (+13 dBm) to less than 0.1 nW (-70 dBm). It consists of an inexpensive Analog Devices AD8307 logarithmic amplifier IC, a common 78L05 voltage regulator, an LM358 op amp, a few common resistors and capacitors, two RF connectors, a SPST switch, a Radio Shack panel meter, and a die-cast or standard Radio Shack aluminum box as the enclosure. A DVM may be connected through a feed-through capacitor when greater resolution is required. Using this device, stage gains can be directly measured in homebrew transmitters and receivers in the development phase. Also, by attaching a signal generator and a return loss bridge (a simple homebrew passive device), RF filters can be measured for insertion loss and even filter adjustment can be done. An auxiliary 40-dB power tap attenuator described in the article extends the measurement level to +50 dBm, which is 100 Watts. Wes suggested that this would be a very valuable instrument for me to use in homebrewing and experimentation prior to building his spectrum analyzer. Wes has updated information on his web site.

I have recently updated the LPM with a different meter, that, like the RadioShack meter, has a 0-15V DC scale, but is actually a 0-1 mA full scale meter. I replaced the scale with a -80 to +10 dBm scale that I created with Jim Tonne's Meter Basic freeware. I also upgraded the circuit of the LPM to include the calibration functionality of the PHSNA version of the LPM (addition of 2 trim pots.) The meter I used is has also been used by several members of the PHSNA Yahoo group. It is from All Electronics, part number PM-376, and at $3.50 is a bargain for a 2.4" square panel meter. New photos to come.

Step Attenuator

A Step Attenuator is one of the most useful test units you can have in the shack. Combined with a signal generator and a Log Power Meter or oscilloscope, you can make very accurate readings of things like stage gain in a receiver or transmitter. I built mine just a bit different than some others that I've seen. Check it out.

40m Superhet

A 40 Meter Superhet with Digital Readout I built this receiver for my grandson, who has an interest in all things electronic. Here's the link to the project.


The ELSIE L-C Meter. The ELSIE LC meter is an accurate, simple device for measuring inductance and capacitance. The ELSIE was designed by Joe Everhart, N2CX and Steve Weber, KD1JV. At one time it was kitted by the American QRP Club, but it's no longer in production. Although it can certainly be built using one of the free-form methods, including Ugly and Manhattan construction, I made a board in EAGLE Cad. Instead of the possibly more familiar PIC microcontrollers, the ELSIE uses Steve's favorite, the Atmel family of microcontrollers. So, along with the ELSIE, I had to build a device programmer and locate software to "flash" the chip, an AT90S2313. My ELSIE is finished and working fine. After initial tests, I replaced the key capacitor that ELSIE uses for internal calibration with a 1% one (was 2%), and it's even more accurate. I use it a LOT. Here's the finished ELSIE.


The NoGa PiG (Power Indicator and Guard)...don't hook up your DC supply to your QRP rig without it. It's invaluable during testing of those new designs and kits...saves your circuit and $ worth of power supply fuses).

SKN Special

A 30 meter transceiver for Straight Key Night.

Updated April 2, 2016

I built this rig for operation on Straight Key Night a few years ago. Click on the link and see the work as it progressed through the building period. This rig uses a modified Vectronics VXO transmitter unit, and the receiver section from the SW-40+ (with components for 30m) designed by K1SWL and described in the Elmer 101 web project. The rig is currently disassembled for a major upgrade. The "temporary" VXO based transmitter has been removed,and a companion to the receiver is to be installed, a transmit board based on the K1SWL SW-30+. The rig will then function as a true transceiver. I am also installing an RIT circuit for the rig.

Enhanced Guppy-WaTTa-PiG

An enhanced Guppy-WaTTa-PiG Multifunction QRP Accessory.This project is a culmination of a lot of work between Russ, AE4NY and some other members of the NoGa QRP Club and me over a couple of years. It combines several NoGa QRP club kits, commercial board units and some homebrew units. The result is a very useful box that simplifies QRP operation of various transceivers, transceivers and receivers. Click here for details.

A -20dBm 20 meter test source, designed by Jim Kortge, K8IQY. I'm not providing any build photos, etc., on this one, because it did it just like Jim did, down to the 1/4" copper shielding tape. This is my primary reference source of RF for adjustment and calibration work in a 50-ohm environment. It does indeed read -20dBm on my log power meter. Check it out on the web site.

40m Transmitter

"The Challenger 40", a homebrewed 40 meter transmitter based on the Wes Hayward, W7ZOI-designed transmitter in Chapter 1 of "Experimental Methods in RF Design".

SLA Charger

A Sealed Lead Acid Battery Charger of a rather unique design, by Bob, AA4PB. The article appeared in the May 2001 issue of QST. Unlike simpler chargers, AA4PB's design does not maintain a fixed-voltage, trickle current float on the batteries. It applies charging cycles only when the voltage is below a level set by a voltage comparator. LEDs indicate when the charging cycle is on (green) or off (red). Even in a fully discharged state, the battery is brought up to full voltage by cycling the charge current. It works very well, and it's a nice project. I keep my stock of 7 AH gel cells charged with it. Check out my finished build photos.

Plug PiG

Protection when you need it: the Plug PiG. This handy little unit includes most of the basic functionality of the NoGa PiG in a small package. I decided to build it because the PiG is an accessory I literally use every day I'm at the workbench or operating in the field. The PiG features reverse power protection, a "polyswitch", also called a resettable fuse for overload protection, and a voltage comparator IC and LED to indicate undervoltage conditions. Then I had the idea that I could sure use one in the car, when I'm connecting low current draw (1 amp or less) 12 volt gadgets to the cigarette lighter socket. I took apart one of those odd-shaped cell phone charger-adapters, and determined that I could re-engineer a PiG to fit. I added an LED to the circuit to indicate that voltage is available at the socket.


A home-brewed circuit board version of the Precision VXO and Crystal Test Fixture designed by Jim Kortge, K8IQY. If you homebrew superhets or SSB transmitters with crystal filters, you really need one of these test sets, or one of the other designs out there, for obtaining crystal parameters. Jim's design provides very comprehensive testing.


Technical Solutions:

Making Twelfth-wave Matching Sections for Coaxial Feed Lines

Updated October 11, 2016

Coaxial feedlines can be easily matched to each other; for example you can use low-loss 75 ohm RG-6U to feed a dipole, and then bring 50 ohm RG-58U into the transmitter, matched at 1:1 SWR. Based on an article on Darrel Emerson, AA7FVs website at, There are several types of connectors and adapters to join the coaxial matching sections for the two main feed lines, and I have created a spreadsheet for performing the calculations for the length of the two matching sections required. Here's the solution.

Download an Excel spreadsheet to calculate 12th-wave matching sections here on this website.

Making Printed Circuit Boards

Here's the process I use to make printed circuit boards.

Restoration work on the Tempo 2020 transceiver - Updated - New source for sprockets!

I've restored 2 Tempo 2020 late '70s vintage transceivers. Here are some procedures (in downloadable PDF format) that I've developed for a couple of particularly difficult issues.

The DOS under Windows 32-bit problem:

If you are having problem running legacy DOS programs in Windows 32-bit, here's a solution: DOSBox, a free and still under development virtual x86 environment that runs on top of Windows 32-bit operating systems ( (Note: DOSBox is available for Linux, Mac OSX and FreeBSD as well.) Many DOS programs that ran in a DOS window under previous versions of Windows run full screen in XP, and there is no way to do a screen capture or printscreen. DOSBox provides its own environment such that the programs run in the DOSBox window. The screen resolution is best if you set it at 800 x 600. Note that since DOSBox is a virtual environment, it runs with a defined memory space, so you may have to temporarily close down other running Windows applications. So far, I have not had to do this. Note: I used version 0.63 when I was evaluating DOSBox. The next version, Version 0.65 gave me problems in running the programs. This was corrected in Version 0.70. Update: I downloaded Version 0.78 in March 2010, and it works with Windows Vista 32-bit (I have not tried DOSBox with Windows 7.) Another program, DosBlaster, is a convenient front end GUI application for DOSBox. That free utility can be downloaded from .

I was pleased to be able to provide WES Hayward, W7ZOI and Kirt Blattenberger of RF Cafe with this solution to their long-standing problem, that of getting certain of their older DOS software to run effectively under Windows 32-bit operating systems.

See Wes's web site and RF Cafe (link below) below for a detailed explanation with examples on how DOSBox is used with legacy programs under Windows.


Selected Web Site Links:

Here are some must-visit links to very fine technical information, used with permission:

Wes Hayward, W7ZOI is the author of many published articles and books on electrical engineering and amateur radio. His designs have inspired thousands of hams over the years to build their own equipment. His book, "Experimental Methods in RF Design", published by the ARRL, is truly one of the most influential works for amateur radio. Visit Wes' web site for updated info on his projects.

Markus Hansen, VE7CA documents his outstanding homebrew creation, the HBR2000 160 to 10 meter transceiver on his pages. Markus's remarkable design was published in the March 2006 issue of QST, and his further work continues with the rig, with details on his site. It is a beacon in the night to those of us who design and build our own equipment without the benefit of a degree in engineering.

If you haven't discovered the web site of Kees Talen, K5BCQ, go there soon. Boatanchor restorations. Vintage test gear, including repair tips on the AN-URM-25D sig gen (of which I have one.) The web's most extensive collection of information on the famous HBR-series of homebrew receivers, including photos, schematics, build notes, coil specs, and a lot more, including some new builds of these classic receivers. Info on how to get your SB-101/102 (or my HW-101) back in shape. If you want 21st century stuff, SDR. Si570 synthesizer. QRP. A veritable plethora of related accesssories. It's mind-boggling. I do not have any pecuniary interest in what you will find; it's just mind-boggling.

Ian Purdie, VK2TIP's excellent tutorials on basic electronics and circuit design.

For some top-notch information on portable HF antenna design and many other homebrew topics visit the web site of Phil Salas, AD5X.

Dean Hemphill, K5DH has a nice site with a lot of the same stuff that I like. That would be boatanchors, homebrewing, verticals and CW, to name a few. Dean has photos of 3 different versions of the venerable BC-348 that he has restored. I had a couple of those, long ago. He's also got a collection of FT-243 crystals that any boatanchor fan would drool over. Also, a clever homebrew iambic paddle key made using a switch contacts from an old mic. One of those old-time telephone switch jacks that I have would work well for that. A must-see item is his GOLD plated Nye Viking Speed-X straight key. He also has photos and descriptions of his mobile installation, with a rather unique antenna mounting arrangement.

If you haven't yet built a QRP rig for 30 meters, check out Jim Kortge, K8IQY's "Manhattan Madness" project page and the 2N2/30. It's evolutionary!

Morse keys and homebrewing...nice, if you have a shop full of power tools and are an accomplished machinist, right? Well, take a look at Richard Meiss, WB9LPU's work, and recalibrate your thinking! Here he provides some insight into his process and thinking, as well as many examples.

RF Cafe is a unique portal for RF and microwave engineering resources. There you will find a vast collection of original content with definitions, equations, references and conversions that cover electrical, mechanical, physical, chemical and mathematical fields. Many interactive calculators are available for everything from filters to voltage dividers. In addition, you will find extensive links to other websites for vendor parts, application notes, test notes, amateur radio information, technical magazines and books, patent and communications standards, and much more. Kirt Blattenberger does a fantastic job in maintaining this site. If you are designing a receiving system, check out his RF Cascade Workbook for Excel, and try out RF Workbench.

Rich Herzer, AF2CW's site. Rich originally contacted me regarding the then-new Straight Key Century Club details, and I got his permission to link to his site. Seems like everybody has a "Mega-Links" site on their page, but Rich has one that has my favorite topics...CW and Classic Radios, along with links to other popular Links sites, such as AC6V.

Ken, K4EAA's web site is dedicated to repair of Japanese hybrid rigs, particularly the popular Kenwood TS-520/820 and TS/530/830 series. Ken has done some amazing stuff, machining custom parts to improve these rigs. His dedication in producing color highlighted high-resolution, 36" wide schematics for the rigs is admirable. Ken has a lot of technical info on repairing (and tuning) these rigs, complete with great photos. Also check out his design for a 1 quart-sized 100+ Watt capable dummy load with built in RF sampling taps. I think I'll building one to supplement my old homebrew "cantenna" filled with 1 gallon of genuine Heathkit oil soon.

Lloyd Butler, VK5BR's web site contains a wealth of articles on theory and technical practices that he has written for the Australian journal "Amateur Radio", as well as several interesting technical projects and experiments. Be sure to check out his heterodyne sweep generator and other homebrew test microcontrollers required!.

Stefan Vorkoetter hosts a great site devoted to electronics and RC aircraft. There is a lot of common ground between ham radio and the RC community in battery performance, charging and maintenance. Stefan has a couple of very interesting projects that he has developed, including a really full-featured battery charging/conditioning system (BattMan II) that is controlled from a PC. The schematic, PC board artwork and Windows software is available for download from his site. The types of batteries that have customized charging profiles in the software include Nickel-Cadmium (NiCd), Nickel-Metal-Hydride (NiMH), Lithium-Ion (Li-Ion), Lithium-Polymer (LiPo), Lithium-Nano-Phosphate (LiNP), and Lead-Acid (Pb-Acid) batteries of 1.2 to 14.7 Volts. The hardware connects to the parallel port of a PC, and it works with all Windows versions from Windows 95 to Vista. Plots of charge and discharge cycles are generated during the process which mave be saved as image files. Sample screen captures are shown on the web site.


This web site was sparsely created using NoteTab Light on Windows XP and is now maintained using gedit on a couple of Linux Mint 17 machines.
Web site links are with the expressed permission of the owners.