K6XX's Writings

Here is an assortment of technical articles I have written for the JUG, the newsletter of the Northern California Contest Club. They discuss various rig modifications, etc. I have made that might interest you.

Attention newsletter editors: If you are interested in reprinting these things (that's a technical term) in your not-for-profit newsletter, e-mail me first. You must agree to some simple terms before publication.

A note regarding formats: most of the files are available both in standard web browser-compatible HTML format and Adobe Acrobat (.PDF) format. I recommend you first browse the HTML file on-line, and then download the PDF if you want a printed copy. Acrobat PDF files are very well compressed, yet the graphics print out with excellent quality--the schematics are much easier to read from a PDF printout. If you do not have the Adobe Acrobat Reader, follow the link into Adobe's web site. The reader is free.

Updated 10 February 2014


"Degetter" Gu-74 Tubes in your Amplifier	                 PDF
The K6XX Automatic Antenna Selector System                       PDF
FT-817 Portable Rig Information and Accessories           HTML      
Fast Relay--accelerate your power amplifier's relay       HTML   PDF
Grid Protection for Alpha 76A Amplifiers (also 374A & 78)        PDF
Intuitive StackMatch Controllers                                 PDF
FT-857 Serial Control Cable (Mic Jack)                           PDF
FT-857 Undocumented "Features"--Good & Bad                       PDF
Better QSK for the TS-950                                 HTML   PDF
Auxiliary Key Input for the TS-950                               PDF
Fix the TS-950 RF Gain Control (de N0SS)                         PDF
Kenwood-to-PC Serial Interface                                   PDF
Visual CW Tuning Indicator                                HTML   PDF
DuneStar 504 Filter Characteristics                       HTML   PDF
DuneStar 600 Filter Characteristics                       HTML   PDF
Super CMOS II Keyer "Cheat Sheet"                                PDF
IC-706 Amplifier Switching--control an external amp       HTML   PDF
CI-V and Band Select Output Interface for Icom Rigs       HTML   PDF
"Contestpedition" Cable for TR-Log and Icom Rigs          HTML   PDF
FT-1000MP Band Select Output and Amp Keying Interface     HTML   PDF
Decade Frequency Standard                                 HTML   PDF

Prepare Old-Stock Vacuum tubes before placing them in service [NEW 10 February 2014]

A completely automatic antenna selection system for up to six rigs has been developed, allowing single-knob control of multiple antennas. Each station may access any of the antennas not already in use. Each transmitter/amplifier always sees a suitable antenna for its band, and full protection keeps things safe. [12 October 2007]

The FT-817 is a very portable MF/HF/VHF/UHF all-mode QRP transceiver. Information on this rig, including performance graphs and accessory designs, is presented on this separate page. [Updated 2 March 2005]

Does your amplifier truncate the first portion of your transmission? On CW, does the T-R relay hot switch? If so, this document may help. It describes a circuit that accelerates the coil of DC relays by momentarily doubling their voltage.

Older ETO Alpha amplifiers use expensive 8874 (3CX400A7) triodes but have minimal protection circuitry built-in. Here is a small, low-cost board that will install inside your 76A, 374A, or 78 that will automatically protect against tube damage from excessive grid current.

Do you have an Array Solutions StackMatch? Want a new, more intuitive controller that doesn't have those small geometric shapes to decipher? Have a two-stack and want to save a few control wires? Have a look!

Here is a serial control (CAT) cable that plugs into the FT-857's microphone jack, freeing the CAT/Linear jack for other purposes.

The FT-857 has a number of undocumented features. Some I like, some I don't. What do YOU think about them? Have you found others?

I have an older TS-950 and it has absolutely horrible CW keying--especially in QSK mode. From the photos of keying waveforms in QST product reviews, this is a common problem afflicting many (most?) rigs. This document describes the timer I installed that compensates for unequal R-T and T-R delays in my '950. It now has a "perfect" CW waveform.

Another TS-950 quirk is that it uses the same jack for key input and paddle input. Kenwood obviously had no idea we'd use a computer or other external keying device as well. After playing inside the rig, I found a clean method of wiring an additional key input while still allowing use of the internal keyer. (Why use that lousy internal keyer? Well, it partially compensates for the horrible element shortening in QSK mode, described above).

A major bug in the TS-950 is an inoperable RF gain control and FM squelch. Kenwood denies the FM problem, but when forced will acknowledge the RF Gain fault. Thanks to Tom, N0SS for this detective work and writeup.

The "Super CMOS II" keyer, as shown in QST a few years ago, and also available as a commercial product, is a great keyer. But it has a non-intuitive method of control--its four push buttons serve several different purposes. I pasted a "cheat sheet" underneath mine in case I forget a necessary command. This sheet only has the commands I consider important, and does not have the truly trivial, everyday ones (like how to program message 1, for example).

I am naturally cheap (not thrifty--cheap), but I still want all the fancy features for my station. When serial control of transceivers became possible a few years ago, I wanted it! One of the necessary items was an interface box that was quite simple, yet Kenwood believed it was worth its list price of about $100. I disagreed.

My design is the simplest low-noise implementation anywhere--it does not need any active devices or power supplies. Several construction articles have since appeared in the magazines using ICs, but my simple little circuit has been working away for eight years without failure.

Another desired bell-and-whistle was the LED CW tuning indicator on the FT-1000MP. Here's how I added this feature to my rigs, using a FSK/Tone decoder IC. [Updated 8 March 1998]

Implementing a two-radio contest station, where either transmitter may be on-the-air without blowing up the other receiver, requires good bandpass filtering. Separate filters per band perform well, but delay band switching. DuneStar builds a relay-switched bandpass filter array that speeds up the process (to instantaneously, if the rig is properly interfaced). Here are the measured filter characteristics of the (older) five-band 504 and the newer six-band 600.

The Icom IC-706 does not have a T/R output for switching an amplifier. This circuit adds that function.
[Updated 25 August 1998]

An Icom IC-756 found its way to my shack shortly after its original introduction. It generated a lot of interest both on-the-air and in visits. Here are my thoughts after two weeks of ownership, plus the reasons it no longer is a part of my shack.[Updated 31 May 97] Note: this rig was not one of the greatly improved later versions.

One good thing resulting from the IC-756 boondoggle was the enjoyable time spent designing a serial interface for PC control and an automatic band switching interface. These circuits are compatible with all medium-to-late model Icom rigs. [Updated 8 December 1997]

Traveling with the IC-706 is relatively easy due to its small size. A cable that allows CW keying (keyboard and paddle inputs), PTT control, and serial frequency control via a notebook PC was designed to eliminate carrying several extra boxes. [15 March 1998]

An FT-1000MP on loan? Well, we must work it into the lineup! This interface box controls the DuneStar filters and keys the amplifier without the noisy internal relay. This box works with the "Mark-V" as well. [Updated 16 June 2000]

Here is an accurate local frequency standard for your radio station. [19 April 1998]

Are any of these papers of interest? If so, please let me know. Send me e-mail at k6xx@arrl.net

73 de Bob, K6XX

E-mail: Bob Wolbert, K6XX

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