A BONIFIDE INSPIRATION: N6GA'S TFR 40-40 TRANSCEIVER

 

 

Editor's note: The tiny, versatile Elecraft KX-1 transceiver was inspired, in part, by a transceiver built by longtime QRPer Cam Hartford, N6GA, who submitted an excellent homebrew rig in the Adventure Radio Society's "Trail Friendly Radio" competition in the late 1990s. Here's his article that led to a whole new way of looking at QRP radios for the field.

 

By Cam Hartford, N6GA

Contributing Editor, The ARS Sojourner

 

As with most of my construction projects, this one began with the box. I pick up stray boxes and enclosures at local swap meets and stockpile them in case a needy radio shows up looking for a home. My criteria for such boxes is undefined, except that it just has to "look" useful. No way to define that. It's just whatever catches the eye.

 

This particular box must have housed some UHF / data interface doo-dad, judging by the empty connector holes. No matter, it was made from 1/4 inch aluminum bar stock with hefty aluminum plates for the top and bottom. Nice and sturdy. Not best for a micro-ounce radio, but solid enough for the rigors of the trail. I had been formulating a rig to put inside the box for about a year when the TFR Challenge came up. Suddenly it gelled. I was having trouble finding a way to mount all the controls on the front panel and all the connectors on the back, in traditional table-radio fashion. The TFR concept gave me the freedom (and the idea) to mount the controls wherever I pleased. Suddenly the parts fit, and the idea became a radio.

 

 

 

Inside the box is everything one needs to get on the air, minus headphones and antenna. The transceiver is an NE 40-40, interfaced with a KC-1 to give frequency readout and keyer functions. A single-band modified Z-match (from the portfolio of Charlie Lofgren, W6JJZ) along with an absorptive bridge SWR circuit provide matching to any random trailside antenna. For power, a 10-pack of AA batteries is included. To key the rig, a set of Galbraith paddles mount on the top of the box.

 

 

 

Because of the size and shape of the box, and the mounting location of the paddles, the box provides a place to rest your hand while keying. While sitting on the ground, a log, a canoe seat or the seat of a car, you can set the rig on your lap and be very comfortable as you operate. You can also set it on the ground next to you and readily access the paddles and controls.

 

 

 

 

The main tuning control (a 10-turn pot), the RF gain control and the KC-1 controls are mounted on the top of the box, next to and very close to the keyer paddles. The tuner controls, which don't need to be accessed as often, are mounted on the back panel, out of the way of operations.

 

I gave the rig a shakedown in the 1996 QRP ARCI Fall QSO Party. The first contact I made with it was from the parking lot of a local swap meet on Saturday morning.

 

I was showing the rig to Richard Fisher, KI6SN, and Charlie Lofgren, W6JJZ, and to do so I had it plugged into a 40 meter Hamstick mounted on the roof of my car with a magnetic mount. Not hearing much activity, I called "CQ QRP" and to my surprise was answered by AE0Q, operating portable in Wyoming. Not bad for 1 watt and a pretty inefficient antenna. Instant KW/mile.

 

On a Sunday I drove to the mountains to get in some quality contest operating time. Forty meters was pretty much a bust in the daytime, so I stuck to 20 meters. After packing up to leave, I again attached my TFR to the mobile whip so I could monitor the waning moments of the contest as I drove home. I heard W7ZOI calling QRZ, gave him a call, and snagged him. What a fitting way to end the contest.

 

This is going to be a fun radio to pack around. Thanks to the ARS for providing the impetus to build it, and thanks to Mike Herr, WA6ARA, for providing the spark that started it all.

 

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Cam Hartford, N6GA, is a veteran QRPer and builder living in Claremont, CA. He is also a contributing editor to The ARS Sojourner.

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