KA8MAV RF Probe

KA8MAV

KA8MAV RF Probe
Build Date: 11/25/2001

This is the RF Probe I built for the Elmer 101 (2001) Course. It's no secret I like to make things "tiny". As with most projects, I always have trouble finding just the right enclosure. This was no exception. I wanted something small, metal, and with a point on one end. I looked and looked... but couldn't find the "perfect" enclosure. While I was sitting at my desk thinking... and staring at my straight key... I saw something. There... right in front of me was the answer. An 1/8" (3.5mm) Shielded Phone Plug!

Please see the Kits & Parts page for ordering details.

Schematic Note: I take no credit for the RF Probe circuit design. Similar circuits have been available in the ARRL Handbook for decades. The only thing I do take credit for is fitting it inside a 1/8" shielded phone plug.

KA8MAV RF Probe The alligator clip jumpers aren't the best thing to use. Shielded cable would be better. But, these were just sitting there and they make it easy to clip to the leads of my DVM. I simply clipped off one end of each. Note: Most alligator clip jumpers are NOT soldered to the wires. Pull back the rubber covering and check them first. Solder the clips to the wires if needed. These came from Radio Shack and were already soldered.

I used a gold-plated header pin as the probe tip. I first used a wire brush on my Dremel to clean the tip of the phone plug. Then, I tinned it with solder. Once it was ready with a little glob of solder on the tip, I touched the header pin and the soldering iron to it quickly to solder the probe tip onto the phone plug. The red covering is a rubber toggle switch cover from Radio Shack with a pin hole poked into the end of it. Once the header pin was soldered onto the end of the phone jack, I simply slid the red cover over the end.

Here's a photo of the inside of the RF Probe. Notice the clear rubber tube covering the components? This is a shielded 1/8" phone plug from Radio Shack. Not only are they GREAT for RF Probes, but they make pretty decent connectors for keys too!

A closer look at the insides. I used the bodies of the components themselves to insulate them from the surrounding metal (GND). Yes, that's a 1/2 watt resistor crammed in there. I also used a little file to clean up the solder joints a bit as they had some sharp points on them.

Here is a much closer look. This shows HOW I used the bodies of the parts as insulators. Also, be VERY careful bending the leads this tightly. That's the second diode I used as the first one shattered. They really are glass! Little glass shards everywhere. Be careful. Check your work with a magnifying glass to make sure there aren't any solder bridges.

To Be Continued...

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