Housings for RF probes

The question of housings for RF probes came up recently on both the Heathkit Yahoo list and the Antique Radio Forum's test equipment forum. Here's a couple of approaches that I've tried.

The classic method is to use an aluminum cigar tube. I'd been saving these for forty years before finally putting one to use. I scarfed them off my dad, though he didn't smoke cigars so I've no idea how he came by them. He probably scarfed them off a buddy and saved them to make RF probes :-)

This probe is a RF probe for my IM-11 VTVM, using the circuit that's been in the ARRL Handbook for umpty-ump years.

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I use a vinyl grommet where the coax enters the tube.

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The probe tip is mounted in the plastic cap.

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I use H. H. Smith model 200 insulated phone tip plugs as the tips for my homebrew probes.

For cigar tubes, I mount them using the plastic handle of the plug as a nut.


For another approach, I use K & S brass tubing from my local model railroad hobby shop. This probe is for my Knight signal tracer, so it's switchable between a straight-through probe and a demodulating RF probe using a subminiature slide switch mounted on the side of the probe housing.

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I used a female BNC connector rather than hard-wiring coax to the probe.

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Again, I used a H. H. Smith model 200 insulated phone tip plug as the tip for the probe.

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You could mount the probe tip plug and the BNC jack using styrene or ABS tubing from the hobby shop to shim down the diameter of the brass tube, but I elected to fabricate the ends from telescoping sections of brass tubing soldered together. If I had a lathe, I'd have turned them from brass stock; it would be cheaper and easier.

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I glued the tip plug in using Walther's Goo. I tapped the other end-piece to match the threads on the BNC jack.

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And that's it.


© Steve Byan 2011-2016