Archive for category Amateur Radio

Bike Helmet Boom Mic: Housing

The last time around, this involved silver soldering the boom wire directly to the mic housing. This time, I filed a fishmouth in the smaller tube and epoxied it to the tube that’ll hold the mic capsule:

Bike Helmet Mic Boom - housing

Bike Helmet Mic Boom – housing

The smaller tube is a loose slip fit for #10 copper wire, but that’s really too heavy for the boom. I’ll probably nestle #12 wire inside another tube and epoxy that whole affair in place.

The mic capsule tube needs a rounded notch filed in one end to accommodate the wire.

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Monthly Image: Hudson River Boating

Much of the boat traffic on the Hudson consists of barges shuttling bulk commodities between the Atlantic and the Port of Albany. I think this is a crude oil barge, based on the Christmas Tree plumbing that was more visible when it passed under the Mid Hudson Bridge:

Walkway and Barge - from Mid Hudson Bridge

Walkway and Barge – from Mid Hudson Bridge

We crossed the Walkway Over the Hudson westbound, where a work crew was tending a crane. That’s how they do repair and inspection:

Walkway Inspection Crane - from Mid Hudson Bridge

Walkway Inspection Crane – from Mid Hudson Bridge

The Hudson River has far fewer power boats than in years gone by, probably due to their gallon-per-minute fuel consumption:

Power boat on Hudson River - from Mid Hudson Bridge

Power boat on Hudson River – from Mid Hudson Bridge

It was a fine day for a ride:

KE4ZNU - APRS track 2014-06-30

KE4ZNU – APRS track 2014-06-30

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3D Printed Things I’ve Designed: Brag Sheets

The whole reason I got a 3D printer in the first place was to make things that would otherwise be too difficult or tedious by hand or on a CNC mill. Most of the things I make look like brackets and I don’t do sculptures … this stuff solves problems!

Being able to go from “I need a part shaped like that” to holding the thing in my hand a few hours (or, for complex designs, days) later is empowering. Being able to adjust a dimension by changing the source code and “recompiling” to get a new part is wonderful.

These five slides from the presentation show my answers to the question “Why would anyone want a 3D printer?” Clicky for more dots.

Things I Designed - 1

Things I Designed – 1

Things I Designed - 2

Things I Designed – 2

Things I Designed - 3

Things I Designed – 3

Things I Designed - 4

Things I Designed – 4

Things I Designed - 5

Things I Designed – 5

You can find those and more by searching for OpenSCAD source code.

They go along with the sheets of solid models.

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Plastic Stress in Polarized Light

Here’s what the (cracked) faceplate of the FC1002 Frequency Meter looks like, through polarizing filters that reveal the internal stress.

A circular polarizer screwed on the lens:

FC1002 Frequency Counter - faceplate - circular polarizer

FC1002 Frequency Counter – faceplate – circular polarizer

A sheet of linear polarizing film held in front of the lens:

FC1002 Frequency Counter - faceplate - linear polarizer

FC1002 Frequency Counter – faceplate – linear polarizer

For reference, none of the other instrument faceplates on the bench show anything other than uniform gray, with one exception that points directly to the plastic injection point.

I’d say this plate cracked due to unrelieved internal stresses and not anything I did or didn’t do.

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FC1002 Frequency Counter Battery Pack

The main reason for taking the FC1002 frequency counter apart was to replace the failed quad-AA NiCd battery pack. Rather than buy new cells with tabs, I recycled some low-discharge “ready to use” NiMH cells from the heap. Back in 2009, they looked like this:

Tenergy RTU Pack A Tests - Aug 2009

Tenergy RTU Pack A Tests – Aug 2009

Nowadays, they’re a bit less peppy:

Tenergy RTU - 2014-01 - loose cells

Tenergy RTU – 2014-01 – loose cells

The red blooper shows that you can’t trust a smart fast charger to get the right answer; it concluded that pair was fully charged. After the discharge test and an overnight C/10 charge, they regained as much enthusiasm as they’ll ever have.

They have slightly less capacity than in 2009 and also a somewhat lower terminal voltage. That shouldn’t matter here, as the frequency meter has a power supply to take care of that problem.

Although I’ve sometimes been able to (quickly!) solder directly to ordinary AA cells, a trial run on a defunct RTU cell showed that wasn’t going to work on whatever variety of steel they used, no matter how much I scuffed it and despite using aggressive flux that normally blends silver solder onto stainless steel.

Fortunately, the top half of a four cell case fit exactly in the space available, so I used woven copper fabric tape inside the case to interconnect the cells, then lashed everything together with the obligatory Kapton tape:

FC1002 Frequency Counter - battery pack

FC1002 Frequency Counter – battery pack

That cracked faceplate isn’t the nicest thing to confront, but it’ll suffice until I get more motivation:

FC1002 Frequency Counter - repaired

FC1002 Frequency Counter – repaired

I’ve misplaced my stack of Round Tuits again…

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FC1002 Frequency Counter Faceplate Repair

The plastic faceplate over the display cracked quite a while ago:

FC1002 Frequency Counter - cracked plastic

FC1002 Frequency Counter – cracked plastic

I don’t recall dropping the poor thing. Given the interesting pattern, it could be inherent stress that finally let loose as the plastic aged.

While I have it apart to rebuild the battery pack (more on that later), I’ve been easing acetone/MEK into those cracks by capillary attraction in the hopes of dissolving just enough plastic to rejoin them, without slobbering solvent all over the faceplate and scarring it.

If all else fails, I suppose I can mill out a replacement from thin acrylic sheet, but those nicely rounded cast / molded edges lie well beyond my abilities…

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2000 Toyota Sienna: Short Battery Adapter

Although automobile batteries have “standard” sizes designated by BCI Group numbers, this Group 34R Sears Diehard battery was about an inch shorter than the previous one:

Toyota Sienna - short Group 34 battery

Toyota Sienna – short Group 34 battery

It arrived with a plastic grid embossed with the helpful notation “Use this height adapter under battery if necessary”, but I figured lower was better. A little bending, two snippets of mouse pad (remember mouse pads?), and a section of white plastic rod faced off / drilled on the lathe anchored it flat on the platform with no wiggle room at all.

With any luck, that’s the last battery the van will ever need…

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