J-37 key project update, and a lesson about mic quality …

Sunday, Oct. 11, 2015 — I’m still working on my J-37 keyer/straight key combo, and I think I’m close to getting ready for paint. I’m going to go with the traditional pre-WWII japanned base with gold carriage striping. I have filled all the holes in the base, primered it and wet sanded and reprimed it a couple of times. I’m ready for the final wet sanding, then paint.

What I would like to do is to give the base a solid coat of black, paint the striping, then give it a clear coat. That way the gold striping is protected by the clear coat; it won’t wear off. That’s the plan, anyway.

The base took some work, but its going to look good. I had considered cutting the base down to a smaller size, but I think I’ll just use it as-is.

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The first “shotgun” mic I purchased had a molded on cable that wasn’t grounded to the mic casing. Unfortunately it was a POS.

MICROPHONE MALADY?  In my other life (the one outside ham radio and code keys), I shoot video of local government meetings for news gathering purposes. I was first handed a GoPro, which worked, but had some serious limitations — audio quality being a biggie. Knowing the audio just plain sucked, I upgraded to a Canon Vixia consumer camcorder.

The Canon audio was much better, however in some of the meetings, the elected officials mumble at low volume. Clearly I needed a good “shotgun” microphone — a directional microphone used to capture distant or weak audio. Hello eBay!

The first one I bought worked pretty well; because the Canon did not have a built-in hot or cold shoe mount (for a flash, a light or mic), I had to use an outboard mount that attaches to the tripod. A little Rube Goldberg, but it works well and is reliable.

But the Canon has an internal battery that cannot be swapped out without removing it from the tripod mount (the battery door is on the BOTTOM). Later cameras have the battery mounted at the rear of the camera, which makes it a breeze to replace a dying battery with a fully changed one. Since I can’t easily change the battery (which is only good for about 45 minutes of recording time), I end up plugging in the AC adapter for the camera and recording that way.

As you probably can guess, wall warts are notoriously noisy devices in the RF spectrum; and the DC they create isn’t exactly devoid of AC components. Recording video with the AC adapter added a low-level 60 Hertz hum to my audio … not so much with the camera mic, but more so with the mic, and incredibly loud with the mic in “tele” mode (the most directional mode).

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The RODE Videomic Pro was a less-than-cheap fix to my problems. It is a quality product and worth every penny.

Being a ham, I thought to myself, “Self, I can fix this!” The mic had a coiled cord and was terminated in a 3.5 mm plug. The hum varied from noticeable to obnoxious, depending on the charge of the battery (my theory). I needed the use of the “tele” function in the worse way, but the hum was unacceptable. I decided to shorten the cable and I found out that the ground on the cable wasn’t directly connected to the metal microphone case. I cut the cable off and replaced it with a better quality (better shielded) cable. This reduced the hum considerably, but did not eliminate it.

I got frustrated with the damn mic and decided I needed to simply pony up and pay the piper — it was time to buy a name brand quality microphone. I purchased a RODE Videomic Pro — not a cheap mic, but it was a great investment. It eliminated the power supply hum the mic was picking up, and it has some features that make it just perfect for what I need it to do.

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This inexpensive shotgun mic uses an XLR connector and was a quality alternative mic that provided hum-free audio.

I also bought a less expensive mic — a traditional shotgun mic — that uses an XLR connector and a much better shielded cable. This mic is head and shoulders above the first one I bought, and if I hadn’t purchased the RODE first, I probably wouldn’t have plunked down the money for it. I’m not inclined to sell the RODE however; the new shotgun is on the order of 15 inches long, not exactly a svelte thing to point around. The RODE is much more compact and easier to pack around in my camera bag.

The lesson here? 1. Cheap-ass mics have cheap-ass cables; 2. All the jury-rigging in the world can’t fix a bad design; 3. XLR cables are superior in their ability to reject hum; 4. Why aren’t there more resources available on adding simple filters to reduce AC hum from wall warts?

Yeah, I know, I could improve the filtering of the wall-wart supplied DC easily, and that was my next move. In the end, it was the mic quality that solved it, no need to mess with the supply quality.

Well, enough non-ham radio stuff … I’ll have more on my key project next update, promise!

73 de KY4Z … sk   CL  …. dit dit ….