Archive for category Amateur Radio

APRS Electronics Case Power Contacts

Mary reported hearing occasional beeps during a recent ride that indicated the Wouxun KG-UV3D radio on her bike was rebooting. It turned out that the nut soldered to the lug atop the screw contacting the radio’s battery contacts had turned itself slightly loose on the stud:

HT-GPS Case - PCB and battery contacts - end view

HT-GPS Case – PCB and battery contacts – end view

Snugging it up against the PCB made everything happy again.

However, while I had the APRS box off, I added strips of copper tape to enhance the connection to the radio:

KG-UV3D APRS interface - power contacts

KG-UV3D APRS interface – power contacts

Mostly, those gadgets just keep working…

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Bicycle GPS Track: Diggin’ Deep and Flyin’ High!

At first glance, I thought Mary had taken a tour of The Great Swamp south of the Vassar Farm gardens:

APRS Bicycle Tracking - Flying High

APRS Bicycle Tracking – Flying High

Having helped put the fence up, I’m absolutely certain nothing growing in the garden could get her to 4373 feet, much less boost the bike that high.

Before that, it seems she did some high-speed tunneling:

2015-05-10 18:17:31 EDT: KF4NGN-9>T1TP4X,WIDE1-1,WIDE2-1,qAR,KB2ZE-4:`eP}nAIb/"/k}
   type: location
   format: mice
   srccallsign: KF4NGN-9
   dstcallsign: T1TP4X
   latitude: 41.67466666666667 °
   longitude: -73.88283333333334 °
   course: 345 °
   speed: 42.596 km/h
   altitude: -371 m
   symboltable: /
   symbolcode: b
   mbits: 101
   posresolution: 18.52 m
   posambiguity: 0

The bike’s altitude began falling while she was on the way to the garden, from a reasonable 66 meters on the entrance road, bottoming out at -371 m as she hit 42.6 km/h (!), rising to 1341 meters with the bike leaning against a fence post, and returning to 53 meters as she started riding home.

Obviously, you shouldn’t trust consumer-grade GPS tracks without verification: it can get perfectly bogus numbers from fixes with poor satellite geometry. Altitude values tend to be only close, at best, even when you’re not too fussy about accuracy.

We experienced small-scale jitter in New Jersey and a friend carrying a commercial satellite link experienced similar randomization. Trust, but verify.


Monthly Image: Bootleg Bell Ringers

MHVLUG meetings end around 8 pm and, depending on this-and-that, the bell atop Old Main on the Vassar College campus will be tolling the hour as we emerge. Here’s a scene-setting photo from Wikimedia, taken from about where I parked the car:

Vassar College Old Main Building

Vassar College Old Main Building

Although the bell didn’t have its usual steady rhythm after the most recent meeting, I didn’t expect this:

Bell Ringers atop Vassar Old Main

Bell Ringers atop Vassar Old Main

The tree grows in the near foreground, not over Old Main.

Two of them realized the risk of permanent hearing damage, but do you see the real hazard?

Take a closer look:

Bell Ringers atop Vassar Old Main - detail

Bell Ringers atop Vassar Old Main – detail

No, it’s not the guy leaning against the historic-but-flimsy railing. That folded-dipole antenna over on the right side most likely connects to Vassar’s 45 W UHF EMS repeater; at that range, RF can burn deeply.

Obviously, the student body needs more amateur radio operators…

Taken with the Canon SX230HS braced on the side of the Forester and zoomed all the way.


APRS Turn Slope Units

There’s a fundamental error in my writeup about setting the APRS Smart Beaconing parameters for the bike trackers: I blundered the units of Turn Slope.

Rich Painter recently explained how that works:

I ran across your blog on Smart Beaconing and saw something that needed correction.

You state the Turn Slope is in units Degrees / MPH

This is incorrect. Although the term Turn Slope is not a real slope (such as rise/run classically) that is what the originators used albeit incorrectly. They do however correctly attribute the units to MPH * Degrees (a product and hence not really a slope).

In their formula they calculate a turn threshold as:
turn_threshold = min_turn_angle + turn_slope / speed

Looking at the units we see:
= Degrees + (MPH * Degrees) / MPH

which yields
= Degrees + Degrees

Which makes sense. It is too bad that the originators used the wrong term of Turn Slope which confuses most people. A better term would have been Turn Product.

In looking back over that post, I have no idea where or how I got the wrong units, other than by the plain reading of the “variable name”.

As he explained in a followup note:

As for units… I was introduced to making unit balance way back in 1967-1968 science class in HS by a really fine science teacher. It has served me all my life and I’m thankful for that training.

I have ever since told that teacher so!

A while back, our Larval Engineer rammed an engineering physics class head-on and sent me a meme image, observing that I’d trained her well: if the units don’t work out, then you’re doing it wrong.

Yes, yes, I do care about the units:

Give a shit about the units

Give a shit about the units


Sony HDR-AS30V Audio vs. Wind Noise

With the Sony HDR-AS30V in its skeleton frame atop my bike helmet, the audio track for all my rides consists entirely of horrendous wind noise. You can get an idea of the baseline quality from the sound track of a recent Walkway Over The Hudson crossing.

The camera has two mics, although I’m not sure 15 mm of separation really produces meaningful stereo sound:

Sony HDR-AS30V - front view

Sony HDR-AS30V – front view

Note that two of the five pores on each side are closed flat-bottom pits. As with earbud vents , it must be a stylin’ thing.

I added a rounded pad of the same acoustic foam that forms an effective wind noise buffer for the boom mic:

Sony HDR-AS30V - foam mic cover

Sony HDR-AS30V – foam mic cover

That reduced the overall noise load by buffering direct wind impact, but non-radio conversations remained unintelligible; there’s just too much low-frequency energy.

Surprisingly, closing the mic pores with ordinary adhesive tape didn’t impair the audio in a quiet room:

Sony HDR-AS30V - closed mic pores

Sony HDR-AS30V – closed mic pores

Out on the road that’s even better than foam over open mic pores; I think it reduces the peak volume enough that the internal compression can regain control. Sticking the foam pad over the tape slightly reduced the noise during high-speed (for me, anyhow) parts of the ride, but didn’t make much difference overall.

The wind noise remains too high for comfort, even if I can now hear cleats clicking into pedals, shifters snapping, and even the horrible background music when I’m stopped next to the Mobil gas station on the corner.

Next step: raid the cloth scrap box for a flap of faux fur to make a mic mop. This might be an opportunity to recycle some roadkill


If You Can Get To BNC, You Can Get To Anything

That’s what Mad Phil taught me, back in the day, and it’s still true:

15 W Dummy Load - Stacked Adapters

15 W Dummy Load – Stacked Adapters

From the top:

  • 15 W dummy load with N female
  • N male to BNC female
  • BNC male to UHF female
  • UHF male to UHF male
  • UHF female on homebrew antenna mount

Obviously, I don’t have enough adapters: I need one with N male to UHF male.

I actually spent money to get from the reverse-polarity SMA connector on the Wouxun radios directly to UHF female, matching the cable to the antenna mount in one step.

Sometimes an unsteady ziggurat of adapters isn’t appropriate.


Tour Easy: Arkel RT-40 Underseat Packs vs. HT Mount

I just replaced the rather old and tattered Easy Reacher underseat packs on my Tour Easy ‘bent with shiny new Arkel RT-40 packs:

Arkel RT-40 bag on Tour Easy - front view

Arkel RT-40 bag on Tour Easy – front view

The retina-burn white reflective tag under the black hand strap is actually a foreshortened view of the Arkel logo.

They’re longer and taller than the old packs, which isn’t entirely a Good Thing: the inside bag gently kisses the pavement during steeply banked high speed turns. The main compartment is slightly narrower, so I bent the license plates (which used to fit neatly on the bottom) to form a hard floor with a low lip on the inside edge. That, in combination with tightening the pack’s internal strap, prevents the foam-core bottom panel from drooping; maybe the edge won’t hit the pavement quite so often.

They also ride much higher on the racks. To install the packs, I had to unbolt the seat to raise it upward, slide the packs underneath, twiddle the clamps onto the rack rods, then reinstall the seat. Those puppies are not getting loose without tools and a struggle!

Because they’re longer, the right pack collided with the HT mount behind the seat:

Arkel RT-40 bag vs HT holder

Arkel RT-40 bag vs HT holder

So I moved the mount up to the middle crossbar:

Arkel RT-40 bag - relocated HT holder

Arkel RT-40 bag – relocated HT holder

I’m not entirely happy with that arrangement, as the holder sits snug against the rear packs. So far, I rarely need those in addition to the RT-40s, as each underseat bag can swallow an upright gallon milk jug or two Butternut squashes in addition to all the other stuff I normally carry.

The array of reflective patches and piping and pull tabs probably makes me look (more) like a low-flying UFO at night, but that’s fine with me: the more it resembles a UFO, the less hassle I get.


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