Archive for category Amateur Radio
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:
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:
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:
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.
That’s what Mad Phil taught me, back in the day, and it’s still true:
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.
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:
So I moved the mount up to the middle crossbar:
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.
The signs at every Dutchess Rail Trail grade crossing and access point seem unambiguous:
More specific signs appear at random intervals along the trail:
You can’t see it, but every sign includes an invisible asterisk introducing the invisible clause “Except Cops”:
Back when the Dutchess County deputy sheriffs rode huge ATVs that occupied nearly the entire paved trail and bulldozed everybody out of their way, I had the temerity to ask why they weren’t riding bikes. The deputy sheriff told me, rather condescendingly, that they had to be prepared for anything and that there had already been incidents.
These little ATVs aren’t quite so imposing and, more likely, also fit on the new bridges and between the bollards, which may explain everything.
I’ve seen what might be their best use case, although ambulances can attract your attention without an ATV escort:
Straight up, I have no objection to police patrols on the rail trail.
I do object to the official mindset that simply adds an invisible exception to any inconvenient rule.
As I see it, the root cause of the militarized police and extralegal government activities we’ve seen across the country in recent years boils down to “That law / regulation / rule does not apply to us, because we are the government.”
I can ride the length of the DCRT and back in about two hours, averaging 12 mph, without getting particularly sweaty in the process; the track in that link shows a three hour ride that includes the HVRT and a Walkway scrum, plus the ride from and to home. A police ATV can’t go much faster than that on the trail, even with lights and sirens, because oblivious pedestrians keep getting in the way.
If an officer on a bike can’t keep up with me, then something has gone badly wrong with the job requirements for becoming a deputy sheriff.
As far as “being prepared for anything” goes, the cargo capacity of those little ATVs rules out a bunch of hardware that fit in the big ones: anything seems an elastic concept. A bike can carry enough equipment for many incidents; my tool kit weighs more than some bike frames, the packs have plenty of room to spare, and there’s always the trailer option. I doubt genuine Mil-Spec assault rifles would come in handy on the rail trail.
It’s also not clear why an officer on a bike can’t call for the same backup as an officer on an ATV: those buggies lack fancy VHF antennas, so they’re using a hand-held radio or phone. The 5 W amateur radio on my bike, through a mobile VHF antenna on a crappy ground system, can easily reach local amateur radio repeaters and APRS nodes. Many pedestrians seem absorbed with their phones, so getting microwaves into and out of the trail doesn’t pose much of a problem.
Cops-on-bikes present a much less aggressive aspect than cops-on-ATVs who ignore the rules that apply to the rest of us.
They could do it differently, as the department has both bikes and ATVs.
While installing new underseat packs (about which, more later) on my Tour Easy, I discovered a bight of PTT cable had been touching the top of the chain:
The gentle ripples to the right of the worn-through section seem particularly nice; you couldn’t do that deliberately if you had to.
This section of cable should have been taped to the upper frame bars. It’s hidden under the seat, just in front of the rear fender, and between the under-seat packs, so it’s basically invisible from any angle.
Soooo, that probably explains a bit of the intermittent trouble I’d been having with the PTT switch, although most of it came from the corroded switch contacts.
Rather than replace the whole cable, I cut out the eroded section, spliced the conductors, and taped it firmly back on the tubes.
The handlebar-mounted PTT button for the amateur radio on my bike once again went toes-up, most like due to the accumlation of road dust and rainwater over the years. Rather than replace the switch, which would require peeling off a massive glob of hot melt glue and resoldering the wires, I just carved the tops off the rivets holding the cover in place, pried off the cover, and removed the button to reveal the top of the switch dome:
The dome flexes outward to contact the (rather crusty) terminals on either side, so all the action happens under the dome.
A lineup of the plastic button, the inverted dome, and the cover plate:
The top and bottom of the dome show some grit: that’s where it contacted the switch terminals.
Wiping the crud out of the switch body, scrubulating everything with contact cleaner, and putting it all back together restored the switch to working order. There’s (once again) a snippet of Kapton tape over the cover holding it in place, but I don’t expect this to last very long:
But it works well enough for now …
I’d like to overlay a timestamp on still images extracted from Sony HDR-AS30V camera videos, ideally including the frame number, to record exactly when the incident occurred. Movie players use relative time, with 00:00:00 at the beginning of the file, so we’ll need either the file timestamp or the timestamp recorded in the image’s Exif data, plus the frame number modulo 60 (or, shudder, 59.94 for NTSC).
The ExFAT format used on 64 GB MicroSD cards stores the file’s creation time, its modification time (writing data), and the most recent access time (reading data). That’s similar to the Linux ext2/3/4 filesystem time and unlike plain old FAT, which omits the access time.
The various FAT formats store local time, with no regard for time zones, Daylight Saving Time, or anything else. Linux stores times as UTC and converts to local time on the fly. This has catastrophic consequences for getting any of this right.
It helps to have
alias ls='ls -h --color=auto --time-style=long-iso' in your
The HDR-AS30V has a year-month-day calendar, a 24-hour clock, a Time Zone value, and a separate DST on/off setting.
Turning DST on adds 1 hr to the Time Zone value, turning it off subtracts 1 hr. That has the side effect of changing the clock time: not what I expected. You must, therefore, set the TZ first, then DST, then the clock, which does not follow the menu’s natural order of things.
The camera sets file timestamps as it creates the files, but Linux also meddles with the values while displaying them. Some doc suggests that Linux regards FAT file timestamps as UTC and applies DST correction, which seems to match what I see. There’s a mount option (
-o tz=UTC) that seems to have no effect, as well as an undocumented time offset (
-o time_offset=60) that also has no effect.
Setting the TZ to GMT+0 (Sony uses GMT, not UTC) for simplicity, setting the clock to the correct local time, and twiddling DST shows that:
- Rebooting (remove /insert battery) doesn’t change anything
- Metadata in file = clock setting – DST setting (-1 on, +0 off)
- MP4 / THM file create / modify times = always clock +1 hour
- MP4 / THM file access times = as create / modify until next Linux access
Under those conditions, with the clock set to (locally accurate) 1908, UTC+1, and DST off, then the Exif timestamp metadata for a movie created at that time look like this:
exiftool /mnt/part/MP_ROOT/100ANV01/MAH00036.MP4 | grep -i date File Modification Date/Time : 2014:09:01 20:08:09-04:00 File Access Date/Time : 2014:09:01 19:10:14-04:00 File Inode Change Date/Time : 2014:09:01 20:08:09-04:00 Create Date : 2014:09:01 19:08:03 Modify Date : 2014:09:01 19:08:08 Track Create Date : 2014:09:01 19:08:03 Track Modify Date : 2014:09:01 19:08:08 Media Create Date : 2014:09:01 19:08:03 Media Modify Date : 2014:09:01 19:08:08
The corresponding filesystem values:
ll /mnt/part/MP_ROOT/100ANV01/ total 146M ... snippage ... -rwxr-xr-x 1 ed root 14M 2014-09-01 20:08 MAH00036.MP4 -rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM ll -c /mnt/part/MP_ROOT/100ANV01/ total 146M ... snippage ... -rwxr-xr-x 1 ed root 14M 2014-09-01 20:08 MAH00036.MP4 -rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM ll -u /mnt/part/MP_ROOT/100ANV01/ total 146M ... snippage ... -rwxr-xr-x 1 ed root 14M 2014-09-01 19:10 MAH00036.MP4 -rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM
The THM file contains a 160×120 pixel JPG thumbnail image taken from the first frame of the corresponding MP4 file. For longer movies, it’s more obvious that the MP4 file creation date is the start of the movie and its modification date is the end. The maximum 4 GB file size of corresponds to exactly 22:43 of 1920×1080 movie @ 60 frame/sec (the metadata says 59.94).
The +1 hour offset in the file create / modify times comes from the FAT timestamp being (incorrectly) adjusted by the Linux DST setting. When exiftool reads the MP4 file, that resets its access time to the actual time as seen by Linux, thereby crushing the bogus FAT time.
Doing the seemingly sensible thing of setting the camera to have the correct local time (roughly 1930), the correct time zone, and the correct DST setting produces this jumble:
exiftool /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4 | grep -i date File Modification Date/Time : 2014:09:01 20:33:15-04:00 File Access Date/Time : 2014:09:01 20:33:14-04:00 File Inode Change Date/Time : 2014:09:01 20:33:15-04:00 Create Date : 2014:09:01 23:33:11 Modify Date : 2014:09:01 23:33:14 Track Create Date : 2014:09:01 23:33:11 Track Modify Date : 2014:09:01 23:33:14 Media Create Date : 2014:09:01 23:33:11 Media Modify Date : 2014:09:01 23:33:14 ll /mnt/part/MP_ROOT/100ANV01/MAH00037* -rwxr-xr-x 1 ed root 11M 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4 -rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM ll -c /mnt/part/MP_ROOT/100ANV01/MAH00037* -rwxr-xr-x 1 ed root 11M 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4 -rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM ll -u /mnt/part/MP_ROOT/100ANV01/MAH00037* -rwxr-xr-x 1 ed root 11M 2014-09-01 19:34 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4 -rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM
The only correct time in that mess is in the next-to-last line: the access time for the MP4 file. Every other timestamp comes out wrong, with the internal metadata values being off by +4 hours; that suggests the camera sets the internal timestamps to UTC.
As nearly as I can figure, the only way to make this work requires setting the clock to the local time, TZ to UTC+0, and DST off. That will screw up the filesystem timestamps, but at least the Exif metadata will be correct, for some value of correct.
The camera’s GPS receiver depends on the clock for its initial synchronization. I don’t know how the TZ and DST settings affect the clock’s correctness for that purpose.
I do not know if / how / when the displayed times have been altered by the programs that display them.
I think exiftool can extract the times from the internal metadata and fix up the filesystem times, but that’ll take more tinkering.
Sheesh & similar remarks…