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Archive for category Amateur Radio

Baofeng UV-5 to Bike Helmet Wiring

Rather than 3D print and hand-wire a plug adapter to fit the socket around the Baofeng UV-5 mic and speaker jacks, I cheated:

Baofeng headset - harvested plug

Baofeng headset – harvested plug

Un-wearably bad Baofeng headsets now cost just over a buck apiece in lots of five, delivered halfway around the planet, and provide:

  • A compatible molded mic+speaker plug
  • A decent length of four-conductor cable with solder-meltable insulation
  • An unlistenably bad earbud on a stick
  • A lump with an electret mic and PTT switch
  • Various junk I’ll never use

The “hook earpiece” seems to have been designed by someone who had read the specs for a human head, but had never actually met a human being.

The wire colors from the dual plug, along with the wire colors for the repurposed USB cable to the headset, and the PTT connection:

Baofeng headset cable vs helmet cable - wire colors

Baofeng headset cable vs helmet cable – wire colors

Then wire it up accordingly:

Baofeng headset wire plate - first wiring

Baofeng headset wire plate – first wiring

The small heatstink tubing surrounding each connection isn’t easily visible, which, in the case of the ground / common lump, is a Good Thing. I chivied a strip of Kapton under the whole mess, folded it over on top, squished it together, then secured it with 1/4 inch tape extending over the plate edges. The cable ties stick out far enough to keep the joints from rubbing on anything; it’s not built to last for a thousand years, but should let us hear how this lashup works.

Now, to the bikes:

Baofeng headset wire plate - in use

Baofeng headset wire plate – in use

I’m convincing myself a little supporting ring under the SMA-to-UHF adapter won’t actually stabilize the precarious-looking joint.

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Baofeng UV-5 Headset Wiring Plate

My venerable amateur radio HT APRS-voice interfaces have recently begun failing and, given poor APRS coverage in Poughkeepsie due to having two iGates shut down (due to the aging radio geek population), I decided it’s time to simplify the radio interface. Given that HTs are designed to run with an external electret mic and earbud, the “interface” becomes basically some wires between the radio’s jacks, a repurposed USB plug on the bike helmet, and the PTT switch on the handlebar.

I expected to add a resistive attenuator to the earbud, but it wasn’t clear whether the mic would need an amplifier similar to the one in the APRS interface, so I decided to start as simply as possible.

The general idea is to anchor all the cables to a plate on the back of the radio, interconnect as needed, then “protect” everything with tape. The pocket clip has M2.5 screws on 26 mm (not 25.4, honest) centers, so that’s how it started:

Baofeng headset wire plate - dimensions

Baofeng headset wire plate – dimensions

The four holes beside the tabs will serve as starting points for rectangular notches holding cable ties lashing the wires to the plate:

Baofeng headset wire plate - drilled

Baofeng headset wire plate – drilled

Like this:

Baofeng headset wire plate - sawed

Baofeng headset wire plate – sawed

That’s hot and nasty, straight from the bandsaw.

After some edge cleanup, add obligatory Kapton tape to insulate stray wires from the aluminum:

Baofeng headset wire plate - installed

Baofeng headset wire plate – installed

The alert reader will note beveled corners on one plate and square corners on the other; think “continuous product improvement”.

The big rectangular gap in the middle of the plate provides (barely enough) finger clearance to push the battery release latch.

Now, to wire it up …

The dimensions of the recess surrounding the jacks on the Baofeng UV-5, just to have them around:

Baofeng headset jack socket - dimension doodle

Baofeng headset jack socket – dimension doodle

Which came from measurements of both the Wouxun and Baofeng radios:

Baofeng Wouxun headset jack sockets - measurements

Baofeng Wouxun headset jack sockets – measurements

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Squidwrench Electronics Workshop: Session 3

Ex post facto notes from the third Squidwrench Electronics Workshop.

Exhibit various 50 Ω resistors, including my all-time favorite, a 600 W 3 GHz dummy load:

600 W Dummy Load Resistor

600 W Dummy Load Resistor

… down to a 1/8 Ω metal film resistor.

The dummy load’s N connector triggered a regrettable digression into RF, belatedly squelched because I wasn’t prepared to extemporize on AC concepts like reactance which we haven’t covered yet.

Discussion of resistor applications, power handling, power derating with temperature, etc:

Whiteboard - Session 3 - Resistor power derating

Whiteboard – Session 3 – Resistor power derating

Why you generally won’t find 50 Ω load resistors in Raspberry Pi circuits. Cartridge heaters for 3D printers, not aluminum power resistors, although everyone agrees they look great:

Power resistors on heat spreader

Power resistors on heat spreader

Discussion of voltage vs. current sources, why voltage sources want low internal resistances and current sources want high resistances. Bungled discussion of current sources by putting diodes in parallel; they should go in series to show how added voltage doesn’t change current (much!) in sources driven from higher voltages through higher resistances:

Whiteboard - Session 3 - Voltage vs Current Sources

Whiteboard – Session 3 – Voltage vs Current Sources

Use Siglent SDM3045X DMM in diode test mode to measure forward drop of power / signal / colored LEDs, discuss voltage variation with color / photon energy. Measure 1.000 mA test current for all forward voltages.

Compute series resistor (500 Ω) to convert adjustable power supply (the digital tattoo box, a lesson in itself) into reasonable current source; roughly 10 V → 20 mA. Find suitable resistor (560 Ω) in SqWr junk box parts assortment, digression into color band reading.

Wire circuit with meters to measure diode current (series!) and voltage (parallel!), measure same hulking power diode (after discovering insulating washers now in full effect) as before in 1 mA steps to 10 mA, then 15 and 20 mA, tabulate & plot results:

Whiteboard - Session 3 - Diode current vs forward drop

Whiteboard – Session 3 – Diode current vs forward drop

Discover warm resistor, compute power at 20 mA, introduce cautionary tales.

Lesson learned about never returning parts to inventory, with 560 Ω resistor appearing in diode drawer. Cautionary tales about having benchtop can of used parts as front-end cache for inventory backing store.

Another intense day of bench work!

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QRPme Pocket Pal II: RF Waveforms and Meter Test

The QRPme Pocket Pal II produces RF test signals in the 20 meter and 40 meter bands, both square-ish waves derived from its 14.31818 MHz oscillator-in-a-can:

QRPme 20 meter - clip leads

QRPme 20 meter – clip leads

That’s the 20 meter signal, seen through the twisted pair test lead with alligator clips clamped on the scope probe, thusly:

QRPme Pocket Pal II - clip leads to probe tip

QRPme Pocket Pal II – clip leads to probe tip

When you’re working with RF signals, the “ground” part of the probe circuit matters:

QRPme 20 meter - probe tip gnd

QRPme 20 meter – probe tip gnd

That’s with the probe and its short spring ground jammed directly into the header:

QRPme Pocket Pal II - probe tip gnd

QRPme Pocket Pal II – probe tip gnd

Well, in this case, signal quality doesn’t matter very much, as you’re using the Pocket Pal II at a hamfest (or your bench) to determine if an HF radio is completely dead.

Here’s the 40 meter output, with the J3 jumper in place and the probe jammed into the header:

QRPme 40 meter - J3 on - probe tip gnd

QRPme 40 meter – J3 on – probe tip gnd

Pulling the J3 jumper off doubles the test signal amplitude:

QRPme 40 meter - J3 off - probe tip gnd

QRPme 40 meter – J3 off – probe tip gnd

Nothing wrong with those signals! In a pinch, those edges probably produce harmonics up in the UHF bands.

For completeness, here’s the 250 μA DC output driving a contestant chosen from the Box o’ Meters:

QRPme Pocket Pal II - 250 uA meter test

QRPme Pocket Pal II – 250 uA meter test

Eyeballometrically, the meter wants to see 1 mA for full-scale deflection, which is the whole point of the tester.

Recommended, with some early notes.

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QRPme Pocket Pal II

A QRPme Pocket Pal II could be a suitable project for a Squidwrench “advanced soldering” class:

QRPme Pocket Pal II - front

QRPme Pocket Pal II – front

Yes, it comes with a tin case:

QRPme Pocket Pal II - tin case

QRPme Pocket Pal II – tin case

You must fit your own insulating sheet under the PCB; polypropylene snipped from a retail package works fine.

It’s intended as a “mint tin sized tester for all kinds of hamfest goodies”, but it seems like a nice source of small currents, voltages, and signals suitable for stimulating all manner of circuitry one might encounter in later sessions of a beginning electronics class.

Before using it, of course, one must solder a handful of small through-hole parts into the PCB, a skill none of us were born with.

For completeness, the back side, hot from the soldering iron:

QRPme Pocket Pal II - rear

QRPme Pocket Pal II – rear

The kits (always buy two of anything like this) arrived minus a few parts, which I suspect was due to an avalanche of orders brought on by a favorable QST review. Fortunately, I (still) have a sufficient Heap o’ Parts to finish it off without resupply, although a hank of 9 V battery snaps will arrive in short order.

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RF Controlled Area Warning

Spotted this at the top of a motel stairwell:

RF Controlled Area - roof access warning

RF Controlled Area – roof access warning

More detail:

RF Controlled Area - detail

RF Controlled Area – detail

The antennas face away from the hatch, so it’s not as if the RF would shear you off as you climbed through:

Hampton Inn - RF Controlled Area - cell sector antennas

Hampton Inn – RF Controlled Area – cell sector antennas

I wonder if the hatch atop Vassar Main sports a similar warning …

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FM DDS: SPI Mock 3

Running some serial I/O in the background adds jitter to the timer interrupt pacing the ADC samples and as-yet-unwired DDS updates. For reference, an overview of the process showing the procession from the IRQ on the left to the SPI outputs near the middle and another IRQ on the far right:

DDS Mock - 0 VAC - SPI

DDS Mock – 0 VAC – SPI

Now, speed up the sweep and delay the trace by 25 μs to put the triggering pulse off-screen to the left and the second pulse at the center division:

ADC Sample IRQ jitter

ADC Sample IRQ jitter

The orange smear in the middle should be a tidy pulse, but it isn’t.

The  25 μs timer interrupt now has the highest priority on the front burner:

IntervalTimer AudioSampler;

... snippage ...

  AudioSampler.priority(0);
  if (!AudioSampler.begin(AudioSamplerIRQ, SamplePeriod)) {
    Serial.printf("Timer start failed\n");
    while (true) {
      FlipPin(BUILTIN_LED);
      delay(75);
    }
  }

Although nothing can interrupt it, other code / handlers may disable interrupts around their own critical sections and delay the tick. If the triggering tick (the off-screen one starting the trace) is delayed, then the on-screen pulse will appear “too soon”, to the left of center. If the triggering tick is on time, but the on-screen pulse is delayed, it’ll appear “too late” on the right.

The blur is (roughly) symmetric around the center graticule line, so the handwaving seems about right.

In round numbers, the jitter moves the interrupt ±325 ns on either side of its nominal position, with most of the pulses within ±100 ns. I doubt the jitter distribution is Gaussian, but vigorous handwaving says the RMS jitter might amount to 75 ns.

At the 4 kHz audio band limit, a 75 ns sampling error a phase error of 0.1°, so the maximum amplitude jitter would be sin(0.1°) = 0.002 = -55 dB, which might suffice for amateur-radio audio.

I think, anyhow.

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