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Baofeng UV-5: Squelch Pop Suppression

Our first ride with the Baofeng UV-5 radios subjected us to loud pops around each transmission. Back on the bench, this is the signal applied to the earbud during a no-audio simplex kerchunk:

Baofeng - squelch pops

Baofeng – squelch pops

The small noise burst to the right of the center, just before the downward pulse, happens after the carrier drops and before the squelch closes; it’s familiar to all HT users.

The huge pulses, upward at the start and downward at the end, cause the pops. They’re nearly 3 V tall, compared with the 300-ish mV squelch noise, and absolutely deafening through an earbud jammed in my ear. Mary refused to listen, so we finished the first ride in companionable silence.

I think the radio switches the audio amp power supply on and off to reduce battery drain. It’s obviously a single-supply design, so we’re looking at a hefty DC blocking capacitor charging and discharging through the earbud resistance. I suppose that’s to be expected in a $25 radio.

The obvious solution: clamp the audio signal to something reasonable, perhaps with a pair of nose-to-tail Schottky diodes across the earbud. Rather than using axial diodes, along the lines of the 1N5819 diodes in the WWVB preamp, I used a BAT54S dual SMD diode as a tiny clamp:

BAT54S dual-Shottky diode - SMD package

BAT54S dual-Shottky diode – SMD package

No pix of the final result, but it’s basically two wires soldered alongside the SMD package, surrounded by a snippet of heatstink tubing to stabilize the wires and protect the SMD leads. It might actually survive for a while, even without the obligatory epoxy blob.

The BAT54S clamps the pops to 200-ish mV, as you’d expect:

Baofeng - squelch pops - clamped - 500mV-div

Baofeng – squelch pops – clamped – 500mV-div

That’s a kerchunk at twice the vertical scale. The very thin spike at the start of each pop isn’t audible, as nearly as we can tell, and I’ve cranked up the audio gain to make the squelch noise more prominent. Your ears will determine your knob setting.

With the audio amp applying 3 V to the diodes at the start of each pop, you’re looking at an absurdly high pulse current. I’m sure the radio exceeds the BAT54 datasheet’s 600 mA surge current limit by a considerable margin, but I’m hoping the short duration compensates for some serious silicon abuse.

Tamping those pops down made the radios listenable.

I’ve often observed that Baofeng radios are the worst HTs you’d be willing to use.

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  1. #1 by Charles on 2018-09-12 - 19:22

    I have the same problem on my Baofeng radio. I am using a headset with 2 speakers (for each ear). Where should this BAT54S diode be soldered in? One diode for each speaker or should it be soldered into the wiring before it is split to each speaker? Sorry I’m an electronics newbie but this issue is almost unbearable. Any pictures or additional information would be greatly appreciated.

    • #2 by Ed on 2018-09-13 - 08:55

      Put the diodes directly across the audio wires, as shown in my doodle: one lead goes to the common terminal and the other to the audio terminal. Through-hole axial-lead Schottky diodes will be easier to handle and certainly more durable!

      The Kenwood headset standard puts those two wires on different plugs. Other posts give the pinout and show how to add a resistor if the audio is absurdly loud.

      Happy listening!

      • #3 by Charles on 2018-09-15 - 11:52

        Ok thanks. So I just need to add 2 BAT85 schtokky diodes (going opposite directions) across the green and blue wires on the kenwood/baofeng connector, correct? Like shown in this diagram:

        • #4 by Ed on 2018-09-15 - 19:30

          Exactly!

          I snagged a surplus deal on an SMD diode assortment quite a while ago, so I had some teeny packages with two nose-to-tail diodes. Separate diodes will work just fine, too.

  1. Baofeng UV-5: Audio Attenuation and Knob Pointer | The Smell of Molten Projects in the Morning
  2. Baofeng UV-5: Squelch Tail Elimination | The Smell of Molten Projects in the Morning
  3. Squelch Pop Suppression on the Baofeng UV-5 HT Portable Radio « Adafruit Industries – Makers, hackers, artists, designers and engineers!

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