ATS Mini SSB Patch Loading and BFO Calibration: Getting Clear Single-Sideband Reception

Single sideband (SSB) is how most amateur radio operators talk on the HF bands, and it is also used by maritime, aviation and utility stations. The Si4732 chip in the ATS Mini can demodulate it, but only after a patch is loaded at power-up and only if the BFO (beat frequency oscillator) is tuned properly. Without those two steps, voices sound like Donald Duck or are completely unintelligible. This guide explains what the patch does, how to switch the ATS Mini into SSB, and how to fine-tune the BFO so speech is clear.

Why SSB Needs a Patch

The Si4732 has AM, FM and SW built in, but SSB demodulation is added by a small firmware patch that the microcontroller uploads over I2C into the chip's RAM. The patch is lost when power is removed, so it must be loaded each time the radio is switched to SSB after a cold start. The ATS Mini firmware includes the patch data and does this automatically when you select LSB or USB; you may see a short pause or a progress indication while it loads.

LSB vs USB

SSB transmits only one sideband of the signal. By convention, amateur stations use lower sideband (LSB) below 10 MHz and upper sideband (USB) above 10 MHz, with the 60 metre band as an exception that uses USB. Aviation and marine HF voice stations use USB. Choosing the wrong sideband inverts the audio frequencies and makes speech unintelligible, so this is the first thing to check.

BandTypical mode 160, 80, 40 m amateurLSB 60 m amateurUSB 30, 20, 17, 15, 12, 10 m amateurUSB Marine, aviation HF voiceUSB CB radio (27 MHz)LSB or USB depending on the channel use, USB is the common choice

Switching to SSB

1. Tune to a band with known SSB activity, for example 40 metres in the evening.
2. Open the mode menu and select LSB or USB. The radio loads the patch.
3. Choose an SSB bandwidth. The Si4732 offers about 0.5, 1.0, 1.2, 2.2, 3.0 and 4.0 kHz. A 2.2 to 3.0 kHz filter is a good starting point for voice, with a narrower filter for weak or crowded signals.
4. Use the finest tuning step available (in SSB the step can be as fine as 10 Hz on typical firmware) for signal centring.

Menu names and step sizes differ between firmware versions, so check the documentation for the version you are running.

Tuning the BFO

SSB signals carry no carrier, so the receiver has to regenerate it. If the reconstructed carrier is off by even a couple of hundred hertz, voices sound higher or lower in pitch. The BFO control moves that regenerated carrier so the pitch sounds natural.

1. Find a station with a strong, stable voice.
2. Adjust the BFO in small steps until the voice sounds natural, neither too deep nor too squeaky. Adjustments of about 10 to 50 Hz per step give good control.
3. Alternatively, tune the main frequency in 10 Hz steps and leave BFO alone, which does the same thing.
4. Once a station is centred, avoid touching the BFO while listening to other signals. The BFO setting is one value for the current band, while the main frequency changes station to station.

Calibrating Against a Known Frequency

All frequency errors on the ATS Mini come down to the accuracy of the chip's reference crystal, which is typically a 32.768 kHz watch crystal. If a known station is consistently off by a fixed amount, use a time-signal broadcast on an AM-capable frequency such as WWV at 5, 10 or 15 MHz as a reference. Tune it in AM mode, note how far the carrier is from the expected frequency, then apply the same offset as a correction (some firmware offers a calibration entry for this). Crystals also drift with temperature, so re-check after the radio has warmed up.

Troubleshooting

SymptomCauseFix Voices sound like a chipmunk or slow motionBFO or tuning off frequencyAdjust BFO or tune in 10 Hz steps Voices are garbled but pitch seems rightWrong sidebandSwitch between LSB and USB No SSB option or patch failsFirmware without SSB patchUpdate to a firmware version that includes SSB Signal drifts over timeTemperature change in the crystalLet the radio warm up, re-tune Loud hiss with weak voicesBandwidth too wide, poor antennaNarrow the filter, add a longer antenna

Closing

The only genuinely difficult part of SSB on the ATS Mini is understanding that there is no carrier to lock onto. Pick the correct sideband for the band, start with about a 2.5 kHz filter, then centre the pitch with BFO or fine tuning. With a decent antenna, you will hear ham operators, nets and maritime traffic that are unreadable in AM mode.