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RPiks / pico-hf-oscillator

Digital controlled radio frequency oscillator based on Raspberry Pi Pico (1 Hz to ~32.333 MHz band). RTTY, MFSK, freq sweep examples are included.
MIT License
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Frequency error / not using GPS reference #1

Open thomasabbott opened 11 months ago

thomasabbott commented 11 months ago

Thanks for the v1.1 .uf2, I tried it today.

I have connected a GPS but see no frequency correction.

SETFREQ 10000000 Frequency (measured) stays at 10 000 014.3 (error of 1.4 ppm) Slightly sensitive to temperature and/or touching the crystal. Even with some careful averaging, against an accurate reference, I can't see any frequency change from turning the GPS on and off. Stated frequency is always:

Working freq: 10000000 Hz + 0 milliHz

so it looks like the GPS correction is not being applied to the pio dco.

GPS NMEA is connected to Pico board pin 2, RP2040 GPIO1 (UART0 Rx) GPS PPS is connected to Pico board pin 5, RP2040 GPIO3. Both seem to be working, so I don't think it's related to this.

Could this come from a ppb / ppt mixup. STATUS reports GPS frequency correction 1446430 ppb is the correct figure, but in parts per trillion not billion.

No, I think it's all correct except for the labelling of "ppb" in many places. piodco.c returns the correct 14465 mHz correction.

Perhaps this is not being applied correctly?

Some STATUS messages for reference:


Pico-hf-oscillator system status
Working freq: 10000000 Hz + 0 milliHz
Output is ENABLED
GPS UART id 0
GPS UART baud 9600
GPS PPS GPIO pin 3
GPS error count 0
GPS NAV solution flag 1
GPS GPRMC receive count 150
GPS PPS period 32000046285760
GPS frequency correction 1446430 ppb
GPS lat 49....... deg1e5
GPS lon -123....... deg1e5
=> STATUS
Pico-hf-oscillator system status
Working freq: 10000000 Hz + 0 milliHz
Output is ENABLED
GPS UART id 0
GPS UART baud 9600
GPS PPS GPIO pin 3
GPS error count 0
GPS NAV solution flag 1
GPS GPRMC receive count 318
GPS PPS period 32000045940753
GPS frequency correction 1435649 ppb
GPS lat 49....... deg1e5
GPS lon -123....... deg1e5
=> STATUS
Pico-hf-oscillator system status
Working freq: 10000000 Hz + 0 milliHz
Output is ENABLED
GPS UART id 0
GPS UART baud 9600
GPS PPS GPIO pin 3
GPS error count 0
GPS NAV solution flag 1
GPS GPRMC receive count 599
GPS PPS period 32000045102318
GPS frequency correction 1409447 ppb
GPS lat 49....... deg1e5
GPS lon -123....... deg1e5```
RPiks commented 11 months ago

Dear Thomas,

Sorry for the belated answer.

I will check this case. Meanwhile, the previous version (w/o console & old pio dco which was up to 9.4M) worked correctly on 7 MHz band, transmitting WSPR. Unfortunately, I had no opportunity to test the new version closely due to starting a Christmas rally.

Thank you for this report, it is useful.

Cheers, Roman R2BDY