Frequency Calibration
The Si570 is fairly well calibrated, yet even 10ppm accuracy mean 100 Hz @ 10Mhz and
almost 300Hz at 28Mhz. The mcHF firmware permits to fine tune the calibration.
Equipment needed:
•
Either an as exact and as high as possible reference frequency signal (single
carrier, no modulated signal OR a strong broadcast station) (RX calibration
approach)
•
OR a precise frequency counter (TX calibration approach).
Preparation: Bring the mcHF up to the normal operating temperature of the TCXO (can
take up to 15 minutes).
Frequency calibration can be done either in TX or in RX mode and has only to be done
in one of the modes, not both! The calibration -once done and saved- is then valid for
both: RX AND TX.
TX calibration approach [from firmware 1.5.8]
1.
Set a "FM" mode (FM-N or FM-W)
2.
Set input to DIG, do not connect USB cable. Alternatively, you may also use any
other input mode, be sure to have no input signal.
3.
Connect frequency counter to mcHF Antenna port (via attenuator)
4.
Start "Tune"
5.
Go into the configuration, item "Frequency Calib.". Now change the PPM value so
that frequency counter displays frequency shown on mcHF display.
6.
Save configuration by long press on "MENU" or "EXIT" button (F1)
RX calibration approach [from firmware 1.5.8]
1.
Set demodulation mode to "SAM"
2.
Tune into China Radio International on the 16m or 19m band (do this at daytime).
You can take any other broadcast station, but China Radio International/Radio
Romania Intl are well known for being exactly on the accurate frequency. Many
broadcast stations are NOT on the accurate frequency, e.g. Voice of Turkey, Voice
of Iran, most (if not all) Brazilian radio stations etc. Alternatively use a well-
calibrated signal generator with a frequency as high as possible (28MHz).
