If you only memorize a few Q Codes. the only ones I use and know are:
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QNH - Altimeter setting (altimeter with field elevation on ground)
QNE - Standard 1013.2 mB - 29.92 in' - 760 mm
QFE - Altimeter setting, reading '0' on ground
(Knowledge of the 3 above is a MUST)
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QDM - Mag bearing to a station (DF)
QDR - Mag bearing from a station (DF)
QDL - Request for series of QDM (i.e. in emergency to home to airfield)
QUJ - True bearing to a station (DF) - rarely used
QTE - True baring from a station (DF) - rarely used
(Knowledge of QDM/QDR is recommended)
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QSY - Change frequency to kHz/mHz
QRX - Standby
QGO - Airport closed (visibility or technical reason)
QFU - Runway in use
QAN - Wind direction (mag) and speed
QBA - Visibility (meters or feet)
QBB - Ceiling (meters or feet, cloud type)
QMU - Temperature
QTH - Station location
QTR - UTC time
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I use QSY, QRX, QTH, QTH, QTR codes frequently.
If you are ham as I am, my call sign is LU4-CAR
I operate on (10), 20 and 40 meters USB
Often as "air mobile" from the plane.
My QTH is generally Mid-Atlantic between Recife and Cape Verde
My QSL is a 747 picture... Try me, I will send you one...
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Happy contrails