microHAM SMORF Manual page 50

Nature of the coaxial cables is that they have monotone (but not linear) attenuation characteristic, with rising
frequency attenuation rises. If cables connecting the SMΩRF are not absolutely same in the electrical length,
also some phase shift is introduced. Both this parameters have huge impact to accuracy and need to be
eliminated. SMΩRF can easily null these adverse effects, but needs to know the attenuation and the phase shift
of cables connecting sensor to meter, and in order to be accurate, for each frequency separately.
For this reason each sensor cable is supplied with its own calibration certificate, table of the attenuation and
relative phase shift for each band. Attenuation is exact value of the cable attenuation to plane of its connectors at
a given frequency. Relative phase shift says nothing alone, but when subtracted from the relative phase shift of
the second cable, result is absolute phase shift between these cables. These parameters need to be entered to
the table from the calibration certificate. SMΩRF then interpolates between these points to get exact value of the
attenuation and the phase for current operating frequency in real time.
By default, the Sensor Cables Table is pre-set using typical values of the attenuations of provided cables, and
zero phase shift, so results obtained from an out-of-the-box meter are not way off. Anyway, to get best out of the
SMΩRF accuracy, you need to edit table using actual values from the certificate.
Phase difference is absolute phase shift between cables and must be worked out using relative phase from two
certificates. It is the relative phase shift of the cable connecting I or REF port of the sensor MINUS relative phase
of cable connecting U or FWD port of the sensor.
Formula for entering phase difference is: ΔΦ = Φ(I or REF) – Φ(U or FWD)
CONTROLS:
1. FWD/U
Attenuation of the cable connecting
U or FWD port of the Sensor.
2. REF/I
Attenuation of the cable connecting
I or REF port of the Sensor.
ΔΦ
3.
Computed phase difference between
both cables (formula above).
SAVE
4.
Saving entered values.
EXIT
5.
Exit from this menu.
Contrary to most menus in the SMΩRF, this menu can be left only using dedicated EXIT button. It is an
intentional change to avoid inadvertent exit from the menu without saving entered values. Still, values must be
SAVED separately by SAVE button prior exit, otherwise they will be lost.
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