SteppIR SARK-110, User Manual

Page: 54 / 78

SteppIR
SARK-110
User’s Manual
Rev 1.1.7 October 29 th , 2014 - 54 - © Melchor Varela – EA4FRB 2011-2014
The second method for changing the transmission length is simply by using Navigator B when the
«TL Len» menu option is active. The length value will change according the current length
multiplier. The length multiplier can be changed from the pop-up transmission line length edit dialog.
Since the precise cable length is not normally known in advance, there is a procedure to get the
cable length as follows. As a precondition the cable must be unterminated at the far end. Set the
SteppIR SARK-110 to Smith Chart mode and select «Preset» «Full HF» . The Smith Chart will show
a spiral from infinite impedance and going towards the centre. When setting negative length values,
this spiral will be progressively unrolled and transposed to the infinite impedance point when the
exact length will be set. Then, if a load is connected at the cable far end, the presence of the
transmission line will be discounted.
The screenshots below show an example of this in operation. A line of 33.9m of RG-58C/U coax
cable is unterminated at the far end. The first screenshot shows the measurement without applying
the TL compensation and the last screenshot shows the measurement once the subtract feature
has been applied.