SARK-110
User’s Manual
Rev 1.2.19 January 12
th
, 2020
- 69 -
© Melchor Varela
– EA4FRB 2011-2020
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 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 center. 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 28.2m 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.