
26
or female connector
via matched 4-6ft (1-
2m) coax lead
BNC female
BNC type
None or double male
if required
BNC female
N type
BNC male to N male
or female connector
via matched 4-6ft (1-
2m) coax lead to
keep strain off the
BNC connector
BNC female
TNC type
BNC male to TNC
male or female
BNC female
SMA type
BNC male to SMA
male or female
BNC female
UHF SO-
239 type
BNC male to UHF
male or female
BNC female
Other
BNC male to Other
male or female via
match 4-6ft (1-3m)
lead
The term “matched” refers to matching the lead’s impedance with the impedance
of the cable to be tested. The TDR can measure through a mis-matched test
lead, but matching is a better method.
Coax Cable Parameters
There are a large number of parameters published for each brand and type of
coax. They include conductor size and type, shield type, cable diameter, weight,
and tables for attenuation at specific frequencies. For the use of the TDR we are
primarily interested in only three cable parameters:
•
Impedance (Z
0
)
•
Velocity Factor (VF) aka Velocity of Propagation (VP or VoP)
•
Loop Resistance
To obtain the best specifications for the cable being tested visit the
manufacturer’s web site and search for the cable type and part number to
download complete specifications. Also pay attention the tolerances (+ / -) for
each as this is important for permitted deviations.
Impedance
Impedance specifies the total AC and DC resistance a cable offers to the RF
signal being transmitted on the cable. It’s important the cable’s impedance
matches the equipment it is connecting. Otherwise there will be unwanted signal
reflections in the system. Measured as VSWR (Voltage Standing Wave Ratio) or
Содержание E20/20
Страница 1: ...Step Time Domain Reflectometer E20 20 Step TDRs and Avionics TDR all models ...
Страница 40: ...33 Figure 3 8 Figure 3 9 Figure 3 10 ...
Страница 79: ...72 ...
Страница 109: ...102 This page intentionally left blank ...