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Cables and signal loss - comparison | Spectrum

Everyone needs cables to interconnect the measurements equipment between Digitizer, Arbitrary Waveform Generator (AWG), Amplifiers, Sensors and Device under Test (DUT). As long as signal frequencies stay low in the range of a few MHz or below any standard coaxial cable with the correct impedance is a good choice. As soon as signal frequencies raise the cable attenuation has to be taken into account. This cable attenuation is depending on the cable length and the signal frequencies.

Comparison between Spectrum standard cables and low loss cables

  Standard Cable Low Loss Cable
Material RG174 MF141
Diameter 1.9 mm 5 mm
Velocity 66% 69%
Impedance 50 ± 3 Ω 50 ± 2 Ω
Line Resistance 0.3 Ω/m n.a.
Line Capacity (max) 106 pF/m 95 pF/m
Attenuation 100 MHz 0.3 dB/m 0.1 dB/m
Attenuation 200 MHz 0.4 dB/m 0.2 dB/m
Attenuation 500 MHz 0.7 dB/m 0.3 dB/m
Attenuation 1 GHz 1.0 dB/m 0.5 dB/m
Attenuation 1.5 GHz 1.2 dB/m 0.6 dB/m
Attenuation 2 GHz 1.4 dB/m 0.7 dB/m
Available Connectors MMCX, SMA, SMB, BNC SMA, BNC

Hints

When using high signal frequencies in the 100 MHz or above range please check the following hints to understand your observations:

  • The signal attenuation is frequency dependent. That means higher frequency components are more attenuated than lower ones. While a DC signal will show with full scale when using a Spectrum standard cable of 2 meters a 500 MHz sine wave will be attenuated by about 1.4 dB. An original sine signal level of 1000 mV will show as 850 mV at the digitizer input.
  • The signal attenuation is also cable length dependent. If you have high signal components short cables are recommended. While a Spectrum standard cable with 200 cm length has an attenuation of 1.4 dB @500 MHz, the 80 cm cables only have an attenuation of 0.6 dB.
  • A general hint: For high speed signals using proper termination of 50 ohm and proper cables with a matching impedance of 50 ohm will help with the acquired signal quality. More details are found in our product note Proper Use of Digitizer Front-End Signal Conditioning.