Brief description
The CAB-SC1 low-capacitance cables are high-quality coaxial cables designed to deliver the highest signal quality. They are recommended for measuring small signals while minimising noise caused by cable capacitance.
Features
- 150 Ω characteristic impedance
- 30 pF/m capacitance
- Pre-assembled with high-quality BNC connectors
- Available in various lengths from 50 cm to 10 m
- Additional lengths are possible (min. order quantity 10 pieces)
Advantage
When measuring small signals – especially small currents using transimpedance amplifiers – the cable between the signal source and the amplifier should be as short as possible to minimise the effect of cable capacitance. A 50 Ω cable has a capacitance of about 100 pF/m. FEMTO’s low-capacitance cables have a capacitance of approximately 30 pF/m, so they generate much less noise for the same cable length.
Note
Low-capacitance cables offer no advantages in terms of triboelectric noise or electromagnetic shielding; in fact, they are even slightly disadvantageous. In such cases, we recommend FEMTO’s low-noise and HF cables.
| Length | Plug BNC – BNC | Quotation Request |
0.5 m | CAB-SC1-BB-050 |  |
|---|---|---|
| 0.8 m | CAB-SC1-BB-080 | |
| 1.5 m | CAB-SC1-BB-150 | |
| 3.0 m | CAB-SC1-BB-300 | |
| 5.0 m | CAB-SC1-BB-500 | |
| 10.0 m | CAB-SC1-BB-1000 | |
| Datasheet |  |
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Why are low-capacitance cables needed?
Amplifier inputs are always sources of noise voltage. According to Ohm's law, this noise voltage generates a noise current across the input impedance. In the case of transimpedance or current amplifiers, this is particularly critical, since the noise current superimposes on the measurement current and is also amplified. It is part of the total noise and can easily even become the dominant noise.
If the impedance at the amplifier’s input is high, the noise current is low and negligible. However, if the impedance is low, the noise current is high. The impedance is particularly low when the capacitance is high; in this case, the capacitance at the input consists of the capacitance of the actual signal source – for example, a photodiode – and the capacitance of the cable. A 50-ohm coaxial cable has 100 pF/m and can therefore easily account for most of the capacitance at the amplifier input.
The solution to this problem is to use cables that are as short as possible and/or cables with lower capacitance. FEMTO's low-capacitance cables have a capacitance of only 30 pF/m, so the current noise caused by impedance is significantly lower.
Figure: Comparison of noise spectra with Low-Capacitance Cable vs. 50 Ohm Cable (RG 58)
Integrated noise (legend, values in brackets) with Low-Capacitance Cable is more than factor 2 lower than a standard RG58 cable
Applications
Measurements of small signals, particularly currents from a remote signal source, where long coaxial cables would introduce excessive noise due to their capacitance.
- Measurements of currents down to the picoampere range
- Photodetectors and Ionisation Detectors
- Scanning Tunnel Microscopy (STM)
- Scanning Probe Microscopy (SPM)
- Spectroscopy
- Piezoelectric and pyroelectric detectors
Comparison of FEMTO's cables
Low-Capacitance Coaxial Cable CAB-SC1
- Low cable capacitance minimises capacitance-induced noise
- Frequency range: DC – 20 MHz
- Suitable for amplifier input stages, particularly for the analysis of small currents in the pA to µA range at moderate frequencies
- Recommended for the input stage of transimpedance amplifiers such as DDPCA-300, DLPCA-200, DHPCA-100, LCA- and HCA Series
- Particularly recommended when the current source is located remotely and the capacitance of a long cable would otherwise increase noise significantly
Low Noise Coaxial Cable CAB-LN1
- Insensitive against disturbances caused by triboelectric and microphonic effects
- Frequency range: DC to 1 MHz
- Suitable for input of amplifiers, especially for the analysis of extremely small currents in the fA to nA range at rather small frequencies
- Recommended for input of DDPCA-300, DLPCA-200, LCA series and HQA-15M-10T
High Performance RF Coaxial Cable CAB-HF1
- Insensitive against electromagnetic interferences (EMI) and currents to ground (ground loops)
- Frequency range: DC - 4 GHz
- Suitable for input and output of amplifiers for the analysis of small signals at rather high frequencies
- Recommended for input of DHPCA-100 and HLVA-100 as well as HCA, DHPVA, HVA and LIA series
- Recommended for outputs of all FEMTO amplifiers and photodetectors with BNC connections
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