Recommended SMA Cables for Time Taggers
SMA cables are ideal for Time Tagger connections. Use double-shielded cables under 5 meters for optimal signal quality and minimal jitter.
SMA cables are the cable of choice when connecting a Time Tagger with a device.
As a reference, to test our devices internally, we mainly use two types of cables. One type for standard usage (see under this link), and one used to achieve better signal-to-noise ratios (see under this link).
More specifically, there are many parameters to consider when selecting an SMA cable:
Length. Ideally, the Time Tagger has to be placed close to the experimental setup, and USB extenders should be used to cover longer distances. When this solution is not possible, we would suggest keeping the length of the SMA cable below five meters. Our devices can work with longer cables, but the signal can degrade, affecting the overall jitter.
Shielding. One should check its effectiveness, in other words, how much an external signal can be transmitted in the line. To achieve better timing jitter, the cable should be shielded as much as possible from external sources of interference, such as electromagnetic and radio frequency signals. Therefore, we would recommend a double-shielded cable instead of a single-shielded one.
S-parameters. Return and insertion losses must be kept as low as possible to avoid signal distortions.
Frequency range. The bandwidth supported by the cable should cover the frequency range of the signal from the detectors. Signal with frequencies out of this range can cause distortions. As a result, the time jitter would no longer reflect the specified one.
Power VS frequency. Depending on the frequency range, there can be differences in the transmitted power and how much of it can be handled by the cable itself.
Temperatures. There are typical ranges given by the manufacturer. One has to pay attention to this parameter, especially when working with cryo temperatures.
What if I have two setups, one at room temperature for some experiments and another one in a separate lab with the SNSPDs and the cryostat, and I have only one Time Tagger?
In the case of detectors being far away, the TT cannot be close to both setups. If you have an SNSPD on one side and APD on the other, we recommend placing the Time Tagger close to the SNSPD. The APDs have a module and the output signal amplitude can be adjusted so that, at in input of the Time Tagger, you still have a good signal in terms of the amplitude. On the other hand, the SNSPD outputs the signal directly, and its properties cannot be adjusted. Moreover, the signal’s front edge is sharp, and the bandwidth is high. This means that the signal degrades easily during propagation.