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DC Block Electrical Filters, Coaxial
>1 Hz DC Block Filter
50 - 60 Hz Mains Hum Filter with DC Block
EF500 Used in Conjunction with a High-Impedance Oscilloscope and Amplified Photodetector
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Figure 1: Each EF500 Series coaxial filter has a male and female BNC connector. It is engraved with the part number, the type of filter, the passband range, and the response curve (the EF599 displays the mains hum suppression values instead of the curve).
Thorlabs' Passive Electrical Filters are feedthrough BNC filters that allow the user to filter unwanted signals and noise. These DC block filters are designed to be driven by a low-impedance source and terminated directly into high-impedance equipment. Examples of typical 50 Ω (low-impedance) sources are Thorlabs' amplified photodetectors, while examples of high-impedance equipment include 1 MΩ oscilloscope terminals, DAQ boards, and 100 kΩ op-amp inputs. This page contains our DC block electrical filters. Thorlabs also offers low-pass and high-pass electrical filters, as well as a DC block filter for RF with SMA connectors.
These are passive filters; therefore, no power supply is needed to run these devices. Additionally, they will not display any of the intermodulation distortions that are often observed when using active filters. Passive filters also have lower noise floors and lower thermal emission than their active counterparts, giving these filters higher signal-to-noise capabilities. Each filter is engraved with the part number, passband range, input/output impedance values, and a frequency response curve.
DC Block Filters
DC offsets are not the only problem to plague signal acquisition and analysis. Most often, noise from the mains electricity becomes written onto a signal. This phenomenon is known as mains hum and manifests itself with a fundamental frequency of 50 to 60 Hz. Spikes at the fundamental, second harmonic (100 Hz to 120 Hz), and third harmonic (150 Hz to 180 Hz) are the most common source of mains hum noise. The EF599, a 2nd order Butterworth filter, is a DC block filter specifically designed to filter out noise caused by mains hum. This filter provides excellent suppression through 400 Hz (3 dB, nominal) for attenuation of mains hum noise at its fundamental frequency and at higher harmonics.
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The graph above shows a signal taken on an oscilloscope with (blue trace) and without (red trace) using a filter. The observed phase shift is introduced by the filter.
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Mechanical Drawing of
The coaxial package of these filters offers one male and one female BNC connector.