DC Block Electrical Filters, Coaxial
- Passive DC Block Filters
- Terminates Directly into High-Impedance Test Equipment
- DC Block Filter with 1 dB Cutoff of >1 Hz
- Mains Hum Filter for 50 - 60 Hz and 100 - 120 Hz Suppression
>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
Click to Enlarge
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).
|Electrical Filters Selection Guide|
|Low-Pass Electrical Filters
|High-Pass Electrical Filters
|DC Block and Mains Hum Electrical Filters|
|DC Block Filter for RF|
- Butterworth DC Block Filter Design
- With and Without Mains Hum Suppression
- Can be Driven by Any 50 Ω Load
- Designed to be Terminated into High-Impedance Equipment
- No External Power Supply Required
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
These DC Block Filters are designed specifically to block out DC and very low frequency noise, allowing most of the signal through to the output. This large passband is advantageous when it is necessary to analyze or compare signals that contain a significant DC offset. The EF500 is a 1st order Butterworth filter designed to attenuate signals with sub-Hz frequencies. Perfect for removing unwanted DC biases, this device has excellent transmission at higher frequencies.
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.
The EF500 series filters are coaxial and feature a cylindrical design with a male and female BNC connector. This allows the filter to be directly attached to a device, such as an oscilloscope (see image above).
Click to Enlarge
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.
|1 dB Passband Windowb (Nominal)||>1 Hz||>650 Hz|
|3 dB Rejection (Nominal)||<0.3 Hz||<400 Hz|
|40 dB Rejection (Nominal)||<3 mHz||-|
|80 dB Rejection (Nominal)||<30 µHz||-|
|50 - 60 Hz Rejection (Nominal)||-||27 dB|
|100 - 120 Hz Rejection (Nominal)||-||19 dB|
|Frequency Response Curve
(Click for Graph)
|Source Impedance (Typical)||50 Ω|
|Load Impedance (Typical)c||≥100 kΩ|
|Input Voltage (Maximum)||±10 V|
|Storage Temperature||-20 to 70 °C|