# www.Hobby-Electronics.info

• • • ## Frequency filters Take a look at the diagram on the right. Assume that the voltage source supplies a 1V/10kHz signal (this means: the amplitude is 1V and the frequency is 10kHz = 10000Hz).

The impedance of inductor L will be XL = 2∙π∙104∙10-3 = 62.8Ω. The output voltage (voltage across inductor L) will be 1V∙(XL/(ZR+L)), where ZR+L is the total impedance of R and L. Because an inductor, just like a capacitor, causes a phase shift in in the current flow, we cannot just state that ZR+L = R + XL. Using some complex math we can prove that:

ZR+L = √(R2+XL2).

In our case ZR+L = √(1k2+62.82) = 1002Ω. Thus, the output voltage is 1V∙(62.8/1002) = 0.0627V.

(By the way, an inductor causes a +90 degrees phase shift, while a capacitor causes a -90 degrees phase shift.)

Now assume that the voltage source supplies a 1V/10MHz signal. The impedance of inductor L will then be XL = 2∙π∙107∙10-3 = 62.8kΩ. So ZR+L = √(1k2+62.8k2) = 62.8k. This is the same as XL, so the output voltage will be 1V. So we created a very simple frequency filter with just a resistor and a inductor.

In this case we created a so called high pass filter (HPF) since high frequency signals pass this filter easily while frequency signals are suppressed. If you swap R and L, you create a low pass filter (LPF).

Let's calculate the cut-off frequency of our filter. The cut-off frequency is the frequency at which R = XL => R = 2∙π∙f∙L => In our case f = 1k/(2∙π∙10-3) = 159kHz.

You are visitor
{"ft_lang_label":"__label__en","ft_lang_prob":0.87800336,"math_prob":0.99835765,"size":1428,"snap":"2020-24-2020-29","text_gpt3_token_len":469,"char_repetition_ratio":0.12289326,"word_repetition_ratio":0.03088803,"special_character_ratio":0.31862745,"punctuation_ratio":0.11285266,"nsfw_num_words":0,"has_unicode_error":false,"math_prob_llama3":0.99944276,"pos_list":[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24],"im_url_duplicate_count":[null,null,null,null,null,null,null,7,null,4,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null],"WARC_HEADER":"{\"WARC-Type\":\"response\",\"WARC-Date\":\"2020-06-03T15:32:08Z\",\"WARC-Record-ID\":\"<urn:uuid:3e064cda-a954-4f20-844d-cb66ddf66aa0>\",\"Content-Length\":\"15860\",\"Content-Type\":\"application/http; msgtype=response\",\"WARC-Warcinfo-ID\":\"<urn:uuid:38eae458-5997-4a4e-a566-94b79ca03ec0>\",\"WARC-Concurrent-To\":\"<urn:uuid:584880fc-e3bf-4aef-b4ce-b1cb5b30187f>\",\"WARC-IP-Address\":\"46.235.40.76\",\"WARC-Target-URI\":\"http://www.hobby-electronics.info/course/html/Inductor-Filter.html\",\"WARC-Payload-Digest\":\"sha1:ZBILGHWI3ERETBYHGEN2SXE3ZNHPJVZT\",\"WARC-Block-Digest\":\"sha1:6ST2SK753ZLRW34KN2ONZMH5G54WVZ3I\",\"WARC-Identified-Payload-Type\":\"application/xhtml+xml\",\"warc_filename\":\"/cc_download/warc_2020/CC-MAIN-2020-24/CC-MAIN-2020-24_segments_1590347435238.60_warc_CC-MAIN-20200603144014-20200603174014-00501.warc.gz\"}"}