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Sie befinden sich hier: shackspace Wiki » Projekte » Hackerspace Global Grid » SHF / Microwaves / Physics » Math and Build instructions on lowpass filters
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project:hgg:shf:lowpass

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project:hgg:shf:lowpass [2012-01-01 21:18] – reloc0project:hgg:shf:lowpass [2012-01-05 10:41] (aktuell) – 84.56.156.215
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 Most of our current findings apply to LC Filters. Here's some stuff about it. Most of our current findings apply to LC Filters. Here's some stuff about it.
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-====== Errata ====== 
- 
-If you find errors, please tell or fix them (this is a wiki after all). 
  
 ===== LC-Lowpass Filter ===== ===== LC-Lowpass Filter =====
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 This Lowpass filter is made of 2 LC filters and a terminating Resistor (R_L). The terminating Resistor can be omited if not needed (?) but is shown in the graph because we will be calculating it here. It's called a T-Filter.  This Lowpass filter is made of 2 LC filters and a terminating Resistor (R_L). The terminating Resistor can be omited if not needed (?) but is shown in the graph because we will be calculating it here. It's called a T-Filter. 
 +Note: Imput and output of the filter must be matched to the system impedance (e.g. 50 Ohm).
  
 ==== What we expect ==== ==== What we expect ====
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 Since we did not have a device for measuring an Inductor but very just inductors (1%) we decided to use one of the inductors. We set our Cutoff Frequency and calculated the needed values. Calculations were performed for one of the base filters (LC). Thus we took two inductivities (L) from the stack and one Capacitor with double the size as for one filter (the picture above says 2C).  Since we did not have a device for measuring an Inductor but very just inductors (1%) we decided to use one of the inductors. We set our Cutoff Frequency and calculated the needed values. Calculations were performed for one of the base filters (LC). Thus we took two inductivities (L) from the stack and one Capacitor with double the size as for one filter (the picture above says 2C). 
  
 +Forget formulas for more complicated filters but use simulation tools instead! There is a very old DOS based software "PUFF" which shows the frequency and phase response of a given filter, consisting of lumped constant components as L, C, R and (!) transmission lines (traces on the pcb). 
  
 +====== A few words on HF ======
 +
 +As we have found out while experimenting, in HF almost everything becomes a lowpass, but not in the way we wanted it to be. Things on how to make the PCBs should be added here.
 +
 +If the wavelength is less than approx. 10 to 100x the size of your components or wires in the circuitry, you will have lots of parasitic effects due to line inductance or stray capacitance which alter network behaviour. Example: At frequencies about 1 GHz, (wavelength 30 cm) you cannot use wires etc. longer than some millimeters without considering its parasitic effects.
 +
 +
 +
 +====== Errata ======
 +If you find errors, please tell or fix them (this is a wiki after all).
  
 ====== Further reading ====== ====== Further reading ======
   * http://en.wikipedia.org/wiki/Electronic_filter   * http://en.wikipedia.org/wiki/Electronic_filter
 +  * http://en.wikipedia.org/wiki/Low-pass
 +  * http://www.elektroniktutor.de/analog/filter.html#halbglied
  
  
  
project/hgg/shf/lowpass.1325449112.txt.gz · Zuletzt geändert: 2012-01-01 21:18 von reloc0