Desgining crystal filters and find out crystal data by measuring it. This resource is listed under Technical Reference/Filters, at Homebrew Crystal Filter Design resource page via dxzone.com ham radio guide. Quartz Crystal Filter Design Equivalent Circuit Determination of Quartz Crystals Before we may design a crystal filter it is necessary to know the crystal's data. Unfortunately this information is not in the datasheet - or we have no datasheet because the crystals were bought on a market some decades ago. ‣ - Amazon Electronic Component Packs. Check out the. What is this LC and crystal filter software? The LC and crystal filter software was written by Neil Heckt of Almost All Digital Electronics as an aid for filter designers to simply plug in various filter parameters and hey presto! There is your finished design. Shortly I will present you with the design example of a crystal filter of the crystal ladder filters variety as designed on my evaluation copy of the downloaded software. DISCLAIMER: I have no connection with Neil or www.aade.com apart from being friends. I receive no remuneration whatsoever for this topic or any registrations of this software. This downloadable software is available from my friend Neil Heckt. ![]() Neil also provided us with his famous and very popular kit featured on one of my other sites. I am quite certain that this LC and crystal filter software will prove equally popular, especially due to the modest cost of $24.95 but for evaluation purposes you may use the software ten times for free. ![]() Designing a crystal filter I was quite thrilled to see a lot of mathematical drudge taken out of the design of a crystal filter by this unique software. Unfortunately you can never get away from from the fact that you must first of all measure the parameters of the low cost crystals you are using. The usual design procedure proceeds as follows: Obtain a good selection of the same frequency surplus crystals. Let's say we can obtain very cheaply some 5 Mhz crystals. We need to determine the crystal parameters in figure 1 below. Figure 1 - parameters of crystal for a crystal filter Now your crystal parameters can be measured relatively easy, albeit indirectly. The crystal is placed between an accurate and stable signal source of known impedance and a load of known impedance, usually a 50 ohm detector. The signal source needs to be at least 10 mW, stable, preferably 50 ohms, capable of fine tuning and monitored by a quality frequency counter with 1Hz resolution. The crystal parameters starting with Cp can now be measured. Cp can be easily determined with a operating at a frequency far removed from the crystal frequency, it's as simple as that. The signal source is slowly adjusted until a peak response is noted, this is series resonance, Fs where both the inductive reactance and capacitive reactance of the crystal cancel one another. The crystal is then replaced by a small value variable resistor and adjusted for a similar response in the detector. The value determined by the variable resistor is Rs in figure 1 above. Next the crystal is reinserted and swept both sides of centre frequency to determine the 3 dB points which gives us the loaded bandwidth Bw or indirectly Q L. Kai's power tools 7. Figure 2 - crystal loaded bandwidth As the crystal is slowly swept slightly higher in frequency, maybe only a 1,000 Hz or more a pronounced dip will be noted, this is the anti resonance or parallel resonant, Fp frequency where the effect of Cp effectively in series with Cm, resonates with Lm. Now I could lay some heavy maths on you on how to determine Lm and Cm BUT with Neil's crystal ladder filter software that is not necessary at all.
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