- LATTICE CRYSTAL FILTER DESIGN SOFTWARE FREE DOWNLOAD FULL
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- LATTICE CRYSTAL FILTER DESIGN SOFTWARE FREE DOWNLOAD SERIES
(A) Reactance characteristics of crystals A and B in the lattice of Fig. Note that the lattice could be redrawn as a bridge circuit.įig.
LATTICE CRYSTAL FILTER DESIGN SOFTWARE FREE DOWNLOAD SERIES
The series crystals, A, are the same frequency, as are the shunt crystals, B.
LATTICE CRYSTAL FILTER DESIGN SOFTWARE FREE DOWNLOAD FULL
Equivalent circuit of a full lattice crystal filter. The anti-(parallel) resonant frequency, fa, is that of the circuit formed by C and L in one branch and Co in the other.įig. The series-resonant frequency, fr, is that of C and L. Co is the electrode and holder capacitance shunting the crystal.įig. C and L are the motional capacitance and inductance of the crystal, and R represents the frictional loss. For the case where the reactance curves in the stop band are equal only at zero frequency and infinite frequency, analysis of the circuit shows that the frequency difference f2 - f1 corresponds to the bandwidth at which the attenuation is approximately 7 dB.įig. It is observed that the pass band of a simple lattice is limited to the region between the antiresonant frequency of the higher-frequency crystals and the resonant frequency of the lower-frequency crystals. 4 shows what happens when the anti-resonant frequency of one pair of crystals is made equal to the resonant frequency of the other pair. The reactance frequency curves of the crystals can then be used to indicate the regions of the pass band and the stop band. When the impedances are equal, the bridge will be balanced. The lattice is a bridge, and it is obvious that maximum unbalance of the bridge will occur when one arm has an impedance which is capacitive while the other arm is inductive. By utilizing crystals in a lattice structure as shown in Fig. L and C are series resonant at fr, and fa is the antiresonant frequency of C, and the LC combination. 1 shows the equivalent circuit of a crystal neglecting its spurious modes. In the filter described in this article the spurious responses are attenuated more than 50 dB even with a crystal whose principal spurious frequency was only 7 dB down from the main response. In filters such as the one used in the transceiver described by W3TLN (6) it is not unusual to obtain spurious responses as close as 15 kc to the pass band which are suppressed by only about 20 dB. A filter constructed according to this design from FT-243 surplus crystals performed as predicted. By inserting a small resistance between two sections of a three-section filter, the ripple was reduced without greatly affecting the shape factor (ratio of the bandwidth at some high attenuation to the bandwidth at low attenuation) of the selectivity curve. The effect of mismatch when filter sections are cascaded without vacuum-tube isolation improved the steepness of the selectivity characteristic, but at the expense of ripple in the pass band. The theoretical shape of the selectivity characteristic attainable with simple crystal filter arrangements was calculated first and found to be inadequate for good sideband suppression. This article describes a particular type of filter that was built for a homemade transceiver. (1-5) However, none of these supplied a design procedure and also gave the precise performance of the resulting filters. Many articles have appeared in QST describing crystal filters for s.s.b. crystal filters to design one for most any frequency, band width and shape factor, and also a ready-tobuild 5.5 Mc filter for s.s.b. Here's a two-in-one special - enough information on h.f.
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