Archive for the ‘Crystal ladder filters’ Category

Homemade crystal filters for K3

September 24, 2013

Elecraft K3 allow to configure details of installed crystal filters. for each filter you can specify bandwidth (50Hz do 13kHz in 50Hz steps) and frequency offset from -1,28kHz to +0,25kHz. attenuation can be compensated from  0 do 8dB.

This allows to develop and use homemade filters. Filter center frequency don’t need to be exact 8215.0kHz – it can be compensated in radio configuration.

kfl3a2k7-1

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Crystal ladder filters – measuring crystal parameters

May 9, 2010

Values of crystal parameters needs to be determined to correctly  design crystal ladder filter.

Measurement examples are for custom ordered resonators 8214 i 8215kHz (RS-3017X) made by polish company Omig.

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1) Selecting crystals based on series resonance frequency (fs)

– crystals for CW filter should be selected to have fs +/- 10Hz
– for SSB filter +/- 50Hz
In general allowed difference between crystals fs is +/-2% of designed filter bandwidth.

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Crystal ladder filters – software

April 5, 2010
Software for designing crystal ladder filters:

1) “Dishal” by DJ6EV

This software takes into account crystal parallel capacitance (Cp).
Crystal Cp is a reason for crystal ladder bandwidth narrower than designed in theory.
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