The crystal D-104 needs more like 500k to 1 Meg to keep from having
excess roll off.
The peak in response is outside the filter pass band. The peak response
has been known to overdrive audio and balanced modulator stages in some
radios.
The high frequency peak of the D-104 crystal microphone was designed for
AM where selectivity of the receivers tended to gently roll off the high
frequencies. It has far less value in SSB.
The piezo element of the crystal microphone was made of Rochelle salts,
definitely fragile and liable to being dissolved in high humidity
atmospheres.
I prefer using some other element like the Shure R-5 communications
cartridge in the D-104 case.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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