Thursday, December 14, 2017

Xtal filter question sparked by TRB post

My first receiver was a Hammarlund HQ-140 the manual can be downloaded here:

Hammarlund HQ140

The set that caused the question can be found here:

Simplex Super

They use a Xtal filter with only one Xtal.
Here is the Xtal filter and brief description from the linked manual.

The circuit from the schematic.

The Hammarlund predated the Simplex. The Simplex was published in a ham handbook so the simple statement would be they modified the commercial product for their project. (Hammarlund held the patent)
The question was about L5 and L6. They do not resonant at the operating frequency.

No, they are filters not tank circuits. See this post filter circuits. If you download the manual and read the alignment section it will explain the circuit operation.

These filters shape the overall filter response and keep undesired signal from passing. (The crystal will pass harmonics and overtones which are undesired.)

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