[Hammarlund] HQ-215

[Robert Kerr]

Crystals that are cut properly can be made to oscillate at a fundamental 
frequency and at odd (3rd, 5th, etc. ) harmonics of that.  Single tube 
circuits that have the crystal oscillating at a fundamental frequency 
but are biased and tuned such that the 2nd harmonic is produced within 
the tube are fairly easy to build.  A bipolar transistor oscillator with 
frequency doubling  was probably considered unsatisfactory compared to 
using a simpler oscillator circuit with an overtone crystal providing 
the higher frequency, at the time the HQ-215 was designed.

Symmetrical "clipping" of a sine wave's peaks produces odd harmonics of 
the fundamental frequency - an ideal square wave has a spectrum made up 
of the fundamental frequency and all its odd harmonics.  Asymmetrical 
clipping of only the positive or only the negative peaks of a sine wave 
produces even harmonics.

Bob K4ERR

On 06/16/2010 02:11 PM, Dan Cotsirilos wrote:
> Note of interest that maybe HQ-215 owners already know. Up until 12 mc the HQ-215 uses the exact same crystals as the Collins S-line. I happen to have a crystal pack and the crystal freq's are the same as the 215. After 12 mc the Collins uses double overtone and the 215 uses triple.
>
> The filters are the same 1/2 the crystals are the same triple vs double is a funny place to make a distinction?
>
>
> Dan K9DTC
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