[time-nuts] locking oscillators - an increase in power and/or stability ?

Bob Camp kb8tq at n1k.org
Wed Oct 8 19:07:18 EDT 2014


Most Gunn oscillators have very basic internals. Isolation between the “oscillator” and the “output” is rarely very good. Injection locking one is quite easy. It’s often done as the final step in a microwave LO multiplier chain.


On Oct 8, 2014, at 6:54 PM, Bruce Hunter via time-nuts <time-nuts at febo.com> wrote:

> This is certainly an interesting phenomenon.  A couple of possible explanations come to mind.
> First, if the pair of Gunn sources are not really locked and are oscillating at two different frequencies, the resulting  voltage envelope would peak at about double the voltage of either oscillator.  This might cause a power detector (that senses only voltage) to read about a 6 dB increase over one Gunn oscillator alone.  The waveguide low-frequency cutoff would not eliminate the envelope modulation as the low-frequency component is encoded as a pair of sidebands close in frequency to the carrier.  Think of a signal generator modulated with 1 kHz square-wave for use with a tuned detector.  
> A second possible explanation involves the combined internal impedance of the Gunn diode oscillators.  Summing two of them may alter the operating point along the E/I negative resistance curves, changing the combined generator impedance, and possibly improving device efficiency.  These devices are relatively inefficient anyway (about 1%), so an increase or decrease in the dc input power is not a good indication of what's going on in the generation of RF. 
> Bruce, KG6OJI
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