[600MRG] Low Noise Oscillators,Etc.

[Frank Lotito]

On occasion this column had messages mentioning the need for low phase noise oscillators. These oscillators were for use in transmitters and receivers intended for weak signal transmissions, e.g. one of the QRSS modes or very narrow bandwidth modes such as WSPR or JT9, etc. I am sure the importance of low-noise oscillators applies to equipment for below 500 KHz as well as the HF bands, including the no-license MedFER and HiFER bands.

As I recall, many of the columns' replies simply stated certain oscillator types are far too noisy to be used in equipment for the very slow speed (long dot length) QRSS or narrow bandwidth modes. I did not recall these replies giving quantitative goals for oscillator noise or drift. Can someone give us guidance on which which oscillator designs should be considered for these different modes, and the oscillator / transceiver specifications (phase noise and drift) we should be striving for vs the modes? Maybe what is needed is someone to publish a compendium in this area similar in format to the "LF / MF Antenna Notes" recently published by N6LF (re: http://www.antennasbyn6lf.com?)

Obviously, not all of us pursue the extremes of weak signal transmission and detection. NDB beacon hunters and those dabbling in QRSS3, possibly even WSPR may not need the "state-of-the-art" as those pursuing QRSS300! Many of us use commercial amateur band transceivers in our receiving systems as the tuneable receiving IF, and / or the variable frequency portion for our transmitter's exciter. We may even be using a "modern" transceiver's receiver directly as a "general coverage receiver" for below 500 KHz, Medfer and HiFer applications. I would assume that the transceiver's noise and drift, and other factors contribute to the suitability of our total system for weak signal applications.

The point of diminishing returns may be tempered not only by our interests, but also the man-made and natural RF noise "trouncing" the weak signal sub-bands of interest. We have little or no control over this type of noise. Our recourse is to use the best we can afford w.r.t. noise reduction techniques, be they the electrical circuit design (e.g. high dynamic range / high 3rd order intercept,) where possible directional / noise cancelling antenna systems, and digital signal processing.

73 Frank Lotito K3DZ / WH2XHA