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Posted by John Davis on February 08, 2024 at 08:49:25.
In Reply to: Re: Two Way HiFER? posted by Ed Holland on January 31, 2024 at 21:30:42.
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Given that Mr Weaver formerly worked at Stanford in Menlo Park, 70-some years ago, it might be interesting to see what you could accomplish with his method from that same general vicinity today. I've been working on a design, but just how simple it can be made depends almost entirely on the range of audio frequencies to be handled, which in turn depends on how many of the WSJT and/or fldigi modes one wants to be able to accommodate. If the desired modes are all WSPR-like and only require an audio band of (say) ±200 Hz centered at 1500 Hz, the whole exciter can be greatly simplified without sacrificing any of the inherent advantages of the Weaver method. However, if one wishes to keep open the possibility of using modes that require more of the SSB voice bandwidth, then there arise some conflicts between simplicity and performance inherent to the Weaver third method; or else one could adopt the "Davis fifth method" instead. Just as the so-called "fourth method" is mathematically no different from the standard phasing method except its sampling time is 90° instead of 180°, the "Davis fifth method" assumes a message bandwidth of 6 kHz and simply ignores the unneeded extra audio bandwidth. That avoids any need for DC coupling between the first and second mixers, which dodges midband response nulls and resulting phase errors in coherent modes, but sacrifices the Weaver advantage of confining any accidental spurs to the nominal message channel. (That's probably not a big issue givwn the practical realities of 22 meters.) It also adds a step or two to the calculation of second LO frequency for a given 'dial frequency.' John
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