Re: QMX RX BPF troubleshooting, a new clue
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Greetings Hans!? Yes, the Tayloe circuit is amazing and very robust! It will tolerate all kinds of misapplication and still provides a virtuous performance!
That its BPF response and Zin response slide about the spectrum with its clock frequency is unavoidable. It is simply what happens, determined by theory.
?What that means, practically, is another matter.
?I shared my concerns about this with you a while back, but noted at that time that QDX and the modified QMX were receiving signals very well. I invoked my long standing belief that one should not fix that which is not broken.
My question to Ryuji attempts to assess his understanding of this beautiful but? arcane bit of circuitry. He is very skilled and is a great add to this forum. I am looking forward to his response.
Regards and best?wishes,? JZ
The Tayloe detector/downconverter is a complex and interesting entity!
Certainly it is! And remarkably high performance at a low cost and simple implementation!?? ?
Further, the BPF and Zin response of the Tayloe circuit moves as the
clock frequency is swept when creating a filter plot.
I'm not sure this is the case. When you sweep the RF, at each of the 80 points on an RF sweep plot, the receiver frequency is set by setting Clk0/Clk1 to 12kHz below the desired reception frequency, and the Clk2 (as signal generator) is set to 1kHz above the desired reception frequency. It creates a 1kHz audio tone, and a 1-bucket FFT (Goertzel algorithm) is done as a convenient way of extracting an amplitude measurement, converted to dB, and sent to my ASCII-graph engine.?
The reception is always done at the same frequency?as far as the QSD is concerned?so why would the BPF and Zin response of the Tayloe circuit move? The source impedance?of the BPF will do, as would be normal for a filter anyway.
Isn't the QDX/QMX design so deliciously rich and hard to explain perfectly from a theoretical perspective? Between the PA, QSD and SMPS, it provides a wealth of opportunity for investigation and debate. And fortunately, even though the thorough theoretical explanation is tough, the suck-and-see approach to refining circuit values results in a highly performant radio.?
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