OOPS. what was I thinking, I was trying to minimize the number of transformers and slipped up. The inputs should be in opposite phase and output in parallel with a bifiler wound toroid transformer to provide balanced outputs, one to the crystal and one to the neutralizing (phasing) capacitor. The advantage of the crystal filter is that it provides much higher Q and to some degree, depending on it's selectivity reduces sideband noise. The crystals are cheap and if you like you can add more stages. No tuning required except for the phasing capacitor. If you happen to have a source of precisely cut series resonant 10MHz crystals you could easily go to 100Hz bandpass or even less by using a small value loading resistor. A ladder filter could be used but there is still coupling far off resonance thru a capacitive ladder network consisting of the crystal holders' capacitances and discrete capacitors. An complex LC filter could be constructed but it requires a number of stages along with careful selection of components. 73 Bill wa4lav
Message: 4 Date: Wed, 04 Feb 2015 06:57:48 -0500 From: Charles Steinmetz <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] 5>10 doubler Message-ID: <[email protected]> Content-Type: text/plain; charset="utf-8"; Format="flowed" Bill wrote: >Push-Push Jfet amplifier with parallel inputs and a Toroid output >transformer, no secondary along with a simple filter using a 10 MHz >series resonate crystal connected to one drain and an adjustable >capacitor connected to the other would work fine. You connect the >other ends of the two together and a loading resistor to >ground. The capacitor is used to neutralize or null out the shunt >capacitance of the crystal so that a capacitive path for the other >frequencies , 5, 15, 20, etc is eliminated. I concur with what Bruce said regarding crystal filters (or any narrow bandpass filter) at the output frequency. More fundamentally, I'm not sure I understand your description of the circuit. You say it is a pair of FETs with parallel input and a transformer (autoformer) output. To me, that suggests the circuit pictured below (one feeds the sources in parallel, the other feeds the gates in parallel -- it doesn't make any difference in how the circuit operates). The usual push-push doubler feeds the FETs differentially, and takes the common-mode output. The diagrammed circuit reverses this -- it feeds the FETs in parallel (common-mode) and takes the 10MHz output differentially. As drawn, the circuit would have essentially no output at the input frequency or any of its harmonics (only that due to the mismatch between the FETs). The only signals it would amplify are uncorrelated signals -- i.e., the FETs' input noise voltages. A quick simulation confirmed no significant output at the input frequency or its harmonics for matched FETs. Simulating mismatched FETs produced a 5MHz signal rich in harmonics, but at a very low level and with no suppression of the 5MHz and its odd harmonics. I assume I misinterpreted your description and that you had a different circuit in mind, or that if you did have this circuit in mind I'm missing something about its operation. Can you please describe again what you had in mind, and how it generates 10MHz? Best regards, Charles -------------- next part -------------- A non-text attachment was scrubbed... Name: Fuqua_doubler_sm.gif Type: image/gif Size: 17911 bytes Desc: not available URL: <http://www.febo.com/pipermail/time-nuts/attachments/20150204/ed4fa496/attachment.gif> ------------------------------ Subject: Digest Footer _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ------------------------------ End of time-nuts Digest, Vol 127, Issue 5 ***************************************** _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
