I started with textbook impedance ratios, then adjust the windings 1 turn at a time to find the optimal combination of power transfer and passband flatness. This can vary with crystal characteristics, circuit strays, etc.
73, Wayne N6KR On Apr 25, 2011, at 3:07 PM, John Magliacane wrote: > Hi Folks. > > I've been perplexed for quite some time as to why RF transformers T1 > and T2 that sit at opposite ends of the crystal ladder filter on the > KSB2 board have different turns ratios. > > T1's turns ratio is 22:7. while T2's is 22:4. > > The impedance of the crystal ladder network appears to be in the > neighborhood of 1200 - 1500 ohms. Since the KSB2 sits inside an IF > having a 150 ohm impedance, T1's 22:7 turns ratio, which performs a > 9.87:1 impedance transformation, makes perfect sense. > > The Balanced Modulator feeds T2's primary with an impedance close to > 1200 ohms, which also makes perfect sense. > > However, T2's secondary, having only 4 turns, presents an output > impedance significantly lower than the 150 ohm IF system it is > feeding. > > What's the deal? :-) > > And I ask this question as I troubleshoot a "narrower than expected" > crystal filter response. I'm curious whether the T2 impedance > mismatch is intentional, or something else is going on that I'm not > aware of. > > Any relevant enlightenment on the subject would be appreciated. > > Thanks. > > > 73, de John, KD2BD > K2/100 #3563 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
