L3 is as described by the OP, a 10.7 MHz trap. It avoids feedback from the IF (10.7 MHz) to make the whole radio to oscillate at that frequency. It works by making the stage an "open circuit", then making gain 0 at the IF frequency. The "one connection" is simply the way to use the interwinding capacitance as the "C" in the LC tuned tank. The resistor in there is just the emitter bias resistor for the common base stage, and is not a part of the IF trap.
On Tuesday, December 3, 2019 at 12:21:39 PM UTC-3, gregebert wrote: > > L3 is before the mixer, so it's still 88-108Mhz raw VHF (FM). My best > guess is that L3 and the resistor make up a crude high-pass filter, > especially if this is an AM/FM radio, to prevent AM (and other signals) > from interfering with the mixer. I dont understand why the other side of > the coil has only 1 connection. Perhaps it's a clever/bizarre way to > minimize noise. > > You are correct about the resistor; it provides a DC path for the bias > current of Q2. > > Do you have an RF oscillator and scope ? You could inject a 100Mhz signal > at the antenna terminals and use a scope to find out where things die. > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/a8c6ab00-0109-4679-9ce3-4a6a94ed917d%40googlegroups.com.
