UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Improving Selectivity In Vintage Receivers

Jon_G4MDC · 30th Oct 2022, 6:29 pm

In Spice it is the abbreviation for the Mutual Inductor Model. It is where you enter L1 and L2 Values along with either Mutual Inductance or Coupling Factor K.
I was having trouble with the fact that it won't accept a Q value so the inductors will appear perfect. Since I have access to the terminals I have added series resistors there to damp the Q down to a likely real world value of about 100 given the coil construction. (Does anyone have an opinion on that?)

I'm still thinking that resistive termination is the right way. Also still in favour of an emitter or source follower. That could be made to still look like 60k as load to the crystal and phasing control but it would give a low impedance output with unity Voltage gain.

The low impedance output would drive the ceramic filter through a series resistor of 2k.
The far side of the filter would have 2k to ground as termination and that would connect to the coil tap through a suitable DC blocking capacitor since that point is carrying AVC Voltage.

Any comments about preference for FET or Transistor follower anyone? Any suggestions for suitable devices?

30th Oct 2022, 6:29 pm	#47
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Improving Selectivity In Vintage Receivers In Spice it is the abbreviation for the Mutual Inductor Model. It is where you enter L1 and L2 Values along with either Mutual Inductance or Coupling Factor K. I was having trouble with the fact that it won't accept a Q value so the inductors will appear perfect. Since I have access to the terminals I have added series resistors there to damp the Q down to a likely real world value of about 100 given the coil construction. (Does anyone have an opinion on that?) I'm still thinking that resistive termination is the right way. Also still in favour of an emitter or source follower. That could be made to still look like 60k as load to the crystal and phasing control but it would give a low impedance output with unity Voltage gain. The low impedance output would drive the ceramic filter through a series resistor of 2k. The far side of the filter would have 2k to ground as termination and that would connect to the coil tap through a suitable DC blocking capacitor since that point is carrying AVC Voltage. Any comments about preference for FET or Transistor follower anyone? Any suggestions for suitable devices? Last edited by Jon_G4MDC; 30th Oct 2022 at 6:47 pm.