UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - 10M FM

Jon_G4MDC · 27th Nov 2018, 8:14 pm

Si5351a RX VFO was patched into my 10m FM10D on Sunday.
Colpitts oscillator robbed of feedback to use as buffer.

Some issue with drive levels, not nearly as much Ic as when working as normal crystal oscillator. Si5351a is nominal 50 Ohms out with variable current drive levels set by software bits.

Making FM10 Cambridge Oscillator more like Common Emitter Amplifier and by stepping up the drive by 4:1 transformer then the buffer (as it was oscillator VT3)
Ic hit near normal levels.

It can hear things in the right places but there is a birdie at around 29.7MHz. It tunes a signal which is not there. Don't know the source of that as yet.

27th Nov 2018, 8:14 pm	#47
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? Si5351a RX VFO was patched into my 10m FM10D on Sunday. Colpitts oscillator robbed of feedback to use as buffer. Some issue with drive levels, not nearly as much Ic as when working as normal crystal oscillator. Si5351a is nominal 50 Ohms out with variable current drive levels set by software bits. Making FM10 Cambridge Oscillator more like Common Emitter Amplifier and by stepping up the drive by 4:1 transformer then the buffer (as it was oscillator VT3) Ic hit near normal levels. It can hear things in the right places but there is a birdie at around 29.7MHz. It tunes a signal which is not there. Don't know the source of that as yet. Last edited by Jon_G4MDC; 27th Nov 2018 at 8:41 pm.