12 November 2010

TTL oscillator as NE602 external source

There are lazy moments in everyone's life when you want to drive the NE602 LO input with a TTL-generated signal. I had asked on the qrp-tech forum few months ago and got helpful replies.

NE602 datasheet reccommends a 200 to 300 mV p-p drive from an external LO.

An application note shows this arrangment with a resistive divider for a TTL signal: 510 and 30 ohm, fed through a 0.1uF capacitor. This results in 277 mVpp for a 0-5V square signal.

Simple, isn't it?

Since I ignore the output switng of the canned oscillator I intend to use, I will try with a 1k multiturn trimmer and tune for an acceptable level.